Technical Field of the Invention
The invention relates to a method for the preparation of a radiopharmaceutical
compound, in particular an amino acid derivative useful as a positron emission
tomography (PET) tracer. The method of the invention is especially suitable when
automated and offers advantages over known methods. Particularly, the invention
relates to a method for preparation of [1 F]-l-amino-3-fluorocyclobutane-l-carboxylic
acid ([1 F]-FACBC, also known as [1 F]-Fluciclovine).
Description of Related Art
The non-natural amino acid [ F]-l-amino-3-fluorocyclobutane-l-carboxylic acid
([1 F]-FACBC, also known as [1 F]-Fluciclovine) is taken up specifically by amino acid
transporters and has shown promise for tumour imaging with positron emission
tomography (PET).
A known synthesis of [1 F]-FACBC begins with the provision of the protected
precursor compound 1-(N-(t -butoxycarbonyl)amino)-3-
[((trifluoromethyl)sulfonyl)oxy]-cyclobutane-l-carboxylic acid ethyl ester. This
precursor compound is first labelled with [1 F]-fluoride:
II
before removal of the two protecting groups:
T III
EP2017258 (Al) teaches removal of the ethyl protecting group by trapping the [1 F]-
labelled precursor compound (II) onto a solid phase extraction (SPE) cartridge and
incubating with 0.8 mL of a 4 mol/L solution of sodium hydroxide (NaOH). After 3
minutes incubation the NaOH solution was collected in a vial and a further 0.8 mL 4
mol/L NaOH added to the SPE cartridge to repeat the procedure. Thereafter the SPE
cartridge was washed with 3 mL water and the wash solution combined with the
collected NaOH solution. Then 2.2 mL of 6 mol/L HCl was then added with heating to
60°C for 5 minutes to remove the Boc protecting group. The resulting solution was
purified by passing through (i) an ion retardation column to remove Na+ from excess
NaOH and Cl~ from extra HCl needed to neutralise excess of NaOH to get a highly
acidic solution before the acidic hydrolysis step, (ii) an alumina column, and (iii) a
reverse-phase column. There is scope for the deprotection step(s) and/or the
purification step in the production of [1 F]-FACBC to be simplified.
Summary of the Invention
The present invention provides a method for the production of [1 F]-FACBC which has
advantages over know such methods. The method of the present invention is
particularly amenable to automation as it permits a simplified purification procedure
compared with known methods. In the method of the present invention an extra high
volume of H+ is not required in the Boc deprotection step as it is in the prior art method.
Furthermore, an ion removal step such as by means of an ion retardation column such
as is required in the prior art method is not required by the method of the invention
because there is no longer a need for excess ions to be removed. Also provided by the
present invention is a system to carry out the method of the invention and a cassette
suitable for carrying out the method of the invention on an automated radiosynthesis
apparatus.
Detailed Description of the Invention
In one aspect the present invention provides a method to prepare l-amino-3-[ 1 F]-
fluorocyclobutanecarboxylic acid ([1 F]-FACBC) wherein said method comprises:
(a) providing a compound of Formula II adsorbed to a solid phase:
wherein:
PG1 is a carboxy protecting group; and,
PG2 is an amine protecting group;
reacting said adsorbed compound of Formula II with a PG1 deprotecting
agent;
sending the PG1 deprotecting agent to waste following said reacting step
(b);
passing an elution solution through said solid phase to obtain an eluted
compound of Formula III:
(e) reacting said eluted compound of Formula III obtained in step (d) with a
PG2 deprotecting agent to obtain a reaction mixture comprising [1 F]-
FACBC.
The "solid phase" used in step (a) of the method of the invention is contained within a
solid phase extraction (SPE) column. Suitably, said solid phase is one having a
hydrophobic functional group such as phenyl, cyclohexyl and alkyl, for example one
having a structure comprising a support to which C2-18 alkyl groups are attached via
silicon. In a preferred embodiment, the SPE column is filled with a solid phase having
octadecylsilyl groups as functional groups. Moreover, it is preferable to use a column
packing having a structure in which the functional groups are not easily detached from
the solid phase under aqueous reaction conditions and/or during a long deesterification
reaction. In one embodiment the SPE column is a tC18 column.
The compound of Formula II is relatively hydrophobic and therefore has a strong
affinity for the solid phase and therefore binds to, or becomes "adsorbed", to said solid
phase by virtue of hydrophobic interactions.
