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.

Fig. 1. Structure of compounds 1–7.

Fig. 2. Key HMBC and ¹H–¹H COSY correlations of 1–4.

Fig. 3. Key NOESY correlations of 1–4.

Scheme 1. The possible biosynthetic pathways of 1–4.