Alkylation method
The present invention relates to a method of radiochemical synthesis. Novel methods useful in the synthesis of a positron emission tomography (PET) tracer, and novel intermediates useful in said method are provided that have advantages over known methods.
1. A method to obtain a compound of Formula I:
wherein:
X 1 is an X group selected from C 1-4 alkyl or halo;
Y 1 is a Y group selected from hydrogen or C 1-4 alkyl;
Z 1 is a Z group which is C 1-4 alkyl; and,
Q is [ 11 C]C 1-4 alkyl- or [ 18 F]—C 1-4 fluoroalkyl-;
wherein said method comprises:
(i) reducing a compound of Formula II:
wherein:
(ii) X 11 and X 12 are the same and are both an X group as defined for X 1 ;
Y 11 and Y 12 are the same and are both a Y group as defined for Y 1 ; and,
Z 11 and Z 12 are the same and are both a Z group as defined for Z 1 ; and,
(ii) adding a base to the product of step (i) and reacting with either [ 11 C]C 1-4 alkyl-LG 1 or [ 18 F]—C 1-4 fluoroalkyl-LG 2 , wherein LG 1 and LG 2 are independently halo, or the group —O—SO 2 —R 1 wherein R 1 represents an optionally-substituted C 6-10 aryl, an optionally-substituted C 1-4 alkyl, or C 1-4 fluoroalkyl;
wherein the molar ratio of added base:thiol in step (ii) is in the range of about 0.2-0.75.
2. The method as defined in claim 1 wherein said compound of Formula II is a compound of Formula IIa:
wherein:
X 11 and X 12 are the same and are both an X group as defined in claim 1 ;
Y 11 and Y 12 are the same and are both a Y group as defined in claim 1 ; and,
Z 11 and Z 12 are the same and are both a Z group as defined in claim 1 .
3. The method as defined in claim 1 wherein said X group is halo.
4. The method as defined in claim 1 wherein said Y group is C 1-4 alkyl.
5. The method as defined in claim 1 wherein said Z group is methyl.
6. The method as defined in claim 1 wherein said X group is chloro, said Y group is methyl and said Z group is methyl.
7. The method as defined in claim 1 wherein reducing step (i) is effected using a reducing agent selected from sodium borohydride (NaBH 4 ), free phosphines, 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU), zinc in hydrochloric acid, zinc in acetic acid, magnesium in hydrochloric acid, sodium hydrogentelluride (NaTeH) in ethanol, lithium aluminium hydride (LiAlH 4 ) in tetrahydrofuran, indium in ammonium chloride, and sodium hydride (NaH), or a solid bound reducing agent such as triphenyl phosphone or phosphine.
8. The method as defined in claim 1 wherein reducing step (i) is effected using NaBH 4 .
9. The method as defined in claim 1 wherein in said reacting step (ii) the thiol product is reacted with [ 18 F]—C 1-4 fluoroalkyl-LG 2 .
10. The method as defined in claim 1 wherein said compound of Formula I is:
11. The method as defined in claim 1 wherein said compound of Formula II is:
12. The method as defined in claim 1 wherein said reducing step (i) and said reacting step (ii) are carried out in the same vessel.
13. The method as defined in claim 1 wherein said reacting step is carried out in an ethanolic solution.
14. The method as defined in claim 1 wherein said reaction step (ii) is carried out for about 5-15 minutes.
15. The method as defined in claim 1 wherein said reaction step (ii) is carried out for about 5-10 minutes.
16. The method as defined in claim 1 wherein said reaction step (ii) is carried out for about 5 minutes.
17. The method as defined in claim 1 wherein said reacting step (ii) comprises about 0.02-0.04 mmol thiol.
18. The method as defined in claim 1 wherein said reacting step (ii) comprises about 0.02-0.035 mmol thiol.
19. The method as defined in claim 1 wherein said reacting step (ii) comprises about 0.03-0.035 mmol thiol.
20. The method as defined in claim 1 wherein said reacting step (ii) comprises about 0.005-0.025 mmol base.
21. The method as defined in claim 1 wherein said reacting step (ii) comprises about 0.01-0.025 mmol base.
22. The method as defined in claim 1 wherein said reacting step (ii) comprises about 0.02-0.025 mmol base.
23. The method as defined in claim 1 wherein said reacting step (ii) is carried out at a temperature between about 80-120° C.
24. The method as defined in claim 1 wherein said reacting step (ii) is carried out at a temperature between about 100-120° C.
25. The method as defined in claim 1 wherein said reacting step (ii) is carried out at a temperature between about 105-110° C.
26. The method as defined in claim 1 wherein said reacting step (ii) is carried out at a temperature of about 110° C.
27. The method as defined in claim 1 wherein said compound of Formula I is:
said compound of Formula II is:
said ratio of base:thiol is about 0.2-0.75; and,
said reacting step (ii) is carried out for about 5 minutes at about 110° C.
28. The method as defined in claim 1 which further comprises step (iii) purifying the reaction mixture obtained in step (ii) using solid phase extraction (SPE).
29. The method as defined in claim 28 wherein said SPE is carried out using one or more reverse phase SPE cartridges.
30. The method as defined in claim 29 wherein said SPE is carried out using one or more environmental tC18 SPE cartridges.
31. The method as defined in claim 30 wherein said SPE is carried out using two tC18 SPE cartridges.
32. The method as defined in claim 31 wherein chemical impurities are removed from said tC18 SPE cartridges using a basic aqueous acetonitrile solution and said purified compound of Formula I is eluted from said tC18 SPE cartridges with an ethanol solution.
33. The method as defined in claim 32 wherein said ethanol solution is an acidified ethanol solution.
34. The method as defined in claim 1 wherein said method is automated.