Isolation of triterpene-rich extracts from outer birch bark by hot water and alkaline pre-treatment or the appropriate choice of solvents

Abstract

Birch bark, left over as residue fuel in the pulp and plywood industry, is rich in pentacyclic lupane-type triterpenes – primarily betulin and lupeol – promising starting materials for the synthesis of biologically active compounds with a broad spectrum of medical applications. A comparative study on the main triterpenes of the outer bark of two birch species – silver birch (Betula pendula Roth.) and downy birch (Betula pubescens Ehrh.) – is reported. The total yield of extractives decreased with crop age. For the first time, pre-treatment with hot water and Na2CO3 water solution of birch outer bark was carried out before extraction. Pre-treatment with Na2CO3 water solution substantially improved the ethanol extracts’ triterpene content (from 67.7 to 99.0%). The effect of different solvents on the yield and composition of extracts was studied. Nonpolar solvents behave more selectively toward triterpenes and admixtures. It is possible to improve the extracts’ triterpene content by modifying the extraction technology employed and choosing the appropriate solvents.