Modified taxols, 8. Deacylation and reacylation of baccatin III.

Hydrogenation of baccatin III over platinum converted it to its hexahydro derivative, and deacylation of this as its 7-triethylsilyl derivative was achieved with methoxide ion. The 10-acetate was hydrolyzed first, followed by the C-4 acetate and then the C-2 cyclohexylcarboxylate; an explanation for this unexpected order is presented. Base treatment also yielded a rearranged analogue with a tetrahydrofuran ring in place of the oxetane ring of baccatin III. Acetylation of 4,10-bis(deacetyl)-2-debenzoyl-7-triethylsilylbaccatin III proceeded readily at the C-13 position, in contrast to baccatin III which is only acetylated with difficulty at this position. Further acylation could be carried out selectively at the C-2 and C-10 positions, but acetylation at C-4 was possible only under vigorous conditions.