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. This work has led to the isolation of a pair of new enantiomers, (±)‐acutalourin [(±)‐1], a new racemic linear monoterpenoid, acutalourone (2), along with five known compounds (3–7) from Argyreia acuta Lour. Compounds (+)‐1 and (−)‐1 possess an unusual 8‐oxa‐bicyclo[3,2,1]oct‐3‐en‐2‐one nucleus that might be derived from [5+2] cycloaddition reaction, and their absolute configurations were assigned by TDDFT‐ECD calculations.