19-Hydroxybaccatin III, 10-deacetylcephalomannine, and 10-deacetyltaxol: new antitumor taxanes from Taxus wallichiana.

Activity-guided, chromatographic fractionation for a polar extract of Taxus wallichiana Zucc. (originally identified as Cephalotaxus mannii Hook.) resulted in the isolation of three new KB cytotoxic taxane derivatives. Nmr and ms spectral analyses permitted their characterization as 19-hydroxybaccatin III (3), 10-deacetylcephalomannine (4), and 10-deacetyltaxol (5). The latter two compounds, which are also active against PS leukemia in vivo, were observed to be especially labile, each forming equilibrium mixtures with their cytotoxic C-7 epimers (9, 10).