18F - FLUCICLOVINE COMPOSITIONS IN CITRATE BUFFERS
Technical Field of the Invention
The present invention relates to a drug product composition and in particular to a
composition comprising a positron emission tomography (PET) tracer. The
composition of the present invention has certain advantages over prior art formulations.
Description of Related Art
The non-natural amino acid [ F -1-amino-3-fluorocyclobutane-l -carboxylic acid
([ 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).
In radioactive diagnostic imaging agents, a problem often arises such that compounds
decompose by self-radiation during delivery of the agents so as to cause decrease in
radiochemical purity due to so-called radiolysis. In PET tracers comprising nuclides
such as C and !8F, radiolysis often becomes more problematic since the half-life of the
nuclides used therein is relatively short, e.g. as compared with nuclides used in single
photon emission tomography (SPECT) such as "Tc and thus radioactivity upon
shipment must be set larger than SPECT agents, thereby making the resulting radiation
energy thereof higher.
Various methods for inhibiting radiolysis in PET tracers have been examined. For
example in compositions comprising [i F]-fluorodeoxyglucose ([ F]FDG). WO
2003/090789 discloses a method of reducing the radiolysis of [ F]FDG by adding a
weak acid-based buffer to an [18F]FDG solution. WO 2004/043497 discloses adding
ethanol to a [ F]FDG solution to obtain a composition of [1 F]-FDG having improved
stability.
In the case of [l F]FACBC different strategies have been adopted. EP 2106808 (Al )
discloses that for a composition comprising [ F]FACBC, when the pH value is not
more than 5.9, stability thereof is maintained even if there exist no pharmaceutical
additives or buffers that prevent radiolysis.
EP 2080526 (Al) discloses that radiolysis can be inhibited by adding a sugar lactone
such as ascorbic acid and glucono-o-lactone to [ F]FACBC. An exemplary
composition taught by EP 2080526 (A has a radioactivity of 1.4GBq in about 2 mL
and contains the sugar lactone in a proportion of lOmmol/mL immediately after
production providing a radioactivity of 50 to 225 MBq when the agent is used,
sufficient for PET imaging in adults. It was also disclosed that ascorbic acid at
concentrations of 0.5-10.0 mol/r- can inhibit decomposition of [ F]FACBC
solution. In this case, radiolysis was inhibited at a concentration of 700 MBq/mL at
maximum.
EP 2 19458 (Al) discloses a method to prepare a stabilised formulation of [1 F]FACBC
comprising diluting a solution of [ F]FACBC and then adding an acid in an amount
sufficient to adjust the pH of the solution to 2.0-5.9. Suitable acids disclosed are
ascorbic acid, benzoic acid, hydrochloric acid, acetic acid, citric acid, gentisic acid, and
oxalic acid, with hydrochloric acid preferred. EP 2 9458 (Al ) also discloses that a
sugar alcohol such as erythritol xylitol, sorbitol or marmitol can be added as a further
additive to inhibit radiolysis and improve stability.
In these known [ F]FACBC compositions radiostabihty is maintained by adjusting pH
within a relatively wide range using an acid and/or including a suitable additive.
Adjustment of pH using an acid rather than using a buffer has the advantage that the
ionic strength of the composition is lower.
Summary of the Invention
The present invention provides a pharmaceutical composition comprising [l F]FACBC
having certain advantages over known compositions comprising [ F]FACBC. Also
provided by the present invention is a method to obtain the composition of the
invention. The composition of the present invention is resistant to degradation, can be
autoclaved or diluted in saline (i.e. 0.9 % NaCl), and still maintain its pH in a narrow
range. Furthermore, the pharmaceutical composition of the present invention does not
require any radiostabiliser in order to maintain good radiostabihty over its shelf-life.
Detailed Description of the Invention
The present invention in one aspect provides a pharmaceutical composition of FFACBC
characterised in that said composition:
(i) comprises 50-100 mM citrate buffer; and,
(ii) has a pH of 4.0-5.0.
The term "pharmaceutical composition" refers to a composition comprising a
pharmaceutical together with a biocompatible carrier in a form suitable for mammalian
administration. A "biocompatible carrier" is a fluid, especially a liquid, in which a
pharmaceutical is suspended or dissolved, such that the composition is physiologically
tolerable, i.e. can be administered to the mammalian body without toxicity or undue
discomfort. The biocompatible carrier is suitably an injectable carrier liquid such as sterile,
pyrogen-free water for injection or an aqueous solution such as saline.
