CONFIGURATIONAL ANALYSIS OF NEW FURANOSESQUITERPENES FROM DYSIDEA-HERBACEA - ASSIGNMENT OF ABSOLUTE STEREOCHEMISTRY

Two new marine furanoterpenes, -4,4a,5,6,8,8a,9-hexahydronaphtho[2,3-b ]furan-6-yl acetate (1) and (+)-(4aS,7R,8aS)-6,9,9-trimethyl-4,4a,7,8, 8a, 9-hexahydronaphtho[2,3-b]furan-7-yl acetate (2) , were isolated fr om a sample of Dysidea herbacea, collected from Harrier Reef on the Gr eat Barrier Reef, Australia. The enantiomer of 1, (-)-(4aR, 6S, 8aR)-4 ,4,7-trimethyl-4,4a,5,6,8,8a, 9-hexahydronaphtho[2,3-b]furan-6-yl acet ate (17) was found in another sample of D. herbacea collected nearby f rom Norman Reef. The structures were determined by spectroscopic metho ds, in particular 2D NMR, and the absolute configurations of the paren t rings of 1 and 2 defined by chemical correlation and application of Kakisawa's modification of the Mosher ester method. Compounds 1 and 2 are diastereomers of acetates 5 and 6, reported earlier from D. herbac ea, but have opposite configuration with respect to the ring junctions . These results and others suggest D. herbacea may possess a dual capa city for antipodal cyclization pathways from a common achiral terpenoi d precursor.