Folate derivatives, particularly useful in the context of assaying folate(s)
Technical field

The present invention relates to folate derivatives, particularly useful for assaying a
folate/folate(s) in an in vitro biological sample, preferably employing non-radioisotopic
competition techniques.
10 State of the art
Vitamin B9 is the generic denomination given to a very chemically and biologically
closely related family of compounds, all derived from folic acid. One of the main
characteristics of these compounds is that their presence in insufficient quantity, or their
15 actual absence, causes anaemia in man or in an animal. The folates family comprises,
inter alia, vitamin M, vitamin Bc, folacin and folic acid. Within the meaning of the present
application, each of the compounds belonging to this family is called “folate”, a plurality
of members of this family is called “folates”, while the mixture of constituents of the
vitamin B9 family of is called “total folate”.
20
As is well-known to the man skilled in the art, folic acid, also called pteroylmonoglutamic
acid, is formed of a pterin group, a p-aminobenzoic group and a glutamate group as
represented hereinafter by general formula (G):
2-amino-4-hydroxy-
6-methylpteridin
(pterin)
p-amino-benzoic
acid
L-glutamate
Pteroic acid
(G)
2
in which n is the integer 1.
As shown in this general formula, folic acid has two carboxylic acid functions on its
glutamate part, one in the α position, the other in the γ position.
5
In food, folates are mostly in the form of reduced methyl- or formyl-polyglutamates. On
digestion, these polyglutamates are transformed into monoglutamates, actively absorbed
by the enterocytes. Then, the monoglutamates are transformed into 5-
methyltetrahydrofolate (5-MTHF), in which form the folates pass through the intestinal
10 barrier and pass into the systemic circulation.
In blood, the major part of the circulating folates is bound with a weak affinity to various
proteins: α2-macroglobulin (40%), albumin (33%) and transferrin (23%). Plasma
concentrations of vitamin B9 vary from 5 to 15 μg/L and are heavily impacted by food
15 intake. The vitamin B9 concentration is approximately 20 times higher in the red blood
corpuscles which can contain up to 95% of the circulating folates. Multiple forms of
folates are present in human serum, but the preponderant circulating and intracellular
form is 5-methyltetrahydrofolate (5-MTHF), which is also the form of hepatic storage.
Generally, the biologically active compounds are solely the reduced forms: dihydrofolate
20 (DHF), and mainly tetrahydrofolate (THF) as well as its methyl or formyl derivatives. As
indicated above, within the meaning of the present application, the denomination
“folates” covers in particular these reduced forms; each of said forms, taken separately,
being called “folate”.
25 Eucaryotic cells, as well as certain procaryotic cells, are incapable of synthesising folic
acid. They therefore use transmembrane transport systems which allow internalisation
of the exogenous molecule. At the present time, two main transport systems have been
described. However, there probably also exist secondary routes such as passive
diffusion. Oxidised folates like folic acid are transported inside cells by the folate
30 receptors (FR), “folate receptors” in the English language (Antony, 1992 [1]). These
proteins were formerly called “folate binding proteins” (FBPs). Three isoforms have
been identified in man, respectively called FRα (P15328), FRβ (P14207) and FRγ
(P41439), the code indicated between parentheses corresponding to the identifier of the
protein in the UniProt database (http://www.uniprot.org). FRα and β are anchored in
3
the plasmatic membrane by a lipid part, glycosylphosphatidylinositol (GPI). The γ
isoform is secreted. The reduced folates, for their part, are transported by a protein
called reduced folate carrier (P41440) or “reduced folate carrier” in the English language
(RFC). This is a highly glycosylated integral membrane protein which has a plurality of
5 transmembrane domains.
Due to their chemical structure, folates play an essential role in the synthesis and
metabolism of the basic constituents of our organism, namely amino acids and bases
(purines and pyrimidines).
10
THF, an essential coenzyme, is capable of fixing and transferring radicals to a carbon
atom. It is involved in the synthesis of glycine and the catabolism of histidine.
5-MTHF permits remethylation of homocysteine to methionine via methylcobalamin and
15 methionine synthase. Folates are also involved in several key steps of the biosyntheses of
purines and pyrimidines, thus affecting the synthesis of the nucleic acids DNA and RNA.
Because of this central role, folate(s) deficiency has serious consequences and many
physiopathological expressions.
20 Severe folate deficiency gives rise to general, haematological and neuropsychiatric signs.
Slowly, asthenia and anorexia appear. Anaemia can be preceded by isolated
macrocytosis. This anaemia, often of megaloblastic type, is one of the most frequent
expressions of folates deficiency. In addition there is often a combined deficiency of
folates and of iron which results, instead of classic macrocytic anaemia, in normocytic
25 anaemia with presence of Jolly bodies on the smear. This anaemia is due to the fact that
purines and pyrimidines are not available in sufficient quantity, thus resulting in the
impossibility of blood stem cells synthesising genetic material and therefore dividing.
Conversely, the existing cells continue to grow, which partially explains the generally
megaloblastic type of the anaemia associated with folate deficiency.
30
Folates are also necessary for proper functioning of the brain, and contribute to mental
health and emotional balance. Thus, vitamin B9 deficiency causes neuropsychiatric
problems. These problems could in part be linked to anomalies in the synthesis of certain
amines and glycine. The latter is also a neurotransmitter.
4
Due to their contribution to the synthesis of genetic material, a satisfactory intake of
folates is particularly necessary during childhood, adolescence and pregnancy. Indeed,
psychomotor retardation and staturo-ponderal hypotrophy are often found in children
having folates deficiencies. During pregnancy, a folate(s) deficiency can cause delay or
5 anomalies in the development of the foetus, or even congenital deformities such as spina
bifida which is incomplete closure of the neural tube, or even trisomy.
Folates deficiency is also associated with increased risk of cardiovascular illnesses, more
precisely arterial and/or venous thromboses and atheroscleroses. The risk is linked to
10 the increase in the plasmatic homocysteine level, resulting from lack of methylation of
this compound into methionine.
This list is not limiting and folates deficiency can cause other disorders/pathologies. It is
therefore of primary importance to be able to assay all or part of the folates in a human
15 or animal individual, preferably the “total” folate, i.e. formed by the mixture of the
different folate forms.
In addition, it is also important to be able to quantify all or part of the folates present in
samples of food origin (intended for human or animal consumption) in order to verify
20 the vitamin B9 contribution of the foods in question. It may also prove advantageous to
assay the folates in products of food type, in order to ensure that these contain a
sufficient quantity/concentration of folate(s). Such food supplements can in particular
serve to prevent possible vitamin B9 deficiencies.
25 Assaying the folates in whole blood, serum, plasma, or in the red blood cells has a certain
advantage from a clinical point of view. Reduction in the blood folates concentration
potentially results inexpresses a deficiency which should be clinically investigated,
possibly in association with other vitamin or metabolite assays. The blood folates level is
subject to variations depending on diet or the taking of medications. It is the folates level
30 of red blood cells which gives the best estimate of the folates reserves of the organism.
Several methods exist to permit the quantification of plasma, serum and/or red blood
cell folates in biological samples of clinical origin, i.e. coming from patients. These
5
methods can be classified in three main groups, i.e.: (1) microbiological techniques, (2)
chromatographic techniques and (3) competition immunoassays.
Microbiological techniques (1) generally use a “folates-dependent” seed, the growth of
5 which is proportional to the vitamin level present in the sample to be assayed. Generally,
the samples are deproteinised at 100°C in the presence of vitamin C, which acts as an
antioxidant. Contact with the bacterial strain is effected for 20 hours at 37°C. The seed
germ most frequently used, Lactobacillus casei, is sensitive to all the oxidised and
reduced forms of folates; other seeds are sensitive to more specific forms. For example,
10 Streptococcus faecalis permits the assay of all forms of folates with the exception of 5-
MTHF. The concentration of 5-MTHF, the preponderant form in serum and red blood
cells, is obtained by the difference between the values of L. casei and of S. faecalis. A third
seed, Pediococcus cerevisiae, is sensitive exclusively to N5- formyl-THF (folinic acid).
15 These microbiological techniques (1), though generally sensitive and reproducible, are
tedious and time-consuming. In addition, they present risks of interference with
antibiotics and antimitotics, such as methotrexate, trimethoprim and pyrimethamine.
Assays of chromatographic type (2) allow the separation of the different compounds
20 belonging to the folates family. As examples of chromatographic assay, can in particular
be cited:
 thin-layer chromatography assay coupled with HPLC (Reif, V.D. et al., 1977
[2]),
25  chromatography assay (generally gas or liquid phase) coupled with mass
spectrometry (MS), for example by:
a) gas phase chromatography/mass spectrometry with isotope dilution
(ID-GCMS) (Dueker, S.R. et al., 2000 [3]), or
b) liquid phase chromatography - mass spectrometry in tandem with
30 isotope dilution (ID-LC-MS/MS) (Pfeiffer, C.M. et al., 2004 [4]).
These assays of chromatographic type (2) notably have the disadvantage of requiring the
development of very technical tests, requiring qualified personnel. In addition, the
instrument proves to be expensive.
6
Having regard to the problems encountered on implementation of the microbiological
(1) and chromatographic (2) techniques (cf. above), competition immunoassays (3) have
been developed. While reducing the analysis time, these latter (3) permit the assay of
“total” folate and therefore the provision of a reliable clinical diagnosis relative to a
5 possible folates deficiency.
These immunoassay processes (3), also called immunological assays or immunochemical
tests, involve the binding of the analyte to be detected - in this case the folate(s)
- with at least a first compound which is a binding partner to this analyte. As the folate(s)
10 assay is effected by competition, the process also involves at least a second compound
which enters into competition with the folate to be assayed in relation to fixing on the
binding partner, this second compound being a folate derivative. The monitoring of this
reaction involves labelling one of the two compounds. This labelled compound is called
labelled conjugate or tracer.
