2-Oxo-triterpenoids of ursane, oleanane and dammarane types and their α-glucosidase inhibitory properties

New 2-oxo-triterpenoids of ursane, dammarane and oleanane types were synthesised from the corresponding 3-oxo-derivatives by Willgerodte-Kindler reaction with yields of 31-42%. It was shown that their C2-oximes are formed as the equimolar mixtures of <i>syn/anti</i>-isomers in contrast to literature data for C3-oximes giving a single <i>E</i>-isomer due to the steric factors. The structures of 2-oxo- and 3-oxo-28-oxo-allobetulones as well as allobetulone 2<i>E</i>-oxime were confirmed by X-ray diffraction analysis. A regioisomer of natural erythrodiol - olean-12(13)-ene-2β,28-diol <b>19</b> was firstly synthesised by the reduction of methyl 2-oxo-oleanoate. The tested triterpenoids were more potent in α-glucosidase (from <i>S. cerevisia</i>) inhibition than acarbose (from 5 to 20 times). Erythrodiol <b>20</b> showed IC₅₀ value of 8.35 μM, while it's regioisomer <b>19</b> was found as the most active and non-cytotoxic in terms of enzyme inhibition with an IC₅₀ value of 14.19 μM.