Acutalourin and Acutalourone: New Metabolites Isolated from Folk Medicinal Plant Argyreia acuta Lour.

A pair of new 8-oxa-bicyclo[3,2,1]oct-3-en-2-one derivative enantiomers, (+/-)-acutalourin [(+/-)-1], a new racemic linear sesquiterpenoid acutalourone (2), along with five known caffeic acid derivatives (3-7), were isolated from Argyreia acuta Lour. The structures were determined by a combination of spectroscopic data interpretation. The absolute stereochemistry of (+)-acutalourin and (-)-acutalourin were proposed by comparison of their experimental electronic circular dichroism (ECD) curves with the time-dependent density functional theory (TDDFT)-calculated curves.