Chemo-enzymatic transformation of naturally abundant naringin to luteolin, a flavonoid with various biological effects

Luteolin [3′,4′,5,7-tetrahydroxyflavone], having multiple biological effects such as anti-inflammation, anti-allergy and anti-cancer, was prepared by chemo-enzymatic synthesis from naringin, a naturally abundant flavonoid glycoside. On the occasion of Candida antarctica lipase B (Novozym 435)-catalyzed transesterification on peracetylated form of naringin, an acetate on C-4′ was exclusively deprotected to give the key intermediate. The oxidation with 2-iodoxybenzoic acid (IBX) followed by the reductive workup provided regioselectively C-3′and C-4′ catechol functionality. After protection of the above-mentioned diol with methoxymethyl (MOM) groups and subsequent hydrolysis of all acetyl groups, a dehydrogenative introduction of double bond between C-2 and C-3 was done by the treatment with I₂. Acid-catalyzed simultaneous removal of MOM groups and glycoside provided luteolin in total 8 steps and 36% overall yield from the starting material. Throughout the synthesis, diglycoside side chain effectively worked as the protective group on C-7 hydroxy group.