U.S. patent application number 13/687485 was filed with the patent office on 2013-04-11 for solid-phase fluorination of benzothiazoles.
This patent application is currently assigned to HAMMERSMITH IMANET LIMITED. The applicant listed for this patent is GE HEALTHCARE LIMITED, HAMMERSMITH IMANET LIMITED. Invention is credited to FRANK BRADY, ALEXANDER MARK GIBSON, SAJINDER KAUR LUTHRA.
Application Number | 20130089501 13/687485 |
Document ID | / |
Family ID | 9950060 |
Filed Date | 2013-04-11 |
United States Patent
Application |
20130089501 |
Kind Code |
A1 |
BRADY; FRANK ; et
al. |
April 11, 2013 |
SOLID-PHASE FLUORINATION OF BENZOTHIAZOLES
Abstract
The invention provides a process for the production of an
.sup.18F-labelled tracer which comprises treatment of a solid
support-bound precursor of formula (I) SOLID
SUPPORT-LINKER-X-TRACER (I) wherein X is a group which promotes
nucleophilic substitution at a specific site on the attached TRACER
and the TRACER is of formula (A) ##STR00001##
Inventors: |
BRADY; FRANK; (LONDON,
GB) ; LUTHRA; SAJINDER KAUR; (AMERSHAM, GB) ;
GIBSON; ALEXANDER MARK; (AMERSHAM, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GE HEALTHCARE LIMITED;
HAMMERSMITH IMANET LIMITED; |
Little Chalfont
London |
|
GB
GB |
|
|
Assignee: |
HAMMERSMITH IMANET LIMITED
LONDON
GB
GE HEALTHCARE LIMITED
LITTLE CHALFONT
GB
|
Family ID: |
9950060 |
Appl. No.: |
13/687485 |
Filed: |
November 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10539169 |
Jun 14, 2005 |
8323616 |
|
|
PCT/GB2003/005574 |
Dec 19, 2003 |
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13687485 |
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Current U.S.
Class: |
424/1.89 ;
422/159; 548/178 |
Current CPC
Class: |
C07D 277/66 20130101;
C07B 2200/05 20130101; A61K 51/0453 20130101; C07B 2200/11
20130101; C07B 59/002 20130101 |
Class at
Publication: |
424/1.89 ;
548/178; 422/159 |
International
Class: |
C07B 59/00 20060101
C07B059/00; A61K 51/04 20060101 A61K051/04; C07D 277/66 20060101
C07D277/66 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 20, 2002 |
GB |
0229686.1 |
Claims
1-8. (canceled)
9. A compound of formula (I), (Ia), (Ib), or (III): (i) SOLID
SUPPORT-LINKER-X-TRACER (I) wherein X is a group which promotes
nucleophilic substitution at a specific site on the attached TRACER
and the TRACER is of formula (A) ##STR00018## wherein: R.sup.1 and
R.sup.2 are independently selected from hydrogen, a protecting
group, C.sub.1-6 alkyl, C.sub.1-6 hydroxyalkyl, and C.sub.1-6
haloalkyl; R.sup.3 to R.sup.10 are independently selected from
hydrogen, halo, C.sub.1-6 alkyl, C.sub.1-6 haloalkyl, C.sub.1-6
hydroxyalkyl, C.sub.1-6 alkoxy, C.sub.1-6 haloalkoxy, hydroxy,
cyano, and nitro; and one of the groups R.sup.1 to R.sup.10 is
bonded to the SOLID SUPPORT-LINKER-X--; (ii) SOLID
SUPPORT-LINKER-SO.sub.2--O-TRACER (Ia) wherein the TRACER is of
formula (Aa) ##STR00019## wherein: R.sup.1 and R.sup.2 are
independently selected from hydrogen, a protecting group, C.sub.1-6
alkyl, C.sub.1-6 hydroxyalkyl, and C.sub.1-6 haloalkyl; R.sup.3 to
R.sup.10 are independently selected from hydrogen, halo, C.sub.1-6
alkyl, C.sub.1-6 haloalkyl, C.sub.1-6 hydroxyalkyl, C.sub.1-6
alkoxy, C.sub.1-6 haloalkoxy, hydroxy, cyano, and nitro; in which
either (a) an R.sup.1C.sub.1-6 alkyl group or (b) an R.sup.3 to
R.sup.10C.sub.1-6 alkyl or C.sub.1-6 alkoxy group is bonded to the
SOLID SUPPORT-LINKER-SO.sub.2--O-- in formula (Ia); ##STR00020##
wherein Y.sup.- is an anion and the TRACER is of formula (Ab)
##STR00021## wherein: R.sup.1 and R.sup.2 are independently
selected from hydrogen, a protecting group, C.sub.1-6 alkyl,
