The biphenyl-containing pseudo-amino acids 2-(aminomethyl)biphenyl-2-carboxylic acid (Abc; 1) and 2 -(aminomethyl)biphenyI-2-acetic acid (Aba; 2) are used as rigid spacers in the backbone of the cyclic peptides cyclo (-Abc-Ala-Phe-Gly-), (S), cyclo(-Abc-Ala-Val-Gly-)2 (6), cyclo(-Aba-Gly-Phe-Ala-)2 (7), and cyclo(-Aba-Ala-PheGly-), (8). Three different interconverting diastereoisomers are found in solutions of each of these cyclopeptides due to the atropisomerism of the biphenyl units. NMR Techniques and molecular-dynamics calculations allow to conclude that the major diastereoisomer of 5 (and 6) in (D,)DMSO adopts a /3-sheet conformation. It is proposed that the pseudo-amino acid 1 of (R)-chirality forms, with attached L-amino acids, a H-bonding pattern comparable to a p-turn (see D in Fig.g.4 and F).

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Gleiche Konformation im Kristall und in Chloroform (NMR‐Daten) hat das biphenylhaltige Cyclopeptid 1, dessen Biphenyleinheiten S,S‐konfiguriert sind. Es kann chromatographisch von den bei der Synthese ebenfalls entstehenden Atropisomeren (R,S) und (R,R) getrennt werden. Die Konformation von 1 wird durch zwei Wasserstoffbrücken zwischen den kurzen Peptidketten stabilisiert.

The same conformation in the crystal and in chloroform (NMR data) is displayed by the biphenyl‐containing cyclopeptide 1, the biphenyl units of which have S,S configuration. It can be separated chromatographically from the atropisomers, (R,S) and (R,R), also formed in the synthesis. The conformation of 1 is stabilized by two hydrogen bonds between the short peptide chains.

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