New tetrahydroisoquinolines bearing nitrophenyl group targeting HSP90 and RET enzymes: synthesis, characterization and biological evaluation

In this study, novel tetrahydroisoquinoline derivatives were synthesized by reacting 7-acetyl-4-cyano-1,6-dimethyl-6-hydroxy-8-(3-nitrophenyl or 4-nitrophenyl)-5,6,7,8-tetrahydroisoquinoline-3(2H)-thiones with methyl iodide, chloroacetonitrile, and ethyl chloroacetate to yield compounds 3–5. Subsequent reactions with N-arylchloroacetamides produced tetrahydroisoquinolin-3-ylthioacetamides (6a–c, 8a–b), which were further cyclized into 6,7,8,9-tetrahydrothieno[2,3-c]isoquinoline-2-carboxamides (7a–c, 9a–b). Additionally, reaction with N-(benzothiazol-2-yl)-2-chloroacetamide afforded compound 10.
The structures of all synthesized compounds were confirmed using elemental and spectral analyses. Their anticancer activity was evaluated against MCF7 and HEPG2 cell lines, revealing that compound 8b exhibited the highest potency against MCF7, while compound 3 was most effective against HEPG2. Further investigation of compound 3 on HEPG2 cells using Annexin V-FITC apoptosis assay and flow cytometry demonstrated a 59-fold increase in apoptosis and cell cycle arrest at the G0-G1 and G2/M phases.
Molecular docking studies showed that compound 8b binds to the RET enzyme with a binding energy of -6.8 kcal/mol, comparable to the standard alectinib (-7.2 kcal/mol). Similarly, compound 3 exhibited strong binding to HSP90 (ΔG = -6.8 kcal/mol), approaching the binding affinity of the reference inhibitor Onalespib (-7.1 kcal/mol).