Conformation of ergopeptam and ergopeptine alkaloids (ergocristam and ergocristine)

The crystal structures of two ergot alkaloids ergocristam (I) and ergocristine acetone solvate (II), have been determined by X-ray diffraction and compared with their conformation in solution obtained from NMR data. The presence of D-proline in I essentially influences the conformation of the alkaloid tripeptide moiety which seems likely to explain why I does not undergo further enzymatical hydroxylation and is found as a terminal step of ergot alkaloid biosynthesis.