The term "protecting group" refers to a group which inhibits or suppresses undesirable
chemical reactions, but which is designed to be sufficiently reactive that it may be
cleaved from the functional group in question to obtain the desired product under mild
enough conditions that do not modify the rest of the molecule. Protecting groups are
well known to those skilled in the art and are described in 'Protective Groups in
Organic Synthesis', Theorodora W. Greene and Peter G. M. Wuts, (Fourth Edition,
John Wiley & Sons, 2007).
The term "reacting" refers to bringing two or more chemical substances (typically
referred to in the art as "reactants" or "reagents") together to result in a chemical
change in one or both/all of the chemical substances. For example, in the present
invention, the step of reacting a PG1 deprotecting agent with an adsorbed compound of
Formula II changes said compound of Formula II to a compound of Formula III.
The PG1 "carboxy protecting group" is preferably linear or branched C1-10 alkyl chain
or an aryl substituent. The term "alkyl" used either alone or as part of another group is
defined as any straight, branched or cyclic, saturated or unsaturated C H2 +i group. The
term "aryl" refers to any C6-14 molecular fragment or group which is derived from a
monocyclic or polycyclic aromatic hydrocarbon, or a monocyclic or polycyclic
heteroaromatic hydrocarbon. In one embodiment of the method of the invention PG1 is
selected from methyl, ethyl, t-butyl and phenyl. In another embodiment of the
invention PG1 is methyl or ethyl and in yet another embodiment PG1 is ethyl.
The PG2 "amine protecting group" suitably prevents reaction between 1 F and the
amino group in the process of providing the compound of Formula II. Examples of
suitable amine protecting groups include various carbamate substituents, various amide
substituents, various imide substituents, and various amine substituents. Preferably, the
amine protecting group is selected from the group consisting of linear or branched C2 _7
alkyloxycarbonyl substituents, linear or branched C3-7 alkenyloxycarbonyl substituents,
C _i2 benzyloxycarbonyl substituents that may have a modifying group, C2-7
alkyldithiooxycarbonyl substituents, linear or branched Ci_ alkylamide substituents,
linear or branched C2_6 alkenylamide substituents, C6-n benzamide substituents that
may have a modifying group, C4-10 cyclic imide substituents, C6-11 aromatic imine
substituents that may have a substituent, linear or branched Ci_6 alkylamine
substituents, linear or branched C2_ alkenylamine substituents, and C6-1 1 benzylamine
substituents that may have a modifying group. In some embodiments of the invention
PG2 is selected from t-butoxycarbonyl, allyloxycarbonyl, phthalimide, and Nbenzylideneamine.
In other embodiments PG2 is selected from t-butoxycarbonyl or
phthalimide. In one embodiment of the invention PG2 is t-butoxycarbonyl.
A "PG1 deprotecting agent" is a reagent capable of removing the carboxy protecting
group PG1 from the compound of Formula II during the reacting step (b). Suitable such
carboxy deprotecting agents are well-known to the skilled person (see Greene and
Wuts, supra) and may be either an acid or an alkaline solution. The concentration of
the PG1 deprotecting agent is not limited as long as it is sufficient to remove the
carboxy protecting group PG1 and does not have an effect on the final purity or is
incompatible with any container used. Preferably the PG1 deprotecting agent is an
alkaline solution. In certain embodiments the PG1 deprotecting agent is a sodium
hydroxide or a potassium hydroxide solution and in a preferred embodiment is a sodium
hydroxide solution, for example of 0.5-5.0 M, preferably 0.5-2.0 M. The reacting step
is enabled by closing the outlet of the SPE column so that the PG1 deprotecting agent is
retained therein for a specified amount of time. The temperature and the duration of
this reacting step need to be sufficient to permit removal of the PG1 carboxy
deprotecting group. In certain embodiments the reacting step is carried out at room
temperature and for a duration of between 1-5 minutes.
