ChemInform Abstract: Isolation, Structural Elucidation, and Chemical Transformation of Interconvertible 8,12-Hemiketal Germacranolide Sesquiterpenoids from Salvia castanea Diels f. tomentosa Stib

From the aerial parts of Salvia castanea Diels f. tomentosa Stib., four new hemiketal germacranolide sesquiterpenoids, castanins C-F (1 -4), were obtained as two pairs of interconvertible forms along with their acetates, 5 and 6. Their structures were elucidated by spectroscopic methods and X-ray analysis of the uninterconvertible isomeric acetates, 5 and 6. The computational study explained that the ratios of 1 and 2, 3 and 4, and their acetates (5 and 6) in the mixtures were 1:1, 1:2, and 1:3, respectively. In addition, the semisynthesis of castanins C (1) and D (2) was conducted by the photooxidation of castanin B (8), the major constituent of this plant. Compounds 5, 6, and 8 were also tested for their inhibitory activity toward MCF-7, HeLa, and HepG2 cell lines. (C) 2008 Elsevier Ltd. All rights reserved.