Stereoselective Synthesis and Binding Properties of Novel Concave-Shaped Indolizino[3,4-b]quinolines

Novel all-cis-configurated indolizino[3,4-b]quinoline receptors 3, 4were prepared via diastereoselective Lewis acid-catalyzed cyclization of N-arylimines 6, 7 as the key step. In order to obtain the indolizino[3,4-b]quinoline derivative 21 without a gem-dimethyl group at C-7, an N-arylimine precursor 18 bearing a vinyldisilane terminus was prepared in 8 steps from L-prolinol 15. In contrast to the known β-effect of silyl groups cyclization of 18 proceeded via an α-carbenium ion species to give the diastereomeric products 19, 20, which were desilylated to 21, 22. The association constants for receptors 2—4 and 21 decreased in the order 21 > 2 > 4 > 3 for both acetic acid and N-Z-phenylalanine as substrates.