An efficient protocol for the synthesis of novel lupane triterpenoid-indazolone hybrids with oxime ester linkage has been developed from naturally accessible precursor betulin. For the first time a series of betulonic acid-indazolone hybrids have been synthesized via an acylation of corresponding 6,7-dihydro-1H-indazol-4(5H)-one oximes with betulonic acid chloride. Diastereoselective reduction of the obtained betulonic acid conjugates with NaBH resulted in a formation of betulinic acid-indazolone hybrids in excellent yields. The configuration of the key compounds has been fully established by X-ray and 2D NMR analysis.

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Monosubstituted Meldrum's acids are found out as a new class of powerful antioxidants. These compounds act as carbon radical scavengers due to the presence of acidic hydrogen in the moiety of cyclic 1,3‐dicarbonyl compound. The presence of phenol and benzylic moiety is favored, but these structural elements are not crucial for the antiradical activity in polar media. The antiradical and antioxidant activity of the substituted Meldrum's acids is not significantly affected by the substituents in the aromatic ring. The 5‐substituted 1,3‐dioxan‐4,6‐diones demonstrate high scavenging capacity of free radicals. The inhibition of DPPH and GO achieved even ∼100 and 80%, respectively. All substituted Meldrum's acids are better antioxidants than BHT, and activity of some of them even exceed vitamin C. It is found out that in polar media the compounds act via SPLET mechanism. Substituted Meldrum's acids turned out as powerful antioxidants for inhibition of oxidation processes of fatty acid alkyl esters, too. The oxidative stability of the last with the title compound additive was significantly higher than with BHT additive. It seems, that the antioxidant activity of the substituted Meldrum's acids in fatty acid esters is both due to benzylic position and 1,3‐dicarbonyl moiety. Practical applications: Arylmethyl Meldrum's acids should be highlighted as potential antioxidants for increasing oxidative stability of various products containing, for example, esters of poly‐unsaturated fatty acids. It should be admitted that the structure of the title compounds can be widely modified by substituents in the aromatic ring without remarkable loss of antioxidant and antiradical activity, but other properties (like solubility) may be improved. In order to apply the title antioxidants into products like cosmetics additional tests regarding toxicity are required. However, these antioxidants can be recommended for increasing oxidative stability for products used in technique. Monosubstituted Meldrum's acids act as carbon radical scavengers due to the presence of acidic hydrogen in the moiety of cyclic 1,3‐dicarbonyl compound. The substituted Meldrum's acids demonstrate high scavenging capacity of free radicals DPPH and GO. These compounds turned out as powerful antioxidants for inhibition of oxidation processes of fatty acid alkyl esters. The antioxidant activity of the substituted Meldrum's acids in fatty acid esters is both due to benzylic position and 1,3‐dicarbonyl moiety. Few of the monosubstituted Meldrum's acids were better antioxidants than BHT, TBHQ, α‐tocopherol, or vitamin C.

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