Design and synthesis of classical and nonclassical 6-arylthio-2,4-diamino-5-ethylpyrrolo[2,3-d]pyrimidines as antifolates

The classical antifolate N- {4-[( 2,4- diamino- 5-ethyl-7H- pyrrolo[ 2,3- d] pyrimidin- 6- yl) sulfanyl] benzoyl}- Lglutamic acid ( 2) and 15 nonclassical analogues ( 3- 17) were synthesized as potential dihydrofolate reductase ( DHFR) inhibitors and as antitumor agents. 5- Ethyl- 7H- pyrrolo[ 2,3- d] pyrimidine- 2,4- diamine ( 20) served as the key intermediate to which various aryl thiols and a heteroaryl thiol were appended at the 6- position via an oxidative addition reaction. The classical analogue 2 was synthesized by coupling the benzoic acid derivative 18 with diethyl L- glutamate followed by saponification. The classical compound 2 was an excellent inhibitor of human DHFR ( IC50 = 66 nM) as well as a two digit nanomolar (< 100 nM) inhibitor of the growth of several tumor cells in culture. Some of the nonclassical analogues were potent and selective inhibitors of DHFR from two pathogens ( Toxoplasma gondii and Mycobacterium avium) that cause opportunistic infections in patients with compromised immune systems.