Addition of 2-methoxyphenylmagnesium bromide (II) to 5-chloroisatin (I) provided the carbinol adduct (III). Chlorination of (III) using SOCl2 in the presence of pyridine gave chloride (IV).

Condensation of N-Boc-4-hydroxyproline (V) with dimethylamine using BOP as the coupling reagent furnished amide (VI). The N-Boc protecting group of (VI) was then removed under acidic conditions to yield prolinaminde (VII). Alkylation of (VII) with the chloro oxindole (IV) produced the N-indolyl proline derivative (VIII) as a mixture of diastereoisomers, separable by column chromatography. Finally, indole N acylation in (VIII) by means of 2,4-dimethoxybenzenesulfonyl chloride (IX) in the presence of NaH furnished the target sulfonamide.