15
Of course, the prefix “immuno”, for example in “immunoassay”, is not to be considered in
the present application as strictly indicating that the binding partner is an
immunological partner, such as an antibody or an antibody fragment. Indeed, as is wellknown
to the man skilled in the art, this term is more widely used to designate tests and
20 processes in which the binding partner, also called ligand, is not an immunological
partner but consists, for example, of a receptor of the analyte which is required to be
assayed. The condition being that the binding partner is capable of binding to the
analyte, preferably in specific manner. Thus, it is known to use the term ELISA (Enzyme-
Linked Immunosorbent Assay) for assays which use non-immunological binding
25 partners stricto sensu, more widely called in English “Ligand Binding Assay”, which could
be translated into French as “Dosage utilisant la liaison à un ligand”, while the term
“immuno” is included in the acronym ELISA. For the sake of clarity and uniformity, the
term “immuno” is used in the present application to designate any assay using a suitable
binding partner to bind to the analyte to be quantified, preferably in specific manner,
30 even when this binding partner is not of an immunological nature or origin in the
strictest sense.
7
In the context of competition immunoassays (3), and when a labelled conjugate is used,
three types of competition immunoassays are distinguished depending on the nature of
the labelled conjugate and on the type of signal emitted by said conjugate, i.e.:
5  radio-isotopic immunoassays (Waxman S. and Schreiber C., 1980 [5]),
 immuno-enzymatic assays or EIA “enzyme-linked immunoassay - assay”;
depending on the selected enzyme substrate, the signal can be of colorimetric
type (Hansen, S.I. and Holm J., 1988 [6]) of fluorescence or chemiluminescent
type,
10  electrochemiluminescent immunoassays (Owen, W.E. and Roberts W. L. 2003
[7]).
The last two types of competition immunoassay are called “non-radioisotopic
competition immunoassays”.
15
The development of the radioisotopic methods (RIA), from the 1960s, revolutionised the
quantification of vitamins and in particular of vitamin B9.
Patent application WO 80/00562 illustrates this by disclosing radioactive folate
20 derivatives, substituted at the carboxylic acid function carried by the α carbon and/or by
the γ carbon of the glutamate derivative. Radioactive labelling comes from the insertion
of iodine-125 or 130 in the phenol ring of a tyrosine structure.
French patent application FR-A-2455602 also relates to obtaining radioiodinated
25 compounds and mentions pteroic acid derivatives of general formula:
8
in which the glutamate group is replaced by the radical X, this radical X representing, as
required, the residue of an amino acid or of a “des-carboxyamino acid” necessarily
containing an aromatic or heterocyclic ring, indispensable for radioisotopic labelling
(with iodine 125, 131 or 123). This iodinated aromatic or heterocyclic ring is separated
5 from the p-aminobenzoic acid group by a chain not including more than 5 carbon atoms,
attached to the p-aminobenzoic group by a secondary amine. As “des-carboxyamino acid
residue” containing an aromatic or heterocyclic ring, the following structures are
disclosed:
10
However, these radioisotopic assays (RIA) had in particular the disadvantage of the
treatment of radioactive waste and the relatively short duration of the half-life of the
labelled reagents.
15 This is why non-radioisotopic competition immunoassays have been developed to the
detriment of RIA which is only rarely used today.
By way of illustration, the publication Arcot J. et al, 2005 [8] describes a process for
assaying folic acid by binding to a protein tagged with an enzyme (“enzyme-labelled
20 protein binding assay” in the English language), said labelled protein being FBP, and the
process method being based on competition between the molecules of folic acid free in
the biological sample and those previously immobilised on a microtitration plate to fix
on the labelled FBPs. After rinsing, the revelation step is performed by introducing a
colourless enzyme substrate, causing blue colouration after cleaving by the enzyme fixed
25 to the FBP. As is generally the case in competition assays, the quantity of free folic acid
present in the sample is determined by reference to a calibration curve, from which the
quantity of free folic acid present in the sample is deduced as a function of the measured
luminous intensity.
9
The Abbott Axsym Folate kit (Cat. No. B7K460, Abbott Laboratories) also permits the
implementation of a competition folates assay process. As a binding partner, this kit uses
the protein FBP and, as the labelled conjugate, pteroic acid (a folate analogue) bonded to
alkaline phosphatase (ALPA). The principle of the test is based on competition between
5 the folic acid to be assayed and the above-mentioned conjugate in the context of fixing to
the soluble FBP. Following the competition reaction, the FBP is brought into contact with
anti-FBP monoclonal antibodies and the antigen-antibody reaction takes place. Said
antibodies are bonded covalently to carboxymethylamylose, a polyanion. Thus, the
complexes are captured by polyanion-polycation electrostatic interactions, on a
10 positively charged matrix. However, the Applicant has discovered that the sensitivity of
this assay was not completely satisfactory, in particular regarding the quantification of
low folates concentrations.
There is therefore an urgent need to improve the analytic sensitivity of non15
radioisotopic folate immunoassays in order to obtain a process usable in samples of
clinical origin (biological samples) and/or in samples of agri-food origin containing a low
folate concentration.
Statement of the invention
20
The Applicant has, against all expectation, discovered novel folate derivatives which
allow all or part of the disadvantages mentioned above to be remedied, in that their use
in a non-radioisotopic competition assay (such as an immunoassay), in particular as
tracer, allows an increased analytic sensitivity to be obtained, in particular in the ranges
25 of lowest folate concentration.
Thus, an object of the invention relates to the use of a folate derivative for assaying
folate(s) in vitro in a sample, such as a biological sample, said assay being a nonradioisotopic
competition immunoassay and said folate derivative being decarboxylated
in the α position. Said α position is such as shown in the general formula (G) mentioned
30 above.
Indeed, the Applicant has in particular discovered, in surprising manner, that the folate
derivatives decarboxylated in the α position significantly improved the analytic
10
sensitivity of non-radioisotopic competition immunoassays allowing the in vitro assay of
folate(s).
Preferably, the folate derivative according to the invention is different from the NSP-
5 DMAE-HD-pteroate and NSP-DMAE-HEG-pteroate compounds represented respectively
by formulae (A) and (B) in claim 1.
Advantageously, the folate derivative according to the invention does not comprise an -
(O-CH2-CH2)- structure and is different from the NSP-DMAE-HD-pteroate compound
10 represented by formula (A) in claim 1.
As indicated above, the prefix “immuno”, for example in the term “immunoassay”, must
not be narrowly interpreted as designating a binding partner of immunological nature
and/or origin, such as an antibody. Indeed, the binding partner used in the competition
15 immunological test can be, for example, a receptor of the analyte which is required to be
assayed, in this case the folates receptor. The non-radioisotopic immunoassay
techniques applicable according to the present invention can be any techniques known
to the man skilled in the art employing a binding partner binding with a sufficient affinity
to the folate(s) for the competition assay to be correctly performed.
20
According to a preferred embodiment, the folate derivative according to the invention is
used to assay a plurality of folates, or even, preferably, the total folate (as defined above).
According to a particular embodiment, the folate derivative according to the invention is
25 used to assay folic acid (pteroylmonoglutamic acid).
The terms “to assay” and “assaying” relate, in the present application, to the
determination of a quantity/concentration of the analyte(s) in question, i.e. of the
folate(s).
30
The invention also has as its object the use of a folate derivative to assay the folate in
vitro in a sample such as a biological sample, said assay being a competition
immunoassay, preferably non-radioisotopic, said folate derivative responding to general
formula (I):
11
in which:
5  X is an aliphatic hydrocarbon chain comprising 1 to 10 carbon atoms in
which the carbon placed in the α position does not carry an acyl function
such as a carboxylic acid function;
 Y represents a functional group suitable to allow bonding to a separate
molecule M, such as a protein, said bonding comprising the formation of at
10 least one covalent bond between Y and a functional group carried by said
separate molecule M.
The invention also has as its object the use of a folate derivative to assay the folate in
vitro in a sample such as a biological sample, said assay being a competition
15 immunoassay, preferably non-radioisotopic, said folate derivative responding to general
formula (I):
20 in which:
- X is an aliphatic hydrocarbon chain containing from 1 to 10 carbon atoms;
12
- Y represents a functional group suitable to allow bonding to a separate molecule M,
such as a protein, said bonding comprising the formation of at least one covalent bond
between Y and a functional group carried by said separate molecule M.
5 By “aliphatic hydrocarbon chain” is understood, within the meaning of the present
invention, a linear or open branched (acyclic) hydrocarbon chain. According to the
definition commonly accepted and presented in the reference works, a hydrocarbon
chain must quite obviously be understood, within the meaning of the present invention,
as only containing hydrogen (H) and carbon (C). In other words the aliphatic
10 hydrocarbon chain X is solely functionalised by the functional group Y mentioned above
and, by definition, does not contain a heteroatom (such as oxygen, nitrogen, sulphur,
phosphorus, halogens, etc.).
The combination of deacylation (of which decarboxylation is an example) in the α
15 position of the folate derivative according to the invention and of an aliphatic
hydrocarbon chain comprising from 1 to 10 carbon atoms results in folate derivatives
giving excellent analytic sensitivity when they are used in competition immunoassays
(preferably non-radioisotopic).
20 Said molecule M is, for example, a labelling molecule Mm. This molecule M can also
consist of a chemical arm or “linker”.
