Selective oxidation of pyrogallol-type catechins with unripe fruit homogenate of Citrus unshiu and structural revision of oolongtheanins. Issue 17 (29th April 2015)

• Record Type: Journal Article
• Authors: Matsuo, Yosuke; Tadakuma, Fumiya; Shii, Takuya; Saito, Yoshinori; Tanaka, Takashi
• Is Part Of: Tetrahedron. Volume 71:Issue 17(2015)
• Page Start: 2540
• Page End: 2548
• Publication Date: 2015-04-29
• Subjects: Catechin -- Oxidation -- Citrus unshiu -- Oolongtheanins -- Black tea; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tet.2015.03.016
• Languages: English
• ISSNs: 0040-4020

Abstract

Abstract: In our previous chemical study of the production mechanism of black tea polyphenols, we demonstrated that Japanese pear fruit homogenate oxidizes green tea catechins bearing pyrogallol-type and catechol-type B-rings to produce theaflavins and dehydrotheasinensins. In contrast, unripe fruit homogenate of Citrus unshiu selectively oxidizes pyrogallol-type catechins to yield only dehydrotheasinensins. The difference in the selectivity of the two homogenates is probably related to the lower redox potential of pyrogallol-type catechins. The oxidation of epigallocatechin with C. unshiu homogenate gave two new compounds, including an ethanol adduct of an oolongtheanin precursor and epigallocatechin 4′- O -rutinoside, together with theasinensin C, dehydrotheasinensin E, and desgalloyl oolongtheanin. The structure of desgalloyl oolongtheanin should be revised based on the spectroscopic and computational data collected in the current study, and a mechanism responsible for the production of oolongtheanins is also proposed. Graphical abstract: