The chemistry of guanidines and their actions at adrenergic nerve endings

Optimization of Substrate-Analogue Furin Inhibitors

The proprotein convertase furin is a potential target for drug design, especially for the inhibition of furin-dependent virus replication. All effective synthetic furin inhibitors identified thus far are multibasic compounds; the highest potency was found for our previously developed inhibitor 4-(guanidinomethyl)phenylacetyl-Arg-Tle-Arg-4-amidinobenzylamide (MI-1148). An initial study in mice revealed a narrow therapeutic range for this tetrabasic compound, while significantly reduced toxicity was observed for some tribasic analogues. This suggests that the toxicity depends at least to some extent on the overall multibasic character of this inhibitor. Therefore, in a first approach, the C-terminal benzamidine of MI-1148 was replaced by less basic P1 residues. Despite decreased potency, a few compounds still inhibit furin in the low nanomolar range, but display negligible efficacy in cells. In a second approach, the P2 arginine was replaced by lysine; compared to MI-1148, this furin inhibitor has slightly decreased potency, but exhibits similar antiviral activity against West Nile and Dengue virus in cell culture and decreased toxicity in mice. These results provide a promising starting point for the development of efficacious and well-tolerated furin inhibitors.

N-hydroxyl derivatives of guanidine based drugs as enzymatic NO donors

Recent research suggests that NO may play a role in the physiological effects of some guanidine-containing drugs. In this report, three guanidine-containing drugs (guanadrel, guanoxan, and guanethidine) together with their N-hydroxyl derivatives were synthesized and their NO-releasing abilities catalyzed by nitric oxide synthases (NOSs) and horseradish peroxidase were evaluated. The guanidine containing compounds could not release NO in the presence of NOS or peroxidase. The corresponding N-hydroxyl compounds exhibited weak NO-releasing ability under the catalyzed of NOS and good NO-releasing ability under the oxidation by horseradish peroxidase in the presence of H(2)O(2). These compounds also displayed vasodilatory activity.

Guanethidine evokes vasodilatation in guinea pig mesenteric artery by acting on sensory nerves

In precontracted, endothelium-free guinea pig mesenteric artery rings, in which adrenergic vasoconstrictor responses had been eliminated, guanethidine (1-30 microM) produced a vasodilatation of 69.3+/-4.4%. The vasodilatation was reduced 89% by capsaicin (10 microM) or 55% by tetrodotoxin (10 microM), indicating mediation of this effect by primary sensory nerves. The nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (100 microM, 30 min) but not its stereoisomer reduced the guanethidine vasodilatation by 70%. Blockade of monoamine uptake with ouabain (25 microM, 15 min) or cocaine (5 microM, 5 min) reduced the guanethidine-induced vasodilatation by 85 and 67%, respectively. These results suggest that guanethidine produced vasodilatation by being transported into capsaicin-sensitive primary sensory nerves where it functioned as a substrate for nitric oxide synthase to generate a vasodilatory substance.

Fluorometric assay of bethanidine in plasma

A fluorometric method for determining bethanidine in blood plasma is described. The bethanidine is extracted into chloroform, a drug-dye complex with eosin Y is formed, and the fluorescence is measured (excitation, 535 nm; fluorescence, 560 nm). The assay detects 0.02 muM bethanidine (4 ng/ml) in plasma. The relative fluorescence of several body constituents and antihypertensive drugs is negligible. The plasma levels of bethanidine in four hypertensive patients receiving this drug were measured.