Peptides, antibiotic homodet

Tyrocidins homodetic, homomeiic, cyclic peptide antibiotics active against Gram-positive bacteria. Like the Gramicidins (see), X are produced by Bacillus brevis. Hie structure of tyrocidin A, confirmed by total synthesis, is cyclo-(-Val-Om-Leu-D-Phe-Pro-Phe-D-Phe-Asn-Gln-IJr-). In tyrocidin B, Phe is replaced by Trp. In tyrocidin C, Phe is replaced by Tip, D-Phc7 by D-Hp, and Asng by Asp. Tyrocidin E differs from tyrocidin A by replacement of Asn by Asp, and Tyrio by Phe. 

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