Preferably, X is a hydrocarbon chain comprising from 2 to 7 carbon atoms, preferably
from 3 to 5 carbon atoms, advantageously X is a hydrocarbon chain of 3 carbon atoms or
25 5 carbon atoms.
Advantageously, X is a saturated hydrocarbon chain.
Preferably, X is a linear hydrocarbon chain.
30
According to a particularly preferred embodiment, X is a linear and saturated aliphatic
hydrocarbon chain, comprising a number of carbon atoms as defined above. In other
words, and according to this particularly preferred embodiment, the folate derivative
according to the invention can be represented by the following general formula (I’):
13
in which:
5  n is an integer between 1 and 10. Advantageously, n is an integer between 2
and 7, preferably between 3 and 5, advantageously n represents the integer 3
or 5.
 Y is as defined above.
10 According to a preferred embodiment, Y is is a group of electrophilic centre type or a
group of nucleophilic centre type, preferably a group of electrophilic centre type, suitable
to allow the formation of an amide, ester, or thioester bond, preferably amide or ester,
advantageously amide, between Y and the functional group carried by said separate
molecule.
15
According to a preferred embodiment, Y is a group of electrophilic centre type,
responding to the following general formula (II):
20
in which Gp is a leaving group, optionally bonded to the carbonyl function by an L arm,
Gp being suitable to be dissociated from the group of electrophilic centre type in a
reaction with a nucleophilic group carried by said separate molecule M, such as a
primary amine.
14
The presence of the L arm is therefore optional in the compound of general formula (II),
for which reason this L arm is shown between parentheses in said formula. Thus, for the
purposes of the present application, the group of formula (L)-Gp can therefore designate
a group of formula L-Gp (presence of the L arm) or a leaving group Gp (absence of said L
5 arm).
Preferably, said reaction of the group of electrophilic centre type of general formula (II)
with said nucleophilic group carried by said molecule M - such as a primary amine - is a
nucleophilic substitution reaction.
10
Still in the preferred embodiment according to which Y is a group of electrophilic centre
type, the (L)-Gp group is selected from groups suitable to allow the formation of an
amide, ester, or thioester bond, preferably amide or ester, advantageously amide,
between said group of electrophilic centre type and a functional group carried by said
15 separate molecule M. Preferably, the latter is a nucleophilic group such as a primary
amine.
Advantageously, the (L)-Gp group is selected from: -OH, -NH-(CH2)m-COOH, -N3,
O-N
O
O ,
HN-H2C-OC-O-N
O
O
m
,
O-N
O
O
SO3Na
20 ,
HN-H2C-OC-O-N
O
O
m
SO3Na
,
O NO2
,
15
O
O2N
,
,
O Cl
Cl Cl
Cl Cl
, and
O-N
O
O ,
m being an integer between 1 and 10.
5
Among the above-mentioned (L)-Gp groups, the man skilled in the art will be able to
distinguish, without excessive difficulty, the Gp leaving groups (such as the groups -OH, -
N3 and -N-oxy-succinimide) from the L-Gp groups, i.e. in particular:
10 -NH-(CH2)m-COOH,
HN-H2C-OC-O-N
O
O
m
HN-H2C-OC-O-N
O
O
m
SO3Na
15 in which the L arm is formed by the -NH-(CH2)m-CO (or -NH-(CH2)m-OC) part.
16
For the sake of clarity, it will be noted that the group called above “-N-oxy-succinimide”
is the group of the following formula:
O-N
O
O
5
The use of such(L)-Gp groups favours the formation of an amide, ester, or thioester bond,
preferably amide or ester, advantageously amide, between the group of electrophilic
centre type Y and a functional group carried by the separate molecule M. These (L)-Gp
groups are particularly suitable to allow the formation of an amide bond between said
10 group of electrophilic centre type and an amine function - such as a primary amine -
carried by the molecule M.
Preferably, m is between 1 and 5, advantageously between 1 and 3.
15 Advantageously, Y is a group of electrophilic centre type of general formula (II) and the
(L)-Gp group is selected from:
- OH and -NH-(CH2)m-COOH and
HN-H2C-OC-O-N
O
O
m
20 , m being between 1 and 10 and preferably m being equal to 1.
According to a particularly preferred embodiment, Y is a group of electrophilic centre
type of general formula (II) and (L)-Gp is the L-Gp group of the following formula:
17
HN-H2C-OC-O-N
O
O
m
In other words, the folate derivatives of the invention are therefore characterised by
general formula (I) such as given above, in which X is as defined above and Y represents
5 a bonding group activated or ready to be activated to allow the formation of an amide,
ester or thioester bond, preferably amide or ester, advantageously amide, between said
derivative and a functional group carried by said separate molecule M.
According to a particularly preferred embodiment, Y is a bonding group activated or
10 ready to be activated to allow the formation of an amide bond with a primary amine of
said molecule M. In this embodiment, the molecules which can be bonded to the folate
derivatives of the invention are all molecules which naturally have a primary amine, such
as a protein, or any molecules which have been chemically modified to include such a
primary amine, for example a modified biotin, having a primary amine.
15
By “bonding group activated or ready to be activated”, is understood a functional group
suitable, where necessary after activation, to allow the bonding of the folate derivatives
of the invention to a functional group carried by said separate molecule M (for example
to a primary amine carried by the latter).
20
According to a particularly preferred embodiment, Y is an activated bonding group
which allows the direct formation of an amide bond with a functional group carried by
the molecule M (for example a primary amine), without this group needing to be
previously modified. By way of example, the following groups can be cited:
18
N3,
O-N
O
O ,
HN-H2C-OC-O-N
O
O
m
,
O-N
O
O
SO3Na
,
HN-H2C-OC-O-N
O
O
m
SO3Na
,
O NO2
,
O
O2N
,
O F
F F
F F
, and
O-N
O
O ,
5 m being an integer, preferably between 1 and 10, which constitutes an embodiment of
the invention.
According to an alternative embodiment of the present invention, Y is a bonding group
ready to be activated, i.e. any group which must be activated, by methods known to the
10 man skilled in the art, to be capable of forming an amide, ester or thioester bond,
preferably amide or ester, advantageously amide.
19
According to a particularly preferred embodiment, Y is a bonding group ready to be
activated to form an amide bond between the folate derivative according to the invention
and said molecule M. Such groups have an -OH or -COOH group. As examples can be cited
the groups -OH and -NH-(CH2)m-COOH; m being an integer, preferably between 1 and
5 10, which constitutes an embodiment of the invention.
According to a particular embodiment of the invention, m is between 1 and 5, or between
1 and 3.
10 According to another embodiment, Y is selected from -OH, -NH-(CH2)m-COOH, and
HN-H2C-OC-O-N
O
O
m
,
m being between 1 and 10 and preferably being equal to 1.
According to another particularly preferred embodiment, the derivative of general
15 formula (I) is used in conjugate form with said molecule M, and said conjugate being
represented by the following general formula (III):
in which X and M are as defined above, and in which Y’ is a derivative of the
functional group Y after bonding of the derivative of general formula (I) to said
20 molecule M,
said molecule M preferably being a labelling molecule Mm.
This conjugate of general formula (III) is different from the compound NSP-TMAE-HDpteroate
represented by formula (A) in claim 1.
20
Preferably, Y’ is represented by the following general formula (IV):
5 or by the following general formula (V):
wherein R1 is -NH-, -O-, or -S-, preferably -NH- or -O-, advantageously -NH-;
Y’ being preferably represented by general formula (IV).
10 When Y’ corresponds to general formula (IV), the conjugate according to the invention
can be represented by the following general formula (III’):
in which X, R1 and M are as defined above.
15 According to a particularly preferred embodiment, R1 is -NH-and formula (III’) is as
follows:
in which X and M are as defined above.
20
21
According to a particularly preferred embodiment, still when Y’ is a group of general
formula (IV), X is -(CH2)n- and the conjugate according to the invention is represented by
the following general formula (III’):
5 in which M and n are as defined above. Thus, n is an integer between 1 and 10. According
to a preferred embodiment, n is an integer between 2 and 7, preferably between 3 and 5,
advantageously n is the integer 3 or 5.
When Y’ corresponds to a group of general formula (still), the conjugate according to the
10 invention is represented by general formula (III”):
in which X, R1, and M are as defined above.
According to a preferred embodiment, R1 is -NH- and the conjugate according to the
15 invention then responds to the following formula (III”):
in which X and M are as defined above.
22
According to a particularly preferred embodiment, X is -(CH2)n- and the conjugate
according to the invention responds to the following general formula (III”):
in which M and n are as defined above. Thus n is an integer between 1 and 10. According
5 to a preferred embodiment, n is an integer between 2 and 7, preferably between 3 and 5,
advantageously n is the integer 3 or 5.
Another object of the invention relates to a process for in vitro assay of the folate(s) in a
sample, such as a biological sample, said assay being a non-radioisotopic competition
10 immunoassay, said process comprising the following steps:
a) bringing into contact, in said biological sample, (i) at least one binding partner of
the folate(s), such as an antibody suitable to bind to the folate(s) or such as the
folates receptor, with (ii) at least one compound selected from a folate derivative
15 such as defined above and a conjugate according to the invention, at least one of
said compounds (i) and (ii) being suitable to emit a signal,
b) optionally leaving a sufficient time lapse to allow the competition reaction,
c) measuring the intensity of the signal and deducing from it the folate(s)
concentration present in said biological sample by reference to a calibration curve
20 establishing a relationship between measured signal intensity and folate(s)
concentration.
This assay process can be implemented in a biological sample of clinical origin, i.e. taken
from a human or animal patient. In addition, this assay process also finds application in
25 the assay of the folate(s) in a sample of agri-food origin, such as foods intended for
human or animal consumption or food supplements. Generally, the assay process
according to the invention is applicable whenever a folate(s) assay is required/necessary
in a given sample.
