Plant biochemistry of saligenin and related compounds

Abstract

When aromatic aldehydes are fed to higher plants, they are readily metabolised and simultaneous oxidation, reduction and glucosylation reactions occur. A detailed study has been made of the products formed when salicylaldehyde is fed to germinating Pisum and Vicia seeds. When a wide range of other higher plant species were fed with salicylaldehyde, the metabolic pattern was very simila in most cases. When other phenolic aldehydes were fed to Pisum, they were also readily metabolised and similar oxidation, reduction and glucosylation reactions occured as with salicylaldehyde. The simultaneous oxidation and reduction of salicylaldehyde to salicylic acid and saligenin has been studied in vitro using higher plant enzyme preparations. The enzymes responsible appear to be a pair of relatively unspecific aromatic aldehyde:NAD oxido-reductases. The biosynthesis of salicin in the Salicaceae has been studied in vive and in vitro. Helicin was found to be converted very largely to salicin in vitro by willow bark and pea enzyme preparations, whereas with saligenin, the isomeric salicyl gluside was the main product. There are strong indications that helicin, rather than saligenin, is the natural direct precursor of salicin. When penols are fed to a variety of higher plants, as well as the phenolic O-glucosides, acid derivatatives of the glucosides are formed. Acid derivatives of alcoholic O-glucosides are also formed as in the case of salicyl glucoside. A detailed study has been made of the acid derivatives of resorcinol glucoside, salicyl glucoside and m-hydroxybenzaldehyde glucoside. The acid moiety has been identified as phosphate by radiochemical and other methods and the compounds shown to be the 6'-phosphate esters of the corresponding glucosides. Trace amounts of salicyl glucoside-6'-phosphate have been found in ethanolic extracts of the flowers of Filipendula ulmaria. These extracts have been found to contain several other interesting phenolic compounds. Until now salicin was believed to be the only naturally occuring glucoside of saligenin. However, its isomer occurs in considerable quantities in various tissues of Filipendula ulmaria and has been found in the flower extracts of a number of related species. Careful examination of a number of Salix species, showed that trace amounts of salicyl glucoside occur in some of the tissues, as well as the much larger quantities of salicin. The flower extracts of Filipendula ulmaria and Filipendula elegantissima were found to contain large quantities of an aldehydic glucoside. The aglycone has been indentified as o-coumaraldehyde, which has not been previously reported to occur naturally.