The step of "sending the PG1 deprotecting agent to waste" means that once step (b) is
complete (i.e. PG1 is removed from the compound of Formula II), the PG1 deprotecting
agent is allowed to pass through the SPE column and is routed out of the reaction
system so that it is no longer part of the reaction mixture. An additional benefit is that
any impurities soluble in the deprotection solution are also routed out of the reaction
system. The PG1 deprotecting agent is therefore substantially removed from the
reaction mixture for subsequent steps (d) and (e). As used herein, the term
"substantially" refers to the complete or nearly complete extent or degree of an action,
characteristic, property, state, structure, item, or result. For example, an object that is
substantially enclosed would mean that the object is either completely enclosed or
nearly completely enclosed. The exact allowable degree of deviation from absolute
completeness may in some cases depend on the specific context. However, generally
speaking the nearness of completion will be so as to have the same overall result as if
absolute and total completion were obtained. For example in the case of removal of the
PG1 deprotecting group, the term "substantially removed" can be taken to mean in the
PG2 deprotection step (e) that only sufficient PG2 deprotecting agent is required to
remove PG2, i.e. it is not required to add extra ion to counter the level of ion present
from the PG1 deprotecting step (b).
The "elution solution" of step (d) is suitably one for which the compound of Formula
III has more affinity than it has for the solid phase. Suitably, because said compound of
Formula III is relatively hydrophilic compared with said solid phase, said elution
solution is a hydrophilic solution. In some embodiments of the invention said elution
solution is an aqueous solution and in other embodiments said elution solution is water.
The "PG2 deprotecting agent" is a reagent capable of removing the amine protecting
group PG2 from the compound of Formula III during the reacting step (e). Suitable
such amine deprotecting agents are well-known to the skilled person (see Greene and
Wuts, supra) and may be either an acid or an alkaline solution. The concentration of
the PG2 deprotecting agent is not limited as long as it is sufficient to remove the
carboxy protecting group PG2. Preferably the PG2 deprotecting agent is an acid
solution. A suitable acid preferably includes an acid selected from inorganic acids such
as hydrochloric acid, sulfuric acid and nitric acid, and organic acids such as
perfluoroalkyl carboxylic acid, e.g. trifluoroacetic acid. In certain embodiments, the
PG2 deprotecting agent is hydrochloric acid, and in other embodiments when HC1 is
used as PG2 deprotecting agent it is at a concentration of 1.0-4.0M. Reacting step (e) is
preferably carried out with heat to allow the removal of PG2 reaction to proceed more
rapidly. The reaction time depends on the reaction temperature or other conditions.
For example, when the reacting step (e) is performed at 60°C, a sufficient reaction time
is 5 minutes.
In a preferred aspect, the [1 F]-FACBC is trans- 1-amino-!
fluorocyclobutanecarboxylic acid ( t -[1 F]-FACBC):
said compound of Formula II is a compound of Formula Ila:
said compound of Formula III is a compound of Formula Ilia:
(Ilia)
wherein PG and PG are as described hereinabove.
Said providing step (a) of the method of the invention may be carried out using methods
known in the art, such as for example described by McConathy et al (2003 Appl Radiat
Isotop; 58: 657-666).
Suitably, said providing step (a) comprises:
(i) reacting a precursor compound of Formula I :
with a suitable source of [1 F]fluoride;
wherein:
LG is a leaving group;
PG1 is as defined hereinabove; and,
PG2 is as defined hereinabove;
to obtain a reaction mixture comprising the compound of Formula II;
(ii) applying the reaction mixture obtained in step (i) to a solid phase so that
said compound of Formula II becomes adsorbed to said solid phase,
wherein said solid phase is as defined hereinabove.
A "precursor compound" comprises a non-radioactive derivative of a radiolabeled
compound, designed so that chemical reaction with a convenient chemical form of the
detectable label occurs site-specifically; can be conducted in the minimum number of
steps (ideally a single step); and without the need for significant purification (ideally no
further purification), to give the desired radiolabeled compound. Such precursor
compounds are synthetic and can conveniently be obtained in good chemical purity.
A suitable "leaving group" in the context of the present invention is a chemical group
that can be displaced by nucleophilic displacement reaction with fluoride ion. These
are well-known in the art of synthetic chemistry. In some embodiments the leaving
group of the present invention is a linear or branched C1-10 haloalkyl sulfonic acid
substituent, a linear or branched C1-10 alkyl sulfonic acid substituent, a fluorosulfonic
acid substituent, or an aromatic sulfonic acid substituent. In other embodiments of the
invention the leaving group is selected from methanesulfonic acid, toluenesulfonic acid,
nitrobenzenesulfonic acid, benzenesulfonic acid, trifluoromethanesulfonic acid,
fluorosulfonic acid, and perfluoroalkylsulfomc acid. In some embodiments the leaving
group is either methanesulfonic acid, trifluoromethanesulfonic acid or toluenesulfonic
acid and in another embodiment the leaving group is trifluoromethanesulfonic acid.
