The stereochemistry of the marine eicosanoid, hybrldalactone, has been determined experimentally to be as in 2, in accord with a proposed scheme of biosynthesis from eicosapentaenoic acid.
Recently a novel eicosanoid, designated hybridalactone, was isolated from the marine alga Laurencia hybrida and was assigned gross structureL on the basis of proton magnetic resonance (pmr) studies.
1 A partial assignment of stereochemistry was also made which included: (1) relative arrangement of substituents on the B-membered ring, (2) cts relationship between carbons on the S-membered ring, and (3) Z-arrangement of the 5,6-and 8,9-double bonds.
1 In this note we present evidence for the complete stereochemistry of hybridalactone (2 ) and also describe a possible pathway to biosynthesis, which correctly predicted absolute stereochemistry.
Research on the total synthesis of hybridalactone, to be published separately, has completely confirmed the assignment of stereoformula 2t.o hybridalactone.
The studies on stereochemistry and synthesis were initiated before a sample of natural hybridalactone was avatlable to us and consisted of a combined analysis of molecular mechanics calculations, published' pmr data and biogenesis.
The vlcinal stereorelationship at C-14/15 was clarlfled first from pmr data and computer calculations performed on a simplified structure, a A 11,12 -olefin with an L-prcpyl group instead of ethylcyclopropyl at C-15. For clarity these results will be discussed relative to the finally determined 5 configuration at C-14. Random starting conformations were generated by a modified EMBED distance-geometry technique.