Alkaloids and Styryl lactones from Goniothalamus ridleyi King and Their α -Glucosidase Inhibitory Activity.

Gonioridleylactam ( 1 ), a new compound, is a unique dimeric aristolactam isolated from the EtOAc extract of the twigs of Goniothalamus ridleyi King. The structure of gonioridleylactam ( 1 ) consists of two different aristolactams linked together with two methylenedioxy bridges at C-3/C-3' and C-4/C-4', generating a ten-membered ring of [1,3,6,8]tetraoxecine. A new natural product, gonioridleyindole (3-hydroxymethyl-1-methyl-1 H -benz[ f ]indole-4,9-dione, 2 ), together with eight known compounds ( 3-10 ) were also isolated from this plant. Their structures were extensively characterized by spectroscopic methods and comparisons were made with the literature. Compounds 1-4 , 7 , and 9 were evaluated for their α -glucosidase inhibitory activity. Of these, 3,5-demethoxypiperolide ( 7 ) displayed the highest α -glucosidase inhibitory activity, with an IC ₅₀ value of 1.25 µM.