Isolation from Rice Bran of a Bound Form of Vitamin B6and Its Identification as 5′-O-(β-d-Glucopyranosyl) Pyridoxine

Abstract

One of the bound forms of vitamin B₆ occurring in rice bran was isolated in a faintly yellowish syrup by repeating ion-exchange and paper-partition chromatographic techniques. The behaviors of the isolate on thin-layer and Aminex A–5 column chromatograms were coincident with those of synthetic pyridoxine-β-d-glucoside which was obtained by Königs-Knorr condensation of α⁴,3-O-isopropylidene pyridoxine and 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide. On acid hydrolysis, the isolate gave pyridoxine and glucose. Glucose was proved to bind to the 5-hydroxymethyl group of pyridoxine, because the isolate did not react with 2,6-dichloroquinone chlorimide in the presence of boric acid. An equimolar amount of pyridoxine and d-glucose was produced with an equivalent consumption of the isolate by the action of β-glucosidase. No essential difference between the isolated and synthetic preparations could be detected in UV- and NMR-spectral features. Thus, the chemical structure of the isolate was identified as 5′-O-(β-d-glucopyranosyl) pyridoxine.