The pharmaceutical composition of the invention preferably 60-90mMcitrate buffer, most
preferably 75-85 mM citrate buffer.
The pharmaceutical composition of the invention preferably has a pH of 4.1-4.5, most
preferably 4.3-4.4.
The pharmaceutical composition of the invention preferably has an end of synthesis (EOS)
radioactive concentration (RAC) of at least 1000 MBq/mL, alternatively at least 1500
MBq/ml.
The term "end of synthesis" refers to the point in time when the labelled compound is
collected in the product collection vial.
The pharmaceutical composition of the present invention has a favourableimpurity profile,
with the main non-radioactive impurities being l-amino-3-hydroxyl-cyclobutane-lcarboxylic
acid (hydroxyl-ACBC), l-amino-3-fiuoro-cyclobutane-l-carboxylic acid
(FACBC) and 1-amino-3-chloro-cyclobutane- -carboxylic acid (chioro-ACBC).
It is preferred that there is not more than 150 m i hydroxyl-ACBC, most preferably not
more than 80 h , hydroxyl-ACBC.
It is preferred that there is not more than 0. FACBC, most preferably not more
than 0.10 mg L FACBC.
It is preferred that there is not more than 2.0 m I chloro-ACBC, most preferably not
more than .0 m L chloro-ACBC.
The term "not more than" should be understood to mean any amount less than the
quoted quantity. Therefore not more than 100 m - means any amount between 0-100
ug mL, and in an ideal embodiment of the composition of the present invention there
would be zero of each impurity present in the composition of the invention.
However, in reality, zero of an impurity might not be achievable and it is more
likely that at least a trace amount of the impurity remains in the composition, i.e. in the
case of hydroxyl-ACBC the term not more than 150 g m covers e.g. 50-150 mL,
not more than 0. 0 L for FACBC covers e.g. 0.05-0. 0 mg mL, and not more than
1.0 g m chloro-ACBC covers e.g. 0.25-1.0 .
An advantage of the composition of the present invention is that the pH, stability and
impurity profile can be kept within a very narrow range over a long shelf-life, at high
activities, and when manipulated e.g. by autoclaving or by dilution with 0.9% saline.
In a preferred embodiment, the pharmaceutical composition of the invention does not
comprise a radiostabiliser. It is common for pharmaceutical compositions comprising
radioactive pharmaceuticals to include a radiostabiliser. For example, known
pharmaceutical compositions of [ F]FACBC include a sugar alcohol or a sugar lactone.
EP 2080526 (Al) discloses that radiolysis can be inhibited by adding a sugar lactone
such as ascorbic acid and glucono-o-lactone to [ F]FACBC, and EP 2 119458 (Al)
discloses that a sugar alcohol such as erythritol xylitol, sorbitol or rnannitol can be
added as an additive to inhibit radiolysis and improve stability. No such radiostabiliser
is required in the radiopharmaceutical composition of the present invention in order to
maintain a shelf-life of up to around 0 hours.
In another aspect the present invention provides a method to obtain a
radiopharmaceutial composition wherein said composition is as defined hereinabove,
and wherein said method comprises:
reacting with a suitable source of [ F]fluoride a precursor compound of
Formula I:
wherein.
LG is a leaving group;
PG1 is a carboxy protecting group; and,
PG2 is an amine protecting group;
to obtain a compound of Formula II:
wherein PG1 and PG2 are as defined for Formula ;
reacting said compound of Formula II with a PG1 deprotecting agent to
obtain a compound of Formula IP:
wherein PG2 is as defined for Formula I;
(iii) reacting said compound of Formula HI with a PG2 deprotecting agent to
obtain [1 F]FACBC;
(iv) formulating said [ F]FACBC with citrate buffer to obtain said
pharmaceutical composition.
The "source of f1 F]fluoride" suitable for use in the invention is normally obtained as an
aqueous solution from the nuclear reaction , 0(p,n) 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 [ F]-fluoride prior to the reaction, and
fluorination reactions are carried out using anhydrous reaction solvents (Aigbirhio et al
95 J Fluor Chem; 70: 279-87). A further step that is used to improve the reactivity of
[ FJ-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 [ F]-fluoride. Therefore,
couttterions 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.
