Improved Preparation of Vitexin From Hot Water Extract of Basella alba, the Commercially Available Vegetable Malabar Spinach ("Tsurumurasaki" in Japanese) and the Application to Semisynthesis of Chafuroside B

Biosci Biotechnol Biochem. 2020 Apr 30;1-6. doi: 10.1080/09168451.2020.1761286. Online ahead of print.

Abstract

Hot water extraction of D-arabinofuranosylvitexin from the raw leaves of commercially available Basella alba "Tsurumurasaki" and subsequent acidic hydrolysis was improved to be a procedure using a high-pressure steam sterilizer to afford vitexin. The amount was estimated to be 14.1 mg from 1 g of dry weight of the raw leaves, whose recovery was calculated to be 95% based on the estimated content of D-arabinofuranosylvitexin in B. alba raw leaves. The product was dehydratively cyclized between hydroxy groups on the carbohydrate and flavone skeletons under modified Mitsunobu reaction conditions in N,N-dimethylformamide to give chafuroside B, which is known to be a bioactive Oolong tea polyphenol. Through these transformations, 10.2 mg of chafuroside B could be semisynthesized from 1 g of dry weight of the raw leaves, and the efficiency was improved compared to that from the extraction from Oolong tea (3.4 μg from 1 g of dry weight).

Keywords: C-glycosylated flavone; D-arabinofuranosylvitexin; hydrolysis.