Decomposition of FK 409, a new vasodilator: Identification of nitric oxide as a metabolite

(±)-(3E)-4-Ethyl-2-hydroxyimino-5-nitro-3-hexenamide, FK 409, is a natural product selected for its strong vasorelaxant properties. In neutral aqueous solution, it decomposes spontaneously giving rise to a diketone as shown by HPLC and mass spectrometry. Also, during decomposition, nitric oxide intermediate formation was demonstrated by EPR1 spectroscopy specific assays. An analog of FK 409, in which the oxime group was selectively hydrolyzed, has lost the ability to generate NO and shows reduced vasorelaxant potency. These results provide a molecular basis for the vasorelaxant effects of FK 409.