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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

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journal contribution
posted on 2020-04-30, 11:38 authored by Kazuki Kurahayashi, Kengo Hanaya, Shuhei Higashibayashi, Takeshi Sugai

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).

Chafuroside B, a bioactive C-glycosylated flavonoid was semisynthesized from hot water extract of Basella alba, a commercially available vegetable “Tsurumurasaki,” via vitexin.

Funding

This work was supported by JSPS KAKENHI [19K05849] for T.S. and is gratefully acknowledged with thanks.

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