Caryopristimerin, the First Example of a Sesquiterpene-Triterpene Homo Diels‑Alder Adduct, and a New 29-nor-Friedelane from Roots of Salacia crassifolia

Two new compounds, caryopristimerin and 2α,3α,22β-trihydroxy-21-oxo-29-nor-friedelan-24-oic acid, were isolated from the hexane/ethyl ether extract of Salacia crassifolia roots. Caryopristimerin represents the first example of a homo Diels-Alder adduct of a sesquiterpene and a triterpene, and the new 29-nor-friedelane displays a highly oxygenated A ring with a carboxylic group at the unusual C-5 position. The new compounds were elucidated by infrared (IR), high-resolution-atmospheric pressure chemical ionization-mass spectrometry (HR-APCI-MS), 1D/2D nuclear magnetic resonance (NMR) and single crystal X-ray diffraction analysis. Additionally, the known compounds 3-oxo-29-hydroxyfriedelane, pristimerin, tingenone and netzahualcoyonol are herein reported for the first time as constituents of S. crassifolia. Their structures were established by spectroscopic analysis.