Targeting Protein Tyrosine Phosphatase 1B (PTP1B) to Improve Insulin Sensitivity Using Indole-Fused Glycyrrhetinic Acid Conjugates with Amino Acids

Protein Tyrosine Phosphatase 1B (PTP1B) is a crucial enzyme that significantly modulates insulin and leptin signaling, making it a highly promising target for the treatment of type 2 diabetes (T2D). We previously reported the synthesis and inhibitory activity of FC-114, an indole-fused glycyrrhetinic acid derivative that potently inhibits PTP1B. In this study, we synthesized four FC-114 conjugates with amino acids at the C30 position to enhance their inhibitory activity against PTP1B <i>in vitro</i>. The results indicated that incorporating glycine (compound <b>5a</b>) and serine (compound <b>5d</b>) substantially enhanced inhibitory activity against PTP1B, achieving up to 4-fold greater potency, with submicromolar IC₅₀ values of 0.64 and 0.54 μM, respectively. Inhibitory assessments of the short form (<i>h</i>PTP1B_1‑285) and long form (<i>h</i>PTP1B_1‑400) of PTP1B, along with enzymatic kinetics studies, molecular docking, and molecular dynamics analyses, suggested a mechanism consistent with uncompetitive inhibition, potentially involving a binding to the disordered C-terminal domain. Furthermore, both FC-114 conjugates with glycine (<b>5a</b>) and arginine (<b>5b</b>) significantly enhanced the mRNA expression of the GLUT4 receptor in C2C12 myoblast cells. Additionally, these compounds reduced glucose levels during the insulin tolerance test in streptozotocin-induced diabetic mice.