Probenecid, its metabolites (including 14C labeled), and several analogs were synthesized. The uv spectral properties, p.Ka's, and partition coefficients were determined. The binding of probenecid and metabolites to human plasma, human albumin, and dog plasma was measured. Pmr parameters of probenecid, its metabolites, and 9 other analogs were obtained. There was no correlation between the nature of the alkyl side-chain substituents or the partition coefficient and the chemical shifts of the aromatic ring protons. In rats all the metabolites with a single exception were terminal metabolites; similar results were obtained in vitro. Propionic acid was identified as one of the metabolic products of probenecid. The effects on urate clearance of probenecid, the various metabolites, and the piperidyl analog were determined in Dalmatian and mongrel dogs. In Dalmatians the clearance decreased while in mongrels it increased. Our studies suggest that the metabolites of probenecid may very well play a significant role in the overall uricosuric effect of the parent drug.The structures of essentially all the metabolites of probenecid in rat bile1 and human urine2'4 have been elucidated.The major routes of biotransformation are oxidation of the side chain (Figure 1, Table I) and glucuronide conjugation. In man, formation of the acyl glucuronide accounts for the disposition of about 0.2 of the drug.2'3 Incubation of probenecid-^C with reinforced rat liver preparations leads to the same metabolites as found in vivo.5The purpose of the present study was (1) to synthesize the metabolites (labeled and unlabeled) of probenecid, (2) to learn whether they could contribute to the overall pharmacologic activity of the parent drug, and (3) to extend previous investigations of structure-activity relationships in this series.6 The latter studies included detailed analyses of high-resolution proton magnetic resonance (pmr) spectra, pAa determinations, and measurement of drug-protein binding.
Experimental SectionA. Synthesis.Our general procedure for synthesis of probenecid analogs (adapted from Miller7) was: to an ice-cold soln of the appropriate secondary amine (0.12 mole) in 25 ml of anhyd MeOH 8.8 g (0.040 mole) of p-(chlorosulfonyl)benzoic acid (1)1 was added and the mixt stirred at room temp overnight. The MeOH was removed in vacuo and the oily residue taken up in 25 ml of H20. The pH was adjusted to 1 with coned HC1 and the resulting ppt collected by filtration, then dissolved in a slight excess of 0.1 N NaOH (pH >10). After one extn with Et20 and repptn with HC1, the compd was crystd from EtOH-H20, with prior charcoal treatment, and dried at 110°in vacuo. Purity of the analogs was detd by capillary mp in a Thomas-Hoover Uni-Melt, by known Rf values on tic,2 and by elemental analysis. The 14C compds# were synthesized by a modification of the procedure of Motoichi, et al.8 Ring 14C-labeled probenecid and some nonlabeled analogs were a gift from Dr.
