U.S. patent application number 13/671768 was filed with the patent office on 2013-05-23 for purification method.
This patent application is currently assigned to HAMMERSMITH IMANET LIMITED. The applicant listed for this patent is Hammersmith Imanet Limited. Invention is credited to ERIK ARSTAD.
Application Number | 20130126409 13/671768 |
Document ID | / |
Family ID | 38671016 |
Filed Date | 2013-05-23 |
United States Patent
Application |
20130126409 |
Kind Code |
A1 |
ARSTAD; ERIK |
May 23, 2013 |
PURIFICATION METHOD
Abstract
The invention relates to methods and apparatus for purifying a
radiolabelled compound. The method comprises (i) passing a crude
reaction mixture comprising the desired radiolabelled compound and
one or more contaminants in a solvent through a narrow bore vessel
at elevated temperature such that the organic solvent and either
the radiolabelled compound or one or more contaminants is vaporised
forming a vaporised component, and (ii) collecting the resulting
vaporised component by condensing into a collection vessel.
Inventors: |
ARSTAD; ERIK; (LONDON,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hammersmith Imanet Limited; |
London |
|
GB |
|
|
Assignee: |
HAMMERSMITH IMANET LIMITED
LONDON
GB
|
Family ID: |
38671016 |
Appl. No.: |
13/671768 |
Filed: |
November 8, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12375555 |
Jan 29, 2009 |
8309054 |
|
|
PCT/GB2007/002845 |
Jul 25, 2007 |
|
|
|
13671768 |
|
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|
|
Current U.S.
Class: |
210/177 |
Current CPC
Class: |
C07B 63/00 20130101;
B01D 15/3876 20130101 |
Class at
Publication: |
210/177 |
International
Class: |
B01D 15/38 20060101
B01D015/38 |
Claims
1.-8. (canceled)
9. Apparatus for purifying a radiolabelled compound which comprises
a narrow bore vessel containing a crude reaction mixture which
crude reaction mixture comprises the desired radiolabelled compound
and one or more contaminants in a solvent, wherein the internal
diameter of the narrow bore vessel is in the range of about 1
micrometre to 1.5 mm and wherein the radiolabelled compound has a
boiling point of 200.degree. C. or more.
10. Apparatus according to claim 9 wherein the narrow bore vessel
is an HPLC loop with no solid support packing.
11. Apparatus according to claim 9 wherein the internal diameter of
the narrow bore vessel is 40 to 200 .mu.m.
12. Apparatus according to claim 9 wherein the radiolabelled
compound is a radiolabelled tracer is either a [.sup.18F]-tracer
wherein said [.sup.18F]-tracer is-[.sup.18F]-FDG, [.sup.18F]-FLT,
[.sup.18F]-FET, [.sup.18F]-FES, or [.sup.18F]-FHBG, or a
[.sup.11C]-tracer wherein said [.sup.11C]-tracer is [.sup.11C]-PIB,
[.sup.11C]-CFT, [.sup.11C]-Raclopride, or [.sup.11C]-thymidine.
Description
[0001] This application is a divisional application of currently
pending application Ser. No. 12/375,555, filed Jan. 29, 2009, now
allowed, which in turn is a filing under 35 U.S.C. 371 of
international application number PCT/GB2007/002845, filed Jul. 25,
2007, which claims priority to application No. 60/821,280 filed
Aug. 3, 2006, in The United States, the entire disclosure of each
of which is hereby incorporated by reference.
[0002] The present invention relates to methods for purifying
radiolabelled compounds, particularly those radiolabelled with
PH-fluoride and PCl-carbon and to apparatus for performing such
methods.
[0003] Radiolabelled compounds are routinely purified using one of
three main techniques; 1) Chromatography by means of High
Performance Liquid Chromatography (HPLC). HPLC is based on the
principle that different compounds have different
solubility/affinity for stationary phases as well as solvent
mixtures and hence by eluting the crude reaction mixture through a
column containing a suitable stationary phase the compounds elute
at different times and hence can readily be separated. Whilst HPLC
is a very powerful technique for separation it represents several
problems for the preparation of radiolabelled compounds. Firstly,
HPLC purification is time consuming and typically takes between 15
and 30 minutes, which in the case of radiolabelled compounds
results in a significant loss of radioactivity due to decay.
Secondly, the purified radiolabelled compound is diluted to volumes
that are too large for subsequent reactions, and for reaction
intermediates an additional concentration step is required.
Thirdly, HPLC is difficult to automate and any procedure involving
HPLC therefore requires manual handling/supervision or highly
complicated equipment. Finally, HPLC equipment takes up relatively
large space compared with other equipment used for radiolabelling,
which restrains the number of productions rigs and other equipment
that can be placed in a hot-cell.
