Synthesis of (S)‐4‐C‐β‐D‐Glucosylquinochalcone: A Common Structure in the Yellow and Red Pigments of Safflower Petals

Abstract

(S)‐4‐C‐β‐D‐Glucopyranosylquinochalcone, which is common to all yellow and red pigments of safflower petals, was synthesized as its stable methyl ether acetate in an overall yield of 3.6% via S‐diastereoselective oxidation of 3‐C‐(per‐O‐acetyl‐β‐D‐glucopyranosyl) phloroacetophenone using bis[(trifluoroacetoxy)iodo] benzene. This synthetic route is different from the previous one, including an oxidative dearomatization of the aryl C‐glycoside.

Biomimetic synthesis of carthamin, a red pigment in safflower petals, via oxidative decarboxylation

“…The new method involved the oxidation of C‐β ‐D‐glucosylphloroacetophenone 7 [ 10 ] with bis(trifluoroacetoxy)iodobenzene (BFIB) in the presence of H 2 O to produce 5 in 17% yield and 48% S ‐selectivity (Scheme 2). [ 11 ] We then synthesized ( S )‐ C ‐ β ‐D‐glucosylquinochalcone methyl ether 8 in 42% yield from 5 via Claisen‐Schmidt condensation with p ‐hydroxybenzaldehyde. [ 7,11 ]…”

“…[ 11 ] We then synthesized ( S )‐ C ‐ β ‐D‐glucosylquinochalcone methyl ether 8 in 42% yield from 5 via Claisen‐Schmidt condensation with p ‐hydroxybenzaldehyde. [ 7,11 ]…”

Synthetic Study of Carthamin: Biomimetic Synthesis of Carthamin Model via Peroxidase‐Catalyzed Oxidative Decarboxylation of Its Precursor Model

“…Regarding the stereochemistry at the chiral quaternary carbon, our previous study confirmed that the circular dichroism (CD) spectra of the S-isomer shows a negative Cotton effect at around 270 nm and a positive Cotton effect at around 310 nm, derived from the cyclohexadienone skeleton [4,14]. As shown in Figure 1, the CD spectra of S-isomer 7a and S,S-isomers 6 and 3 showed the abovementioned characteristic curves, and the spectrum of R-isomer 7b showed a symmetrical curve.…”

“…( S )‐ and ( R )‐2‐acetyl‐4‐ C ‐(per‐ O ‐acetyl‐β‐ d ‐glucopyranosyl)‐3,4,5‐trihydroxy‐cyclohexa‐2,5‐dienone ( 7a , b ) produced by the oxidation of 3‐ C ‐(per‐ O ‐acetyl‐β‐ d ‐glucopyranosyl)phloroacetophenone ( 8 ) with bis[(trifluoroacetoxy)iodo]benzene (BFIB) were carefully separated by silica gel column chromatography (CHCl 3 –MeOH) because of their instability, and 7a ( S ‐isomer, 21% yield) and 7b ( R ‐isomer, 7.4% yield) were afforded as ivory‐white powders (Scheme ). The diastereomeric ratio ( S / R ) was 74:26.…”

“…As this method does not involve de-O-acetylation of the resistant carbinol acetate, de-O-acetylation of the glucose moiety under weakly basic conditions is expected to proceed smoothly. [14] were carefully separated by silica gel column chromatography (CHCl 3 -MeOH) because of their instability, and 7a (S-isomer, 21% yield) and 7b (Risomer, 7.4% yield) were afforded as ivory-white powders (Scheme 4). The diastereomeric ratio (S/R) was 74:26.…”