The mansumbinanes: Octanordammaranes from the resin of Commiphora incisa

The resin of Commiphora incisa (Burseraceae) has yielded three C22 compounds derived by loss of the C-17 side chain from a dammarane triterpene. They have been ident̀ified by spectral analysis and chemical modification as 4α,4β,8β,10β,14α-pentamethyl-5α-gon-16-en-3-one (mansumbinone), the corresponding 3-hydroxy compound (mansumbinol) and the derivative 3,4-seco-mansumbinoic acid in which the A-ring has opened between C-3 and C-4. A fourth compound was characterized as 16(S),20(R)-dihydroxydammar-24-en-3-one, a possible precursor of the mansumbinanes.