Configuration and conformation of a cyclopropane peptide

The absolute configuration of the cyclopropane phenylalanine moiety in N‐benzyloxycarbonyl‐(+)‐E‐cyclopropane‐phenylalanyl‐l‐leucine methyl ester (Z‐(+)‐▿EPhe‐Leu‐OMe) has been determined by X‐ray crystallographic methods. The conformation of the cyclopropane amino acid and its effect on the peptide is also discussed. The peptide crystallizes in the monoclinic space group P2, and the structure was solved using MULTAN and refined by block diagonal least‐squares to a present R value of 11 %. The absolute configuration of the (+)‐▿EPhe residue is seen to be 2R, 3S.