Low Molecular Weight Phenols in Higher Plants

Phenolic compounds are second only to carbohydrates in abundance in higher plants. They display a great variety of structures ranging from deriva­ tives of simple phenols, such as quinol, to complex polymeric materials, such as lignin. In recent years, naturally occurring phenolics have been the subject of several reviews. Past editions of this publication alone have contained articles on lignin (1), the biosynthesis of flavonoids (2) , and general bio­ synthetic pathways (3). In other periodicals, accounts of the chemistry and biochemistry of coumarins (4) and lignin (5, 6, 7) can be found. For the purposes of this review the author intends, wherever possible, to limit the discussion to those naturally occurring compounds which possess only one aromatic ring and to concentrate on the biochemical and physio­ logical aspects which have not received detailed attention in the past. The compounds which come within these terms of reference and which will receive attention include simple mono-, di-, and trihydroxybenzenes, phenolic alcohols, aldehydes and carboxylic acids, hydroxycinnamic acids, and phenolic amino acids and amines.