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2,5-Bis(4-guanylphenyl)-1,3-oxazole, 2,5-bis(4-guanylphenyl)-1,3,4-oxadiazole and -1,3,4-thiadiazole, and 3,6-bis(4-guanylphenyl)pyridazine and several of their "cyclic guanyl" analogues have been synthesized. 2,5-Bis(4-guanylphenyl)-1,3-oxazole and -1,3,4-thiadiazole showed good activity, whithout acute toxicity, against Trypanosoma rhodesiense in mice, producing cures at a 3 mg/kg dosage level. This activity is comparable to stilbamidine, hydroxystilbamidine, and pentamidine in this test. In contrast, 2,5-bis(4-guanylphenyl)-1,3,4-oxadiazole shows a sharp reduction in activity in our test system. Generally, the cyclic guanyl analogues exhibit low orders of activity, and toxicity begins to appear at moderate dosage levels. All guanyl and cyclic guanyl compounds were synthesized from bisnitrile precursors by way of imidate ester hydrochlorides in a classical Pinner-type approach.

Eighteen substituted 2,5-bis(4-guanylphenyl)furans and related analogues, including "masked" amidines in which the guanyl function is incorporated into a heterocyclic ring, have been synthesized and their antimalarial and antitrypanosomal activity has been evaluated. None of the compounds exhibited high orders of antimalarial activity; however, 11 were very active against Trypanosoma rhodesiense in mice. Six compounds, including 2,5-bis(4-guanylphenyl)furan (4) and its 3-chloro (32), 3,4-dichloro (31), 3-methyl (25), 3,4-dimethyl (20), and 3-chloro-4-methyl (38) derivatives, produced cures in mice at submilligram dosage levels; the 3,4-dimethyl (20) analogue exhibited a prolonged curative effect providing protection for 30 days after a single dose against a challenge by T. rhodesiense. These six compounds are somewhat more active in this screen than stilbamidine, hydroxystilbamidine, and pentamidine. The "masked" amidines generally exhibited lower antitrypanosomal activity than their true guanyl counterparts. Compound 4 was synthesized from 1,4-di-p-bromophenyl-1,4-butanedione by cyclodehydrative furanization to 2,5-bis(4-bromophenyl)furan (2) which was allowed to react with Cu2(CN)2 to produce the corresponding bis-nitrile 3. The latter compound was ultimately converted by way of an imidate ester into 4. Similarly, the 3- and/or 4-substituted derivatives of 2 were employed to prepare the other members of the series.