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2-(4'-aminobenzenamine)-pyrimidine, a new alpha-antagonist from Autonoë madeirensis.

A new natural pyrimidine derivative, 2-(4'-aminobenzenamine)-pyrimidine (1), was isolated from the bulbs of Autonoë madeirensis, a Hyacinthaceae of the Madeira Archipelago (Portugal) and the structure determined on the basis of spectroscopic data. As some pyrimidine compounds are important alpha1-adrenergic antagonists, we investigated the effect of 1 on rat vas deferens contractility induced by the alpha1-agonist phenylephrine. In concentrations virtually devoid of effect on the rat vas deferens contractility, 1 shifted to the right the concentration-response curves of phenylephrine without changing the maximal effect. These results provide evidence that 1 acts as an alpha1-adrenoceptor antagonist and suggest a competitive mechanism of action.