Processes for preparing clarithromycin and clarithromycin intermediate, essentially oxime-free clarithromycin, and pharmaceutical composition comprising the same

The present invention relates to processes for preparing protected silylated clarithromycin oxime, preferably 6-O-methyl-2', 4''-bis(trimethylsilyl)-erythromycin A 9-O-(2-methoxyprop-2-yl)oxime ("S-MOP oxime"), and for converting protected silylated clarithromycin oxime, preferably S-MOP oxime, to clarithromycin. Processes for preparing protected silylated clarithromycin oxime according to the present invention, include reacting a silyl oxime derivative with methylating agent in the presence of at least one solvent and a base, where the solvent comprises methyl tertbutyl ether. Processes for converting protected silylated clarithromycin oxime to clarithromycin according to the present invention, include reacting protected silylated clarithromycin oxime with ethanol and water at an ethanol to water ratio of about 1:1, in the presence of an acid and a deoximating agent and cooling the reaction mixture prior to adding sodium hydroxide, where the process takes place without any additional water addition. Further processes for converting protected silylated clarithromycin oxime to clarithromycin, include heating a mixture of protected silylated clarithromycin oxime, acid, and deoximating agent in an ethanol/water solvent to reflux for more than 4 hours, with a two-fold addition of deoximating agent to produce essentially oxime-free clarithromycin.