A "precursor compound" comprises a non-radioactive derivative of a radiolabelled
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 radiolabelled 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 C Ohaloalkyi sulfonic acid substituent,
a linear or branched C o 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 perfluoroalkylsulfonic 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.
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 PGl carboxy protecting group" is preferably linear or branched C O 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 H i group. The
term "aryl" refers to any C - 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 PG 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 F and the amino
group in the process of providing the compound of Formula P. 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
alkyloxycarbonyl substituents, linear or branched C3-7 alkenyloxycarbonyl substituents,
C7.12 benzyloxycarbonyl substituents that may have a modifying group, C2-7
alkyldithiooxycarbonyi substituents, linear or branched Ci. alkylamide substituents,
linear or branched C2-6 alkenylamide substituents, C - benzanoide substituents that may
have a modifying group, C 4-10 cyclic imide substituents, C - aromatic imine
substituents that may have a substituent, linear or branched Ci alkylamine substituents,
linear or branched C2 alkenylamine substituents, and - 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.
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.
A "PG1 deprotecting agent" is a reagent capable of removing the carboxy protecting
group PG1 from the compound of Formula 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 results in an
incompatibility 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 0.5-2.0M. 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 "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 PG deprotecting
agent is hydrochloric acid, and in other embodiments when HC1 is used as PG2
deprotecting agent it is at a concentration of .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.
Precursor compounds of Formula I may be obtained by following or adapting methods
known in the art, such as for example described by McConathy et al (2003 Appl Radiat
Isotop; 58: 657-666) or by Shoup and Goodman (1999 J Label Co p Radiopharm; 42:
215-225).
In a preferred aspect, the [l F]-FACBC is trans4-amino-3-[ F]-
fiuorocyclobutanecarboxylic acid ( i-[ F]-FACBC):
said compound of Formula I is a compound of Formula la:
compound of Formula Pis a compound of Formula Iia:
said compound of Formula PI is a compound of Formula Ilia:
(Ilia)
wherein PG1 and PG2 are as described hereinabove.
In some embodiments the method of present invention additionally includes a step
following the reacting step and before the formulating step of purifying the reaction
mixture obtained in the reacting step to obtain substantially pure [ 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 [ F]FACBC encompasses
completely pure [ F]FACBC or [ 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 [ F]FACBC
product is suitable for intravenous administration to a mammalian subject followedby PET
imaging to obtain one or more clinically-useful images of the location and/or distribution of
[ F]-FACBC.
A suitable purifying step comprises:
(i) carrying out a first purification step comprising passing said reaction
mixture through a hydrophilic lipophilic balanced (HLB) solid phase; and,
(ii) 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 can be said to consist
essentially of the above-defined steps. In particular, the purifying step 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 (2003 Appl
adiat Isotop; 58: 657-666), and in EP20172580029 (A)). 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 carried out on an automated
synthesis apparatus. By the term "automated synthesis 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. Such automated synthesis apparatuses are preferred for the method of the
present invention especially when a radiopharmaceutical composition is desired. They are
commercially available from a range of suppliers (Satyamurthyetal, above), including: GE
Healthcare; CTI Inc; Ion Beam Applications S.A. (Chemin du Cyclotron 3, B-1348
Louvain-La-Neuve, Belgium); Raytest (Germany) and Bioscan (USA).
A commercial automated synthesis apparatus also provides suitable containers for the
liquid radioactive waste generated as a result of the radiopharmaceutical preparation.
Automated synthesis apparatuses 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. The automated synthesis apparatus preferably comprises a cassette. By the term
"cassette" is meant a piece of apparatus designed to fit removably and interchangeably onto
an automated synthesis apparatus, in such a way that mechanical movement of moving
parts of the synthesizer controls the operation of the cassette from outside the cassette, i.e.
externally. Suitable cassettes comprise a linear array of valves, each linked to a port where
reagents or vials can be attached, by either needle puncture of an inverted septum-sealed
vial, or by gas-tight, marryingjoints. Each valve has a male-female joint which interfaces
with a corresponding moving arm of the automated synthesis apparatus. External rotation
of the arm thus controls the opening or closing of the valve when the cassette is attached to
the automated synthesis apparatus. Additional moving parts of the automated synthesis
apparatus are designed to clip onto syringe plunger tips, and thus raise or depress syringe
barrels.