C.sub.1-6 hydroxyalkyl, and C.sub.1-6 haloalkyl; one of R.sup.3 to
R.sup.10 is a bond to the SOLID SUPPORT-LINKER-I.sup.+-- group in
formula (Ib) and the others are independently selected from
hydrogen, halo, C.sub.1-6 alkyl, C.sub.1-6 haloalkyl, C.sub.1-6
hydroxyalkyl, C.sub.1-6 alkoxy, C.sub.1-6 haloalkoxy, hydroxy,
cyano, and nitro; or ##STR00022## wherein R.sup.11 and R.sup.12 are
independently selected from C.sub.1-6 alkyl and the TRACER is a
compound of formula (Ac): ##STR00023## wherein: R.sup.1 and R.sup.2
are independently selected from hydrogen, a protecting group,
C.sub.1-6 alkyl, C.sub.1-6 hydroxyalkyl, and C.sub.1-6 haloalkyl;
one of R.sup.3 to R.sup.10 is a bond to the Sn in formula (III) and
the others are independently selected from hydrogen, halo,
C.sub.1-6 alkyl, C.sub.1-6 haloalkyl, C.sub.1-6 hydroxyalkyl,
C.sub.1-6 alkoxy, C.sub.1-6 haloalkoxy, hydroxy, cyano, and
nitro.
10. A radiopharmaceutical kit for the preparation of an
.sup.18F-labelled tracer for use in PET, which comprises: (i) a
vessel containing a compound of formula (I), (Ia), or (Ib) as
defined in claim 9; and (ii) means for eluting the vessel with a
source of .sup.18F.sup.-; (iii) an ion-exchange cartridge for
removal of excess .sup.18F.sup.-.
11. A cartridge for a radiopharmaceutical kit for the preparation
of an .sup.18F-labelled tracer for use in PET which comprises: (i)
a vessel containing a compound of formula (I), (Ia), or (Ib) as
defined in claim 9; and (ii) means for eluting the vessel with a
source of .sup.18F.sup.-.
12. A radiopharmaceutical kit for the preparation of an
.sup.18F-labelled tracer for use in PET, which comprises: (i) a
vessel containing a compound of formula (III) as defined in claim
9; and (ii) means for eluting the vessel with a source of
.sup.18F.sup.-.
13. A cartridge for a radiopharmaceutical kit for the preparation
of an .sup.18F-labelled tracer according to claim 12 for use in PET
which comprises: (i) a vessel containing a compound of formula
(III) as defined in claim 9; and (ii) means for eluting the vessel
with a source of .sup.18F.
14. A method for obtaining a diagnostic PET image which comprises
the step of using a radiopharmaceutical kit according to claim 10
or a cartridge for a radiopharmaceutical kit according to claim 11.
Description
[0001] The present invention relates to novel solid-phase processes
for the production of radiolabelled tracers, in particular for the
production of .sup.18F-labelled benzothiazole compounds which may
be suitable for use as Positron Emission Tomography (PET)
radiotracers. The invention also comprises radiopharmaceutical kits
using these novel processes.
[0002] The favoured radioisotope for PET, .sup.18F, has a
relatively short half-life of 110 minutes. .sup.18F-labelled
tracers for PET therefore have to be synthesised and purified as
rapidly as possible, and ideally within one hour of clinical use.
Standard synthetic methods for introducing fluorine-18 are
relatively slow and require post-reaction purification (for
example, by HPLC) which means that it is difficult to obtain the
.sup.18F-labelled tracer for clinical use in good radiochemical
yield. There is also a need for automation to protect the operator
from radiation exposure. Many radiofluorinations are complicated
procedures and it is necessary to simplify them to facilitate
automation.
[0003] The present invention provides solid-phase processes for
producing .sup.18F-labelled tracers quickly and with high specific
activity yet avoiding time-consuming purification steps, such that
the resultant .sup.18F-labelled tracer is suitable for use in PET.