[0004] 2) Chromatography by means of cartridges/Sep-Pak. This
technique is based on the same principles as HPLC, but rather than
using a highly pressurised column this technique utilises a small
cartridge containing a suitable stationary phase with elution of a
solvent using mild pressure. Whilst this method is less time
consuming and space demanding than HPLC it represents several of
the same problems to radiosynthesis as HPLC. Firstly, the isolated
radiolabelled compound is usually obtained in diluted form and
hence further concentration is required for reaction intermediates.
Secondly, the method involves a number of technical steps, i.e.
diluting the product mixture in a suitable solvent (usually aqueous
phase), passing the diluted mixture through the cartridge, washing
the cartridge with a suitable solvent (usually water) and thirdly
eluting the radiolabelled compound in a suitable solvent (usually
an organic solvent). While this is easier to automate than HPLC,
the additional steps introduce significant extra complication to
any automated equipment. Fourthly, as the cartridge usually has to
be washed with an aqueous solution as part of the procedure, a
drying step is often required. Finally, the overall procedure is
relatively time consuming and hence results in significant loss of
radioactivity due to radioactive decay.
[0005] 3) Purification by means of distillation. Conventional
distillation of radiolabelled compounds is often problematic.
Distillation is usually carried out by heating a reaction vessel
containing the product under reduced pressure or under a stream of
an inert gas such as nitrogen, argon or helium. Successful
distillation requires heating slightly above the boiling point of
the solvent, lower temperature gives low distillation rate and a
higher temperature often results in vigorous boiling with the
effect that parts of the crude mixture is carried over with the
product. It is also difficult to effectively collect the
radiolabelled compound as the inert gas stream must by sufficient
to carry the radiolabelled compound over to a collecting vessel but
if the gas stream is too strong condensation efficiency is reduced
as the gas carries the radiolabelled compound beyond the collection
vessel. As a result distillation yields are difficult to make
reproducible, the procedure is time consuming and automation is
complicated. As the equipment required for distillation typically
has a relatively large volume compared with the volume of the
reaction mixture, losses in the process are significant. Finally,
as the procedure entails prolonged heating of reaction mixtures
decomposition is often o problem, particularly with labile
radiolabelled compounds such as acid halides.
[0006] Radiochemical processes which make use of narrow bore
reaction vessels are known. For example, US 2002/0155063 describes
a process in which .sup.11 C methyl iodide and a PET precursor
compound are reacted together in an HPLC injection loop. However,
the resulting .sup.11C methylated product is then purified by
conventional HPLC.
[0007] Thus, there exists a need for new methods for purifying
radiolabelled compounds, particularly for methods which are
susceptible to automation and can be incorporated into or used in
conjunction with automated radiosynthesis apparatus.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1. FIG. 1 depicts a schematic of an apparatus suitable
for performing a method according to the invention having
restrictors 1 and 2, HPLC injector loop 3, electrical heating
cylinder 4, heating module 5, a temperature control unit 6, glass
syringe 7, product vial 8, and vent 9.
[0009] According to the invention, there is provided a method for
purifying a radiolabelled compound which comprises (i) passing a
crude reaction mixture comprising the desired radiolabelled
compound and one or more contaminants in a solvent through a narrow
bore vessel at elevated temperature such that the solvent and
either the radiolabelled compound or one or more contaminants is
vaporised forming a vaporised component, and (ii) collecting the
resulting vaporised component by condensing into a collection
vessel.
[0010] In contrast to the purification methods for radiolabelled
compounds described in the prior art, the methods of the present
invention are simple, easy to automate, do not lead to dilution of
the product and involve short exposure to heat. No carrier gas is
required as the evaporated solvent itself serves to carry the
vaporised component through the narrow bore vessel. Following
vaporisation, the vaporised component can be directed into a
collection vessel, which can be sealed or open as required, and by
keeping the collection vessel below the boiling point of the
solvent, condensation by nature will prevent built up of pressure.
The vaporised component can be led into a collection vessel of
choice using valves, which greatly simplifies automation. As there
is no carrier gas or reduced pressure in the system effective
collection of the vaporised component is ensured. The method is
highly robust as the sensitivity to temperature changes is limited
and there is no need to tightly control gas flow. As the exposure
of the reaction mixture to heat occurs over a very short
time-period decomposition of labile compounds should be minimal. An
additional benefit is the speed with which purification can be
achieved, which only is limited to the rate of vaporisation.
Finally, as the total volume of the apparatus is small, loss of
radioactivity in the process is kept to a minimum.
