Method for the preparation of maytansinoid esters

1. A process of making a maytansinoid ester comprising forming an anion of maytansinol or a maytansinoid bearing a free C-3 hydroxyl moiety and reacting the anion with an activated carboxyl compound to thereby produce the maytansinoid ester.

2. The process of claim 1 , wherein the anion is formed by reacting the maytansinol or the maytansinoid bearing a free C-3 hydroxyl moiety with a non-aqueous base.

3. The process of claim 2 , wherein the non-aqueous base is a metal hexamethyldisilazide, an alkyl metal, an aryl metal, a metal hydride, sodamide, or potassium amide.

4. The process of claim 3 , wherein the metal hexamethyldisilazide is zinc hexamethyldisilazide, sodium hexamethyldisilazide, lithium hexamethyldisilazide, or potassium hexamethyldisilazide.

5. The process of claim 3 , wherein the alkyl metal or aryl metal is methyl lithium, n-butyl lithium, tert-butyl lithium, phenyl lithium, lithium di-isopropylamide (LDA), pentyl sodium, or 2-phenyl isopropyl-potassium.

6. The process of claim 3 , wherein the metal hydride is sodium hydride or potassium hydride.

7. The process of claim 1 , wherein the activated carboxyl compound is at least one member selected from the group consisting of an acid anhydride, a mixed anhydride, a cyclic anhydride, an acid halide, an acylimidizolide, an acyl substituted imidazolide, and a carboxyl ester.

8. The process of claim 7 , wherein the acid anhydride is selected from acetic anhydride, isobutyric anhydride, or an anhydride of an amino acid derivative.

9. The process of claim 7 , wherein the mixed anhydride is selected from the group consisting of a mixed anhydride between a phosphate or sulfate with the acid moiety of acetic acid, propionic acid, butyric acid or an amino acid derivative.

10. The process of claim 7 , wherein the cyclic anhydride is selected from the group consisting of an N-carboxyanhydride of N-methyl-L-alanine and an N-carboxyanhydride of N-methyl-D-alanine.

11. The process of claim 7 , wherein the acid halide is an acid fluoride, an acid chloride, an acid bromide or an acid iodide.

12. The process of claim 7 , wherein the carboxyl ester is a N-hydroxysuccinimide ester, a para-nitrophenyl ester, an ortho-nitrophenyl ester, a dinitrophenyl ester, or a pentafluorophenyl ester.

13. The process of claim 1 , wherein the activated carboxyl compound is a compound of formula RCOX, wherein X is a halide, an alkoxy group, an aryloxy group, an imidazole or —OY, wherein Y is succinimide, phthalimide, aryl or substituted aryl, and R is a linear, branched or cyclic alkyl or alkenyl having from 1 to 10 carbon atoms or a substituted amino acid moiety.

14. The process of claim 13 , wherein the substituted amino acid moiety is N-methyl-L-alanyl moiety.

15. The process of claim 13 , wherein X is fluoride, chloride, bromide or iodide, pyridyl, imidazolyl or substituted imidazolyl, or —OY, wherein Y is succinimide, phthalimide, aryl or substituted aryl.

16. The process of claim 13 , wherein the substituted aryl is at least one member selected from the group consisting of para-nitrophenyl, ortho-nitrophenyl, dinitrophenyl and pentafluorophenyl.

17. The process of claim 1 , wherein the activated carboxyl compound is an acid anhydride of the formula RCOOCOR′, wherein R and R′ are the same or different and are a linear, branched or cyclic alkyl or alkenyl having from 1 to 10 carbon atoms or a substituted amino acid moiety.

18. The process of claim 17 , wherein the substituted amino acid moiety is N-methyl-L-alanyl moiety.

19. The process of claim 1 , wherein the activated carboxyl compound is a carboxyl-activated amino acid containing compound.

20. The process of claim 19 , wherein the carboxyl-activated amino acid containing compound is a compound of the formula (Ia), (Ib), (Ic) or (Id):

wherein:

X represents a halide, an alkoxy group, an aryloxy group, an imidazole, —OY, wherein Y is succinimide, phthalimide, aryl or substituted aryl, an anhydride or a mixed anhydride; Q represents H, or a branched or linear alkyl group; V represents H, or a branched or linear alkyl group; and Y 2 represents (CR 7 R 8 ) l (CR 5 R 6 ) m (CR 3 R 4 ) n CR 1 R 2 (SZ 2 ) p , wherein: R 1 and R 2 are each independently H, linear, branched or cyclic alkyl or alkenyl having from 1 to 10 carbon atoms, phenyl or substituted phenyl, and in addition R 2 can be H; R 3 , R 4 , R 5 , R 6 , R 7 and R 8 are each independently H, linear, branched or cyclic alkyl or alkenyl having from 1 to 10 carbon atoms, phenyl or substituted phenyl; 1, m and n are each independently 0 or an integer of from 1 to 5; Z 2 is R 9 , SR 9 or COR 9 , wherein R 9 is linear alkyl, branched alkyl or cyclic alkyl having from 1 to 10 carbon atoms, or simple or substituted aryl or heterocyclic,

p is either 0 or 1.

21. The process of claim 20 , wherein X is fluoride, chloride, bromide, iodide, pyridyl, imidazolyl, substituted imidazolyl, or —OY, wherein Y is succinimide, phthalimide, aryl or substituted aryl.

22. The process of claim 20 , wherein X is —OCOR 9 , wherein R 9 is linear alkyl, branched alkyl or cyclic alkyl having from 1 to 10 carbon atoms, or simple or substituted aryl or heterocyclic.

23. The process of claim 20 , wherein X is a substituent that gives a symmetrical anhydride of formula (Ia) or (Ib).

24. The process of claim 1 , 12 or 20 , wherein the anion is formed by reacting the maytansinol or a maytansinoid bearing a free C-3 hydroxyl moiety with zinc hexamethyldisilazide.

25. The process of claim 1 , 12 or 20 , wherein the activated carboxyl group is an acid fluoride.

26. The process of claim 1 , 12 or 20 , wherein the maytansinoid ester is substantially a single diastereomer.

27. The process of claim 26 , wherein the diastereomer is an L-aminoacyl ester.