α-Glucosidase Inhibitory Isomeric Corniculatolides from the Stems of the Indian Mangrove Plant, Xylocarpus granatum

Three new isomeric corniculatolides (1, 2, and 3) with an unusual caffrane and isocorniculane framework, and five known metabolites were isolated from the chloroform extract of the stems of Xylocarpus granatum. The structures of the new metabolites were deduced as corniculatolide B (1), isocorniculatolide B (2), and corniculatolide C (3) by spectroscopic data analysis and a combination of chemical transformations and supported by single-crystal X-ray crystallographic data of 1 and 3. The isolated compounds were evaluated for their in vitro cytotoxicity and alpha-glucosidase (Saccharomyces cerevisiae) inhibitory potential. Compound 3 possessed alpha-glucosidase inhibitory activity with an IC50 value of 24.8 mu M, whereas these rare macrolides showed no effect on the mammalian cancer cell lines MIAPaCa-2, DU145, MCF-7, and HTC-116.