[0011] The narrow bore vessel preferably takes the form of a tube
with a narrow bore, for example an HPLC loop with no solid support
packing. The internal diameter of the narrow bore vessel is usually
in the range of about 1 micrometre to 1.5 mm, preferably 40 to 200
.mu.m. It is particularly convenient if the narrow bore vessel is
open at both ends so that the crude mixture can be flushed
through.
[0012] The length of the narrow bore vessel will be chosen such
that it is long enough for the purification to be effected but is
sufficiently short to minimise residence time in the vessel. A
convenient length for the narrow bore vessel is from about 5 cm to
50 cm long, more usually 5 cm to 20 cm and typically about 15
cm.
[0013] Suitable solvents for use in the methods of the invention
include acetonitrile, ethanol, tetrahydrofuran, diethylether,
dichloromethane, chloroform, water, acetone, ethyl acetate, and
dimethylformamide. In a separate aspect of the invention
supercritical carbon dioxide may be used as solvent.
[0014] In one embodiment of the invention, restrictor tubes at
inlet and outlet of the narrow bore vessel may be used to promote
the build-up of pressure necessary for generating the vaporised
component. These tubes have a smaller inner diameter (typically
0.1-0.2 mm) than the narrow bore vessel. By choosing a longer
restrictor tube for the sample inlet compared with the outlet, the
flow of the distilling vaporised component will be guided during
feeding-in of the crude mixture.
[0015] The elevated temperature used in the method is suitably in
the range of 80.degree. C. to 400.degree. C., preferably 50.degree.
C. to 250.degree. C., more preferably 90.degree. C. to 150.degree.
C. In one aspect of the invention, the elevated temperature used is
such that the solvent reaches a supercritical state. Where
supercritical carbon dioxide is used as solvent, the temperature
used in the method can be as low as -80.degree. C.
[0016] The methods of the invention may be utilised for rapid and
efficient purification of radiolabelled compounds during
radiosynthesis. Following labelling of a precursor compound with a
radionuclide the crude reaction mixture is passed through a heated
narrow bore vessel thereby producing a vaporised component of all
volatile compounds whereas non-volatile compounds remain in the
narrow bore vessel. The crude reaction mixture may be introduced
into the narrow bore vessel by any convenient means, for example by
injection, applying external pressure to the narrow bore vessel
using pressurised gas or heating the narrow bore vessel to generate
vapour. The flow rate of the crude reaction mixture is preferably
in the range 0.1 to 1.0 ml/min.
[0017] If the crude reaction mixture contains a volatile
radiolabelled compound it will form part of the vaporised component
and can therefore readily be directed into a collection vessel
where the radiolabelled compound and the solvent is condensed. By
designing the radiolabelling reaction such that the precursor
compound is non-volatile, e.g. by using non-volatile fragments such
as a para-toluenesulphonic acid leaving group or a charged fragment
such as a quaternary amine as part of the precursor compound, the
precursor compound will remain in the heated narrow bore vessel. In
effect, this provides an efficient and rapid way of isolating the
radiolabelled compound from a crude reaction mixture.
[0018] Thus, in one aspect of the invention, the radiolabelled
compound is suitably a low molecular weight compound with a boiling
point of up to 200.degree. C. such that the radiolabelled compound,
along with an organic solvent, is separated from higher boiling
contaminants during the method. The purified radiolabelled compound
may be collected in a suitable vessel such as a vial ready for
further use. The narrow bore vessel may be cleaned by passing a
suitable solvent down its length, alternatively disposable narrow
bore vessels may be used. Suitable low molecular weight
radiolabelled compounds include many radiolabelling
[.sup.18F]-synthons such as [.sup.18F]-fluoroalkyls,
[.sup.18F]-fluoroalkenyls, [.sup.18F]-fluoroalkylazides,
[.sup.18F]-fluoroarylaldehydes, [.sup.18F]-fluoroalkylaldehydes,
[.sup.18F]-fluoroalkylthiols, or [.sup.11C]-synthons such as
[.sup.11C]-alkylhalides.
[0019] Alternatively, the radiolabelling reaction can be designed
such that the radiolabelled compound is non-volatile whereas the
precursor compound is volatile, e.g. by forming a quarternary amine
or other non-volatile group in the radiolabelled compound from a
volatile precursor compound such as a tertiary amine. The synthesis
of C-11 cholin and F-18 fluoroalkyl cholin are good examples of
such reactions. In this way the radiolabelled compound can be
obtained solvent free in the heated tubing, whereas the solvent and
excess precursor compound is directed into a separate vessel and/or
waste in the form of the vaporised component.
