To a solution of 17-ethyl-1-hydroxy-12-[2'-(3", 4"-dihydroxycyclohexyl)-1'-methylvinyl]-23,25-dimethoxy- 13,19,21,27-tetramethyl-11,28-dioxa-4-azatricyclo[22.3.1.04,9 ]octacos-18-ene-2,3,10,16-tetraone (Example 2, 3.01 g) in dry methylene chloride (70 ml) was added an excess of imidazole (809 mg) followed by tertbutyldimethylsilyl chloride (716 mg). After 3 days of stirring at room temperature, the mixture was diluted with ethyl acetate which in turn was washed with 1N HCl, saturated sodium bicarbonate and brine, dried over magnesium sulfate and purified by flash chromatography (ethyl acetate:hexane (1:3)) to give the title compound (941 mg). 1H NMR consistent with the desired structure.
