CONSTITUENTS OF ROSACEOUS PLANTS .1. STRUCTURES OF NEW TRITERPENOIDS FROM COWANIA-MEXICANA

In our search for possible anti-tumor-promoters, we carried out an inv estigation of the leaves and branches of Cowania mexicana D. DoN (Rosa ceae). Two new cucurbitane type triterpenes, 15-oxo-cucurbitacin F (3) and 15-oxo-23,24-dihydrocucurbitacin F (4), were isolated together wi th cucurbitacin F (1) and 23,24-dihydrocucurbitacin F (2). These trite rpenes were inhibitors of Epstein-Barr virus early antigen activation induced by 12-0-tetradecanoylphorbol-13-acetate, a well-known tumor-pr omoter. The structures of 3 and 4 were determined from 2D-NMR spectral data and difference NOE experiments.