23
Whatever the sample, of clinical origin or of food origin, the folates assay requires a prior
step of treatment of the sample in order to dissociate the folates from other molecules
present in these samples and with which they interact. Such dissociation techniques are
well known to the man skilled in the art. By way of example, we can cite European patent
5 EP 0382334 which discloses a method for preparation of serum samples for assay of
vitamin B12 and folates. Patent US 4,418,151 discloses an alternative pre-treatment
method. The manual of the Abbott Axsym Folate kit (Cat. No. B7K460, Abbott
Laboratories) describes a protocol for preparation of a haemolysate from a whole blood
sample in order to make all the folate molecules present in the red blood cells accessible
10 to the assay.
The man skilled in the art, very well acquainted with non-radioisotopic competition
immunoassay techniques will manage, without excessive difficulty, to implement steps
b) and c). In particular he will be fully capable of constructing a calibration curve, on the
15 basis of samples containing known concentrations of folate(s), thus establishing a
relationship between the measured signal intensity and concentration of folate(s).
As mentioned above, competition immunological assay (also called “immunoassay by
competition”) is an assay widely known to the man skilled in the art. It consists in
20 assaying the analyte, here the folate, in a sample in question, by creating competition
between the analyte of the sample and a derivative of this analyte, here the folate
derivative according to the invention, with regard to fixing to a binding partner of
immunological origin (for example an antibody or an antibody fragment) or otherwise
(for example the folates receptor). The binding of the derivative of the analyte in
25 question and of the binding partner is revealed by means of the presence of a tracer.
The derivative of the analyte (in this case the folate derivative) can be used in the
competition reaction, as indicated above, without prior bonding or after bonding to a
marker to form a conjugate or tracer.
30
When the analyte derivative (in this case the folate derivative) is not bonded to a marker
(in which case, it does not form the tracer but the capture partner), the binding partner
is then labelled to form the tracer of the reaction. When the analyte derivative (in this
case the folate derivative) is bonded to a marker (in this case a marker molecule Mm) to
24
form a conjugate, the latter then constitutes the tracer and the binding partner then
becomes the capture partner.
The measured signal, emitted by the tracer, is then inversely proportional to the quantity
5 of folate(s) present in the sample to be assayed.
As binding partner of the folate(s), is used any molecule capable of binding to the
folate(s). As examples of binding partner to the folate(s), can be cited antibodies,
antibody fragments, nanofitins, the folates receptor or any other protein known to bond
10 to the folate(s) with sufficient affinity to perform the non-radioisotopic competition
immunoassay according to the invention.
When antibodies are used as binding partners, they can be, for example, polyclonal or
monoclonal antibodies.
15
Polyclonal antibodies can be obtained by immunisation of an animal with the target
folate as immunogen, followed by recovery of the required antibodies in purified form,
by taking serum from said animal and separation of said antibodies from the other
constituents of the serum, in particular by affinity chromatography on a column on
20 which is fixed an antigen specifically recognised by the antibodies, in particular the
immunogen.
Monoclonal antibodies can be obtained by the hybridomas technique widely known to
the man skilled in the art. The monoclonal antibodies can also be recombinant antibodies
25 obtained by genetic engineering, by techniques well-known to the man skilled in the art.
As examples of antibody fragments can be cited the Fab, Fab’, F(ab’)2 fragments as well
as the scFv (Single chain variable fragment), dsFv (Double-stranded variable fragment)
chains. These functional fragments can in particular be obtained by genetic engineering.
30
Nanofitins (trade name) are small proteins which, like antibodies, are capable of binding
to a biological target thus permitting its detection, its capture or quite simply its
targeting in an organism.
25
The binding partners used can be specific or not specific to the folate(s). They are called
specific when they are capable of binding exclusively or virtually exclusively to the
folate(s). They are called non-specific when the binding selectivity to the folate(s) is low,
and they are capable of binding to other ligands, such as proteins or antibodies.
5 According to a preferred embodiment, at least one specific binding partner is used in the
context of the non-radioisotopic competition immunoassay process according to the
present invention.
When they are used in capture, the binding partners or the folate derivatives according
10 to the invention can be bound or not bound to a support by any technique known to the
man skilled in the art.
The second step b) of the process of the invention is a conventional step of a competition
immunoassay process.
15
The last step c) of the process according to the invention consists in determining the
folate(s) concentration. The measured signal is inversely proportional to the quantity of
folate(s) in the sample. In order to determine the folate(s) concentration, the intensity of
the signal is measured and this intensity is plotted on a calibration curve previously
20 obtained by techniques widely known to the man skilled in the art. Thus, for example,
the calibration curve is obtained by performing a competition immunoassay using the
same binding partner as well as increasing quantities of folate(s). A curve is thus
obtained by placing, for example, the folate(s) concentration on the abscissa and the
corresponding signal obtained after immunoassay on the ordonnate.
25
When compound (ii) is a conjugate according to the invention, as described above, which
constitutes an embodiment of the invention, the signal is generated by the tagging
labelling of the labelling molecule Mm, as described above.
30 When compound (ii) is a folate derivative of the invention, as described above, i.e. it is
not bound to a marker molecule Mm, the signal consists in the direct reading of the
binding partner/folate derivative binding, which can in particular be performed by
plasmon surface resonance or by cyclic voltammetry.
26
Preferably, compound (ii) is a conjugate according to the invention.
As indicated above, the folate derivatives and conjugates according to the invention can
be used to assay folate(s) in a sample. Preferably, these derivatives and conjugates are
5 used to assay a plurality of (at least two) folates, i.e. a plurality of folate forms (in
particular the reduced forms) in said sample.
According to a particular embodiment of the invention, the folate derivatives and
conjugates mentioned above are used to assay the total folate in a sample.
10
The invention also relates to an in vitro diagnostic method intended to determine
whether a human or animal patient, preferably human, has a folate(s) deficiency, said
method comprising the following steps:
15 a) in a biological sample, preferably of whole blood, of plasma or of serum,
taken from said patient, assaying the folate(s) by implementing the in vitro
assay process according to the invention, in order to deduce from it the
folate(s) concentration in the biological sample,
b) comparing said concentration with a threshold value, corresponding to a
20 predetermined folate(s) concentration below which a patient is considered
as deficient in folate(s), and
c) if the assayed concentration is less than said threshold value, deducing from
this that the patient has a folate(s) deficiency.
25 Another object of the invention relates to a folate derivative of general formula (I)
in which:
- X is as defined above;
27
- Y is a group of electrophilic centre type or of nucleophilic centre type, preferably a
group of electrophilic centre type, suitable to allow the formation of an amide,
ester, or thioester bond, preferably amide or ester, advantageously amide, between
Y and a functional group carried by a separate molecule M; and in which:
5 - when X is a linear and saturated hydrocarbon chain comprising a number of
carbon atoms equal to 2, Y is not an -(O-CH2-CH2)2-NH2 group;
- when Y is a group of nucleophilic centre type consisting in a primary amine, X
comprises a number of carbon atoms different from 6,
- when Y is a group of electrophilic centre type, the latter respond to the following
10 general formula (II):
in which Gp is a leaving group, optionally connected to the carbonyl function by an L
arm, Gp being suitable to be dissociated from the group of electrophilic centre type in a
reaction with a nucleophilic group carried by said separate molecule M, such as a
15 primary amine, and in which, when L is absent and Gp is -OH, X comprises a number of
carbon atoms greater than 4.
According to a particular embodiment, the functional group Y does not comprise an -(OCH2-
CH2)- structure.
20
This folate derivative of general formula (I) is suitable for implementation of a nonradioisotopic
competition immunoassay of the folate(s) in a sample. It does not therefore
include a radioisotope/radioelement.
25 Said folate derivative of general formula (I) as such is not labelled. Where necessary, said
folate derivative will be labelled after bonding to a marker molecule Mm, said bonding
comprising the formation of a covalent bond between the functional group Y of said
folate derivative and a functional group carried by said marker molecule Mm.
30 The folate derivative of general formula (I) is different from the NSP-DMAE-HD-pteroate
compound represented by formula (A) in claim 1.
28
According to a particular embodiment, Y is different from group (C):
(C)
5 According to another particular embodiment, when X is a linear and saturated
hydrocarbon chain comprising a number of carbon atoms equal to 2, Y is different from
the following groups (D) and (E):
(D) ; (E)
10
According to a modification of this “other particular embodiment”, Y is different from the
above-mentioned groups (D) and (E), and this whatever the definition of X.
Preferably, said reaction of the group of electrophilic centre type of general formula (II)
15 with said nucleophilic group carried by said molecule M - such as a primary amine - is a
nucleophilic substitution reaction.
According to a particular embodiment, when Y is a group of nucleophilic centre type, the
latter consists in a functional group different from a primary amine.
20
According to a preferred embodiment, when Y is a group of electrophilic centre type
responding to general formula (II), (L)-Gp is a group selected from: -OH, -NH-(CH2)m-
COOH, -N3,
29
O-N
O
O ,
HN-H2C-OC-O-N
O
O
m
,
O-N
O
O
SO3Na
,
HN-H2C-OC-O-N
O
O
m
SO3Na
,
O NO2
,
O
O2N
,
O F
F F
F F
,
O Cl
Cl Cl
Cl Cl
, and
O-N
O
O ,
5 m being an integer of between 1 and 10, preferably between 1 and 5,
advantageously between 1 and 3, in which when L is absent and Gp is -OH, X
comprises a number of carbon atoms greater than 4.
