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

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).

Genome-wide identification of UDP-glycosyltransferases in the tea plant (Camellia sinensis) and their biochemical and physiological functions

“…This is thought to form when Prechafuroside is exposed to heat and, via a S N 2 mechanism and transition state, causes the deprotonation of O -7 which attacks C-2” causing desulfonation and subsequent cyclization. Chafuroside is found in trace amounts in Oolong tea that has been heat treated to >140°C; a post-harvesting processing step done to enhance flavour, taste, and stability of the tea leaves ( Ishida et al., 2009 ; Kurahayashi et al., 2020 ). Chafurosides show potential as anti-inflammatory therapeutics and therefore, further investigation into their in vivo synthesis is warranted ( Furuta et al., 2004 ; Onoue et al., 2012 ).…”

“…Chafurosides show potential as anti-inflammatory therapeutics and therefore, further investigation into their in vivo synthesis is warranted ( Furuta et al., 2004 ; Onoue et al., 2012 ). While there are methods for the synthesis of Chafuroside and Prechafuroside no biological pathway has been identified for the formation of Prechafuroside ( Furuta et al., 2004 ; Nakatsuka et al., 2004 ; Furuta et al., 2009 ; Ishida et al., 2009 ; Kurahayashi et al., 2020 ). Prechafuroside A and B are unusual in that the sulphate is bound to the glycosylated sugar and not to the flavonoid skeleton.…”