Phenylethanol glycosides

Phenylethanol glycosides Plantaginoside, acteoside (verbascoside), isoacteoside, calcerolioside B,... 

The HPLC- peak profile of MeOH-extract of Semen Plantaginis (extract sample 1 and 3) is characterized by the peaks 1-4 in the Rt-range 2.0-10.0 which can be assigned to Catalpol (Rt=2.50), Geniposidic acid (Rt=3.23) and (Aucubin Rt=4.11). The second Rt-range between 25.0 and 32.0 (numbered with 9 and 11) were identified as verbascoside and another not identified phenylethanol glycoside respectively. 

Control experiments do not provide evidence for oxidation of the secondary alcohol groups in the glycoside or for degradation of the ligand backbone. A similar regioselectivity was also observed in a benzyl alcohol/1-phenylethanol model system that showed no proof for the oxidation of the secondary alcohol by formation of acetophenone (18, 23,26). 

Fig. 4.5 Extent of hydrolysis of glycoside of different volatile compounds during MLF with four strains of malolactic bacteria (MLB). Values are calculated as a percentage ratio between the concentration of glycosides in MLF samples and in a non-MLF control. Sum of 1-hexanol, trans- and CM-3-hexenol, trans- and c/i-2-hexenol sum of isoamyl alcohols, heptanol, and 4-hydroxy-4-methyl-2-pentanol sum of benzyl alcohol and 2-phenylethanol sum of vanillin and benzaldehyde sum of 4-vinylphenol and 4-vinylguaiacol sum of Unalool and a-terpineol sum of nerol and geraniol sum of cis- and rrani-linalool oxides (pyranic and furanic) sum of 3,7-dimethyl-l,5-octadien-3,7-diol and the two 2,7-dimethyl-2,7-octadien-l,6-diol isomers (from Ugliano and Moio 2006, reproduced with permission)...

Williams, P.J., Strauss, C.R., Wilson, B., Massy-Westropp, R.A. (1983). Glycosides of 2-phenylethanol and benzyl alcohol in Vitis vinifera grapes. Phytochem., 22, 2039-2041. 

In order to lower water activity and therefore favor synthesis over hydrolysis, the effect of the addition of a high concentration of lithium chloride in the )3-galactosidase-catalyzed reaction between phenylethanol and lactose was studied [18]. Concentrations of LiCl in the range 0.4 and 0.7 M did not improve the yield of phenylethyl o-galactopyranoside however, it prevented the disappearance of the glycoside product, which may facilitate the control of product formation. 

Glycosides. Finally, it should be mentioned that in our studies on papaya fruit volatiles and their precursors, glycosidic forms of several volatiles were detected. At this time, we have identified the B-D-glucosides of benzyl alcohol and 2-phenylethanol. There are also indications for the occurrence of glycosidic forms of terpenoids, but from the data available exact structures of the sugar moieties cannot be elucidated as yet. 

The structure of the sugar moieties in the terpenol glycosides have not yet been investigated, but further work in this area is in progress. In a separate study, we have also found evidence of aromatic glycosides in blackcurrants, in particular, glycosides of phenylethanol, benzyl alcohol and p-cymene-8-ol. 

Figure 4. Top trace Gas chromatogram of aglycons generated by enzyme hydrolysis of C retained monoterpene glycosides. Lower trace The same glycosidic material treated with denatured enzyme. For peak assignments refer to Figure 1. B benzyl alcohol P=2-phenylethanol and i.s. internal standard (octan-l-ol).

Other known examples of natural (3-D-allopyranosides include an iridoid glycoside, together with its several acetylated derivatives,69 an alloside of phenylethanol,70 and caffeoyl phenylethanoid allosides.71... 

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