Studies of the Biosynthesis of DTX-5a and DTX-5b by the Dinoflagellate <i>Prorocentrum </i><i>m</i><i>aculosum</i>:  Regiospecificity of the Putative Baeyer−Villigerase and Insertion of a Single Amino Acid in a Polyketide Chain

The biosynthetic origins of the diarrhetic shellfish poisoning toxins DTX-5a and DTX-5b have been elucidated by supplementing cultures of the producing organism <i>Prorocentrum maculosum</i> with stable isotope labeled precursors and determining the incorporation patterns by <sup>13</sup>C NMR spectroscopy. The amino acid residue in the sulfated side chain is found to originate from glycine, and oxygen insertion in the chain is shown to occur after polyketide formation.