Structure and Conformation of a New Longipinene Diester from Stevia nepetifolia

The roots of Stevia nepetifolia afforded the new longipinene derivative (4R,5S,7S,8S,9S,10R,11R,2'S,2″S)-(+)-7,8-di-(α-methylbutyryloxy)-9-hydroxylongipin-2-en-1-one (1), together with the known 7-angeloyloxy-8-(α-methylbutyryloxy)-9-hydroxylongipin-2-en-1-one (2), 7,8-diangeloyloxy-9-hydroxylongipin-2-en-1-one (3), valeranone, 2,3-epoxybisabol-10-en-1-one, γ-cadinene and α-cadinol. The new substance was fully characterized by 1D- and 2D- NMR spectroscopy, molecular modelling, and by partial synthesis using (S)-(+)-α-methylbutyric acid.