The solid-phase methods also lend themselves to automation with
advantages of ease of production and greater throughput. The
invention also comprises radiopharmaceutical kits which use such
processes and thus provide the radiopharmacist or clinician with a
convenient means of preparing an .sup.18F-labelled tracer.
[0004] Various substituted benzothiazole compounds, having utility
for in vivo imaging of Alzheimer's Disease have been described in
WO02/16333. Solid-phase nucleophilic fluorination methods are
described in co-pending International Patent Application
PCT/GB02/02505.
[0005] In a general aspect, the invention provides a process for
the production of an .sup.18F-labelled tracer which comprises
treatment of a solid support-bound precursor of formula (I)
SOLID SUPPORT-LINKER-X-TRACER (I)
wherein the TRACER is of formula (A)
##STR00002##
wherein: R.sup.1 and R.sup.2 are independently selected from
hydrogen, a protecting group, C.sub.1-6 alkyl, C.sub.1-6
hydroxyalkyl, and C.sub.1-6 haloalkyl; R.sup.3 to R.sup.10 are
independently selected from hydrogen, halo, C.sub.1-6 alkyl,
C.sub.1-6 haloalkyl, C.sub.1-6 hydroxyalkyl, C.sub.1-6 alkoxy,
C.sub.1-6 haloalkoxy, hydroxy, cyano, and nitro; and one of the
groups R.sup.1 to R.sup.10 is bonded to the SOLID
SUPPORT-LINKER-X--; with .sup.18F.sup.- to produce the labelled
tracer of formula (II)
.sup.18F-TRACER (II)
wherein the TRACER is as defined for the compound of formula (I)
except that one of the groups R.sup.1 to R.sup.10 is bonded to the
.sup.18F instead of to the SOLID SUPPORT-LINKER-X-- in formula (I);
optionally followed by: (i) removal of excess .sup.18F.sup.-, for
example by ion-exchange chromatography; and/or (ii) removal of any
protecting groups; and/or (iii) removal of organic solvent; and/or
(iv) formulation of the resultant compound of formula (II) as an
aqueous solution.
[0006] As the .sup.18F-labelled tracer of formula (II) is removed
from the solid-phase into solution, all unreacted precursor remains
bound to the resin and can be separated by simple filtration, thus
obviating the need for complicated purification, for example by
HPLC. The .sup.18F-labelled tracer of formula (II) may be cleaned
up by removal of excess F, for example by ion-exchange
chromatography and/or by removal of any organic solvent. The
resultant .sup.18F-labelled tracer of formula (II) may then be
further made-up into an aqueous formulation for clinical use.
[0007] In the compounds of formula (I), X is a group which promotes
nucleophilic substitution at a specific site on the attached
TRACER. Examples of X include --SO.sub.2O-- as in formula (Ia)
below, and I.sup.+ as in formula (Ib) below.
[0008] In a further aspect, the invention provides a process for
the production of an .sup.18F-labelled tracer which comprises
treatment of a solid support-bound precursor of formula (Ia):
SOLID SUPPORT-LINKER-SO.sub.2--O-TRACER (Ia)
wherein the TRACER is of formula (Aa)
##STR00003##
wherein: R.sup.1 and R.sup.2 are independently selected from
hydrogen, a protecting group, C.sub.1-6 alkyl, C.sub.1-6
hydroxyalkyl, and C.sub.1-6 haloalkyl; R.sup.3 to R.sup.10 are
independently selected from hydrogen, halo, C.sub.1-6 alkyl,
C.sub.1-6 haloalkyl, C.sub.1-6 hydroxyalkyl, C.sub.1-6 alkoxy,
C.sub.1-6 haloalkoxy, hydroxy, cyano, and nitro; in which either
(a) an R.sup.1C.sub.1-6 alkyl group or (b) an R.sup.3 to
R.sup.10C.sub.1-6 alkyl or C.sub.1-6 alkoxy group is bonded to the
SOLID SUPPORT-LINKER-SO.sub.2--O-- in formula (Ia); with
.sup.18F.sup.- to produce the labelled tracer of formula (IIa)
.sup.18F-TRACER (IIa)
wherein the TRACER is as defined for the compound of formula (Ia)
except that either (a) an R.sup.1C.sub.1-6 alkyl group or (b) an
R.sup.3 to R.sup.10C.sub.1-6 alkyl or C.sub.1-6 alkoxy group is
bonded to the .sup.18F instead of to the SOLID
SUPPORT-LINKER-SO.sub.2--O-- in formula (Ia); optionally followed
by: (i) removal of excess .sup.18F.sup.-, for example by
ion-exchange chromatography; and/or (ii) removal of any protecting
groups; and/or (iii) removal of organic solvent; and/or (iv)
formulation of the resultant compound of formula (IIa) as an
aqueous solution.