In a preferred embodiment, said compound of Formula I is a compound of Formula la:
and said compound of Formula II is a compound of Formula Ila:
wherein LG, PG and PG are as previously defined herein.
The "source of 1 F1fluoride" suitable for use in the invention is normally obtained as an
aqueous solution from the nuclear reaction 1 0(p,n) 1 F. In order to increase the reactivity
of fluoride and to reduce or minimise hydroxylated by-products resulting from the presence
of water, water is typically removed from [1 F]-fluoride prior to the reaction, and
fluorination reactions are carried out using anhydrous reaction solvents (Aigbirhio et al
1995 J Fluor Chem; 70: 279-87). A further step that is used to improve the reactivity of
[1 F]-fluoride for radiofluorination reactions is to add a cationic counterion prior to the
removal of water. Suitably, the counterion should possess sufficient solubility within the
anhydrous reaction solvent to maintain the solubility of the [1 F]-fluoride. Therefore,
counterions that are typically used include large but soft metal ions such as rubidium or
caesium, potassium complexed with a cryptand such as Kryptofix™, or
tetraalkylammonium salts, wherein potassium complexed with a cryptand such as
Kryptofix™, or tetraalkylammonium salts are preferred.
In some embodiments the present invention additionally includes the further step (f) of
purifying said reaction mixture obtained in step (e) to obtain substantially pure [1 F]-
FACBC.
The term "substantially " as used in "substantially pure " takes the meaning as presented
above. The term "substantially pure " as used in the context of [1 F]-FACBC encompasses
completely pure [1 F]-FACBC or [1 F]-FACBC that is sufficiently pure to be suitable for
use as a PET tracer. The term "suitable for use as a PET tracer" means that the [1 F]-
FACBC product is suitable for intravenous administration to a mammalian subject
followed by PET imaging to obtain one or more clinically-useful images of the location
and/or distribution of [1 F]-FACBC.
In one embodiment, step (f comprises:
(i) carrying out a first purification step comprising passing said reaction
mixture through a hydrophilic lipophilic balanced (HLB) solid phase; and,
(ϋ) optionally carrying out a second purification step comprising passing said
reaction mixture through an alumina solid phase.
In certain embodiments of the present invention said purifying step (f) can be said to
consist essentially of the above-defined steps. In particular, the purifying step (f as used
in the present invention does not require that the reaction mixture is passed through an ion
retardation column. This is a notable distinction over the prior art methods where this is a
required step in order to remove ions and to neutralise the reaction mixture (e.g. as
described by McConathy et al, supra, and in EP-A 20172580029). As such, the method of
the present invention is simplified over the prior art methods and as such is more suitable
for automation. In a preferred embodiment the method of the invention is automated, and
in this embodiment suitably carried out on an automated synthesis apparatus.
In another aspect of the invention is provided a system for carrying out the method of the
invention wherein said system comprises:
(a) a solid phase as defined herein for the method of the invention;
(b) a source of PG deprotecting agent herein for the method of the invention;
(c) a source of elution solution as defined herein for the method of the
invention;
a source of PG2 deprotecting agent as defined herein for the method of the
invention;
(e) a reaction container; and,
(f a waste means;
wherein said system further comprises means permitting sequential flow from:
(i) (e) to (a);
(ii) (b) to (a);
(iii) (a) to (f);
(iv) (c) to (e) via (a); and,
(v) (d) to (e).
The "reaction chamber" is any vessel suitable for carrying out an 1 F labelling reaction.
The term "waste means" refers for example to a dedicated vessel into which is sent any
components of the reaction that are no longer required, along with associated tubing and
valves permitting the transfer of these components away from the reaction.
In particular, the system of the invention does not comprise an ion retardation column.
In another embodiment, the system of the invention further comprises:
(g) a source of said precursor compound of Formula I as defined herein; and,
(h) a source of [1 F]fluoride.
In a further embodiment, the system of the present invention may also comprise (i) means
for purifying said reaction mixture obtained in step (e) to obtain substantially pure [1 F]-
FACBC. Said means (i) in certain embodiments may comprise a HLB solid phase and an
alumina solid phase.
