The catecholic antioxidant piceatannol is an effective nitrosation inhibitor via an unusual double bond nitration

Piceatannol (1) was more effective than caffeic acid, an established antinitrosating agent, in inhibiting N-nitrosation of 2,3-diaminonaphthalene. Product anal. of the reaction mixt. of 1 (20 mM) with nitrite ions (80 mM) at pH 3.0 and at 37 showed conversion to a single major nitration product, (E)-3,3',4,5'-tetrahydroxy-b-nitrostilbene (2) (68% yield). This would result from an unexpected nitration at the double bond sector via the 4-phenoxyl radical, which was analyzed at the unrestricted DFT level.