[0009] In the compound of formula (Ia), the TRACER is suitably of
formula (Aa1)
##STR00004##
wherein R.sup.1 and R.sup.2 are independently selected from
hydrogen, a protecting group, C.sub.1-6 alkyl, C.sub.1-6
hydroxyalkyl, and C.sub.1-6 haloalkyl; R.sup.5 is hydrogen or
C.sub.1-6 alkyl, R.sup.8 is hydroxy, C.sub.1-6 alkoxy, C.sub.1-6
haloalkyl, or C.sub.1-6 alkyl; provided that one of R.sup.1,
R.sup.5 and R.sup.8 is C.sub.1-6 alkyl bonded to the SOLID
SUPPORT-LINKER-SO.sub.2--O-- in formula (Ia) or R.sup.8 is
C.sub.1-6 alkoxy bonded to the SOLID SUPPORT-LINKER-SO.sub.2--O--
in formula (Ia).
[0010] As shown in Scheme 1, the compound of formula (Ia) may be
conveniently prepared from any sulphonic acid functionalised
commercially available resin, such as Merrifield Resin,
NovaSyn.RTM. TG Bromo Resin, (Bromomethyl)phenoxymethyl
polystyrene, or Wang Resin which may be reacted with a chlorinating
agent to give the corresponding sulphonyl chloride resin. This may
be carried out by treating the resin with, for example, phosphorus
pentachloride, phosphorus trichloride, oxalyl chloride, or thionyl
chloride, in an appropriate inert solvent such as dichloromethane,
chloroform, or acetonitrile, and heating at elevated temperature
for a period of time. The excess reagent may then be removed from
the resin by washing with further portions of the inert solvent.
The sulphonyl chloride resin may then be reacted with the alcohol
analogue of the tracer to produce the resin-bound precursor of
formula (Ia). This may be carried out by treating the resin with a
solution of the alcohol in an inert solvent such as chloroform,
dichloromethane, acetonitrile, or tetrahydrofuran containing a
non-nucleophilic soluble base such as sodium hydride or a
trialkylamine, for example triethylamine or diisopropylethylamine.
The reaction may be carried out at a temperature of 10 to
80.degree. C., optimally at ambient temperature for a period of
from around 1 to 24 hours. The excess alcohol and base may then be
removed from the solid support by washing with further portions of
an inert solvent such as chloroform, dichloromethane, or
tetrahydrofuran. Alternatively, the LINKER may be attached to the
TRACER, before being attached to the SOLID SUPPORT to form the
compound of formula (Ia), using analogous chemistry to that
described above.
##STR00005##
[0011] In the compounds of formulae (I) and (Ia) and in the
following aspects of the invention, the "SOLID SUPPORT" may be any
suitable solid-phase support which is insoluble in any solvents to
be used in the process but to which the LINKER and/or TRACER can be
covalently bound. Examples of suitable SOLID SUPPORT include
polymers such as polystyrene (which may be block grafted, for
example with polyethylene glycol), polyacrylamide, or polypropylene
or glass or silicon coated with such a polymer. The solid support
may be in the form of small discrete particles such as beads or
pins, or as a coating on the inner surface of a cartridge or on a
microfabricated vessel.
[0012] In the compounds of formulae (I) and (Ia) and in the
following aspects of the invention, the "LINKER" may be any
suitable organic group which serves to space the reactive site
sufficiently from the solid support structure so as to maximise
reactivity. Suitably, the LINKER comprises zero to four aryl groups
(suitably phenyl) and/or a C.sub.1-16alkyl (suitably
C.sub.1-6alkyl) or C.sub.1-16haloalkyl (suitably
C.sub.1-6haloalkyl), typically C.sub.1-16 fluoroalkyl (suitably
C.sub.1-6 fluoroalkyl), or C.sub.1-16alkoxy or C.sub.1-16haloalkoxy
(suitably C.sub.1-6alkoxy or C.sub.1-6haloalkoxy) typically
C.sub.1-16-fluoroalkoxy (suitably C.sub.1-6-fluoroalkoxy), and
optionally one to four additional functional groups such as amide
or sulphonamide groups. Examples of such linkers are well known to
those skilled in the art of solid-phase chemistry, but include:
##STR00006## ##STR00007##
wherein at each occurrence, k is an integer of 0 to 3, n is an
integer of 1 to 16, and R.sup.L is hydrogen or C.sub.1-6 alkyl.
