Synthesis of azepino[4,5-b]indol-4-ones via MCR/free radical cyclization and in vitro-in silico studies as 5-Ht₆R ligands.

A series of nine new 3-acetamide-azepino[4,5-b]indol-4-ones were synthesized in two steps: (i) multicomponent reaction (Ugi-4CR/SN2) and (ii) free radical-mediated cyclization. These compounds, along with their tetrazole-based analogs, were studied in vitro to assess their binding with the 5-hydroxytryptamine type 6 receptor (5-Ht6R). The 3-acetamide-azepino[4,5-b]indol-4-ones displayed moderate affinity, whereas the 3-tetrazolylmethyl-azepino[4,5-b]indol-4-ones affinity values are lower. However, one of the 3-acetamide-azepino[4,5-b]indol-4-ones exhibited a hit value of Ki (211.2nM) to the 5-Ht6R. Minimal-energy structures of one cis-amide and its tetrazole-based analog (calculated by means of the Density Functional Theory) were analyzed to assess some interesting bioisosterism aspects. Interactions and binding energies between all products and the 5-Ht6R were calculated through in silico molecular couplings. Finally, a QSAR model was proposed using the results of the in vitro assays.