C-C bond formation at C-2 of a quinoline ring: Synthesis of 2-(1H-indol-3-yl)quinoline-3-carbonitrile derivatives as a new class of PDE4 inhibitors

A number of 2-(1H-indol-3-yl)quinoline-3-carbonitrile derivatives were synthesized via AlCl ₃-mediated C-C bond forming reaction between 2-chloroquinoline-3-carbonitrile and various indoles. The methodology does not require any N-protection of the indoles employed and provided the corresponding products in good yields. The molecular structure of a representative compound was established unambiguously by single crystal X-ray diffraction and structural elaboration of a compound synthesized has been demonstrated. Many of these compounds synthesized showed PDE4 inhibitory properties in vitro. A brief structure-activity relationship studies within the series along with docking results of a representative compound (EC ₅₀ ∼0.89 μM) is presented.