Isolation, structural determination, and biological activity of 6 alpha-hydroxytaxol, the principal human metabolite of taxol.

The principal biotransformation product of taxol was found to be identical for human hepatic microsomes, human liver slices, and patient bile samples. We have isolated this metabolite from the bile of a patient given taxol, and we report its structure and its cytotoxicity relative to taxol. The NMR and SIMS data presented here indicate that, in humans, taxol is regiospecifically hydroxylated at the 6-position on the taxane ring and that this hydroxyl is stereospecifically placed trans to the hydroxyl at position 7, yielding 6 alpha-hydroxytaxol.

13C nuclear magnetic resonance study of the pyruvate dehydrogenase-catalyzed acetylation of dihydrolipoamide.

The dihydrolipoyl transacetylase component of the pyruvate dehydrogenase complex catalyzes a reversible reaction between acetyl-CoA and dihydrolipoamide that results in the formation of S-acetyldihydrolipoamide. We have used 13C nuclear magnetic resonance to investigate this reaction using exogenous forms of dihydrolipoamide in place of the protein-bound substrate. With substrate levels of dihydrolipoamide and enzymatically generated [1-13C]acetyl-CoA, both 6-S-[1-13C]acetyl- and 8-S-[1-13C]acetyldihydrolipoamide were formed in the transacetylation reaction and both species participated in the reverse reaction to yield [1-13C]acetyl-CoA and free dihydrolipoamide.