Verdoppelungsreaktionen beim Ringschluss von Peptiden. II. Cyclo‐glycyl‐glycyl‐DL‐phenylalanyl‐glycyl‐glycyl‐DL‐phenylalanyl. Verwendung aktivierter Ester zur Synthese makrocyclischer Peptide. Molekulargewichtsbestimmungen in Dimethylsulfoxyd. 8. Mitteilung über homodet cyclische Polypeptide

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Abstract
New combinations of activated ester groupings with N‐substituents are described for preparing activated esters of peptides which may be used for cyclization (to homodetic cyclic polypeptides). Various activated esters of glycyl‐glycyl‐DL‐phenylalanine and glycyl‐DL‐phenylalanyl‐glycine yield cyclo‐glycyl‐glycyl‐DL‐phenylalanyl‐glycyl‐glycyl‐DL‐phenylalanyl. These reactions present new examples for the «doubling reaction» during cyclization. The same cyclopolypeptide was obtained on cyclization of the p‐methanesulfonylphenyl ester of glycyl‐glycyl‐DL‐phenylalanyl‐glycyl‐glycyl‐DL‐phenylalanine, indicating that one of the diastereoisomers might be predominantly formed during the cyclization.Dimethylsulfoxide has been found to be a useful solvent for the cryoscopic determination of molecular weights of cyclopolypeptides.