The structures of the new antibiotics Streptocidins A-D were elucidated as cyclic decapeptides cyclo[L-Val
1-L-Orn
2-L-Leu
3-D-Phe
4-L-Pro
5-L-Leu
6-X
7-L-Asn
8-L-Gln
9-X
10] with X
7-D-Trp (A, B, C) or D-Phe (D) and X
10=L-Tyr (A), L-Trp (B, D), or D-Trp (G). The amino acid composition (including the configuration) of the substances was determined by chiralphase GC-MS of the hydrolysates. The sequences were established by EDMAN degradation following linearisation of the cyclic peptides upon treatment with LiAIH
4. NMR spectroscopic studies of Streptocidins C and D confirmed the proposed sequences and provided conformational data which indicate a molecular topology of Streptocidins C and D similar to those of tyrocidine A and gramicidin S.
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