Metabolites from microbially infected potato. Part 1. Structure of phytuberin

Abstract

Phytuberin (1) was obtained from bacterially rotted potato tubers and shown to be a novel tricyclic sesquiterpene acetate. Two heterocyclic rings, a dihydrofuran ring which was hydrated under acid conditions to give the lactol (6) and readily oxidised to the γ-lactone (8), and a relatively inert tetrahydrofuran ring, were shown to be present. N.m.r. studies, including the use of lanthanide shift reagents, established an overall constitution for phytuberin {8-(1-acetoxy-1-methylethyl)-5,5a,6,7,8,9-tetrahydro-3a,5a-dimethyl-3aH-furo[3,2-c]isobenzofuran} and showed that the third ring was a cyclohexane held rigidly in a chair conformation by the two fused heterocyclic rings. Catalytic hydrogenation of phytuberin provided a dihydro-derivative (2) which was used in an independent X-ray crystallo-graphic structure determination.