ABSOLUTE STEREOCHEMISTRY OF PETROFORMYNES, HIGH-MOLECULAR POLYACETYLENES FROM THE MARINE SPONGE PETROSIA-FICIFORMIS

The absolute stereochemistry of some petroformynes (1-7), characteristic metabolites of the Mediterranean sponge Petrosia ficiformis displaying terminal 1-yn-3-ol-4-ene moieties, has been elucidated by applying high field H-1-NMR to Mosher method. Esterification of Petrosia polyacetylene with (R)- and (S)-alpha-methoxy-alpha-trifluoromethylphenylacetyl (MTPA) chloride yielded the corresponding (S)- and (R)-MTPA esters. Careful NMR measurements led to assign the S absolute stereochemistry at all the chiral centers of petroformynes. The R absolute stereochemistry of 3-hydroxydocosa-4(E), 15(E)-dien-1-yne (8), previously established on the basis of a questionable extention of the application of the exciton chirality method, is confirmed by applying advanced Mosher method. The structures of petroformyne-5 (7) and petroformyne-8 (11) are now supported by additional evidence.