The cassette is versatile, typically having several positions where reagents can be attached,
and several suitable for attachment of syringe vials of reagents or chromatography
cartridges (e.g. for SPE). The cassette always comprises a reaction vessel. Such reaction
vessels are preferably 0.5 to 10 L, more preferably 0.5 to 5mL and most preferably 0.5 to
4 mL in volume and are configured such that 3 or more ports of the cassette are connected
thereto, to permit transfer of reagents or solvents from various ports on the cassette.
Preferably the cassette has 15 to 40 valves in a linear array, most preferably 20 to 30, with
25 being especially preferred. The valves of the cassette are preferably each identical, and
most preferably are 3-way valves. The cassettes are designed to be suitable for
radiopharmaceutical manufacture and are therefore manufactured from materials which are
of pharmaceutical grade and ideally also are resistant to radiolysis.
Preferred automated synthesis apparatuses for use with the present invention 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 radiofluorinated
radiopharmaceutical. The cassette means that the automated synthesis apparatus has the
flexibility to be capable of making a varietyof different radiopharmaceuticals with minimal
risk of cross-contamination, by simply changing the cassette. The cassette approach also
has the advantages of: simplified set-up 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.
The following example serves to further illustrate the invention.
Brief Description of the Examples
Example 1 describes a method to obtain the composition of the present invention.
List of Abbreviations used in the Examples
ATR attenuated total reflectance
DTGS deuterated triglycine sulphate
[ F]FACBC l-amino-3-[ FJfluorocyclobutane-l-carboxylic acid
FT- R Fourier transform infrared
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
AHreagents and solvents were purchased from Merck and used without further
purification. The [1 F]FACBC precursor, 5>n-l-(N-(tert-butoxycarbonyl)amino)-3-
[[(trifluoromethyl)sulfonyl]oxy]-cyclobutane- -carboxylic acid ethyl ester was obtained
from GE Healthcare. The Oasis HLB plus cartridge and the Sep-Pak cartridges: QMA
light Plus 2C03 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
60F2 ).
Example 1; Synthesis and Formulation of FIFACBC Composition of the Invention
No-carrier-added [ F]fiuoride was produced via the l 0(p,n) F nuclear reaction on a
GE PETtrace 6 cyclotron (Norwegian Cyclotron Centre, Oslo). Irradiations were
performed using a dual-beam, 30 A current on two equal Ag targets with HAVAR foils
using 16.5 MeV protons. Each target contained 1.6 ml of > 96% [ 0]water (Marshall
Isotopes). Subsequent to irradiation and delivery to a hotcell, each target was washed
with 1.6 ml of [l O]water (Merck, water for GR analysis), giving approximately 2-5
Gbq in 3.2 ml of [ 0]water.
All radiochemistry was performed on a commercially available GE FASTlab™ with a
single-use cassette. 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
[ F]FACBC followed the three general steps: (a) [ F]fluorination, (b) hydrolysis of
protection groups and (c) SPE purification.
Vial A contained (156 mihoΐ), K2C0 (60.8 mh o ) in 79.5% (v/v) MeCN a ( 105
mί). Vial B contained 4M HC1. Vial C contained MeCN. Vial D contained precursor
(123.5 m ho ) in its dry form (stored below ~5 °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 citrate buffer (10 ml). Aqueous [ F]fluoride (1-1.5 ml, 100-200 Mbq) was
passed through the QMA and into the 0-H 20 recovery vial. The QMA was then
flushed with MeCN and sent to waste. The trapped [ F]fluoride was eluted into the
reactor using eluent from vial A (730 m ) and then concentrated to dryness by azeotropic
distillation with acetonitrile (80 m , 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
72.7 m o 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. The labelled intermediate (without the ester group) was eluted off
the tCl 8 cartridge into the reactor using water. The BOC group was hydrolysed by
adding 4 HCl ( .4 mi) and heating the reactor for 5 min at 60 °C. The reactor content
with the crude [ 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 (9.1
ml total) and collected in the product vial. Finally, 2M NaOH (0.9 ml) and water (2.
ml) was added to the product vial, giving the purified formulation of [ F]FACBC with
a total volume of 26 ml. Radiochemical purity was measured by radio-TLC using a
mixture of MeCN:MeOH:H20:CH 3COOH (20:5:5:1) as the mobile phase. The
radiochemical yield (RCY) was expressed as the amount of radioactivity in the
[ F]FACBC fraction divided by the total used [1 F]fluoride activity (decay corrected).
