CALOPHYCIN, A FUNGICIDAL CYCLIC DECAPEPTIDE FROM THE TERRESTRIAL BLUE-GREEN-ALGA CALOTHRIX-FUSCA

A broad-spectrum fungicide, calophycin, has been isolated from Calothrix fusca EU-10-1, a terrestrial blue-green alga belonging to Nostocaceae, and identified to be a cyclic decapeptide, cyclic (L-Ala-D-Asp-L-Asn-L-Gln-Gly-L-Arg-L-N-MeAsn-L-Pro-(2R,3R,4S)-Hamp-L-Val), where Hamp is a (2R,3R,4S)-3-amino-2-hydroxy-4-methylpalmitic acid unit and MeAsn is an N-methylasparagine residue. Its total structure, including absolute stereochemistry, was determined by a combination of spectral and chemical studies, including synthesis of the unusual beta-amino acid Hamp.