Biosynthesis of phenolic glucosides

Abstract

An Investigation of the biosynthesis of phenolic glycosides in vivo and in vitro has been carried out. Introductory experiments using the broad-bean (Vicia faba) showed that a relatively high yield of mono B-glucosides was obtained when phenols were fed to geminating broad-bean seeds.The mono B-glucosides of quinol,resorcinol and catechol formed in this way have been characterised. Phenolic and alcoholic glucoside derivatives of both o and p-hydroxybenzyl alcohols were produced, the phenolic derivative predominating in the latter case and o-hydroxybenzyl B-glucoside in the former, and not the naturally occurring phenolic glucoside, salicin. A possible route for the formation of salicin in plants is discussed.With two trihydric phenols, pyrogallol, and 1,2,4-trihydroxybenzene, all the possible isomeric mono B-glucosides were obtained, with 2,3-dlhydroxyphenyl B-glucoside predominating withpyrogallol and 2,4-dihydroxyphenyl B-glucoside with 1,2,4-trihydroxybenzene. A possible generalmechanism for the formation of glucosides in vivo is considered in the light of these results.The acid-soluble nucleotide content of broad-bean seeds was examined in an attempt to find the glucose donor for these syntheses. No definite conclusion could he reached but there were some indications that uridine diphosphate glucose (UDPG) was present.The formation of mono B-glucosides from phenols and UDPG or precursors of UDPG in the presence of wheat germ or bean enzymes were studied. There appeared to he a close similarity between the glucosides formed by the in vivo and in vitro syntheses. o-Hydroxybenzyl B-fructofuranoside was formed from saligenin, and sucrose in the presence of invertase, but B-fructofuranosyl transfer to a phenolic hydroxyl group could not he accomplished in this way.Acidic derivatives of the mono B-glucosidesof the dihydric phenols were detected. An investigation of the structure of the acidic derivative of resorcinol B-glucoside suggested that the 6-position of the glucose was substituted and the substituent was tentatively identified as a sulphate. The reactions of this compound and in particular the action of alkali were difficult to interpret so a model compound, 6'-tosyl arbutin, was synthesised and its reactions studied.