NOVEL HYPOTENSIVE AGENTS FROM VERBESINA-CARACASANA .2. SYNTHESIS AND PHARMACOLOGY OF CARACASANAMIDE

Caracasanamide, one of the hypotensive agents isolated from Verbesina caracasana, is a mixture of (Z)-1a and (E)-lb forms of )amino]-4-[(3-m ethyl-2-butenyl)-guanidino]butane.1 The structure of (E)-caracasanamid e (1b) was confirmed by high-yielding synthesis starting from N,N'-bis (tert-butoxycarbonyl)-S-methylisothiourea. The water-soluble Z-form of 1a, assayed by iv route in anesthetized rats at doses ranging from 50 to 1600 mug/kg body weight, was found to decrease blood pressure, to increase cardiac inotropism, respiratory frequency, and tidal volume, and to induce a very slight and not significant tachycardia. Higher do ses determined respiratory depression and, in some cases, consequent c ardiac arrest. The compound was shown to affect cardiovascular functio n by acting at the vascular level in inducing arterial vasodilation, b y determining sympathetic hypotone through central neurogenic mechanis ms, and by interacting with the cardiac beta1-adrenoreceptors. The res piratory effects were independent of the cardiovascular ones. In lower ing blood pressure, the compound was more potent than guanethidine and not less potent than reserpine and papaverine. (Z)-Caracasanamide may therefore be useful in the treatment of arterial hypertension of mode rate degree.