[0013] As would be apparent to the person skilled in the art, it
may be necessary to protect functional groups in the TRACER to
avoid unwanted reactions during the radiolabelling process. Such
protection may be achieved using standard methods of protecting
group chemistry. After the radiolabelling is complete, any
protecting groups may be removed by simple procedures which are
also standard in the art. Suitable protection and deprotection
methodologies may be found, for example, in Protecting Groups in
Organic Synthesis, Theodora W. Greene and Peter G. M. Wuts,
published by John Wiley & Sons Inc. Preferred amine protecting
groups include alkoxycarbonyl (such as t-butoxycarbonyl),
trifluoroacetamide, fluorenylmethoxy carbonyl, and formamide.
Preferred hydroxy protecting groups include alkyl or benzyl ethers,
alkyloxymethyl ethers, alkoxycarbonyls (such as t-butoxycarbonyl)
and silyl groups. Such protecting groups may be conveniently
removed by hydrolysis, for example in the presence of acid or base.
Such deprotection may be effected using a solid supported acid or
base catalyst that renders the need for post deprotection
neutralisation unnecessary
[0014] Treatment of the compound of formula (I) or (Ia) with
.sup.18F.sup.- may be effected by treatment with any suitable
source of .sup.18F.sup.-, such as Na.sup.18F, K.sup.18F,
Cs.sup.18F, tetraalkylammonium .sup.18F fluoride, or
tetraalkylphosphonium .sup.18F fluoride. To increase the reactivity
of the fluoride, a phase transfer catalyst such as 4,7,13,16,21,24
hexaoxa-1,10-diazabicyclo[8,8,8]hexacosane may be added and the
reaction performed in a non protic solvent. These conditions give
reactive fluoride ions. The treatment with .sup.18F.sup.- is
suitably effected in the presence of a suitable organic solvent
such as acetonitrile, dimethylformamide, dimethylsulphoxide,
tetrahydrofuran, dioxan, 1,2 dimethoxyethane, sulpholane,
N-methylpyrrolidinineone, at a non-extreme temperature, for
example, 15.degree. C. to 180.degree. C., preferably at elevated
temperature. On completion of the reaction, the .sup.18F-labelled
tracer of formula (II) dissolved in the solvent is conveniently
separated from the solid-phase by filtration. The same fluorination
techniques may also be used in the following aspects of the
invention.
[0015] Any excess .sup.18F.sup.- may be removed from the solution
of .sup.18F-tracer by any suitable means, for example by
ion-exchange chromatography or solid phase absorbents. Suitable
ion-exchange resins include BIO-RAD AG 1-X8 or Waters QMA and
suitable solid phase absorbents include alumina. The excess
.sup.18F.sup.- may be removed using such solid phases at room
temperature in aprotic solvents.
[0016] Any organic solvent may be removed by any standard method
such as by evaporation at elevated temperature in vacuo or by
passing a stream of inert gas such as nitrogen or argon over the
solution.
[0017] Before use of the .sup.18F-labelled tracer, it may be
appropriate to formulate it, for example as an aqueous solution by
dissolving the .sup.18F-labelled tracer in sterile isotonic saline
which may contain up to 10% of a suitable organic solvent such as
ethanol, or a suitable buffered solution such as phosphate buffer.
Other additives may be added such as ascorbic acid to reduce
radiolysis.