[0020] Thus, in an alternative aspect of the invention, the
radiolabelled compound is suitably a high molecular weight
compound, with a boiling point of 200.degree. C. or more . In this
aspect, the radiolabelled compound is left behind in the narrow
bore vessel while lower boiling impurities may be collected in a
suitable vessel such as a vial ready for disposal. In this aspect
of the invention, the purified radiolabelled compound may
subsequently be removed from the narrow bore vessel by eluting it
with a suitable solvent or used to perform a radiochemical reaction
inside the narrow bore vessel. Suitable radiolabelled compounds for
this aspect of the invention include radiolabelled tracers such as
2-[.sup.18F]fluoro-2-deoxy-D-glucose ([.sup.18F]-FDG),
3'-deoxy-3-[.sup.18F]fluorothymidine ([.sup.18F]-FLT),
2-[.sup.18F]-fluoroethyl-L-tyrosine ([.sup.18F]-FET),
[.sup.18F]-fluorooestradiol ([.sup.18F]-FES),
9-[4-[.sup.18F]fluoro-3-(hydroxymethyl)butyl]guanine
([.sup.18F]-FHBG), [.sup.11C]-PIB or its analogues as described in
WO 02/16333, 2.beta.-carbomethoxy-3.beta.-(4-fluorophenyl)tropane
([.sup.11C]-CFT), [.sup.11C]-raclopride, or
[.sup.11C]-thymidine.
[0021] In a further aspect of the invention, there is provided a
method as described above, which comprises the further step of
(iii) reaction of the resulting purified radiolabelled compound in
a narrow bore vessel to form a second radiolabelled compound. The
narrow bore vessel used in step (iii) may be the same narrow bore
vessel as used in steps (i) and (ii), or a separate narrow bore
vessel in fluid connection therewith. For example in this aspect of
the invention, steps (i) and (ii) may be used to purify a
radiolabelling synthon such as a [.sup.18F]-synthon or
[.sup.11C]-synthon, suitably a [.sup.18F]-fluoroalkyl,
[.sup.18F]-fluoroalkenyl, [.sup.18F]-fluoroalkylazide,
[.sup.11C]-alkylhalide, [.sup.18F]-fluoroarylaldehyde,
[.sup.18F]-fluoroalkylaldehyde, or [.sup.18F]-fluoroalkylthiol,
which is then used in step (iii) to react with a further precursor
compound to prepare a radiolabelled tracer such as a
[.sup.18F]-tracer or [.sup.11C] tracer.
[0022] According to a further aspect of the invention, there is
provided an apparatus for purifying a radiolabelled compound which
comprises a narrow bore vessel containing a crude reaction mixture
which crude reaction mixture comprises the desired radiolabelled
compound and one or more contaminants in a solvent. Suitably, the
narrow bore vessel is a tube with a narrow bore, such as an HPLC
loop with no solid support packing. More suitably, the internal
diameter of the narrow bore vessel is in the range of about 1
micrometre to 1.5 mm, preferably 40 to 200 .mu.m.
[0023] The following example is described with reference to FIG. 1
which is a schematic of an apparatus suitable for performing a
method according to the invention.
EXAMPLE
Preparation of [.sup.18F]2-Fluoroethylazide
Distillation Apparatus
[0024] A scheme of the apparatus is shown in FIG. 1. The tubing
material consists of standard HPLC parts. Restrictors 1 and 2 are
narrow bore stainless steel tubes (i.d. 0.127 mm) of 13.5 cm and
7.0 cm length, respectively. The HPLC injector loop 3 has a
capacity of 1.0 mL. The electrical heating cylinder 4 can be heated
up to 200.degree. C. by a heating module 5 with a temperature
control unit 6.
Preparation of [.sup.18F]2-Fluoroethylazide
[0025] Toluene-4-sulfonic acid 2-azido-ethyl ester (1.5 .mu.l, 7.5
.mu.mol) in acetonitrile (0.2 ml) is stirred with
[.sup.18F]KF-Kryptofix complex (5 mg) and potassium carbonate (1
mg) for 15 minutes at 80.degree. C. The reaction mixture is loaded
into a glass syringe 7 (Hamilton, Gastight, 1 ml) and passed
through the apparatus at 130.degree. C. with a flow rate of 0.2
ml/min. Acetonitrile (0.05 ml) is used as trapping solvent in the
product vial 8 fitted with a vent 9. After 2 minutes, the majority
of [.sup.18F]2-fluoroethylazide has distilled with acetonitrile as
carrier.
[0026] The decay corrected radiochemical yield of
[.sup.18F]2-fluoroethylazide is 50%.+-.7% (n=10) with a
radiochemical purity of >99%. The corrected distillation
efficiency of the apparatus is 71%.+-.4% (n=10).
* * * * *