SYNTHESIS AND ANTIFOLATE ACTIVITY OF -DIAMINO-5,6,7,8-TETRAHYDROPYRIDO[4,3-D]PYRIMIDINE ANALOGS OF TRIMETREXATE AND PIRITREXIM

Diamino-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidines with di- and trimet hoxyaralkyl substitution at the 6-position were synthesized from the N 6-unsubstituted compound and appropriate aralkyl bromides in N,N-dimet hylformamide solution containing a catalytic amount of sodium iodide. An improved method of preparation of -diamino-5,6,7,8-tetrahydropyrido [4,3-d]pyrimidine from 5,6,7,8-tetrahydropyrido[4,3-d]pyrimidin-4(3H)- one was also developed, in which N2 was protected by reaction with piv alic anhydride and the resulting product was subjected consecutively t o reaction with 4-chloro-phenylphosphorodichloridate and 1,2,4-triazol e, ammonolysis to replace the 4-imidazolido group and remove the N2-pi valoyl group, and catalytic hydrogenolysis to remove the 6-benzyl grou p. In assays of the ability of the products to inhibit dihydrofolate r eductase from Pneumocystis carinii, and Toxoplasma gondii, and rat liv er the most active of the compounds tested was benzyl)-5,6,7,8-tetrahy dropyrido[4,3-d]pyrimidine. The concentration of this compound needed to inhibit enzyme activity by 50% was 0.51 muM against the P. carinii enzyme, 0.09 muM against the T. gondii enzyme, and 0.35 muM against th e rat enzyme. Thus, there was selectivity of binding to T. gondii enzy me, but not P. carinii enzyme, relative to rat enzyme. 2',5'-Dimethoxy benzyl analogues were less active than the corresponding 3',4',5'-trim ethoxybenzyl analogues, and compounds with a CH2CH2 or CH2CH2CH2 bridg e were less active than those with a CH2 bridge. ybenzyl)-5,6,7,8-tetr ahydropyriod[4,3-d]pyrimidine showed greater selectivity than trimetre xate or piritrexim for the P. carinii and T. gondii enzyme, but was le ss selective than trimethoprim or pyrimethamine. However its molar pot ency against both enzymes was greater than that of trimethoprim, the a ntifolate most commonly used, in combination with sulfamethoxazole, fo r initial treatment of opportunistic P. carinii and T. gondii infectio ns in patients with AIDS and other disorders of the immune system.