Biosynthetic studies of amphidinolides G and H: unusual labeling patterns in feeding experiments with 13C-labeled acetates

The biosynthetic origins of amphidinolides G (1) and H (2) were investigated on the basis of 2D NMR data of 13C-enriched samples obtained by feeding experiments with [1-13C], [2-13C], and [1,2-13C2] sodium acetates in cultures of a marine dinoflagellate Amphidinium sp. These incorporation patterns suggested that 1 and 2 were generated from three unusual C2 units derived only from C-2 of acetates in addition to three successive polyketide chains. Furthermore, it is noted that six oxygenated carbons of C-1, C-18, C-20, C-21, C-22, and C-26 in 1 and 2 were not derived from the C-1 carbonyl but from the C-2 methyl of acetates.