Configurational and conformational studies on the group A peptide antibiotics of the mikamycin (streptogramin, virginiamycin) family

Abstract

The crystal conformations of griseoviridin (3) and ostreogrycin A (5), which are shown to bear a close resemblance over a large part of the macrocycle, have been compared with those adopted in solution. It is concluded, on the basis of ¹³C and ¹H n.m.r. as well as i.r. data, that one predominant solution conformer exists for both molecules which is essentially the same as that adopted in the crystal lattice. An earlier claim that ostreogrycin A is stabilised by an intramolecular hydrogen bond is reviewed. Spectral data on madumycin (A2315) are used to confirm the proposed structure (6) and comparisons with compounds (3) and (5) have allowed tentative assignments of the relative configuration and the ring conformation. Absolute configurational assignments are made for compounds (5) and (6) and the significance of the molecular geometry of the group is discussed.