From shikimic acid pathway via phenylalanine B From malonic 4 acid pathway A‖C OH Anthocyanidin The three-carbon bridge Basic flavonoid skeleton OH FIGURE 13 12 Basic flavonoid carbon skeleton. Flavonoids are biosynthesized from products of the shikimic acid and malonic acid pathways. Positions on the flavonoid ring sys C tem are numbered as shown 0- Sugar Figure 5-11 5-12 Anthocyanin There Are Four Major Groups of Flavonoids FIGURE 13 13 The structures of anthocyanidins(A)and The flavonoids are one of the largest classes of plant phe. anthocyanin(B). The colors of anthocyanidins depend in nolics. The basic carbon skeleton of a flavonoid contains 15 part on the substituents attached to ring B(see Table 13. 1) An increase in the number of hydroxyl groups shifts carbons arranged in two aromatic rings connected by a absorption to a longer wavelength and gives a bluer color. three-carbon bridge eplacement of a hydroxyl group with a methoxyl group (OCH,) shifts absorption to a slightly shorter wavelength, c6 resulting in a redder colorFigure 5-11 5-12