Cerexin B

The isolation and total synthesis of the antimicrobial lipopeptide cerexin A1 is reported. This synthesis includes the preparation of orthogonally protected γ-hydroxylysine, utilizing a nitrile Reformatsky-type reaction as a key step to yield both diastereomers more efficiently than previously reported methods. The configuration of the β-hydroxyl in the lipid tail was determined by the use of a modified Ohrui-Akasaka approach. Furthermore, new cerexin analogues from Bacillus mycoides ATCC 21929 were isolated and characterized, revealing an ε-amino succinylation of a hydroxylysine residue that is unusual in a nonribosomal peptide synthetase product.

A selective isolation medium was devised for Pseudomonas bacteria. An antibiotic mixture which contained 10 micrograms per ml of cerexin A, 10 micrograms per ml of nalidixic acid and 30 micrograms per ml of cycloheximide was used. With the antibiotic medium, 58 strains of bacteria presumed to be Pseudomonas which were subdivided into 18 taxonomically different groups were isolated from 3 soil samples with 9% of contaminants. With this method, it was possible to isolate a Pseudomonas bacterium from a sample containing about 400 times as many other Gram-positive and -negative bacteria.

By high performance liquid chromatography, cerexin B was separated into four components (B1, B2, B3 and B4), cerexin D into four components (D1, D2, D3 and D4), tridecaptin A into components (A alpha and A beta), tridecaptin B into four components (B alpha, B beta, B gamma and B delta) and tridecaptin C into three components (C alpha 1, C alpha 2 and C beta 1). All components were preparatively isolated, and their fatty acid and amino acid compositions determined for structural elucidation.