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. 2016 Jul 21;17(7):1177. doi: 10.3390/ijms17071177

Figure 2.

Figure 2

General structures of the three most important classes of phenolic compounds for human health. Benzoic acids: p-hydroxybenzoic acid, R3=OH; vanillic acid, R2=OCH3 and R3=OH; gallic acid, R2=R3=R4=OH; syringic acid, R2=R4=OCH3 and R3=OH. Cinnamic acids: p-coumaric acid, R3=OH; caffeic acid, R3=R4=OH; ferulic acid, R2=OCH3 and R3=OH; sinapic acid, R2=R4=OCH3 and R3=OH. Flavonoids: R3–R6=H or other groups such as OH or oxo- groups. For most food flavonoids: R4’=R6=H and R5=OH. In biochanin A, R4’=OCH3; formononetin, R4’= OCH3 and R5=R6=H; glycetein, R5=H and R6=OH.