An efficient approach to flavan-4-ols via radiolysis and their inhibitory activity against cytokine production

Facile structural modification of naringin (1) induced by γ-irradiation produced five novel hydroxymethylated flavan-4-ols, namely, narinflavans A (2), B (3), C (4), D (5), and E (6). The structures of the newly synthesized flavan derivatives were determined through comprehensive one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) analyses, whereas their absolute configurations were confirmed by electronic circular dichroism (ECD) spectroscopy. The new unusual flavan derivatives 4 and 5 containing a hydroxymethyl, instead of a ketone moiety, exhibited significantly modulated inhibitory effects on cytokine production than the parent compound. These results highlight γ-irradiation as an efficient one-step approach to generate structurally novel flavan-4-ols with biological functions.