Swietemicrolides A–D, mexicanolide-type limonoids from the bark of Swietenia macrophylla with in vitro cytotoxic and α-glucosidase inhibitory activities

Abstract

Four new mexicanolide-type limonoids, swietemicrolides A–D (1–4), together with three known compounds (5–7) were isolated from an ethyl acetate extract of the bark of Swietenia microphylla. 1 and 2 had 1,8-hemiacetal systems whilst 3 and 4 shared hexacyclic skeletons consisting of three fused five-membered rings. The structures of the isolated compounds were determined using spectroscopic methods. The five limonoids (1–5) were tested in vitro for their cytotoxic effects against two human cancer cell lines (KB carcinoma and A549 lung cancer cells) and α-glucosidase inhibitory activity. None of them showed significant cytotoxic activity, however, swietemicrolide C (3) exhibited strong effect towards α-glucosidase. Moreover, a possible biosynthetic pathway for compounds 1–4 was proposed to support a comprehensive understanding of the configurations of the new limonoids.