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The present work aimed at the valorization of biomass derived compounds by their transformation into new added-value compounds with enhanced antioxidant properties. In this context, betulinic acid (BA) was decorated with polyphenolic fragments, and polyhydroxylated ( E )-2-benzylidene-19,28-epoxyoleanane-3,28-diones  4a – d  were obtained. For that, the synthetic strategy relied on base-promoted aldol condensation reactions of methyl betulonate, which was previously prepared from natural BA, with appropriate benzaldehydes, followed by cleavage of the methyl protecting groups with BBr 3 . It is noteworthy that the HBr release during the work-up of the cleavage reactions led to the rearrangement of the lupane-type skeleton of the expected betulonic acid derivatives into oleanane-type compounds  4a – d . The synthesized compounds  4a – d  were designed to have specific substitution patterns at C-2 of the triterpene scaffold, allowing the establishment of a structure-activity relationship. The radical scavenging ability of  4a – d  was evaluated using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH • ) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid radical cation (ABTS •+ ) scavenging assays. In particular, derivative  4c , bearing a catechol unit, revealed to be the most efficient scavenger against both free radicals DPPH •  and ABTS •+ . Subsequently, we designed two analogues of the hit derivative  4c  in order to achieve more potent antioxidant agents: (i) the first analogue carries an additional unsaturation in its lateral chain at C-2 (analogue  5 ) and (ii) in the second analogue, E-ring was kept in its open form (analogue  6 ). It was observed that the presence of an extended π-conjugated system at C-2 contributed to an increased scavenging effect, since analogue  5  was more active than  6 , α-tocopherol, and  4c  in the ABTS •+  assay.

Functionalization of Betulinic Acid with Polyphenolic Fragments for the Development of New Amphiphilic Antioxidants