Dual-acting agents that possess reversing resistance and anticancer activities: Design, synthesis, MES-SA/Dx5 cell assay, and SAR of Benzyl 1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo[3′,4′:1,2]pyridin[3,4-b]indol-2-substitutedacetates Original

Based on the structural analysis of fumitremorgin C (FTC), imidazoline and β-carboline amino acid benzylester, 14 novel 2-substitutedtetracyclic derivatives of tetrahydrocarboline 4a–n were prepared. We demonstrated that the exposure of MES-SA/Dx5 cells to some of 4a–n resulted in significant reduction of resistance of the cells against doxorubicin. This reduced resistance was accompanied by lowering of IC50 value to doxorubicin from 1.55 ± 0.26 μmol/L to 0.33 ± 0.05 μmol/L for 2-(2-butyl)-derivative 4c, to 1.03 ± 0.22 μmol/L for 2-methyl-derivative 4d, to 0.46 ± 0.04 μmol/L for 2-benzyl-derivative 4f, to 0.98 ± 0.25 μmol/L for 2-indole-3-yl-methyl-derivative 4h, to 0.36 ± 0.03 μmol/L for 2-benzyloxycarbonylmethyl-derivative 4i, to 0.77 ± 0.08 μmol/L for 2-benzyloxycarbonylethyl-derivative 4j, and to 0.77 ± 0.08 μmol/L for 2-benzyloxycarbonylamino-n-butyl-derivative 4l. Proliferation assays of 4a–n indicated 4c,f,i,j were able to inhibit the proliferation of doxorubicin resistant MES-SA/Dx5 cells. The SAR analysis revealed that the benzylester form and the tetracyclic structure of 4a–n were critical for both sensitizing doxorubicin and the cellular anti-proliferative effect.