The system of the invention in one embodiment consists essentially of the above-described
features.
[1 F]-radiotracers in particular are now often conveniently prepared on an automated
radiosynthesis apparatus. The method of the invention may therefore be carried out using
an automated radiosynthesis apparatus. By the term "automated radiosynthesis apparatus"
is meant an automated module based on the principle of unit operations as described by
Satyamurthy et al (1999 Clin Positr Imag; 2(5): 233-253). The term "unit operations "
means that complex processes are reduced to a series of simple operations or reactions,
which can be applied to a range of materials. Suitable automated synthesiser apparatus are
commercially available from a range of suppliers including: GE Healthcare Ltd (Chalfont
St Giles, UK); CTI Inc. (Knoxville, USA); Ion Beam Applications S.A.(Chemin du
Cyclotron 3, B-1348 Louvain-La-Neuve, Belgium); Raytest (Straubenhardt, Germany) and
Bioscan (Washington DC, USA).
Commercial automated radiosynthesis apparatus also provide suitable containers for the
liquid radioactive waste generated as a result of the radiopharmaceutical preparation.
Automated radiosynthesis apparatus are not typically provided with radiation shielding,
since they are designed to be employed in a suitably configured radioactive work cell. The
radioactive work cell provides suitable radiation shielding to protect the operator from
potential radiation dose, as well as ventilation to remove chemical and/or radioactive
vapours.
Preferred automated radiosynthesis apparatus of the present invention are those which
comprise a disposable or single use cassette which comprises all the reagents, reaction
vessels and apparatus necessary to carry out the preparation of a given batch of
radiopharmaceutical. By use of such cassettes the automated radiosynthesis apparatus has
the flexibility to be capable of making a variety of different radiopharmaceuticals with
minimal risk of cross-contamination, by simply changing the cassette. The cassette
approach also has the advantages of: simplified set-up and hence reduced risk of operator
error; improved GMP (Good Manufacturing Practice) compliance; multi-tracer capability;
rapid change between production runs; pre-run automated diagnostic checking of the
cassette and reagents; automated barcode cross-check of chemical reagents vs the synthesis
to be carried out; reagent traceability; single-use and hence no risk of cross-contamination,
tamper and abuse resistance.
In a further aspect the present invention provides a cassette for carrying out the method
of the invention on an automated synthesis apparatus wherein said cassette comprises
the elements as defined for the system of the invention.
For each aspect of the invention, features having the same name have all the same
embodiments as described in relation to other aspects of the invention.
Brief Description of the Examples
Example 1 describes the synthesis of [1 F]FACBC according to the method of the
invention.
List of Abbreviations used in the Examples
[1 F]FACBC 1-amino-3-[1 F]fluorocyclobutane-l-carboxylic acid
K222 Kryptofix 222
MeCN acetonitrile
MeOH methanol
QMA quaternary methyl ammonium
RCY radiochemical yield
SPE solid-phase extraction
TLC thin layer chromatography
UV ultraviolet
Examples
All reagents and solvents were purchased from Merck and used without further
purification. The [1 F]FACBC precursor; Syn-l-(N-(tert-butoxycarbonyl)amino)-3-
[[(trifluoromethyl)sulfonyl]oxy]-cyclobutane-l-carboxylic acid ethyl ester was obtained
from GE Healthcare. The Oasis HLB plus cartridge and the Sep-Pak cartridges: QMA
light Plus (K2CO3 form), tC18 light, Alumina N light were purchased from Waters
(Milford, MA, USA). A Capintec Nal ion chamber was used for all radioactive
measurements (model CRC15R). Radio-thin layer chromatography (radio-TLC) was
performed on a Packard instant imager using pre-coated plates of silica gel (Merck
60F254) .
Example 1: Synthesis of FIFACBC
No-carrier- added [1 F]fluoride was produced via the 1 0(p,n) 1 F nuclear reaction on a
GE PETtrace 6 cyclotron (Norwegian Cyclotron Centre, Oslo). Irradiations were
performed using a dual-beam, 30mA current on two equal Ag targets with HAVAR foils
using 16.5 MeV protons. Each target contained 1.6 ml of > 96% [1 0]water (Marshall
Isotopes). Subsequent to irradiation and delivery to a hotcell, each target was washed
with 1.6 ml of [1 0]water (Merck, water for GR analysis), giving approximately 2-5
Gbq in 3.2 ml of [1 0]water.
