The Conformations of Virginiamycin M1 Diacetate, an Inhibitor of Guinea Pig Brain CCK-B Receptors, in Selected Solvents

The Virginiamycin M1 derivative Virginiamycin-14,16-diacetate (VM1-diAc) is not naturally occurring and must be synthesised by those wishing to study its properties. It possesses very little if any of the antibiotic capabilities of its parent compound, Virginiamycin M1. However, VM1-diAc has been reported to bind competitively to guinea pig brain cholecystokinin (CCK-B) receptors at concentrations very near that of CCK-B itself. CCK-B may bind to the CCK-B receptor as an octa- or a tetrapeptide, suggesting that a portion of the VM1-diAc molecule has a conformation very similar to the binding site of the CCKB peptide. Since the conformations of the VM1-diAc are constrained by its cyclic structure, studies of its binding to the CCK-B receptor might provide useful information about the CCK-B peptide receptor binding. To begin such a project, we report herein results of a study of the conformations of VM1-diAc dissolved in chloroform and methanol, two solvents of different polarities.