Conformational Analysis of Tricyclic Ketolide TE-802 and Its Analogues

The conformations of tricyclic ketolide TE-802 (1) and its analogue were determined by crystallographic analysis and NMR spectroscopy. The 3-carbonyl function of 1 took an 'exo' orientation against the lactone ring, and the orientation of the amino sugar at the 5-position differed from that in clarithromycin (CAM:2). On the other hand, di- and tricyclic ketolides and a tricyclic macrolide were found to exist in 'semi-fold-out (4H-downward)' conformation in deuteriochloroform. The conformation of 1 in deuteriochloroform was closely similar to that in D2O. The newly formed tetrahydrodiazepine ring existed in chair form or boat form, governed by the presence of a substituent and its position.