α‑Glucosidase Inhibitory and Cytotoxic Taxane Diterpenoids from the Stem Bark of <i>Taxus wallichiana</i>

From a CH₂Cl₂ extract of the bark of <i>Taxus wallichiana</i>, six new taxoids, wallitaxanes A–F (<b>1</b>–<b>6</b>), were isolated, together with 29 known compounds. The structures of the new compounds were elucidated on the basis of spectroscopic data interpretation. Wallitaxane D (<b>4</b>) was identified as an opened oxetane-type taxoid having the first naturally occurring C­(H)-20 acetal group, while wallitaxanes E (<b>5</b>) and F (<b>6</b>) are representative of the rare <i>abeo</i>-taxoid class. The isolated compounds were evaluated for their α-glucosidase inhibitory activity and for cytotoxicity against the HeLa human cervical cancer cell line. In the present work, taxanes were found to exhibit α-glucosidase inhibitory activity for the first time, and wallitaxane A (<b>1</b>) showed the most potent effect, with an IC₅₀ value of 3.6 μM. In turn, 7-<i>epi</i>-taxol (<b>16</b>) and 7-<i>epi</i>-10-deacetyltaxol (<b>17</b>) showed IC₅₀ values of 0.05 and 0.085 nM, respectively, against HeLa cells