REVISED STRUCTURES AND BIOSYNTHETIC-STUDIES OF TANTAZOLES-A AND TANTAZOLES-B

Revised structures are presented for tantazoles A (3) and B (4) and preliminary studies on their biosyntheses in the terrestrial blue-green alga Scytonema mirabile BY-8-1 are reported. Marfey analysis of the acid hydrolyzates shows that the absolute configuration of C4 in thiazoline ring A of the two alkaloids is R. Feeding experiments with [1,2-C-13]acetate, [1,2-C-13]glycine, [1,2-C-13,N-15]glycine and [methyl-C-13]methionine indicate that 3 and 4 are modified pentapeptides assembled from acetate, four cysteines and a threonine and that the methyl groups on the four thiazoline rings, the amide nitrogen, and the methine attached to ring A originate from the tetraydrofolate C1 pool via methionine.