Impact of C18 Epimerization of Indole- and Pyrazole-Fused 18β-Glycyrrhetinic Acid Derivatives on PTP1B and TCPTP Inhibitory Activity: Synthesis, In Vitro, and In Silico Studies.

Protein tyrosine phosphatase 1B (PTP1B) is crucial for negatively regulating the canonical insulin and leptin signaling pathways. This enzyme is a validated target for treating various disorders, including diabetes and obesity. However, to date, no PTP1B inhibitors have been approved for use. In earlier studies, we developed two modified versions of 18β-glycyrrhetinic acid (18β-GA) called FC-114 and FC-122, which showed better inhibitory PTP1B activity than ursolic acid, a well-known inhibitor. To develop even stronger inhibitors, we looked at another compound, 18α-glycyrrhetinic acid (18α-GA), which is more potent than 18β-GA. Thus, in this study, we aimed to synthesize the analogs 18epi-FC114 (3c) and 18epi-FC-122 (5c). These compounds were prepared with and without the carbonyl group at C11. The results showed that converting 18β-H to 18α-H, as well as the absence of the 11-carbonyl group, negatively impacted the PTP1B inhibitory activity. However, the synthesized compounds exhibited an uncompetitive type of inhibition toward PTP1B and did not inhibit the TCPTP enzyme. Molecular docking and dynamics simulations suggest that the inversion of 18β-H pushes the 30-COOH group away, disrupting interactions at the C-terminal site of PTP1B_1-400. Additionally, the absence of the 11-carbonyl group positions the compounds unfavorably, limiting critical interactions in the same region.