6-[5-(4-Amidinophenyl)furan-2-yl]nicotinamidine (8a) was synthesized from 6-[5-(4-cyanophenyl)furan-2-yl]nicotinonitrile (4a), through the bis-O-acetoxyamidoxime followed by hydrogenation. Compound 4a was prepared via selective bromination of 6-(furan-2-yl)nicotinonitrile (2a) with N-bromosuccinimide, followed by Suzuki coupling with 4-cyanophenylboronic acid. In a similar way, diamidines 8b and 8c were prepared from the dicyano derivatives 4c and 4d, respectively. N-Methoxy-6-[5-[4-(N-methoxyamidino)phenyl]-furan-2-yl]-nicotinamidine (6a) was prepared via methylation of the respective diamidoxime 5a with dimethylsulfate. Prodrugs 6b and 6c were also prepared by methylation of the respective diamidoximes 5b and 5d. The symmetrical diamidines 14a,b were synthesized through the corresponding bis-O-acetoxyamidoxime followed by hydrogenation. The key compounds 11a,b were conveniently obtained by Stille coupling between 2,5-bis(tri-n-butylstannyl)furan and the corresponding heteroaryl halides. These compounds have been evaluated in vitro for activity against Trypanosoma b.rhodesiense (T. b. r.) and P. falciparum (P. f.). The diamidines 8a, 8c, and 14b gave IC(50) values versus T. b. r. of less than 10 nM. Against P. f. 8a, 8b, and 14b exhibited IC(50) values less than 10 nM. In an in vivo mouse model for T. b. r. four compounds 6a, 6c, 6d, and 8a were curative. Compound 6a produced cures at an oral dosage of 5 mg/kg.

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Five O-alkoxyamidine analogues of the prodrug 2,5-bis[4-methoxyamidinophenyl]furan were synthesized and evaluated against Trypanosoma brucei rhodesiense in the STIB900 mouse model by oral administration. The observed in vivo activity of these prodrugs demonstrates that compounds with an O-methoxyamidine or O-ethoxyamidine group effectively cured all trypanosome-infected mice, whereas prodrugs with larger side-chains did not completely cure the mice. Permeability across Caco-2 cell monolayers and microsomal metabolism were used to identify the underlying mechanisms of prodrug efficacy.