engleski

Enzymatic glucosylation in the synthesis of natural glucosides of volatile compounds

Alkyl(C4– C9)-glycosides, glycoconjugates of phenylpropane derivatives and terpenes belong to naturally occurring glycosides of volatile compounds. They are present in aromatic plants mostly in the form of β -O-glycosides. They can be considered as flavour precursors, since their enzymatic/acidic hydrolysis or pyrolysis liberates volatiles. These glycosides are involved in the flower fragrance formation, in the release of aroma compounds of fruits or spicy materials and in the aroma formation of tea and vine. It was demonstrated that glycosidically bound volatiles are gradually changed to fragrant materials by skin microflora, suggesting that they might be useful as fragrant materials with alternative lasting effects. As a part of Croatian grant No. 0011010, β -D-glucopyranosides of pentan-1-ol, (&plusmn ; )-pentan-2-ol, hexan-1-ol, octan-1-ol, benzyl alcohol, 2-phenylethanol, (&plusmn ; )-2-phenyl-propan-1-ol, 3-phenyl-propan-1-ol, geraniol and nerol were synthesized by reverse hydrolysis of the respective alcohols using almond β -glucosidase. These alcohols were also used in transglucosylation reaction with the same enzyme starting from cellobiose. The reactions were carried out in acetonitrile with aqueous acetate buffer (vol. ratio 9:1). Exclusively β -anomers were formed, and the obtained yields for both methods were comparable. The methodology of monitoring the reaction course by GC-MS (after product acetylation) was developed on the model reaction of enzymatic condensation with 1-pentanol and (&plusmn ; )-pentan-2-ol. The products were characterized by GC-MS analysis of prepared tetraacetyl glucosides. Fragment ion characteristics of the aglucone moiety are present in all mass spectra, along with the fragments obtained from acetylated glucose, similar as in other papers. Acetylated glucosides are separable on HP-101 column (even diastereomeric tetracetyl β -glucosides of enantiomeric alcohols). β -Glucosidase did not favour exclusively enantioselection, since both alcohols of the racemic mixture were glucosylated. The results of this work could be useful for preparative purposes as well as for analytical determination of these glucosides in various plants.

synthesis of glucosides of volatile compounds; enzymatic glucosylation and transglucosylation; GC-MS

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