Ring A Modified Novel Triterpenoids from Dysoxylum hainanense

Six ring A modified novel triterpenoids, dysoxyhainic acids A–E ( 1 – 3 , 5 , and 6 ) and dysoxyhainol ( 4 ), were isolated from the twigs and leaves of Dysoxylum hainanense . Compounds 1 – 4 are a group of triterpenoids featuring a contracted five‐membered ring A. Dysoxyhainic acid A ( 1 ) possessed an unprecedented 2‐nor‐1,3‐cyclotirucallane skeleton, whereas 5 and 6 possessed a rare six‐membered δ‐lactone formed between C‐2 and C‐11. The structures of 1 – 6 were established by extensive spectroscopic analysis, and that of 1 was confirmed by single‐crystal X‐ray diffraction. A hypothetical biosynthetic pathway for compound 1 was also proposed. All the compounds were tested on antimicrobial assays, and compounds 2 and 3 exhibited moderate antibacterial activity against Gram‐positive bacteria. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)