Ursolic acid-based 24-nor- and A--24-oxy-triterpenoids.

Using methyl 2-cyano-3,4--12(13),4(23)-diene-ursolate as a starting scaffold a series of 3-oxo-24-nor-ursolate and A--ursanes holding hydroxy-, furoyloxy-, -tosyloxy- as well as aldehyde fragments at C24 that possess cytotoxic activity has been synthesised. The structures of the new ursanes were confirmed by detailed spectral data analysis. The chemoselectivity of methyl 2-cyano-3,4--12(13),4(23)-diene-ursolate oxidation involving the double bond in the A cycle was observed.

An unexpected conversion of 2E-furfurylidene-3-oxo-24-nor-allobetulin to 23-nor-allobetulins.

A series of 2E-furfurylidene-23-nor- and 24-nor-allobetulins has been synthesized by the Claisen-Schmidt condensation and conditions of their formation were studied in detail. It was found that among an expected 2E-furfurylidene-3-oxo-24-nor-allobetulin 4 two byproducts holding 3-oxo-4α-hydroxy- 5 and 3β,4α-dihydroxy- 6 substituents were formed, which could become the main products under the change of reaction time and amount of the base solution. Moreover, a conversion of individual 2E-furfurylidene-23-nor-3-oxo-4α-hydroxy- 5 into 2E-furfurylidene-23-nor-3β,4α-dihydroxy-derivative 6 under the treatment with the base solution was observed.

24-Nor-allobetulins possess strong α-glucosidase inhibitory activity.

A series of 24-nor-allobetulin derivatives holding 3β-hydroxy-, oxime, methoxyoxime, lactame and 4-bromobenzylidene substituents have been synthesized and their differences in the NMR spectra were studied in detail. It was revealed that 3-oxo-24-nor-allobetulin loses selectivity in the reaction of oximation and forms a mixture of oximes (and methoxyoximes) in contract to the related derivatives of native scaffold (that forms only -isomers). The screening of α-glucosidase inhibitory activity revealed that 24-nor-allobetulins are more active than allobetulins.