Conformational behaviour of azithromycin 11-OMe derivative 2 (Scheme 1) has been studied in the solid and solution state. In the CDCl3 and DMSO solution, 2 mainly adopts the »folded-in« conformation. 11-OMe group is oriented toward the centre of aglycone ring. The crystal structure of DMSO solvate of 2 has been solved by the molecular replacement method using the solution state conformation as the search model. Conformation of 2 in the solid and solution state is very similar. Molecules of 2 are held together in the crystal by van der Waals interactions, forming a solvent channel along the b axis. The DMSO molecule is found to be disordered and bound to cladinose moiety of 2 by H-bond O4"-H...01s
