Total syntheses of lyngbyabellins A and B, potent cytotoxic lipopeptides from the marine cyanobacterium Lyngbya majuscula

The first total syntheses of lyngbyabellins A and B, Lyngbya majuscula derived lipopeptides, are described. The functionalized thiazole carboxylic acid units were prepared by the oxidative dehydrogenation of the corresponding thiazolidines with chemical manganese dioxide. The asymmetric synthesis of the dichlorinated β-hydroxy acid by a chiral oxazaborolidinone mediated aldol reaction. Finally, fragment condensation followed by macrolactamization provided lyngbyabellin A. The total synthesis of lyngbyabellin B was accomplished by formation of the sensitive thiazoline ring after the macrolactamization.