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

From an ethyl acetate extract of the bark of Swietenia microphylla Cam., five new mexicanolide-type limonoids, swietemicrolides E-I (1–5), along with the known compound, grandifotane A (6), 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 in vitro cytotoxicity of compounds 1–6 was tested against HepG2 hepatoma and MCF-7 breast cancer cell lines, revealing no significant effect. Additionally, their α-glucosidase inhibitory activity was evaluated, with compounds 2 and 6 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).