Total synthesis time was 43 min.

Claims
A pharmaceutical composition of F-FACBC characterised in that said
composition:
(i) comprises 50- 00 mM citrate buffer; and,
(ii) has a pH of 4.0-5.0.
The pharmaceutical composition as defined in Claim 1 comprising 60-90 mM
citrate buffer.
The pharmaceutical composition as defined in either Claim 1 or Claim 2
comprising 75-85 mM citrate buffer.
The pharmaceutical composition as defined in any one of Claims 1-3 that has a pH
of 4.1-4.5.
The pharmaceutical composition as defined in any one of Claims 1-4 that has an
end of synthesis (EOS) radioactive concentration (RAC) of at least 1000 MBq/mL.
The pharmaceutical composition as defined in any one of Claims 1-5 that has an
end of synthesis (EOS) radioactive concentration (RAC) of at least 500 MBq/ml.
The pharmaceutical composition as defined in any one of Claims 1-6 which
comprises not more than 150 m l-amino-3-hydroxyl-cyclobutane-l-carboxylic
acid (hydroxyl-ACBC).
The pharmaceutical composition as defined in any one of Claims 1-7 which
comprises not more than 80 / å hydroxyl-ACBC.
The pharmaceutical composition as defined in any one of Claims 1-8 which
comprises not more than 0.1 mg mL l-amino-3-fluoro-cyclobutane-l-carboxylic
acid (FACBC).
The pharmaceutical composition as defined in any one of Claims 1-9 which
comprises not more than 0. 0 , FACBC.
( ) The pharmaceutical composition as defined in any one of Claims 1-10 which
comprises not more than 2.0 l-amino-3-chloro-cyclobutane-l-carboxylic
acid (chloro-ACBC).
(12) The pharmaceutical composition as defined in any one of Claims 1-11 which
comprises not more than 1.0 chloro-ACBC.
( 3) The pharmaceutical composition as defined in any one of Claims 1-12 with the
proviso that said composition does not comprise a radiostabiliser.
(14) The pharmaceutical composition as defined in Claim 13 wherein said
radiostabiliser is a sugar lactone or a sugar alcohol.
(15) A method to obtain a radiopharmaceutial composition wherein said composition is
as defined in any one of Claims 1-14 and wherein said method comprises:
(i) reacting with a suitable source of [ F]fluoride a precursor compound of
Formula Ϊ :
wherein:
LG is a leaving group;
PG is a carboxy protecting group; and,
PG2 is an amine protecting group;
to obtain a compound of Formula :
wherein PG and PG are as defined for Formula II;
reacting said compound of Formula with a PG1 deprotecting agent to
obtain a compound of Formula :
wherein PG is as defined for Formula I;
(iii) reacting said compound of Formula HI with a PG2 deprotecting agent to
obtain [1 F]FACBC;
(iv) formulating said [l F]FACBC with citrate buffer to obtain said
pharmaceutical composition.
(16) The method as defined in Claim 15 wherein said [ F]-FACBC is trans- l-amino-3-
[ F]-fluorocyciobutanecarboxylic acid ( ni .·-[r l 8F]-FACBC):
said compound of Formula I is a compound of Formula la:
said compound of Formula Pis a compound of Formula Ila:
said compound of Formula PI is a compound of Formula a:
wherein PG and PG2 are as defined in Claim 15 for Formula I.
(17) The method as defined in either Claim 5 or Claim 16 wherein PG is ethyl.
(18) The method as defined in any one of Claims 15-17 wherein PG2 is tbutoxycarbonyl.
(19) The method as defined in any one of Claims 5-1 wherein said PG deprotecting
agent is NaOH.
(20) The method as defined in any one of Claims 15-19 v/herein said PG2 deprotectmg
agent is HC1.
(21) The method as defined in any one of Claims 5-20 which is carried out on an
automated synthesis apparatus.