Patent ID: 7279571

Claim:
A process for preparing pimecrolimus comprising: a) dissolving ascomycin in an organic solvent; b) activating ascomycin at C-32 by combining ascomycin with an organic or inorganic base and a conversion reagent to obtain an activated ascomycin derivative, wherein the conversion agent is selected from the group consisting of fluorosulfonic anhydride, fluorosulfonyl chloride, trifluoromnethanesulfonic anhydride, trifluoromethanesulfonyl chloride, methanesulfonic anhydride, methanesulfonyl chloride, phenylmethanesulfonic anhydride, phenylmethanesulfonyl chloride, p-toluenesulfonic anhydride, p-toluenesulfonyl chloride, benzenesulfonic anhydride, and benzenesulfonyl chloride; c) reacting the activated derivative of ascomycin with a chloride ion source to obtain pimecrolimus; and d) recovering the obtained pimecrolimus.