Preferably, when Y is a group of electrophilic centre type of formula (II), (L)-Gp is
10 selected from:
30
-OH and -NH-(CH2)m-COOH and
, m being between 1 and 10 and preferably m being equal to 1,
in which when L is absent and Gp is -OH, X comprises a number of carbon atoms
greater than 4.
5
According to a particularly advantageous embodiment, when Y is a group of electrophilic
centre type of formula (II), (L)-Gp is:
10 According to a particular embodiment, and still when Y is a group of electrophilic centre
type of general formula (II), Gp is a group different from an -OH (hydroxyl group) group.
The invention also relates to a conjugate comprising a folate derivative according to the
invention and a separate molecule M, said derivative and said molecule M being linked
15 by at least one amide, ester, or thioester bond, preferably an amide or ester bond,
advantageously an amide bond, between Y and a functional group carried by said
molecule M.
According to a particularly preferred embodiment, said molecule M is selected from
20 chemical arms or “linkers” or from the marker molecules Mm, said molecule M preferably
being a marker molecule Mm permitting the direct or indirect labelling of said folate
derivative (the latter then being called “tagged conjugate”).
HN-H2C-OC-O-N
O
O
m
HN-H2C-OC-O-N
O
O
m
31
Another object of the invention relates to a kit permitting the implementation of the
process according to the invention, said kit comprising:
 (i) at least one binding partner of said folate(s), such as an antibody
suitable to bind to the folate(s) or such as the folates receptor,
5  (ii) at least one compound selected from a folate derivative such as
defined above and a conjugate according to the invention,
at least one of said compounds (i) and (ii) being suitable to emit a
signal,
and
10  at least one calibration means.
Of course, this kit (also called “detection kit”) can comprise other constituents allowing
or favouring the implementation of the immunoassay according to the invention, such as,
for example, wash buffers and one or more other reagent(s) allowing the labelling to be
15 visualised, or the emission of a detectable signal.
The folate derivatives of the invention can be used in two different manners in the
processes for assay of the folate(s) by competition immunoassay, such as diagnostic
tests. Indeed, they are either used as such, or they are used bonded to another molecule
20 to form a conjugate.
Said “other molecule” is either a direct or indirect marker, or a chemical arm or “linker”,
or a chemical compound the bonding of which to a folate derivative has an advantage, in
particular for implementation of a folate assay by competition immunoassay (preferably
25 non-radioisotopic).
Thus, the present invention also has as its object conjugates comprising or formed of a
folate derivative such as described above and of another molecule, in particular of a
marker or of a chemical arm.
30
By marker, is understood any molecule capable of directly or indirectly generating a
detectable signal. A non-limiting list of these direct detection markers consists in:
32
 enzymes which produce a detectable signal for example by colorimetry,
fluorescence, luminescence, like horseradish peroxidase, alkaline
phosphatase, β-galactosidase, glucose-6-phosphate dehydrogenase,
 chromophores such as fluorescent, luminescent, colourant compounds,
5  fluorescent molecules such as Alexa or phycocyanins,
 electrochemiluminescent salts such as organometallic derivatives based on
acridinium all ruthenium.
Indirect detection systems can also be used, like for example ligands capable of reacting
10 with an anti-ligand. The ligand then corresponds to the marker molecule Mm to
constitute, with the folate derivative mentioned above, the conjugate of the invention.
The ligand/anti-ligand pairs are well known to the man skilled in the art. By way of
example can in particular be cited the following pairs: biotin/streptavidin,
15 hapten/antibody, antigen/antibody, peptide/antibody, sugar/lectin,
polynucleotide/complementary polynucleotide.
The anti-ligand can then be directly detectable by the direct detection markers described
above or itself be detectable by another ligand/anti-ligand pair, and so on.
20
These indirect detection systems can lead, under certain conditions, to amplification of
the signal. This technique of amplification of the signal is well known to the man skilled
in the art, and reference can in particular be made to prior patent applications
FR98/10084 and WO-A-95/08000 of the Applicant.
25
Depending on the type of labelling used, the man skilled in the art will add reagents
permitting the labelling to be visualised or the emission of a signal detectable by any
appropriate type of measuring apparatus, like for example a spectrophotometer, a
spectrofluorometer or a camera (for example a high-definition camera).
30
By chemical arm or “linker”, is understood any molecule able to be bonded to the
derivative according to the present invention, said molecule being in addition capable of
fixing onto a solid phase, covalently or non-covalently, in selective or non-selective
manner.
33
As indicated above, the folate derivatives and the corresponding conjugates according to
the present invention are particularly useful for in vitro determination of the folate(s)
concentration in a sample of clinical origin (for example a biological sample taken from a
human or animal patient) or a sample of agri-food origin (taken from a food or from a
5 food supplement).
The determination of the folate(s) concentration using the derivative or conjugate
according to the present invention may be performed in the culture supernatant or in the
cellular lysate.
10
Another object of the invention relates to the process for obtaining a derivative
according to the invention, said process comprising the following steps:
a) synthesising, from pteroic acid, the compound of general formula (VI):
15 in which W represents a group increasing the solubility of said compound in
organic solvent(s), such as a trifluoroacetyl group (COCF3),
b) reacting said compound of formula (VI), obtained in step a), with a compound of
following general formula (VII):
20
under conditions permitting the obtaining, by bonding, of the compound of
following general formula (VIII):
34
X being as defined above,
Z being an inert group, preferably alkyl or aryl, and
Y” being a derivative of the Y group (such as defined above) after bonding to said
5 Z group.
c) unprotecting, under conditions permitting this unprotection, the compound of
formula (VIII), in order to obtain the folate derivative of formula (I) according to
the invention.
10
According to a preferred embodiment, in step b), said compound of formula (VI),
obtained in step a), is reacted with a compound of following general formula (VII):
15
in which Y” is -C(O)O-,
in order to prepare a folate derivative of formula (I), in which Y is -COOH.
In this preferred embodiment, if Z is a methyl or ethyl group, Y-Z is respectively -C(O)O20
CH3 or -C(O)O-CH3 in compounds of formulae (VII) and (VIII). If Z is an aryl group, then
Y-Z is -C(O)O-Ar in said compounds (Ar symbolising this aryl group).
At the end of the unprotection step c), and still within this preferred embodiment, the
above-mentioned group -C(O)O- results in a -COOH group. The folate derivative of
25 general formula (I) according to the invention thus obtained is called “acid” folate
derivative. According to a preferred aspect of this embodiment, the process then
comprises, after step c), the following additional step:
35
d) obtaining, from said acid folate derivative (in which Y = -COOH), the NHSfolate
derivative ester, i.e. the compound responding to the following general
formula (IX):
5 in which X is as defined above.
This compound of general formula (IX) represents one of the preferred folate derivatives
or the preferred folate derivative within the meaning of the present invention.
Advantageously, X is a saturated linear aliphatic hydrocarbon chain comprising a
10 number of carbon atoms between 1 and 10, preferably between 2 and 7, advantageously
between 3 and 5.
The methods for obtaining NHS (N-hydroxysuccinimides) esters are well known to the
person skilled in the art. Examples of obtaining folate derivatives of formula (IX)
15 according to the invention are presented below (cf. examples 3 and 4 below) as
illustrative and non-limiting examples.
Pteroic acid is a commercially available compound. Unfortunately, this compound proves
to have low solubility in organic solvents. It is therefore transformed, in step a), into a
20 compound of general formula (VI) to facilitate the continuation of the present process.
Preferably, this compound of formula (VI) is N-trifluoroacetylpteroic acid (W = -COCF3).
In this case, the pteroic acid is made to react, preferably, with trifluoroacetic anhydride,
advantageously protected by nitrogen.
25 As indicated above, step b) is performed under reaction conditions allowing the required
reaction to be obtained. These reaction conditions, preferably, include the use of a
bonding agent.
36
As indicated above, the inert group Z consists, for example, in a methyl or ethyl group (in
particular when Y” is -C(O)O-, to give-C(O)O-Mp or -C(O)O-Et) or in an Fmoc group (in
particular when Y” is -NH-, to give-NH-Fmoc).
According to a particular embodiment, step b) comprises the following two sub-steps:
5 b.1) forming, from the compound of formula (VI), obtained in step a), an active
intermediate such as N-trifluoroacetylpteroic acid isobutylformiate of the following
general formula (VI’):
b. 2) reacting said active intermediate obtained in step b.1) with a compound of
10 following general formula (VII):
under conditions allowing the obtaining, by bonding, of the compound of following
general formula (VIII):
15
in which W, X, Y” and Z are as defined above.
According to a preferred embodiment, in steps b) and/or b.2) mentioned above, the
bonding is obtained by transamidification.
20
37
The unprotection step c) results in the elimination of the W group and, concurrently or
subsequently, of the Z group, advantageously under the protection of nitrogen.
This unprotection step c) is, preferably, performed in a basic medium, for example in a
5 solution of NaOH. This basic solution allows the elimination of the W group and,
concurrently, of the Z group (consisting for example in a methyl or ethyl group), by
saponification reaction.
Detailed description
10
The invention will be better understood by means of the following examples which are
given in illustrative and non-limiting manner, with reference to figures 1 and 2, in which:
 figure 1 shows the synthesis steps of folate-C4-acid (4-(4-((2-amino-4-oxo-
15 3,4-dihydropteridin-6-yl)methylamino)benzamido)butanoic acid) and NHSC4-
folate, and
 figure 2 shows the synthesis steps of folate-C6-acid (6-(4-((2-amino-4-oxo-
3,4-dihydropteridin-6-yl)methylamino)benzamido)hexanoic acid) and NHSC6-
folate.
