CRYSTAL-STRUCTURE OF L-PHENYLALANYL-GLYCINE - TRICHLOROACETATE AND ITS RELEVANCE TO THE BIOACTIVE CONFORMATION OF THE ENKEPHALINS

A dipeptide L-phenylalanyl-glycine has been crystallized as a 1:1 comp lex with trichloroacetic acid. The crystal structure has been determin ed using direct methods and refined to a final R-index of 0.059 for 12 03 reflections (with sin theta/lambda less-than-or-equal-to 0.60 angst rom-1 and I greater-than-or-equal-to 3sigma(I)). The trans-peptide uni t shows significant deviation from planarity. The peptide backbone is folded with torsion angles at glycine adopting a D-residue conformatio n. Relevance of the study to bioactive conformation of enkephalins is discussed.