Verdoppelungsreaktionen beim Ringschluss von Peptiden IV. Die stereoisomeren Cyclo‐phenylalanyl‐glycyl‐glycyl‐phenylalanyl‐glycyl‐glycyle und die stereospezifische Entstehung der meso‐Form. Konformationen cyclischer Polypeptide. 11. Mitteilung über homodet cyclische Polypeptide

Cyclisation of active esters of the racemic tripeptides glycyl‐glycyl‐DL‐phenylalanine and glycyl‐DL‐phenylalanyl‐glycine as well as of the hexapeptide glycyl‐glycyl‐DL‐phenylalanyl‐glycyl‐glycyl‐DL‐phenylalanine (unidentified mixture of diastereoisomers) has yielded as main product the meso‐cyclohexapeptide, cyclo‐glycyl‐L‐phenylalanyl‐glycyl‐glycyl‐D‐phenylalanyl‐glycyl (IV). This is proven by comparison of the X‐ray powder diagram of the said product with those of the corresponding meso, L‐L, D‐D, and racemic cyclohexapeptides (Fig.1). The synthesis of these isomers by the azide procedure is described. The hydrazide function was introduced in a protected form early in the synthesis (as ‐NHNH·CO·OC(CH3)3) and the blocking group (t‐butoxy‐carbonyl) removed in one of the last steps (schemes 2 and 3).