p-Toluenesulfonic acid → 17-Ethyl-1-hydroxy-12-[2'-(4"-hydroxy-3"-methoxycyclohexyl)-1'-methylvinyl]-14-t-butyl-dimethylsilyloxy-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

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To a solution of 17-ethyl-1-hydroxy-14-(tert-butyldimethylsiloxy)-12-[2'-(4"-(tert-butyldimethylsiloxy)-3"-methoxycyclohexyl)-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 (2.37 g) (STEP 11A) in dry methylene chloride (25 ml) was added a solution of 10% p-toluenesulfonic acid in methanol (25 ml), and the mixture was stirred at room temperature. After 10 minutes, the mixture was cooled to 0° C. and quenched with saturated sodium bicarbonate. The mixture was diluted with ethyl acetate and the layers were separated. The organic layer was washed with saturated sodium bicarbonate and brine and dried over magnesium sulfate. Purification of the concentrate by flash chromatography on silica gel (ethyl acetate:hexane (1:2)+1% methanol) gave the title compound (2.1 g). 1H NMR consistent with the desired structure.

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