Synthesis and binding properties of anion receptors containing multiple hydrogen bond donors

A new biindolyl scaffold, 7,7'-diamino-2,2'-biindolyl, 2 was efficiently synthesized and modified into anion receptors 9 and 10 with extended hydrogen bond donors. The receptor 9 possesses two indole NHs and two amide NHs, while 10 contains two indole NHs and four urea NHs. The receptors 9 and 10 bind oxoanions such as phosphates and carboxylates by multiple hydrogen bonds in DMSO, both of which bind two or three orders of magnitudes higher than does a reference molecule 8 with only two indole NHs. In addition, binding affinities of 10 with a series of dicarboxylates were also investigated, showing the association constants in between 1.6 x 10(5) M-1 (malonate) and 8.1 x 10(5) M-1 (adipate) in 10% (v/v) MeOH/DMSO at 22 +/- 1 degrees C.