Three Pairs of Enantiomeric Sesquiterpenoids from <i>Syringa pinnatifolia</i>

Abstract

Three pairs of enantiomeric sesquiterpenoids, (∓)-syringanoid A (<b>1a</b> and <b>1b</b>) and (±)-pinnatanoids A (<b>2a</b> and <b>2b</b>) and B (<b>3a</b> and <b>3b</b>), that represent an unprecedented 5/4/6 tricyclic backbone and a rare 6/7 bicyclic backbone, respectively, were isolated from the peeled stems of <i>Syringa pinnatifolia</i>. The structures were elucidated by extensive spectroscopic analysis, single-crystal X-ray diffraction, a modified Mosher's method, and quantum chemical calculations. A plausible biotransformation pathway for <b>1</b>-<b>3</b> was proposed, and their cardiomyocyte-protective and anti-inflammatory activities were evaluated.