Title compound was prepared by two synthetic ways. Friedel-Crafts acylation of N-(phenylsulfonyl)indole (II) with acid chloride (I) with concomitant O-debenzylation in the presence of AlCl3 yielded ketone (III). Then, hydroxyl group alkylation of (III) with alpha-bromo-p-xylene (IV) provided p-methylbenzyl ether (V). Subsequent displacement of the chloro group in (IV) by 1-(2-ethoxyphenyl)piperazine (VI) furnished (VII). After hydrolysis of sulfonyl group of (VII) with KOH, the resulting deprotected indole (VIII) was alkylated with ethyl 4-bromobutyrate to give (IX). Finally, hydrolysis of the ethyl ester of (IX) by means of ethanolic KOH provided the title carboxylic acid potassium salt.
In a related procedure, dihydroxybenzoyl indole (X) was selectively alkylated at 4-hydroxyl group with alpha-bromo-p-xylene (IV) to provide ether (XI). Further alkylation of (XI) with 1-bromo-3-chloropropane gave (XII). Then, halogen displacement in (XII) by piperazine (VI) furnished the precursor ethyl ester (IX), which was finally hydrolyzed to the target carboxylic acid as above.