The reaction of 7-ethyl-10-hydroxycamptothecin (I) with phosgene gives 7-ethyl-10-(chlorocarbonyloxy)camptothecin (II), which is then condensed with 4-(1-piperidyl)piperidine.

The condensation between 4-(acetylamino)thiophenol (I) and 5-chloro-2-nitroaniline (II) produced the diaryl sulfide (III). Nitro group reduction in (III) employing SnCl2 gave the phenylenediamine (IV), which was cyclized to the benzimidazole (VI) upon treatment with N,N'-bis(methoxycarbonyl)-S-methylisothiourea (V). Hydrolysis of the acetamido group of (VI) with HCl in MeOH afforded aniline (VII). This was acylated with N-Boc-alanine (VIII) in the presence of EDC to yield amide (IX). The N-Boc protecting group of (IX) was finally removed by treatment with trifluoroacetic acid.

The condensation between 4-(acetylamino)thiophenol (I) and 5-chloro-2-nitroaniline (II) produced the diaryl sulfide (III). Nitro group reduction in (III) employing SnCl2 gave the phenylenediamine (IV), which was cyclized to the benzimidazole (VI) upon treatment with N,N'-bis(methoxycarbonyl)-S-methylisothiourea (V). Hydrolysis of the acetamido group of (VI) with HCl in MeOH afforded aniline (VII). This was acylated with N-Boc-alanine (VIII) in the presence of EDC to yield amide (IX). The N-Boc protecting group of (IX) was finally removed by treatment with trifluoroacetic acid.