Triterpenoid Dimerization as a Bioactivity-Modulating Strategy: From Natural Pristimerin Dimers to Semi-Synthetic Oleanolic Acid Derivatives

Introduction: Dimerization is an important but still underexploited strategy for modulating the biological potential of plant-derived triterpenoids. Natural pristimerin dimers illustrate the structural diversity of triterpenoid dimers, whereas semi-synthetic oleanolic acid dimers provide a convenient model for evaluating how controlled molecular pairing affects bioactivity.

Methods: This work combines a focused review of naturally occurring triterpenoid dimers with original experimental studies on oleanolic acid derivatives. Oleanolic acid dimers were obtained by linking two triterpenoid units through the C-17 carboxyl group using α,ω-dihalogenoalkanes or α,ω-dihalogenoalkenes, followed by acetylation of selected derivatives. The compounds were characterized by spectroscopic methods and evaluated using QSAR analysis, MTT cytotoxicity assays, selectivity index determination, DPPH and CUPRAC antioxidant assays, molecular docking and ADMETox prediction.

Results: The reviewed data indicate that natural triterpenoid dimerization does not always lead to stronger cytotoxic or antimicrobial activity, suggesting that the biological consequences of dimer formation are highly structure-dependent. In contrast, synthetic oleanolic acid dimers showed markedly improved cytotoxic/cytostatic activity compared with the parent compound in multiple cancer cell models. Several non-acetylated dimers displayed IC50 values below 10 μM, while acetylated analogues often showed even stronger activity, with IC50 values below 5 μM. Antioxidant activity was also enhanced in selected derivatives, and computational studies suggested favorable interactions with cancer-related targets and acceptable predicted ADMETox profiles.

Conclusions: Dimerization, especially when combined with rational linker design and post-dimerization acetylation, represents a promising strategy for transforming oleanolic acid into highly active triterpenoid-based derivatives.