Biosynthetic Origin of the 3-Amino-2,5,7,8-tetrahydroxy-10-methylundecanoic Acid Moiety and Absolute Configuration of Pahayokolides A and B

Pahayokolides A (1) and B (2) are cyclic undecapeptides that were isolated from the cyanobacterium Lyngbya sp. They contain the unusual alpha-hydroxy-beta-amino acid 3-amino-2,5,7,8-tetrahydroxy-10-methylundecanoic acid (Athmu). The absolute configurations of the amino acids of the pahayokolides, except for the four oxygen-bearing stereocenters of Athmu, have been determined by Marphy's method. Incorporation of labeled leucine and acetate precursors into the pahayokolides has established that Athmu is derived from a leucine or alpha-keto isocaproic acid starter unit, which is further extended with three acetate units.