[0018] In a further aspect, the invention provides a process for
the production of an .sup.18F-labelled tracer which comprises
treatment of a solid support-bound precursor of formula (Ib)
##STR00008##
wherein Y-- is an anion and the TRACER is of formula (Ab)
##STR00009##
wherein: R.sup.1 and R.sup.2 are independently selected from
hydrogen, a protecting group, C.sub.1-6 alkyl, C.sub.1-6
hydroxyalkyl, and C.sub.1-6 haloalkyl; one of R.sup.3 to R.sup.10
is a bond to the SOLID SUPPORT-LINKER-I.sup.+-- group in formula
(Ib) and the others are independently selected from hydrogen, halo,
C.sub.1-6 alkyl, C.sub.1-6 haloalkyl, C.sub.1-6 hydroxyalkyl,
C.sub.1-6 alkoxy, C.sub.1-6 haloalkoxy, hydroxy, cyano, and nitro;
with .sup.18F.sup.- to produce the labelled tracer of formula (IIb)
.sup.18F-TRACER (IIb) wherein the TRACER is as defined for the
compound of formula (Ib) except that one of R.sup.3 to R.sup.10 is
a bond to the .sup.18F instead of a bond to the SOLID
SUPPORT-LINKER-I.sup.+-- group in formula (Ib); optionally followed
by: (i) removal of excess .sup.18F.sup.-, for example by
ion-exchange chromatography; and/or (ii) removal of any protecting
groups; and/or (iii) removal of organic solvent; and/or (iv)
formulation of the resultant compound of formula (IIb) as an
aqueous solution.
[0019] In the compound of formula (Ib), the TRACER is suitably a
compound of formula (Ab1)
##STR00010##
wherein: R.sup.1 and R.sup.2 are independently selected from
hydrogen, a protecting group, C.sub.1-6 alkyl, C.sub.1-6
hydroxyalkyl, and C.sub.1-6 haloalkyl; R.sup.5 is hydrogen,
C.sub.1-6 alkyl, or a bond to the SOLID SUPPORT-LINKER-I.sup.+--
group in formula (Ib); R.sup.8 is hydroxy, C.sub.1-6 alkoxy,
C.sub.1-6 haloalkyl, C.sub.1-6 alkyl, or a bond to the SOLID
SUPPORT-LINKER-I.sup.+-- group in formula (Ib); provided that only
one of R.sup.5 and R.sup.8 is a bond to the SOLID
SUPPORT-LINKER-I.sup.+-- group in formula (Ib).
[0020] The compound of formula (Ib) may be conveniently prepared
from a functionalised commercially available resin such as a
Merrifield Resin or Wang Resin. Suitably, a hydroxyiodoaryl (such
as an iodophenol) containing LINKER group is treated with an
inorganic base, such as cesium carbonate and then added to the
resin, pre-swollen with an inert solvent, such as
N,N-dimethylformamide and allowed to react at elevated temperature,
for example 30 to 80.degree. C. Excess reagents may be removed by
washing the resin with further inert solvent. The resultant
iodophenol functionalised resin may then be treated with a source
of acetate anions (such as acetic acid, acetic anhydride, or acetyl
chloride) in the presence of an oxidising agent, such as hydrogen
peroxide to provide the corresponding diacetoxy-iodophenyl
functionalised resin. The diacetoxy-iodophenyl functionalised resin
may then be stirred in an inert solvent, such as dichloromethane,
in the presence of acid such as hydrochloric acid, trifluoromethane
sulphonic acid, or acetic acid at a low temperature, suitably
-40.degree. C. to 10.degree. C. before addition of the tracer,
suitably functionalised as a boronic acid or trialkyl tin
derivative which may be coupled to the resin at a non-extreme
temperature. As in previous steps, the desired compound of formula
(Ib) may be separated by filtration and washing with an inert
solvent.
[0021] In the compound of formula (Ib), the LINKER is as defined
above but comprises an aryl group (suitably phenyl) adjacent to the
I.sup.+. Preferred examples include
##STR00011##
wherein each phenyl ring is optionally substituted by 1 to 4 groups
selected from C.sub.1-6alkyl and C.sub.1-6alkoxy, but is suitably
unsubstituted.
[0022] In the compound of formula (Ib), Y.sup.- is an anion,
preferably trifluoromethylsulphonate (triflate) anion or
tetraphenyl borate anion.
[0023] The compounds of formula (I) are novel and thus form a
further aspect of the present invention. Thus, for example,
compounds of formula (Ia) and (Ib), form separate aspects of the
present invention.
[0024] In an alternative aspect, the present invention provides
electrophilic solid-phase processes for production of
.sup.18F-labelled benzothiazoles.
