Two New and Four Known Triterpenoids from Boswellia sacra Fluckiger

: Two new O-acetyl derivatives of pentacyclic triterpenic acids, 3α-acetoxyurs -5:12-dien-24-oic acid ( 1 ) and 3α-acetoxylup -12:20 (29)-dien-24-oic acid ( 2 ) were isolated from Omani frankincense of Boswellia sacra Flueckiger along with four known compounds: commic acid-D (3), 9,11-dehydro-β-boswellic acid (4), 3β-Hydroxy-11-oxours-12-ene (5), and 11β-Hydroxy-3-oxours-12-ene (6) . The structures of new compounds 1 and 2 were elucidated on the basis of detailed mass and NMR spectroscopic analysis using 1H NMR, 13C NMR, HMQC, HMBC, COSY, and HREIMS techniques. The relative configurations of 1 and 2 were assigned by comparative analysis of the NMR spectral data with the related known triterpenoids together with NOESY experiments. The structures of the known compounds 3-6 were confirmed by the comparative analysis of the reported mass and NMR data.