Configurational analysis of new furanosesquiterpenes from Dysidea herbacea. Assignment of absolute stereochemistry.

Abstract

Two new marine furanoterpenes (+)-(4a S, 6 R,8a S)-4,4,7-trimethyl-4,4a,5,6,8,8a,9-hexahydronaphtho[2,3- b]furan-6-yl acetate ( 1) and (+)-(4a S,7 R,8a S)-6,9,9-trimethyl-4,4a,7,8,8a,9-hexahydronaphthol[2,3 b]furan-7-yl acetate ( 2), were isolated sample of Dysidea herbacea collected from Harrier Reef on the Great Barrier Reef, Australlia. The enantiomer of 1, (−)-(4a R,6 S,8a R)-4,4,7–trimethyl– 4,4a,5,6,8,8a,9–hexahydronaptho[2.3–b]furan–6–yl acetate (17) was found in another sample of D. herbacea collected nearby from Norman Reef. The structures were determined by spectroscopic methods, in particular 2D NMR, and the absolute configurations of the parent rings of 1 and 2 defined by chemical correlation and application of Kakisawa's of the Mosher ester method. Compounds 1 and 2 are diastereomers of acetates 5 and 6, reported earlier from D. herbacea, but have opposite configuration with respect to the ring junctions. These results and others suggest D. herbacea, may possess a dual capacity for antipodal cyclization pathways from a common achiral terpenoid precursor.