20
Example 1: Preparation of 4-(4-((2-amino-4-oxo-3,4-dihydropteridin-6-
yl)methylamino) benzamido) butanoic acid (folate-C4-acid)
For the sake of clarity, the compound called “folate-C4-acid” is a derivative according to
25 the invention, responding to the following general formula (I):
in which X is a linear and saturated aliphatic hydrocarbon chain comprising 3 carbon
atoms and Y is a group of electrophilic centre type responding to general formula (II):
38
in which L is absent and Gp is -OH.
1.1. Introduction
5
The reagents pteroic acid (CAS-Nr. 119-24-4), trifluoroacetic anhydride (CAS-Nr.
407-25-0), methyl 4-aminobutyrate (CAS-Nr. 3251-07-8), isobutyl chloroformiate (CASNr.
543-27-1) amino-6-hexanoic acid (CAS-Nr. 60-32-2 also called 6-aminocaproic acid)
and anhydrous dichloromethane (CAS-Nr. 75-09-2) were obtained from Sigma-Aldrich.
10
At each synthesis step, high pressure liquid chromatography (HPLC) is used to
monitor the reaction progress and for analysis of the products. The column used is a
Vydac 218TP54, C18, 250x4.6mm, 5m and the eluent is a gradient acetonitrile, water
(0.1% trifluoroacetic acid) mixture.
15
1.2. Step 1: obtaining N-trifluoroacetylpteroic acid
500 mg (1.60 mmole) of pteroic acid are introduced into a 50 mL flask provided with
magnetic agitation, with an inlet and an outlet for protection nitrogen. 10 mL of
20 trifluoroacetic anhydride are added under nitrogen protection, drop by drop, over 30
minutes. The reaction mixture is agitated at ambient temperature for 24 hours in the
dark. The reaction medium is evaporated under reduced pressure at ambient
temperature and the residue is dried under vacuum for 1 hour. The product obtained is
washed with 5 mL of ethyl ether and then dried under vacuum. The product is analysed
25 by HPLC and used directly for the continuation of the synthesis.
1.3. Step 2: obtaining N-trifluoroacetyl-folate-C4-Me
A mixture of 171 mg (0.42 mmole) of N-trifluoroacetylpteroic acid, 0.111 mL of
30 triethylamine (CAS-Nr. 121-44-8) and 2 mL of dry dimethylformamide (DMF, CAS-Nr.
68-12-2) is prepared and agitated at ambient temperature under nitrogen for 45
39
minutes to give medium No. 1. In another 10 mL flask, 150 mg (0.98 mmole) of methyl 4-
aminobutyrate hydrochloride are mixed with 2 mL of dry DMF, and then 0.111 mL of
triethylamine are added. After agitation for 30 seconds, the mixture obtained is added
under nitrogen protection to the prepared medium No. 1. The agitation is maintained at
5 ambient temperature for 3 hours and the reaction is monitored by HPLC. The reaction
medium is dried, without heat under vacuum. The residue is purified by silica gel 60
chromatography (0.040-0.063 mm, Merck Cat. No. 109385) with
dichloromethane/methanol eluent, 5/1, v/v. 85 mg of product are obtained, which
corresponds to a 40% yield. The purity is 96%, determined by HPLC.
10
1.4. Step 3: obtaining folate-C4-acid
85 mg (0.168 mmole) of prepared N-trifluoroacetyl-folate-C4-Me acid are mixed with 6
mL of methanol. 2 mL of a 1N NaOH mixture are added. The mixture is agitated at
15 ambient temperature and in the dark for 16 hours. The reaction medium is neutralised at
pH 2 with 50% of trifluoroacetic acid and then dried under reduced pressure at ambient
temperature. The residue is washed with 10 mL of the demineralised water and dried
under vacuum. 66 mg of folate-C4-acid are obtained, which corresponds to a yield of
98%. The purity is 97.2%, determined by HPLC.
20
The synthesis of folate-C4-acid is summarised in figure 1.
Example 2: Preparation of 6-(4-((2-amino-4-oxo-3,4-dihydropteridin-6-
yl)methylamino)benzamido) hexanoic acid (folate-C6-acid)
25
The folate derivative called “folate-C6-acid” is a derivative according to the present
invention responding to the following general formula (I):
40
in which X is a linear and saturated aliphatic hydrocarbon chain comprising 5
carbon atoms, and in which Y is a group of electrophilic centre type, responding to the
following general formula (II):
5
in which L is absent and Gp is -OH.
Folate-C6-acid (6-(4-((2-amino-4-oxo-3,4-dihydropteridin-6-yl)methyl-amino)
10 benzamido) hexanoic acid) is synthesised in similar manner to folate-C4-acid. In the
above-mentioned step 2, the methyl 4-aminobutyrate (NH2-C4-Me) arm is replaced by an
ethyl 6-aminocaproate arm (NH2-C6-Et, ethyl ester of amino-6-hexanoic acid). This
compound is prepared from amino-6-hexanoic acid in the presence of ethanol and acetyl
chloride.
15
60 mg of folate-C6-acid are obtained from 171 mg of N-trifluoroacetylpteroic acid, which
corresponds to an overall yield of 34%. The purity is 96%, determined by HPLC.
The synthesis of folate-C6-acid is summarised in Figure 2.
20
Generally, the length of the hydrocarbon chain X in the derivative of general formula (I)
can be varied by using, in step 2, alkyl aminoalkanoate reagents of which the length of
the hydrocarbon part of the alkanoate varies (4 carbon atoms to obtain the compound
called “folate-C4-acid”; 6 carbon atoms to obtain the compound called “folate-C6-acid”).
25
Example 3: Preparation of the esters of folate-C4-NHS
The reagents, N-hydroxysuccinimide (NHS, CAS-Nr. 6066-82-6), 1, 3-
dicyclohexylcarbodiimide (DCC, CAS-Nr. 538-75-0), dimethylsulphoxide (DMSO, CAS-Nr.
30 67-68-5) and tetrahydrofuran (CAS-Nr. 109-99-9) were obtained from Sigma-Aldrich.
41
66 mg (0.166 mmole) of folate-C4-acid obtained in example 1, 28.8 mg (or 1.5 x 0.166
mmole) of NHS and 4 mL of dry DMSO are introduced into a flask. 41.1 mg (or 1.2 x0.166
mmole) of DCC are introduced after 2 minutes of agitation. The agitation is maintained at
ambient temperature in the dark for 48 hours. HPLC is used to monitor the progress of
5 the activation. 7 mg of NHS and/or 4 mg of DCC are added and the agitation is
maintained for 72 additional hours.
The reaction mixture is filtered and the solution obtained is mixed with 5 mL of dry
tetrahydrofuran, then 170 mL of dry dichloromethane are added. The mixture is
10 centrifuged after 15 minutes without agitation to recover the precipitate which is then
dried under reduced pressure, without heat and in the dark. 42 mg of folate-C4-NHS are
obtained, which corresponds to a yield of 51%. The purity is 69%, determined by HPLC.
The obtaining of the folate-C4-NHS ester is represented in figure 1 (cf. last reaction step).
15
Example 4: Preparation of the esters of folate-C6-NHS
As for the folate-C4-NHS ester, the reagents used are the following: Nhydroxysuccinimide
(NHS, CAS-Nr. 6066-82-6), 1, 3-dicyclohexylcarbodiimide (DCC,
20 CAS-Nr. 538-75-0), dimethylsulphoxide (DMSO, CAS-Nr. 67-68-5) and tetrahydrofuran
(CAS-Nr. 109-99-9), and were obtained from Sigma-Aldrich.
60 mg (0.14 mmole) of folate-C6 acid obtained in example 2, a mixture of DMF (2.5 mL)
and DMSO (3 mL) dry solvents and 17.7 mg (1.1 x 0.14 mmole) of NHS are introduced
25 into a flask. 32 mg (1.1 x 0.14 of DCC are added after 2 minutes of agitation. The agitation
is maintained at ambient temperature, in the dark, for 24 hours. HPLC is used to monitor
the progress of the activation. 30 mg of NHS and 30 mg of DCC are added and the
agitation is maintained for 96 additional hours.
30 The reaction medium is centrifuged for 3 minutes at 3000 rpm and the recovered liquid
is mixed with 30 mL of the mixture of the solvents dichloromethane/petroleum ether
(1/1) and then centrifuged again to obtain a yellow precipitate. The product is dried
under reduced pressure, without heat and in the dark. 21 mg (29% yield) of folate-C6-
NHS are obtained with an HPLC purity of 83.1%.
42
The synthesis of the folate-C6-NHS ester is summarised in figure 2 (cf. last reaction step).
Example 5: Preparation of the folate-C4-NHS-alkaline phosphatase and folate-C6-
NHS-alkaline phosphatase conjugates
5
0.5 mL of a 20 mg/mL solution of recombinant alkaline phosphatase (ALP) (Roche, Ref.
03-535-452) are dialysed in Spectra/Por® tubing (cut-off level 6000-8000 Da, Spectrum
Laboratories, USA) against 500 mL of 100 mM pH 8.3 carbonate buffer, under magnetic
agitation, for one night, at +2/8°C. At the dialysis outlet, the concentration of the protein
10 is determined by reading the optical density at 280 nm and this concentration is adjusted
to 4 mg/mL.
The activated folate-C4-NHS and folate-C6-NHS esters obtained in example 2 are again
used in DMSO at concentrations of 0.39 mg/mL and 0.5 mg/mL respectively, taking into
15 account the purity.
For bonding of type (1-5) (one mole of alkaline phosphatase-5 moles of folate ester),
1.125 mL of the ALP solution are mixed with 256 μL of the folate-C4-NHS ester solution
on the one hand and 255 μL of the folate-C6-NHS ester solution on the other. The
20 percentage of DMSO in the reaction medium is 18.5%. The mixtures are incubated for
one night at +2/8°C, under agitation on a wheel, in brown bottles.
