Benzene‐induced ¹H NMR shifts of flavone protons: Detection of H‐3

Abstract

Deuteriated benzene-induced shifts [A ppm = S(CDC1,) -S(C,D,)] in the 'H NMR spectra of some naturally occurring polyoxygenated flavones isolated from Ageratum conyzoides and Eupatorium odoraturn have been studied. The downfield shift of the pyrone ring proton H-3, particularly in B-ring methoxylated flavones, is significant; as it is in the opposite direction to that of an aromatic proton it could be of diagnostic value in structural elucidation. The benzene-induced shifts of all the other protons have also been studied.

5,6,7,5′-Tetramethoxy-3′,4′-methylenedioxyflavone monohydrate

“…For the isolation of 5,6,7,5 0 -tetramethoxy-3 0 ,4 0 -methylenedioxyflavone, see: Chen et al (1984); Vyas et al (1986a); Souza et al (1995); Tomazela et al (2000). For the NMR spectroscopic studies, see Vyas et al (1986b). For the biological activity of flavonoids, see: Genoux et al (2011); Bodewes et al (2011); Jacob et al (2011); Veitch & Grayer (2011).…”