Identification of new grandifotane limonoids with <i>α</i>-glucosidase inhibitory activities from the bark of a Vietnamese <i>Swietenia</i> species

From an ethyl acetate extract of the bark of <i>Swietenia microphylla</i> Cam., five new mexicanolide-type limonoids, swietemicrolides E-I (<b>1–5</b>), along with the known compound, grandifotane A (<b>6</b>), were isolated using column chromatography method. The six compounds are mexicanolides sharing a unique grandifotane scaffold with three fused five-membered rings. Their chemical structures were elucidated on the basis of spectroscopic analyses and comparison of the spectral data with relevant literature. Furthermore, a possible biosynthetic pathway for the formation of the isolated compounds was proposed. The <i>in vitro</i> cytotoxicity of compounds <b>1</b>–<b>6</b> was tested against HepG2 hepatoma and MCF-7 breast cancer cell lines, revealing no significant effect. Additionally, their <i>α</i>-glucosidase inhibitory activity was evaluated, with compounds <b>2</b> and <b>6</b> exhibiting potent inhibition (IC₅₀ = 151.77 and 161.95 μg/mL, respectively), which are comparable to the positive control (acarbose, IC₅₀ = 166.57 μg/mL).