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[Study on surfactin, a cyclic depsipeptide. I. Isolation and structure of eight surfuctin analogs produced by Bacillus natto KMD 2311].

Crude surfactin was simply prepared from the culture filtrate of Bacillus natto KMD 2311 twice by acidification of the filtrate and extraction of the precipitate with ethanol. Eight surfactin analogs were isolated from the crude surfactin by RP-HPLC and gel filtration. The structure of each analog was deduced by means of amino acid composition of the acid hydrolysate and FAB-MS measurement to be a cyclic depsipeptide containing a hydroxyfatty acid. The structure of the hydroxyfatty acid moieties was elucidated as n- or iso- or anteiso-3-hydroxyfatty acid composed of carbon number 13-16 by GC analysis and EI-MS after the methanolysis of the analogs. The amino acid sequence of the peptide portion was assigned as acyl-Glu-Leu-Leu-Val-Asp-Leu-Leu by EI-MS for eight analogs. The isolated four compounds were found to be identical with the known surfactin analogs, A1, B1, B2 and C1. Although surfactin A2 and C2 had not been isolated, their structures were deduced to be a surfactin analog. Surfactin A3 and D were novel analogs. The acyl groups of surfactin A2, A3, C2 and D were anteiso-3-hydroxytridecanoic acid, n-3-hydroxytridecanoic acid, anteiso-3-hydroxypentadecanoic acid and iso-3-hydroxyhexadecanoic acid, respectively.