Gallic occurrence

Pyrogallol (1) was first observed by Scheele in 1786 as a product of the dry distillation of gallic acid [149-91-7] (3,4,5-trihydroxybenzoic acid). Pyrogallol, which is of widespread occurrence in nature, is incorporated in tannins, anthocyanins, flavones, and alkaloids (1). 

Naturally occurring phenolic compounds such as catechol, resorcinol, pyro-gallol, salicylic, gallic, ferulic, caffeic, and coumaric acids all serve as germination inhibitors. Indeed, some of the selective herbicides such as the substituted phenols and cresols also serve as germination inhibitors. Because of the widespread occurrence of coumarin in plants and its demonstrated inhibitory effects at levels found in fruits and some seeds, it is considered to be a natural germination inhibitor (Lerner et al. 1959). In time, of course, coumarin is metabolized in resting seeds to a level below inhibition. 

In environmental applications, rosmarinic acid and gallic acids in fermentation liquors (193), and humic acid in river water (194) have been investigated. The occurrence of hippuric, mandelic and phenylglyoxylic acids in urine has been studied (195). 

Gallic acid is almost invariably found in plant tissues in ester form (109). Various simple esters of gallic acid have been described from plant sources (Table 1 and Table 5) and these metabolites are in many ways analogous to the hydroxycinnamoyl esters occurring in plants (31). These esters are thus formed by association with sugars, polyols, glycosides and other phenols. In contrast to the hydroxycinnamic acids however (100), fully authenticated examples of the occurrence of N-acyl derivatives (with amines, amino-acids and alkaloids) of gallic acid have not yet been described in the literature. 

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