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 syn/anti-isomers in contrast to literature data for C3-oximes giving a single E-isomer due to the steric factors. The structures of 2-oxo- and 3-oxo-28-oxo-allobetulones as well as allobetulone 2E-oxime were confirmed by X-ray diffraction analysis. A regioisomer of natural erythrodiol - olean-12(13)-ene-2β,28-diol 19 was firstly synthesised by the reduction of methyl 2-oxo-oleanoate. The tested triterpenoids were more potent in α-glucosidase (from S. cerevisia) inhibition than acarbose (from 5 to 20 times). Erythrodiol 20 showed IC₅₀ value of 8.35 μM, while it's regioisomer 19 was found as the most active and non-cytotoxic in terms of enzyme inhibition with an IC₅₀ value of 14.19 μM.