[0025] Thus in a further aspect, the present invention provides a
process for the production of an .sup.18F-labelled tracer which
comprises treatment of a solid support-bound precursor of formula
(III):
##STR00012##
wherein R.sup.11 and R.sup.12 are independently selected from
C.sub.1-6 alkyl and the TRACER is a compound of formula (Ac):
##STR00013##
wherein: R.sup.1 and R.sup.2 are independently selected from
hydrogen, a protecting group, C.sub.1-6 alkyl, C.sub.1-6
hydroxyalkyl, and C.sub.1-6 haloalkyl; one of R.sup.3 to R.sup.10
is a bond to the Sn in formula (III) and the others are
independently selected from hydrogen, halo, C.sub.1-6 alkyl,
C.sub.1-6 haloalkyl, C.sub.1-6 hydroxyalkyl, C.sub.1-6 alkoxy,
C.sub.1-6 haloalkoxy, hydroxy, cyano, and nitro; with a source of
.sup.18F, suitably .sup.18F.sub.2, .sup.18F--CH.sub.3COOF or
.sup.18F--OF.sub.2; to give the labelled tracer of formula
(IV);
.sup.18F-TRACER (IV)
wherein the TRACER is as defined for the compound of formula (III)
except that one of R.sup.3 to R.sup.10 is a bond to the .sup.18F
instead of a bond to the Sn in formula (III); optionally followed
by: (i) removal of excess fluorinating agent and .sup.18F.sup.-
ions produced in the generation of the fluorinating agent or in the
reaction; and/or (ii) removal of any protecting groups; and/or
(iii) removal of organic solvent; and/or (iv) formulation of the
resultant compound of formula (IV) as an aqueous solution.
[0026] In a preferred compounds of formula (III), R.sup.11 and
R.sup.12 are both methyl.
[0027] In the compound of formula (III), the TRACER is suitably a
compound of formula (Ac1)
##STR00014##
wherein: R.sup.1 and R.sup.2 are independently selected from
hydrogen, a protecting group, C.sub.1-6 alkyl, C.sub.1-6
hydroxyalkyl, and C.sub.1-6 haloalkyl; R.sup.5 is hydrogen,
C.sub.1-6 alkyl, or a bond to the Sn in formula (III); R.sup.8 is
hydroxy, C.sub.1-6 alkoxy, C.sub.1-6 haloalkyl, C.sub.1-6 alkyl, or
a bond to the Sn in formula (III); provided that only one of
R.sup.5 and R.sup.8 is a bond to the Sn in formula (III).
[0028] Treatment of the compound of formula (III) with .sup.18F may
be effected by treatment with any suitable source of .sup.18F, such
as .sup.18F.sub.2, .sup.18F--CH.sub.3COOF, or .sup.18F--OF.sub.2,
in the presence of a suitable organic solvent, suitably a
chlorofluorocarbon or fluorocarbon, such as trichlorofluoromethane,
at a non-extreme temperature, for example, -10.degree. C. to
60.degree. C., preferably at ambient temperature. On completion of
the reaction, the .sup.18F-labelled tracer of formula (IV)
dissolved in the solvent is conveniently separated from the
solid-phase by filtration. The .sup.18F.sub.2 may be produced, for
example, by the 20Ne(d,.alpha.) .sup.18F reaction using the 13.5
Mev deuterons of the Rossendorf cyclotron U-120 with Ne+0.2%
F.sub.2 (100 umol) as target gas. Alternatively, the .sup.18F.sub.2
may be produced by the .sup.18O.sub.2 (p,n) .sup.18F reaction,
using 11 Mev protons from a cyclotron (A. J. Bishop et al, J. Nucl.
Med., 32:1010 (1991)).
[0029] After reaction of the compound of formula (III), any excess
fluorinating agent or .sup.18F.sup.- ions produced in the
generation of the fluorinating agent or in the reaction and may be
removed from the solution of .sup.18F-tracer of formula (IV) by any
suitable means, for example by passing through a column of sodium
sulphite and silica gel in a suitable solvent, suitably a
chlorofluorocarbon or a chlorocarbon, such as chlorofluoromethane
or methylene chloride.
[0030] Compounds of formula (III) may be prepared from commercially
available starting materials as outlined in Scheme 2 or Scheme
3.
##STR00015##
##STR00016##
[0031] As described above, the advantages of such solid-phase
processes for preparation of .sup.18F-labelled tracers include the
relative speed of the process, simplified purification methods and
ease of automation--all of which mean that the processes are
suitable for preparation of .sup.18F-labelled tracers for use in
PET. Accordingly, the present invention provides a process for the
preparation of a .sup.18F-labelled tracer of formula (II), (IIa),
(IIb), or (IV) for use in PET.
