Synthesis of [C-14(2)]taxol: Application of (+)/(-)-[C-13,14(n)]BABS, part3

A multiple step stereoselective procedure was successfully applied to doubl y C-14 labelled Taxol 1 in its pharmacologically essential (2R,3S)-N-benzoy l-3-phenylisoserine side chain. A highly stereocontrolled aldol reaction of internally developed (+)-[C-14(2)]BABS 4a with benzaldehyde followed by so me functional group conversions provided (3R,4S)-3-(tert-butyl-dimethyl-sil anyloxy)-4-phenyl- [2,3-C-14(2)] azetidin-2-one 9a in an overall radiochemi cal yield of 34%. Attachement of the activated benzoyl beta-lactam 9b to th e baccatine skeleton 10 and subsequent deprotection provided the expected d oubly labelled drug substance.