2,4-Diamino-5-methyl-6-substituted arylthio-furo[2,3-d]pyrimidines as novel classical and nonclassical antifolates as potential dual thymidylate synthase and dihydrofolate reductase inhibitors

Abstract

A novel classical antifolate N-{4-[(2,4-diamino-5-methyl-furo[2,3-d]pyrimidin-6-yl)thio]-benzoyl}-l-glutamic acid 5 and 11 nonclassical antifolates 6-16 were designed, synthesized, and evaluated as inhibitors of dihydrofolate reductase (DHFR) and thymidylate synthase (TS). The nonclassical compounds 6-16 were synthesized from 20 via oxidative addition of substituted thiophenols using iodine. Peptide coupling of the intermediate acid 21 followed by saponification gave the classical analog 5. Compound 5 is the first example, to our knowledge, of a 2,4-diamino furo[2,3-d]pyrimidine classical antifolate that has inhibitory activity against both human DHFR and human TS. The classical analog 5 was a nanomolar inhibitor and remarkably selective inhibitor of Pneumocystis carinii DHFR and Mycobacterium avium DHFR at 263-fold and 2107-fold, respectively, compared to mammalian DHFR. The nonclassical analogs 6-16 were moderately potent against pathogen DHFR or TS. This study shows that the furo[2,3-d]pyrimidine scaffold is conducive to dual human DHFR-TS inhibitory activity and to high potency and selectivity for pathogen DHFR.

Figure 1

Figure 2

Figure 3

Stereoview 5 (yellow) superimposed on pemetrexed (green) in the X-ray crystal structure of pemetrexed in human TS (PDB: 1JUJ) using SYBYL 8.1.

Figure 4

Stereoview of minimized 5 (yellow) superimposed onto MTX (green) in the X-ray crystal structure of MTX in human DHFR. (PDB: 1U72).

Scheme 1^a

^aConditions: (a) DMF, 50–60 °C, 72 h; (b) 4-mercaptobenzoic acid, EtOH/H₂O (2:1), 100–110 °C, I₂; (c) 2-chloro-4,6-dimethoxy-1,3,5-triazine, N-methylmorpholine, diethyl-l-glutamate hydrochloride, 0 °C to r.t.; (d) 1 N NaOH, 0 °C to r.t.; (e) ArSH, I₂, 80–90 °C, 4 h (6 and 7); (f) ArSH, 100–110 °C, I₂ (8–16).