p-Toluenesulfonic acid → 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-14,18-diene-2,3,10,16-tetraone

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A solution of 17-ethyl-1,14-dihydroxy-12-[2'-(4"-hydroxy-3"-hydroxycyclohexyl)-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 (210 mg) and a catalytic amount of p-toluenesulfonic acid in 40 ml of benzene was refluxed for 4 hours under a nitrogen atmosphere. The solvent was removed under reduced pressure and the dark residue was purified by chromatography (silica gel, 7% i-propanol/CH2Cl2) to give 17-ethyl-1-hydroxy-12-[2'-(4",3"-dihydroxycyclohexyl)-1'-methylvinyl]-23,25-dimethoxy-13,19,21,-27-tetramethyl-11,28-dioxa-4-azatricyclo-[22.3.1.04,9 ]octacos-14,18-diene-2,3,10,16-tetraone (180 mg) as a white solid. This material was dissolved in ethanol (20 ml) and treated with 5% Rh/C (40 mg).

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