Anion-induced conformational changes in 2,7-disubstituted indole-based receptors

Abstract

The conformational preorganization and anion-induced conformational changes of indole-based receptors functionalized with amido group at C2 and a variety of amido, urea and thiourea moieties at C7 have been studied by the means of NMR spectroscopy. NOE experiments showed that antianti orientation across C2-C2α and C7-N7α bonds is preferred for receptors 1-4 in acetone 10 solution in the absence of anions. Anion-receptor interactions have been evaluated through 1 H and 15 N chemical shift changes. In bis-amido 2,7-functionalised indoles the interaction with chloride and bromide anions primarily occurs at H1 proton. The formal introduction of urea and thiourea moieties increases the number of hydrogen bond donor sites which manifests itself in distribution of halide-receptor interactions among H1, H7α and H7γ protons. Acetate anions also interact 15 strongly with indole and urea NH donor groups, whereas nitrate anions interact solely with H7α and H7γ urea/thiourea protons. NOE enhancements in the presence of anions revealed that anionreceptor complexes favor syn-syn conformation of C2 and C7 substituents.

Macrocyclization Reactions: The Importance of Conformational, Configurational, and Template-Induced Preorganization

“…XXXX, XXX, XXX−XXX an effect on the thermodynamic and/or kinetics of the macrocyclization reaction). 461 Anions have also been used for the construction of sophisticated interweaved motifs and for the amplification of DCLs. 462,463 As has been mentioned in the case of metal templates, many cyclization reactions also take place in the presence of different anions and the relative importance of conformational, configurational, and template effects, including those of the corresponding countercations, is again difficult to analyze.…”

NMR studies of anion-induced conformational changes in diindolylureas and diindolylthioureas

“…We have recently analyzed the conformational preferences of several 2,7-disubstituted indoles with amide substituents at C2 and urea substituents at C7, which showed preference for distinct conformations in the presence and in the absence of anions [33–35]. In addition, indole and urea groups were strongly involved in hydrogen-bonding interactions with the bound anionic guest, whilst the amide group interacted only weakly with the bound anion.…”

Applications of nuclear shielding

“…Anion-receptor interactions were evaluated through 1 H and 15 N chemical shift changes. 378 The 13 C and 15 N MAS NMR spectra of well-characterised paramagnetic metal cyanide coordination polymers were acquired at natural abundance, without the need for polarisation transfer methods such as cross-polarisation or INEPT. For systems where the paramagnetic centre is outside of the cyanide framework, well-resolved 13 C and 15 N spectra of cyanide ligands were obtained.…”