Structural studies of azacyclols derived from linear tripeptides

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Abstract
N-Benzyloxycarbonyl-L-alanyl-L-phenylalanyl-L-proline p-nitrophenyl ester (4) and its N-p-bromobenzyloxycarbonyl analogue (2) each cyclize in alkaline aqueous medium to give a tricyclic system containing a free hydroxy-group derived from intramolecular addition of NH to amide carbonyl. Both the five-membered rings of the tricyclic system assume an envelope conformation. In the six-membered ring only the carbon atom bearing the cyclolic hydroxy-group is out of the plane of the other ring atoms. The benzylic side-chain of the phenylalanine residue adopts an extended conformation in both azacyclols. The crystal and molecular structures and spectral data for the tricyclic compounds (3) and (5) are reported.