Novel erythromycin A 9-tritylhydrazone: selective 6-O-methylation and conformational analysis

A new erythromycin A derivative (9-tritylhydrazone) is described and easily transformed into clarithromycin by regioselective O-methylation at C(6)-OH. Conformational analysis based on X-ray diffraction, 1H NMR data and molecular mechanic calculations was aimed to understand the observed high regioselectivity. The facile synthesis of 6,12-O-dimethylerythromycin A is also reported.