Then, the reaction is stopped by addition of 10 mM lysine diluted in water. The quantity
of lysine added is equimolar with the quantity of ester used for bonding. Therefore 20.5
25 μL of the lysine solution are added for each of the bondings. The mixtures are incubated
for 20 minutes on a wheel, at +18/25°C.
After stopping the reaction, 1 mL of each of the conjugates are dialysed in Spectra/Por®
tubing (cut-off level approximately 7000 Da) for 3h at +18/25°C against 500 mL of 50
30 mM Tris pH 7.4, 9 g/L NaCl, 0.9 g/L azide buffer, under magnetic agitation. After 3 hours
the tubes are transferred into new baths again containing 500 mL of the same buffer. The
dialysis is continued overnight at +2/8°C, under magnetic agitation.
43
At the dialysis outlet, 10x conservation buffer (500 mM Tris pH 7.4, 90 g/L NaCl, 50 mM
MgCl2, 1 mM ZnCl2, 0.01% SDS, 9 g/L azide) is added to the volumes recovered from the
tubes. The volume obtained is approximately 1 mL per conjugate. Following dialysis the
conjugates are only semi-purified: the dialysis permits elimination of the free, unreacted
5 folate but not the free alkaline phosphatase. The conjugates can be used in an
immunoassay at this stage and this is what has has been done in example 6 below.
To eliminate the free ALP and thus obtain conjugates with improved purity, hydrophobic
interaction chromatography was performed using a RESOURCE Phenyl column (Cat No.
10 17-1186-01, GE Healthcare Lifesciences) mounted on an ÄKTA chromatography system.
The flow rate of the pump is set to 2 mL/min. The TA buffer is 50 mM Tris pH 7.4, 9 g/L
NaCl, 5 mM MgCl2, 0.1 mM ZnCl2, 0.9 g/L azide, 1.6 M (NH4)2SO4 . The TB buffer is 50 mM
Tris pH 7.4, 9 g/L NaCl, 5mM MgCl2, 0.1 mM ZnCl2, 0.9 g/L azide. The RESOURCE Phenyl
column is equilibrated with TA buffer. The conjugate to be purified is mixed volume for
15 volume with the TB buffer. Then, 2 volumes are added of the 50 mM Tris pH 7.4, 9 g/L
NaCl, 5mM MgCl2, 0.1 mM ZnCl2, 0.9 g/L azide, 3.2 M (NH4)2SO4 buffer. This step allows
the conjugate to be in the TA buffer. The injection of the conjugate (628 μL for folate-C4-
NHS-ALP and 560 μL for folate-C6-NHS-ALP, in a 5 mL loop) is followed by a 20 mL wash
in TA buffer. Then a 0 to 57% gradient of TB is applied for 30 mL, then a wash in 57% of
20 TB buffer for 20 mL. This step is followed by a second gradient of 57 to 100% of TB
applied for 30 mL, then by a wash in TB buffer for 20 mL. The last step consists in a
gradient of 0 to 100% in water for 20 mL, and then a wash in water for 20 mL. The
progress of the chromatography is monitored by measuring the optical density at 280
nm. The fractions from 74 mL of elution up to 104 mL (or in total 30 mL) are recovered,
25 combined and then concentrated by diafiltration using an Amicon cell (Amicon stirred
cells, Millipore), an Amicon PM membrane with a cut-off level of 10 000 Da and the TB
buffer. In this step, the volume of the conjugate solution is reduced to approximately 0.5
mL. The conjugates are stored at +2/8°C until their use in an immunoassay.
30 Example 6: Vitamin B9 assay using the conjugates folate-C4-NHS-alkaline
phosphatase and folate-C6-NHS-alkaline phosphatase and comparison with the
Axsym assay conjugate (Abbott Laboratories)
44
The immunological assays were performed using the VIDAS® automated immunoassay
analysis system (bioMérieux). The single-use cone is used both as the solid phase for the
reaction and as the pipetting system. The cartridge is composed of 10 wells covered with
a sealed and labelled sheet of aluminium. The first well includes a previously cut-out part
5 to facilitate the introduction of the sample. The last well is an optical cuvette in which the
fluorescence of the substrate is measured. The different reagents necessary for the
analysis are contained in the intermediate wells.
a) Sensitisation and passivation of the cones
10
The cones were sensitised with 300 μL of an “anti-folate binding protein” monoclonal
mouse antibody (clone P8C5E4, ) diluted to 5 μg/mL in a 0.2 M tris, pH 6.2 buffer. After 6
hours of incubation at +18/25°C, a wash is performed with a 1M solution of NaCl. Then,
300 μL of a solution of “folate binding protein” (FBP, Cat. No. F0524, Scripps
15 Laboratories) diluted to 6 ng/mL in a 100 mM, pH 7.4 NaCl 0.15 M phosphate buffer
containing human albumin and a sugar are added. The sensitisation / passivation is
continued at +18/25°C overnight. The cones are emptied, dried and then stored at +4°C
until use.
20 b) Preparation of a range from biological samples
Human serum samples containing different folate concentrations were obtained from
the Biomnis laboratory (Lyon, France). The samples having the same concentrations
were mixed in order to increase the available volume per range point. The mixtures were
25 then aliquoted at 120 μL and frozen at -20°C until use. The nominal concentrations of
each of the points are: 1.3 ng/mL - 4.4 ng/mL - 10 ng/mL - 20 ng/mL. The range point 0
ng/mL was prepared by dissolving 10% of human serum albumin in 10 mM pH 8.5, 0.15
M NaCl phosphate borate buffer.
30 c) Extraction of the samples
The objective of the extraction step is to dissociate the serum folate from its binding
partners and to make it accessible for the assay. To 250 μL of sample are added 50 μL of
a 62.5 mg/mL TCEP (tris2-carboxyethyl)phosphine) solution and 215 μL of a solution of
45
0.8N NaOH+0.005% KCN. The mixture is incubated at+18/25°C for 15 minutes, in the
dark. After this stage, 1 mL of 1M pH4 glycine buffer is added.
d) Modus operandi of the immunoassay reaction
5
The sample to be assayed (200 μL), extracted according to the protocol described in c), is
introduced into the first well of the cartridge. Then all the assay reaction steps are
performed automatically by the VIDAS®. The cones prepared according to the protocol
described in a) are wetted by a 1M pH 10, 0.1 M NaCl glycine and 2% saccharose buffer.
10 The sample to be assayed is mixed with 200 μL of a dilution of conjugate which is a folate
derivative labelled with alkaline phosphatase. The sample/conjugate mixture is
incubated in the cone for approximately 20 minutes during which competition takes
place between the folates present in the sample and the folate derivative of the conjugate
for FBP protein sites presented on the cone. Then, 3 successive washes with a 100 mM
15 Tris pH 7.4, 0.15M NaCl, 0.1% Tween® 20 buffer are performed in order to eliminate the
non-fixed compounds. At the final revelation step, the 4-methylombelliferyl phosphate
substrate is aspirated and then discharged into the cone; the enzyme of the conjugate
catalyses the hydrolysis reaction of this substrate into 4-methylombelliferone, the
emitted fluorescence of which is measured at 450 nm. The value of the fluorescence
20 signal is inversely proportional to the folate concentration present in the sample.
In the experiment presented in Table 1, three conjugates have been compared. These are
the two conjugates obtained in example 3 and, as reference, the conjugates used in the
Abbot Axsym Folate kit (Cat. No. B7K460, Abbot Laboratories).
25 (i) the folate-C4-ALP and folate-C6-ALP conjugates were diluted to a
concentration of between 0.50 - 0.75 ng/mL in the conjugate diluting buffer
which contains 100 mM of Tris pH 8.5, 0.15 M NaCl, 20 mg/L of mouse IgG,
stabilisation agents, preserving agents and other additives.
(ii) the conjugate of the folate Axsym kit is a conjugate of pteroic acid (folate
30 analogue) and alkaline phosphatase. This conjugate was diluted to 1/80 with
the conjugate diluting buffer before use in the VIDAS®.
The range points prepared in b) were measured with each assay format. Table 1 below
summarises the results obtained with the RFV (=relative fluorescence value) signal and
46
B/B0% ratio. The B/B0% ratio is the signal obtained for the range point tested divided
by the signal obtained for the range point 0 ng/mL of folate, multiplied by 100.
Table 1
REF = Axsym
conjugate
Folate-C4-ALP Folate-C6-ALP
[c] folate (ng/mL)
Signal
(RFV)
B/B0%
Signal
(RFV)
B/B0%
Signal
(RFV)
B/B0%
0 3399 100 3544 100 4118 100
1.3 3329 98 3095 87 3563 87
4.4 2442 72 2016 57 2619 64
10 925 27 995 28 1131 27
20 39 1 24 1 34 1
5
An 87% reduction in the signal is observed at 1.3 ng/mL of folate with the folate-C4-ALP
and folate-C6-ALP conjugates of the invention, while with the reference conjugate the
signal reduction scarcely begins.
10 Consequently, the assays using the folate-C4-ALP and folate-C6-ALP conjugates are more
sensitive than the assay using the reference conjugate and permit better detection and
quantification of concentrations less than 4.4 ng/mL, and even less than 1.3 ng/mL.
Regarding the folate derivatives and conjugates according to the invention, in particular
15 those responding to general formulae (I), (I’), (III), (III’), (III’’), (VI), (VI’), (VIII) and (IX)
mentioned above, it should be noted that, even if the pterin part of these is shown
diagrammatically in its ketone form, the present invention quite obviously covers all -
and each of the - tautomeric forms of said folate derivatives and conjugates able to be
obtained at said pterin part, and in particular the 2-amino-4-hydroxy-6-methylpteridin
20 form.
