Cinnamic acids

There are six common cinnamic acids, which have a C6 - C3 skeleton. All plants probably contain at least three of them. Shown below are cinnamic, acid (1.12), p-coumaric acid (1.13), caffeic acid (1.14), ferulic acid (1.15), 5-hydroxyferulic acid (1.16), and sinapic acid (1.17).

O^OH

OCH3 HO'

OCH3 HO'

O OH

O OH

OCH3 H3CO'

OCH3 H3CO'

O^OH

O OH

O OH

OCH3

OCH3

Cinnamic acids are commonly found in plants as esters of quinic acid, shikimic acid, and tartaric acid. For example, chlorogenic acid (1.18) is an ester of caffeic acid and quinic acid.

OH

Cinnamic esters are also found as sugar esters, or as esters of a variety of other organic acids. For example, sinapoyl esters represent a class of UV-absorbing compounds in the family of the Brassicaceae. Examples include sinapoyl malate (1.19) present in leaves, and sinapoyl choline (1.20) present in roots (Ruegger and Chapple, 2001).

H3CO

H3CO

H3CO

H3CO

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