STRUCTURE AND SYNTHESIS OF PETROSYNES, NEW ACETYLENIC ENOL ETHER GLYCERIDES FROM THE OKINAWAN MARINE SPONGE OF THE GENUS PETROSIA

Acetylenic enol ether glycerides, 1 and 3, were found in the Okinawan marine sponge of the genus Petrosia. The plane structures of these glycerides were deduced from spectroscopic analysis. Their complete structures were established by enantioselective total synthesis of all possible stereoisomers using (R)-1-O-benzylglycerol and its (S)-enantiomer, prepared from D-mannitol and L-ascorbic acid, respectively, as chiral building blocks. The synthesis involves the palladium(O)-catalyzed coupling reaction of bromo enol ether 9 with enediyne 21 as a key step. It became evident from the synthesis that the natural product 1 consisted of a mixture of (7R,2'S)-24 (petrosyne Ia) and (7S,2S)-24 (petrosyne Ib), and the natural product 3 consisted of a mixture of (7R,2'S)-28 (petrosyne IIa) and (7S,2'S)-28 (petrosyne IIb).