Biindole-Bridged Porphyrin Dimer as Allosteric Molecular Tweezers
作者:Chi-Hwa Lee、Hongsik Yoon、Woo-Dong Jang
DOI:10.1002/chem.200901988
日期:2009.10.5
Allostericmoleculartweezers: By the introduction of porphyrin units to anion‐acceptable biindole moiety (see scheme), the binding affinity of Cl− was significantly enhanced owing to the π–π interaction of porphyrin units. Furthermore, the biindole‐bridged zinc porphyrindimer binds Cl− as well as 1,4‐diazabicyclo[2.2.2]octane (DABCO) in a strong positive allosteric manner.
Oligoindole-based chiral foldamers have been synthesized by incorporating (S)- or (R)-1-phenylethylamine to both ends of the tetraindole scaffold. The oligoindoles fold into a helical conformation upon binding an anion by hydrogen bonds, which gives rise to an induced circular dichroism (CD) signal of large amplitude, implying the preferential formation of one helical isomer over another. Theoretical calculations suggest that the (P)-helix of the (SS)-oligoindole 8a be more energetically stable than the corresponding (M)-helix.
Biindolyl-based molecular clefts that bind anions by hydrogen-bonding interactions
Molecular clefts were synthesized from 2,2'-biindolyl scaffold that contains good hydrogen bond donors of two indole NHs. The molecular clefts were systematically modified in two different manners to increase binding affinities toward chloride. The association constant dramatically increased when additional hydrogen-bonding sites of two benzamide units were incorporated to the biindolyl scaffold. For example, the association constants of 1a and 1b are 5.1 x 10(3) and 1.4 x 10(4) M-1 in CH3CN at 22 +/- 1 degrees C, while reference molecule 10 having only two indole NHs showed the association constant of 340 M-1 under the same conditions. When the biindolyl backbone was structurally preorganized, the binding affinities toward anions were further increased with additional stabilization energy (-Delta Delta G) of 2.0 +/- 0.2 kcal/mol). (c) 2006 Elsevier Ltd. All rights reserved.