2-Nitrobenzenesulfonyl chloride → 17-Ethyl-1-hydroxy-14-(tert-butyldimethylsiloxy)-12-[2'-(4"-(o-nitrobenzenesulfonyloxy)-3"-allyloxycyclohexyl)-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

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To a solution of 17-ethyl-1-hydroxy-14-(tert-butyldimethylsiloxy)-12-[2'-(4"-hydroxy-3"-allyloxycyclohexyl)-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 (65 mg) in dry methylene chloride (1 ml) was added an excess of diisopropylethyl amine (29 μl) and o-nitrobenzenesulfonyl chloride (31 mg) followed by addition of 4-dimethylaminopyridine (20 mg). The mixture was stirred at room temperature for 4 hours at which time it was diluted with ethyl acetate, extracted from saturated sodium bicarbonate solution and washed with brine. The combined organics were dried over magnesium sulfate and the concentrate purified by flash chromatography on silica gel (ethyl acetate:hexane (1:2)+1% methanol to give the title compound (68 mg).

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