Question

Why are flavonoids, which are glycosylated at the C3-position not prone to enzymatic

oxidation?

( 10 V3 54

Answer 1

Flavonols differ from flavanones by a hydroxyl group at the 3-position and a C2–C3 double bond. Flavonoids are often hydroxylated in positions 3, 5, 7, 2, 3′, 4′, and 5′. Methyl ethers and acetyl esters of the alcohol group are known to occur in nature. When glycosides are formed, the glycosidic linkage is normally located in positions 3 or 7 and the carbohydrate can be L-rhamnose, D-glucose, glucorhamnose, galactose, or arabinose.

Due to the absence of OH-group at the C-3 position, when glycosylated at the C3-position, they are not prone to enzymatic oxidation. For the enzymatic oxidation, OH-group should be substituted at the C-3 position. Upon glycosylation at C-3, there won't be any free OH-group at C-3, but there will be ether linkage, which is not prone to enzymatic oxidation.