All radiochemistry was performed on a commercially available GE FASTlab™ with
single-use cassettes. Each cassette is built around a one-piece-moulded manifold with
25 three-way stopcocks, all made of polypropylene. Briefly, the cassette includes a 5 ml
reactor (cyclic olefin copolymer), one 1ml syringe and two 5 ml syringes, spikes for
connection with five prefilled vials, one water bag (100 ml) as well as various SPE
cartridges and filters. Fluid paths are controlled with nitrogen purging, vacuum and the
three syringes. The fully automated system is designed for single-step fluorinations
with cyclotron-produced [1 F]fluoride. The FASTlab was programmed by the software
package in a step-by-step time-dependent sequence of events such as moving the
syringes, nitrogen purging, vacuum, and temperature regulation. Synthesis of
[1 F]FACBC followed the three general steps: (a) [1 F]fluorination, (b) hydrolysis of
protection groups and (c) SPE purification.
Vial A contained K222 (58.8 mg, 156 mpioΐ), K2C0 3 (8.1 mg, 60.8 m oΐ) in 79.5% (v/v)
MeCN(aq) ( 1105 mΐ) . Vial B contained 4M HC1 (2.0 ml). Vial C contained MeCN
(4.1ml). Vial D contained the precursor (48.4 mg, 123.5 mihoΐ) in its dry form (stored at
-20 °C until cassette assembly). Vial E contained 2 M NaOH (4.1 ml). The 30 ml
product collection glass vial was filled with 200 mM trisodium citrate (10 ml). Aqueous
[1 F]fluoride (1-1.5 ml, 100-200 Mbq) was passed through the QMA and into the 1 0 -
H20 recovery vial. The QMA was then flushed with MeCN and sent to waste. The
trapped [1 F]fluoride was eluted into the reactor using eluent from vial A (730 mΐ) and
then concentrated to dryness by azeotropic distillation with acetonitrile (80 mΐ , vial C).
Approximately 1.7 ml of MeCN was mixed with precursor in vial D from which 1.0 ml
of the dissolved precursor (corresponds to 28.5 mg, 72.7 mmol precursor) was added to
the reactor and heated for 3 min at 85°C. The reaction mixture was diluted with water
and sent through the tC18 cartridge. Reactor was washed with water and sent through
the tC18 cartridge. The labelled intermediate, fixed on the tC18 cartridge was washed
with water, and then incubated with 2M NaOH (2.0 ml) for 5 min after which the 2M
NaOH was sent to waste. The labelled intermediate (without the ester group) was then
eluted off the tC18 cartridge into the reactor using water. The BOC group was
hydrolysed by adding 4M HC1 ( 1.4 ml) and heating the reactor for 5 min at 60 °C. The
reactor content with the crude [1 F]FACBC was sent through the HLB and Alumina
cartridges and into the 30 ml product vial. The HLB and Alumina cartridges were
washed with water (9. 1ml total) and collected in the product vial. Finally, 2M NaOH
(0.9 ml) and water (2.1 ml) was added to the product vial, giving a purified formulation
of [1 F]FACBC with a total volume of 26 ml. Radiochemical purity was measured by
radio-TLC using a mixture of MeCN:MeOH:H 20:CH 3COOH (20:5:5:1) as the mobile
phase. The radiochemical yield (RCY) was expressed as the amount of radioactivity in
the [1 F]FACBC fraction divided by the total used [1 F]fluoride activity (decay
corrected). Total synthesis time was 43 min.
The RCY of [1 F]FACBC was 62.5% ± 1.93 (SD), n=4.

WE CLAIMS:-
(1) A method to prepare l-amino-3-[ 1 F]-fluorocyclobutanecarboxylic acid
FACBC) wherein said method comprises:
(a) providing a compound of Formula II adsorbed to a solid phase:
wherein:
PG1 is a carboxy protecting group; and,
PG2 is an amine protecting group;
reacting said adsorbed compound of Formula II with a PG1 deprotecting
agent;
sending the PG1 deprotecting agent to waste following said reacting step
(b);
passing an elution solution through said solid phase to obtain an eluted
compound of Formula III:
(e) reacting said eluted compound of Formula III obtained in step (d) with a
PG2 deprotecting agent to obtain a reaction mixture comprising [1 F]-
FACBC.
