Crystal structure of vinblastine

Vinblastine sulfate has been successfully crystallized by the hanging-drop vapor diffusion method against polyethylene glycol and lithium sulfate, and its structure determined by X-ray crystallography. The molecular geometry is rather similar to that of vincristine, with the most notable difference being that the key COOCH3 group in the C18' position is oriented in an oppo site direction from that in vincristine. Half of the 9-membered azacyclonon ane ring in the catharanthine portion of the molecule is remarkably flat an d coplanar with the indole ring, while the other half is in a boat conforma tion and fused with the piperidine ring in a chair conformation. The title compound crystallizes with an unusually large number of water molecules (ni neteen), which form intriguing patterns of interconnected 5-membered rings (and some 6-membered rings) over substantial portions of the unit cell.