Synthesis and evaluation of N-acyl-2-(5-fluorouracil-1-yl)-D,L-glycine as a colon-specific prodrug of 5-fluorouracil.

N-nicotinyl-2-(5-fluorouracil-1-yl)-D,L-glycine (NFG) and N-isonicotinyl-2-(5-fluorouracil-1-yl)-D,L-glycine (INFG) were synthesized as colon-specific prodrugs of 5-fluorouracil (5-FU). As N-aromatic acyl amides of glycine, they are expected to be stable in the upper intestine and delivered to the colon as an intact form if they are nonabsorbable. Microbial hydrolysis of amide bond in the colon will give 2-(5-fluorouracil)-D,L-glycine, which releases 5-FU by spontaneous decomposition. NFG and INFG were soluble in water and stable in pH 1.2 and 7.4 buffer solutions. The apparent partition coefficient of NFG or INFG in 1-octanol/pH 7.4 phosphate buffer solution at 37 degrees was 0.025 or 0.024, respectively. On incubation with cecal contents of rats, conversion of NFG or INFG proceeded only 9 or 5% in 8 h, respectively, producing 5-FU and a metabolite. The metabolite formation was inhibited in the presence of diazouracil, a dihydrouracil dehydrogenase inhibitor. The HPLC retention time of the metabolite from the incubation of 5-FU, NFG, or INFG with cecal contents was identical to dihydro-5-fluorouracil (dihydro-5FU). When N-nicotinyl-2-hydroxy-D,L-glycine methyl ester (NHGM) was incubated with the cecal contents, the extent of amide bond hydrolysis was 85% in 24 h. The result suggested that steric hindrance imposed by 5-FU at 2-position of glycine retarded the hydrolysis of the amide bond in NFG or INFG and suppressed the prodrug conversion.