The known indole-2-carboxylate intermediate (I) was protected as the N-benzenesulfonyl derivative (II) using benzenesulfonyl chloride and NaH, and the tert-butyl ester group of (II) was subsequently cleaved by means of formic acid. The resulting carboxylic acid (III) was activated as the 2-pyridyl thioester (IV) upon treatment with 2,2'-dipyridyl disulfide and triphenylphosphine. Selective protection of 4-aminobenzyl amine (V) with Boc2O produced the amino carbamate (VI). This was coupled with pyridyl thioester (IV) in refluxing THF to yield amide (VII). Subsequent removal of the N-Boc group of (VII) with trifluoroacetic acid afforded the free amino derivative (VIII), which was converted to the required urea (IX) upon treatment with trimethylsilyl isocyanate. Further hydrolysis of the benzenesulfonyl group of (IX) with ethanolic NaOH furnished the deprotected indole (X).

In a more direct route, 4-aminobenzyl amine (V) was treated with trimethylsilyl isocyanate to yield amino urea (XVI). This was subsequently coupled with pyridyl thioester (XIII) to furnish the previously described intermediate (X).

Hydrolysis of the ethyl ester function of (X) by means of LiOH, followed by acidic workup, gave rise to carboxylic acid (XI), which was finally isolated as the title sodium salt by treatment with aqueous NaOH and subsequent freeze drying. Alternatively, hydrolysis of ethyl ester (X) with NaOH in isopropanol-water provided directly the target sodium salt.

The precursor ethyl ester (X) was also prepared from the unprotected indole carboxylic acid (XII). Conversion into amide (XIV) was carried out using activation of the carboxyl group via formation of the corresponding 2-pyridyl thioester (XIII) and then coupling with aniline (VI). Trifluoroacetic acid-promoted cleavage of the N-Boc group of (XIV) provided amine (XV). This was converted to urea (X) by means of trimethylsilyl isocyanate.