Effect of stereochemistry at position C14 on the antiproliferative activity and selectivity of simplified oridonin O-acylated derivatives.

Oridonin is an ent-kaurane diterpenoid with broader antitumor properties. Much efforts have been devoted to develop methods for rational chemical modification of oridonin to obtain synthetic derivatives with higher anticancer activity than the native structure. However, no study has examined the effect of stereochemistry on antiproliferative activity of oridonin and its derivatives thus far. In this study, a novel oridonin analogue with C14α-OH (6) was first synthesized via a Retro-Aldol-Aldol cascade reaction based on a configuration inversion strategy. Its structure was unambiguously confirmed by single-crystal X-ray diffraction analysis. The C14α-OH analogue (6), along with its native counterpart 2 (C14β-OH), was transformed into a series of forty-six C14-O-acylated products (6a-6w and 2a-2w). In vitro antiproliferative activities screening revealed that the α-configured derivative 6 (IC50 = 0.53 μM) exhibited 1.7-fold enhanced potency over its native β-form (2, IC50 = 0.88 μM) specifically in SU-DHL-6 cell lines, despite similar activity against solid tumors. The C14α-configured compounds 6k (IC50 = 0.12 μM) and 6l (IC50 = 0.31 μM) exhibited superior activity compared to their C14β-configured counterparts with the same substituents, 2k (IC50 = 0.71 μM) and 2l (IC50 = 0.47 μM), respectively. On the other hand, the aliphatic derivatives of C14α-O- series generally demonstrated reduced solubility, underscoring the importance of synergistic optimization of the substituent and configuration. Overall, the most potent compound 6k with a C14α-acrylate substitution (IC50 = 0.12 μM) demonstrated a 4.4-fold increase in potency compared to its parent compound 6 and was 16-fold more active than oridonin in the SU-DHL-6 cell lines. Mechanistic studies established that the most potent derivative 6k induces apoptosis and downregulates p-Akt in SU-DHL-6 cells without affecting cell cycle progression. Our study for the first time demonstrates that the stereochemistry at position C14 could affect the selectivity and antiproliferative activity of oridonin derivatives, providing novel natural product-derived lead compounds for further development of anti-cancer drugs.