Conjugates of Lupane Triterpenoids with Arylpyrimidines: Synthesis and Anti-inflammatory Activity

Semisynthetic triterpenoid betulonic acid is of significant interest due to its biological activity and synthetic application. In this study, we report the synthesis of hybrid compounds, containing betulonic acid carboxamide and arylpyrimidine fragments. A total of 15 conjugates were prepared using the cyclocondensation reaction of new terpenoid alkynyl ketones with amidinium salts. The main synthetic approach to betulonic acid amide-derived alkynylketones was based on the cross-coupling reaction of N-(4-ethynylphenyl)- or N-(2-(4-ethynylphenyl)-1-(methoxycarbonyl)ethyl)- substituted betulonic acid carboxamide with aroylchlorides. Cyclocondensation of alkynones with amidine or guanidine hydrochlorides by reflux in MeCN in the presence of K₂CO₃ led to the formation of terpenoid pyrimidine hybrids in 52-89% isolated yield. Anti-inflammatory properties of new type of triterpenoid-pyrimidine conjugates were studied using the histamine- and concanavalin A- induced mouse paw edema models. In a model of acute inflammation betulonic acid amide-arylpyrimidines containing a 4-fluorophenyl substituent at the C-6 position of pyrimidine ring exhibited significant and selective anti-inflammatory activity. Compounds containing the 4-bromophenyl- substituent in the pyrimidine ring revealed selective anti-inflammatory activity in the model of immunogenic inflammation (concanavalin-A model). It should be noted that the methoxycarbonyl substituted ethane link between pharmacophore ligands (betulonic acid carboxamide and arylpyrimidine) has a significant effect on anti-inflammatory activity in both in vivo models of inflammation. It was shown by molecular docking that the new derivatives are incorporated into the binding site of the protein Keap1 Kelch-domain by their pyrimidine substituent with the formation of more non-covalent bonds.