47
Bibliographical References
1. Antony AC, The biological chemistry of folate receptors, Department of Medicine,
Indiana University School of Medicine, Indianapolis, Blood. 1992 Jun
5 1;79(11):2807-20
2. Reif VD, Reamer JT, Grady LT., Chromatic assays for folic acid, J Pharm Sci. 1977
Aug:66(8):1112-6 PMID:894496
3. Dueker SR, Lin Y, Jones AD, Mercer R, Fabbro E, Miller JW, Green R, Clifford AJ.,
Determination of blood folate using acid extraction and internally standardized gas
10 chromatography-mass spectrometry detection, Anal Biochem. 2000 Aug
1;283(2):266-75 PMID:10906248
4. Pfeiffer CM, Fazili Z, McCoy L, Zhang M, Gunter EW, Determination of folate
vitamers in human serum by stable-isotope-dilution tandem mass spectrometry
and comparison with radioassay and microbiologic assay, Clin Chem. 2004
15 Feb;50(2):423-32. Epub 2003 Dec 11 PMID:14670827
5. Waxman S. and Schreiber C., Determination of folate by use of radioactive folate
and binding proteins, Methods Enzymol. 1980; 66:468-83. No abstract available.
PMID:7374487
6. Hansen, S. I. and Holm, J., A competitive enzyme-linked ligand sorbent assay
20 (ELLSA) for quantitation of folates, Anal Biochem. 1988 Jul;172(1):160-4.
PMID:3189760
7. Owen, W.E. and Roberts, W. L., Comparison of five automated serum and whole
blood folate assays, Am J Clin Pathol. 2003 Jul;120(1):121-6. PMID:12866382
8. Arcot J. and Shrestha A., Folate: methods of analysis, Food Science and
25 Technology, School of Chemical Engineering and Industrial Chemistry, The
University of New South Wales, Sydney, Australia, 2005
48
Claims
1. Use of a folate derivative to assay in vitro the folate(s) in a sample, such as a
biological sample, said assay being a non-radioisotopic competition immunoassay,
5 said folate derivative being decarboxylated in the α position, and said folate
derivative being different from the NSP-DMAE-HD-pteroate and NSP-DMAE-HEGpteroate
compounds represented respectively by the following formulae (A) and
(B):
10
2. Use of a folate derivative to assay in vitro the folate(s) in a sample, such as a
49
biological sample, said assay being a non-radioisotopic competition immunoassay,
and said folate derivative responding to general formula (I):
5 in which:
- X is an aliphatic hydrocarbon chain containing from 1 to 10 carbon atoms;
and
- Y represents a functional group suitable to permit bonding to a separate
molecule M,
10 such as a protein, said bonding comprising the formation of at least one covalent
bond between Y and a functional group carried by said separate molecule M.
3. Use according to claim 2, in which X is a hydrocarbon chain containing from 2 to 7
carbon atoms, preferably from 3 to 5 carbon atoms, advantageously X is a
15 hydrocarbon chain of 3 carbon atoms or 5 carbon atoms.
4. Use according to claim 2 or 3, in which X is a saturated hydrocarbon chain.
5. Use according to one of claims 2 to 4, in which X is a linear hydrocarbon chain.
20
6. Use according to one of claims 2 to 5, in which Y is a group of electrophilic centre
type or a group of nucleophilic centre type, preferably a group of electrophilic
centre type, suitable to allow the formation of an amide, ester, or thioester bond,
preferably amide or ester, advantageously amide, between Y and the functional
25 group carried by said separate molecule M.
7. Use according to one of claims 2 to 6, in which Y is a group of electrophilic centre
type, responding to the following general formula (II):
50
in which Gp is a leaving group, optionally bonded to the carbonyl function by an L
arm, Gp being suitable to be dissociated from the group of electrophilic centre type
in a reaction with the nucleophilic group carried by said separate molecule M, such
5 as a primary amine.
8. Use according to claim 7, in which the (L)-Gp group is selected from the groups
suitable to allow the formation of an amide, ester, or thioester bond, preferably
amide or ester, advantageously amide, between said group of electrophilic centre
10 type and a functional group carried by said separate molecule M.
9. Use according to claim 7 or 8, in which the (L)-Gp group is selected from: -OH, -NH-
(CH2)m-COOH, -N3,
O-N
O
O ,
HN-H2C-OC-O-N
O
O
m
,
O-N
O
O
SO3Na
,
HN-H2C-OC-O-N
O
O
m
SO3Na
,
O NO2
15 ,
51
O
O2N
,
O F
F F
F F
,
O Cl
Cl Cl
Cl Cl
, and
O-N
O
O ,
m being an integer between 1 and 10.
5 10. Use according to claim 9, in which m is between 1 and 5, advantageously between
1 and 3.
11. Use according to one of claims 7 to 10 in which the (L)-Gp group is selected from
-OH and -NH-(CH2)m-COOH and
10 , m being between 1 and 10 and preferably m being equal to 1.
12. Use according to one of claims 2 to 11, in which the derivative of general formula
(I) is used in conjugate form with said molecule M, and said conjugate being
represented by the following general formula (III):
HN-H2C-OC-O-N
O
O
m
52
in which X and M are as defined in one of claims 2 to 11, and in which Y’ is a
derivative of the functional group Y after bonding of the derivative of general
formula (I) to said molecule M,
5 said molecule M preferably being a marker molecule Mm.
13. Use according to claim 12, in which Y’ is represented by the following general
formula (IV):
10 or by the following general formula (V):
in which R1 is -NH-, -O-, or -S-, preferably -NH- or -O-, advantageously -NH-;
preferably Y’ being represented by general formula (IV).
15 14. Process for in vitro assay of the folate(s) in a sample, such as a biological sample,
said assay being a non-radioisotopic competition immunoassay, said process
comprising the following steps:
a) bringing into contact, in said biological sample, (i) at least one binding
20 partner of the folate(s), such as an antibody suitable to bind to the folate(s)
or such as a receptor of the folates, with (ii) at least one compound selected
from a folate derivative as defined in one of claims 1 to 11 and a conjugate as
defined in claim 12 or 13, at least one of said compounds (i) and (ii) being
suitable to emit a signal,
25 b) optionally leaving a sufficient time lapse to allow the competition reaction,
53
c) measuring the intensity of the signal and deducing from it the folate(s)
concentration present in said biological sample by reference to a calibration
curve establishing a relationship between the measured signal intensity and
folate(s) concentration.
5
15. Process according to claim 14, characterised in that the compound (ii) is a
conjugate as defined in claim 12 or 13.
16. In vitro diagnostic method intended to determine whether a human or animal
10 patient, preferably human, has a folate(s) deficiency, said method comprising the
following steps:
a) in a biological sample, preferably of whole blood, plasma or serum, taken
from said patient, assaying the folate(s) by implementing the in vitro assay
15 process according to claim 14 or 15, in order to deduce from it the folate(s)
concentration in the biological sample
b) comparing said concentration with a threshold value, corresponding to a
predetermined folate(s) concentration below which a patient is considered
as folate(s) deficient, and
20 c) if the assayed concentration is lower than said threshold value, deducing
from this that the patient has a folate(s) deficiency.
17. Folate derivative of general formula (I):
25 in which:
- X is as defined in one of claims 2 to 11;
- Y is a group of electrophilic centre type or of nucleophilic centre type,
preferably a group of electrophilic centre type, suitable to allow the
54
formation of an amide, ester, or thioester bond, preferably amide or ester,
advantageously amide, between Y and a functional group carried by a
separate molecule M; and in which:
- when X is a linear and saturated hydrocarbon chain containing a number of
5 carbon atoms equal to 2, Y is not an -(O-CH2-CH2)2-NH2 group;
- when Y is a group of nucleophilic centre type consisting in a primary amine,
X comprises a number of carbon atoms different from 6,
- when Y is a group of electrophilic centre type, the latter responds to the
following general formula (II):
10
in which Gp is a leaving group, optionally connected to the carbonyl function by an
L arm, Gp being suitable to be dissociated from the group of electrophilic centre
type in a reaction with a nucleophilic group carried by said separate molecule M,
15 such as a primary amine, and in which, when L is absent and Gp is -OH, X
comprises a number of carbon atoms greater than 4.
18. Folate derivative according to claim 17, in which Y is a group of nucleophilic centre
type consisting in a functional group different from a primary amine.
20
19. Folate derivative according to claim 17, in which Y is a group of electrophilic centre
type responding to general formula (II) and in which (L)-Gp is a leaving group
selected from: -OH, -NH-(CH2)m-COOH, -N3,
O-N
O
O ,
HN-H2C-OC-O-N
O
O
m
,
O-N
O
O
SO3Na
,
55
HN-H2C-OC-O-N
O
O
m
SO3Na
,
O NO2
,
O
O2N
,
O F
F F
F F
,
O Cl
Cl Cl
Cl Cl
, and
O-N
O
O ,
m being an integer between 1 and 10, preferably between 1 and 5, advantageously
5 between 1 and 3, in which when L is absent and Gp is -OH, X comprises a number
of carbon atoms greater than 4.
20. Folate derivative according to claim 19, in which (L)-Gp is selected from:
-OH and -NH-(CH2)m-COOH and
HN-H2C-OC-O-N
O
O
m
10
, m being between 1 and 10 and preferably m being equal to 1,
in which when L is absent and Gp is -OH, X comprises a number of carbon atoms
greater than 4.