6-epi-Albrassitriol

Three new drimane sesquiterpenoids, 12-hydroxyalbrassitriol (1), drim-8(12)-en-6β,7α, 9α,11-tetraol (2), and drim-68(12)-dien-9α,11-diol (3), along with one known analog albrassitriol (4), were isolated from cultures of the tin mine tailings-associated fungus Penicillium sp. The new structures were determined on the basis of extensive spectroscopic analyses. All compounds were tested for their cytotoxicities against five human cancer cell lines.

A novel synthesis of natural drimanic compounds, (-)-albrassitriol (2) and (-)-6-epi-albrassitriol (3), has been carried out starting from an easily available labdane diterpenoid, (+)-larixol (1). In a two-step procedure, (+)-larixol (1) was converted into 14,15-bisnorlab-7-ene-6,13-dione (9), which was then submitted to a Norrish type II photochemical degradation yielding drim-7,9(11)-diene-6-one (10), whose treatment with OsO4 led selectively to the formation of drim-7-ene-9α,11-diol-6-one (12). The same compound was obtained by selective epoxidation of the C(9)-C(11) double bond in drim-7,9(11)-diene-6-one (10) with monoperphtalic acid. Treatment of the resulting mixture of α- and β-epoxides (13 and 14) with HClO4 yielded drim-7-ene-9α,11-diol-6-one (12). Reduction of the C6-carbonyl group in drim-7-ene-9α,11-diol-6-one (12) with LiAlH4 afforded (-)-albrassitriol (2) and (-)-6-epi-albrassitriol (3), 12.4% and 13.6% overall yields, respectively.