Identification and total synthesis of novel fatty acids from the siphonarid limpet Siphonaria denticulata

The novel fatty acids 17-methyl-6(Z)-octadecenoic acid and 17-methyl-7(Z)-o ctadecenoic acid were identified for the first time in nature in the mollus k Siphonaria denticulata from Queensland, Australia. The principal fatty ac ids in the limpet were hexadecanoic acid, octadecanoic acid, and (Z)-9-octa decenoic acid, while the most interesting series of monounsaturated fatty a cids was a family of five nonadecenoic acids with double bonds at either De lta (7), Delta (9), Delta (11), Delta (12), or Delta (13). The novel compou nds were characterized using a combination of GC-MS and chemical transforma tions, such as dimethyl disulfide derivatization. The first total syntheses for the two novel methyl-branched nonadecenoic acids are also described, a nd these were accomplished in four to five steps and in high yields.