Mayombensin, a New Azadirachtin I Derivative with Unusual Structure from Guarea mayombensis

A new highly oxidized tetranortriterpenoid, named mayombensin (1), was isolated from the twigs of Guarea mayombensis together with five known compounds and, further, two ceramides, 3,4-dimethyl-secotirucalla-4(28),7,24-trien-3,21-dioic acid (3), the glucosides of stigmasterol and β-sitosterol, and the respective aglyca. The structure of 1 was elucidated by detailed NMR analysis and confirmed as a novel azadirachtin homologue.