Siamenols A-D, four new coumarins from Mammea siamensis

Further investigation of the dichloromethane extract of the twigs of Mammea siamensis led to the isolation of four novel coumarins, named siamenols A-D (1-4) together with three known xanthones. The structures of the new coumarins were elucidated by spectroscopic analysis, including 2D NMR spectroscopic data. In addition, the absolute stereochemistry of hydroxyl group of siamenol C (3) was determined to be S configuration by using modified Mosher's method.