(2) The method as defined in Claim 1 wherein said [1 F]-FACBC is trans- l-amino-3 -
[1 F]-fluorocyclobutanecarboxylic acid ( t -[1 F]-FACBC):
said compound of Formula II is a compound of Formula Ila:
said compound of Formula III is a compound of Formula Ilia:
(Ilia)
wherein PG1 and PG2 are as defined in Claim 1.
(3) The method as defined in either Claim 1 or Claim 2 wherein PG is ethyl.
(4) The method as defined in any one of Claims 1-3 wherein PG2 is t-butoxycarbonyl.
(5) The method as defined in any one of Claims 1-4 wherein said solid phase is a tC18
solid phase extraction (SPE) column.
(6) The method as defined in any one of Claims 1-5 wherein said PG1 deprotecting
agent is NaOH.
(7) The method as defined in any one of Claims 1-6 wherein said PG2 deprotecting
agent is HC1.
(8) The method as defined in any one of Claims 1-7 wherein said elution solution is
water.
The method as defined in Claim 1 wherein said providing step (a) comprises
reacting a precursor compound of Formula I
with a suitable source of [1 F]fluoride;
wherein:
LG is a leaving group;
PG is as defined in either Claim 1 or Claim 3; and,
PG is as defined in either Claim 1 or Claim 4;
to obtain a reaction mixture comprising said compound of Formula II;
applying the reaction mixture obtained in step (i) to a solid phase so that
said compound of Formula II becomes adsorbed to said solid phase,
wherein said solid phase is as defined in either Claim 1 or Claim 5.
(10) The method as defined in Claim 9 wherein said compound of Formula I is a
compound of Formula la:
and said compound of Formula II is a compound of Formula Ila:
(Ila)
wherein LG is as defined in Claim 7, PG1is as defined in either Claims 1or
Claim 3 and PG2 is as defined in either Claim 1 or Claim 4.
( 11) The method as defined in either Claim 9 or Claim 10 wherein LG is
trifluoromethanesulfonic acid.
(12) The method as defined in any one of Claims 1-1 1which comprises the further step
(f) of purifying said reaction mixture obtained in step (e) to obtain substantially
pure [1 F]-FACBC.
(13) The method as defined in Claim 12 wherein step (f) comprises carrying out a first
purification step comprising passing said reaction mixture through a hydrophilic
lipophilic balanced (HLB) solid phase.
(14) The method as defined in Claim 13 wherein step (f) further comprisescarrying out a
second purification step comprising passing said reaction mixture through an
alumina solid phase.
(15) The method as defined in any one of Claims 1-14 which is automated.
(16) A system for carrying out the method as defined in any one of Claims 1-8
comprising:
(a) a solid phase as defined in either Claim 1 or Claim 5;
(b) a source of PG1 deprotecting agent as defined in either Claim 1or Claim 6;
(c) a source of elution solution as defined in either Claim 1 or Claim 8;
(d) a source of PG2 deprotecting agent as defined in either Claim 1or Claim 7;
(e) a reaction container; and,
(f) a waste means;
wherein said system further comprises means permitting sequential flow from:
(i) (e) to (a);
(ϋ) (b) to (a);
(iii) (a) to (f);
(iv) (c) to (e) via (a); and,
(v) (d) to (e).
A system for carrying out the method as defined in any one of Claims 9-1 1
comprising the system as defined in Claim 16 and further comprising:
(g) a source of said precursor compound of Formula I; and,
(h) a source of [1 F]fluoride.
(18) A system for carrying out the method as defined in any one of Claims 12-14
comprising the system as defined in Claim 16 and further comprising (i) means for
purifying said reaction mixture obtained in step (e) to obtain substantially pure
[1 F]-FACBC.
(19) The system as defined in Claim 18 wherein said means for purifying comprises a
HLB solid phase and optionally an alumina solid phase.
(20) A cassette for carrying out the method as defined in any one of Claims 1-8 on an
automated synthesis apparatus wherein said cassette comprises the system as
defined in Claim 16.
(21) A cassette for carrying out the method as defined in any one of Claims 12-14 on an
automated synthesis apparatus wherein said cassette comprises the system as
defined in Claim 19.