Studies of the chemical composition of birch bark extracts (Cortex betula) from the Betulaceae family

Abstract

This report presents the results obtained from chemical studies of the composition of dried birch bark extracts (DBBE) from Betula pubescens Ehrh. analyzed by GLC, HPLC, and IR and PMR spectroscopy. The extract contained the following groups of natural compounds: terpenoids (75.2%) and their esters (fatty acid esters of betulinol and lupeol, 4.4%), ether oils (0.08%), hydrocarbons (6.3%) and their epoxides (1.0%), steroids (β-sitosterol, 2.7%), tannins (2.1%), flavonoids (1.56%-mainly kaempferol, its 7-methyl ester, quercetin, the 4-methyl ester of naringenin, etc.), hydroxycoumarins (0.85%-umbelliferone, esculetin, etc.), and a number of unidentified compounds (about 4.0%). The major components of DBBE were triterpenoids and hydrocarbons. Preparative chromatographic separation of fractions containing triterpenoids and hydrocarbons yielded isolated samples which allowed the following compounds to be identified: the terpenoids betulinol, isobetulinol, lupeol, lupenone, betulonic aldehyde, betulonic acid, betulinic acid, and platanic acid, and the hydrocarbons α-santalene, β-trans-bergamotene, and α-trans-bergamotene, and their epoxy derivatives. The chemical composition of DBBE varied depending on the preparation method used, this particularly affecting the content of the major component betulinol, which varied from 54 to 82%. These studies led to the development of a contemporary preparative technology for betulinol with a yield of 95%, along with production of many of its acyl derivatives (for example, the diacetate, succinate, benzoate, etc.) with quite high yields (95–98%); betulinic acid was synthesized in mild conditions with a yield of at least 99.0%. These compounds are currently subject to pharmacological studies.