Quinone derivatives by chemical transformations of 16-hydroxycarnosol from Salvia species

The known diterpenes 12,16-epoxycarnosol (2), isotanshinone II (6), and (+)-neocryptotanshinone (8) were obtained by partial synthesis from 16-hydroxycarnosol (1), a C-16 hydroxylated abietatriene diterpene isolated in relative abundance from the aerial part of Salvia mellifera GREENE. The physical and spectroscopic data of these semisynthetic diterpenes were identical to those given for the natural ones in the literature. These abietane diterpenes have very interesting biological activities and the semisynthetic approach described here represents an alternative to obtain them from other major diterpenes isolated from Salvia species. Additionally, seven new semisynthetic diterpene analogues, 11,14-dioxo-12,16-epoxy-8,12-abietadien-20,7β-olide (3), 11,14-dioxo-12,16-epoxy-8,12,15(16)-abietatrien-20,7β-olide (4), 15,16-didehydro-12,16-epoxycarnosol (5), 1-oxoisotanshinone II (7), 16-hydroxycolumbaridione (9), 12,16-diacetoxycolumbaridione (10), and 14-methoxy-12,16-epoxycarnosol (13), were obtained from 1. The structures of the new compounds were established based on their spectroscopic data.