Prodrugs for amidines: synthesis and anti-Pneumocystis carinii activity of carbamates of 2,5-bis(4-amidinophenyl)furan.

Syntheses of several carbamate analogues of 2, 5-bis(4-amidinophenyl)furan (1) under mild conditions and their evaluation as prodrugs against Pneumocystis carinii pneumonia (PCP) in an immunosuppressed rat model are described. Thus, nine new bis-carbamates: methoxycarbonyl (2), 2,2,2-trichloroethoxycarbonyl (3), ethylthiocarbonyl (4), benzyloxycarbonyl (5), (4-methyl-2-oxo-1, 3-dioxol-4-en-5-yl)methoxycarbonyl (6), phenoxycarbonyl (7), 4-fluorophenoxycarbonyl (8), 4-methoxyphenoxycarbonyl (9), and (1-acetoxy)ethoxycarbonyl (10) and a bis-carbonate ethoxycarbonyloxy (11) of the bis-amidine 1 have been synthesized and evaluated. The in vivo results show that the 4-fluorophenyl carbamate 8 and the 4-methoxyphenyl carbamate 9 in this series had the best anti-PCP activity by both intravenous and oral administration at a dosage level of 22 mol and 33 micromol/kg/day, respectively. Compounds 3-7 were also more active than the parent drug (1) on oral administration. The acute toxicity usually exhibited by the parent amidine 1 at a dosage level of 22 micromol/kg/day on intravenous administration has been significantly reduced by the prodrug modifications, with the exception of compound 10 which exhibited some toxicity. This report also describes the synthesis of several aryl-alkyl and aryl-aryl carbonates (12-14, 16-23) as efficient reagents for the preparation of carbamate derivatives from bis-arylamidines.