CONFORMATIONAL-ANALYSIS OF DIRITHROMYCIN AND EPI-DIRITHROMYCIN

The solution conformations of dirithromycin (3) and epi-dirithromycin (4) were determined by NMR spectroscopy and molecular mechanics calcul ations. Dirithromycin exists in a ''folded-in'' conformation which is similar to its crystalline conformation, while epi-dirithromycin exist s in a ''folded out'' conformation which is similar to the crystalline conformation of erythromycin A hydroiodide dihydrate. Included is a d iscussion of the kinetically versus thermodynamically controlled forma tion of the remote aminal stereocenter.