[0032] Conveniently, the solid support bound precursor of formula
(I) or (III) could be provided as part of a kit to a radiopharmacy.
The kit may contain a cartridge which can be plugged into a
suitably adapted automated synthesiser. The cartridge may contain,
apart from the solid support-bound precursor, a column to remove
unwanted fluoride ion, and an appropriate vessel connected so as to
allow the reaction mixture to be evaporated and allow the product
to be formulated as required. The reagents and solvents and other
consumables required for the synthesis may also be included
together with a compact disc carrying the software which allows the
synthesiser to be operated in a way so as to meet the customers
requirements for radioactive concentration, volumes, time of
delivery etc.
[0033] Conveniently, all components of the kit are disposable to
minimise the possibilities of contamination between runs and may be
sterile and quality assured.
[0034] The invention further provides a radiopharmaceutical kit for
the preparation of an .sup.18F-labelled tracer for use in PET,
which comprises: [0035] (i) a vessel containing a compound of
formula (I), (Ia), or (Ib) as defined above; and [0036] (ii) means
for eluting the vessel with a source of .sup.18F.sup.-; [0037]
(iii) an ion-exchange cartridge for removal of excess
.sup.18F.sup.-; and optionally [0038] (iv) a cartridge for
solid-phase deprotection of the resultant product of formula (II),
(IIa), or (IIb) as defined above.
[0039] The invention further provides a cartridge for a
radiopharmaceutical kit for the preparation of an .sup.18F-labelled
tracer for use in PET which comprises:
(i) a vessel containing a compound of formula (I), (Ia), or (Ib);
and (ii) means for eluting the vessel with a source of
.sup.18F.sup.-.
[0040] The invention further provides a radiopharmaceutical kit for
the preparation of an .sup.18F-labelled tracer for use in PET,
which comprises: [0041] (i) a vessel containing a compound of
formula (III) as defined above; and [0042] (ii) means for eluting
the vessel with a source of .sup.18F; and optionally [0043] (iii) a
cartridge for removal of excess fluorinating agent and
.sup.18F.sup.- ions; and optionally [0044] (iv) a cartridge for
solid-phase deprotection of the resultant product of formula (IV)
as defined above.
[0045] The invention further provides a cartridge for a
radiopharmaceutical kit for the preparation of an .sup.18F-labelled
tracer for use in PET which comprises:
(i) a vessel containing a compound of formula (III) as defined
above; and (ii) means for eluting the vessel with a source of
.sup.18F.
[0046] In a further aspect of the invention, there is provided a
method for obtaining a diagnostic PET image which comprises the
step of using a radiopharmaceutical kit or a cartridge for a
radiopharmaceutical kit as described above.
[0047] The invention is illustrated by way of the following
Examples:
EXAMPLE 1
##STR00017##
[0049] 6-Methoxymethoxy-2-(phenyl-4'-aminopropanol)-benzothiazole 1
is dissolved in pyridine/DCM (1:1) in presence of
4-(chlorosulfonyl)benzoic acid (1 eq). The reaction is stirred at
room temperature for 12 hours. After an aqueous work-up, compound 2
is purified on silica gel.
[0050] In an oven-dried Radleys reaction tube is placed 1 g of
polystyrene resin (1 g, 1.30 mmolg.sup.-1, Novabiochem 01-64-0143,
100-200 mesh) and 16 mL of dry DCM (Aldrich). To this is added
sequentially compound 2
[0051] (1.1 equivalent), Hunig's base (2.0 equivalent) and DPPCI
(1.1 equivalent). After 5 hours the resin is filtered of and washed
thoroughly with DCM and methanol. The solid is dried at reduced
pressure.
EXAMPLE 2
Radiofluorination to Prepare [.sup.18F]-Benzothiazole Tracer
[0052] To a portion of the resin (prepared as described in Example
1 compound 3) held in a cartridge is added a solution in dry
acetonitrile of kryptofix, potassium carbonate and
[.sup.18F]-fluoride. The suspension is heated to 85.degree. C. for
10 minutes and then the solution is filtered off. The solution is
diluted with water, passed onto a C.sub.18 solid phase extraction
cartridge and washed with water to remove acetonitrile, kryptofix,
potassium carbonate and unreacted [.sup.18F]fluoride. The
radiofluorinated product is eluted from the cartridge with organic
solvent and the protecting groups are removed by heating in an
acidic solution before neutralization and analysis.
* * * * *