Acetone, anthocyanins pyranoanthocyanins

Fig. 2.107. The formation of pyranoanthocyanins 6-10 from anthocyanins 1-5 and acetone. Reprinted with permission from Y. Lu et al. [242].

Novel pyranoanthocyanins have also been isolated and identified in blackcurrant (Ribes nigrum) seed using HPLC, 2D NMR and ES-MS. Blackcurrant seeds were extracted with acetone-water (70 30, v/v) and the components of the extract were separated in a polyamide column followed by HPLC-DAD. The new pigments were finally separated in an MCI-HP20 column. The chemical structures of anthocyanins 1-2 and the novel pyranoanthocyanins 3-6 with the pyrano[4,3,2-de]-l-bcn/opyrylium core structure are shown in Fig. 2.110. It was stated that the analytical method developed separated well the novel pyranoanthocyanins [245],... 

Y. Lu and Y. Foo, Unusual anthocyanin reaction with acetone leading to pyranoanthocyanin formation. Tetrahedron Lett. 42 (2001) 1371-1373. 

This mechanism can be extrapolated to other enolizable precursors potentially present in wine, including yeast metabolites such as a-ketoglutatic acid and 2-hydroxybutan-2-one, but also to acetone, which can react with anthocyanins during solvent extraction proced-ures. The resulting products are pyranoanthocyanins as presented in Figure 5.11, with Rs = CH2-COOH, R4 = COOH R3 = H, R4 = CHOH CH3 R3 = H, R4 = CH3. 

Lu and Foo (27) report at anthocyanins may undergo reactions with acetone to give rise to pyranoanthocyanins. This point must be addressed as our extraction of the whole cranbeny fruit and subsequent chromatographic isolation employed aqueous acetone solutions. While our mass spectral data does not reveal masses corresponding to pyranoanthocyanins we remain vigilant of the effects organic solvents may have on phenolic compounds. 

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