The methylation of the protected ketoside (I) with dimethyl sulfate and NaH gives the trimethoxy compound (II), which is treated with AcOH to eliminate the cyclic ketal protecting group to yield the dihydroxy compound (III). The hydrolysis of the methyl ketal and the ester group of (III) with NaOH affords the hydroxyacid (IV), which is converted into the chloroester (V) by methylation with TFA/methanol and acetylation and chlorination with acetyl chloride. The condensation of (V) with 1-acetyl-5-bromoindol-2-ol (VI) by means of NaOH gives the adduct (VII), which is deacetylated with sodium methoxide in methanol yielding the dihydroxy ester (VIII). Finally, the ester group of (VIII) is hydrolyzed with NaOH.

The methylation of the protected ketoside (I) with dimethyl sulfate and NaH gives the trimethoxy compound (II), which is treated with AcOH to eliminate the cyclic ketal protecting group to yield the dihydroxy compound (III). The hydrolysis of the methyl ketal and the ester group of (III) with NaOH affords the hydroxyacid (IV), which is converted into the chloroester (V) by methylation with TFA/methanol and acetylation and chlorination with acetyl chloride. The condensation of (V) with 1-acetyl-5-bromoindol-2-ol (VI) by means of NaOH gives the adduct (VII), which is deacetylated with sodium methoxide in methanol yielding the dihydroxy ester (VIII). Finally, the ester group of (VIII) is hydrolyzed with NaOH.