The Structure of Pyroergotamine

Abstract

Abstract The molecular structure of pyroergotamine has been determined by single‐crystal X‐ray diffraction analysis to be the pyruvoyldiketopiperazine 1 . The diketopiperazine ring exists in a folded or boat conformation, with a dihedral angle of 40° between the two almost planar peptide units. The R‐group of the phenylalanine residue occupies a quasi‐axial position of the diketopiperazine ring, while that of the proline residue is in a quasi‐equatorial position. Puzzling spectroscopic and chemical properties of the compound can be rationalised in terms of crowding within the molecule.