The syntheses of nine new derivatives of 2, 5-bis[4-(N-alkylamidino)phenyl]furans with extended aromatic systems are reported. The interaction of these dicationic furans with poly(dA)poly(dT) and with the duplex oligomers d(CGCGAATTCGCG)2 and d(GCGAATTCGC)2 was determined by Tm measurement, and the effectiveness of these compounds against the immunosuppressed rat model of Pneumocystis carinii was evaluated. At a screening dose of 10 micromol/kg, 4 of the 12 amidino furans described here are more active than the parent compound 1. In general, extension of the aromatic system in the absence of a substitution of the amidino nitrogens resulted in higher affinity for DNA than the parent compound as judged by the larger DeltaTm values and suggests enhanced van der Waals interactions in the amidino furan-DNA complex. Three of the compounds, 3, 5, and 11, yield cysts counts of less than 0.1% of control when administered at a dosage of 10 micromol/kg. Compound 3, which does not have an extended aromatic system, is the most active derivative. Although a direct correlation between anti-P. carinii activity and DNA binding affinity was not observed, all compounds which have significant activity have large DeltaTm values.

Dicationic 2,4-bis(4-amidinophenyl)furans 5-10 and 2, 4-bis(4-amidinophenyl)-3,5-dimethylfurans 14 and 15 have been synthesized. Thermal melting studies revealed high binding affinity of the compounds to poly(dA-dT) and to the duplex oligomer d(CGCGAATTCGCG)2. All of the new compounds were effective against Pneumocystis carinii pneumonia in the immunosuppressed rat model with up to 200-fold increase in activity compared to the control compound pentamidine. No toxicity was noted for 5, 7-10 at the dose of 10 micromol/kg/d; however, the isopropyl analogue 7 showed toxicity comparable to pentamidine at the dosage of 20 micromol/kg/d. Dimethylation of the parent compound on the furan ring resulted in reduced activity and increased toxicity.