Macrocyclic binding group

We have also synthesized a catalyst related to 131 in which the cyclodextrin rings were replaced with synthetic macrocyclic binding groups [196], Also, we have examined catalysts related to 131 in which substrate binding involved metal ion coordination, not hydrophobic binding into cyclodextrins or macrocycles [198]. 

Winkler, J., Coutouli Argyropoulou, E., Leppkes, R. and Breslow, R., Artificial transaminase carrying a synthetic macrocyclic binding group, /. Am. Chem. Soc., 1983,105, 7198-7199. 

The chemical structures of [2]catenane 19 and the related [3]catenane 20 (Fig. 8) were conceived as an extension of their work on molecular shuttles. The larger macrocycle in 19 comprises two fumaramide stations with differing macro cycle binding affinities. In station B (red) the methyl groups on the fumaramide motif cause it to have lower affinity than the standard fumaramide station. The non-methylated fumaramide station (station A, green) is located next to a benzophenone unit. This allows selective, photosensitized isomerization of station A by irradiation at 350 nm. Station B (red) can be photoisomerized by direct irradiation at 254 nm. The third station, a succinic amide ester (station C, orange), is not photoactive and is intermediate in macrocycle binding affinity between the two fu-... 

The CO2 binding constants of the corresponding [CoHMD]+ isomers are quite different N-rac-[CoHMD], (1.2 0.5) x 10 M A - evo-[CoHMD]+, 165 15 M l [5,6]. While hydrogen bonding interactions between the bound CO2 and amine protons of the macrocycle will tend to stabilize both adducts, the N-meso adduct is destabilized by the steric repulsion by the macrocycle methyl group. 

The metal ion within the vicinity of the critical distance should be able to replace its coordinated solvent molecules step-by-step by the ligand binding groups. Concomitantly, the conformation of the macrocycle shrinks so that the chelating cavity in its interior adapts to the size of the unsolvated metal ion. Such a mechanism is formally depicted in Fig. 12. 

At first glance, the structure of these macrocycles may appear very different from classical HD AC inhibitors. However, they share the same common features the macrocyclic structure comprises the surface recognition element, which is connected to the metal-binding group via a relatively flexible linker moiety. Notably, reductive cleavage of the disulfide bond in romidepsin is required to liberate a mercapto group that can bind the zinc ion within the catalytic site. 

Picolinamide and thiopicolinamide have been introduced on the lower rims of calixarene scaffolds of various sizes in order to study whether the size of the macrocycle, the cooperation and stereochemical disposition of these binding groups affect the efficiency of extraction and selectivity in the actinide/lanthanide separation. Thus, picolinamide conjugates of calix[4]arene 38-40 and those of calix[6]arene 42-44 and of calix[8]arene 45 and 46 have been formed from appropriate amino derivatives of the corresponding calixarenes and picolinic acid pentafluorophenyl ester. The thiopicolinamide analog 41 has been synthesized from 40 and Lawesson s reagent (2005EJO2338). 

Another comparison substituted the cyclodextrin-binding group by a synthetic macrocycle that also strongly binds hydrophobic substrates in water solution. We synthesized... 

A large variety of receptor molecules and catalytic sites is based on the idea that the inner cavity of macrocycles entraps metal ions or guest molecules if several binding groups are present. Protonation or thermal movement of these binding sites may then cause release of the metal ion or guest molecule [4]. Cyclic molecules usually only bind ions in water, e.g. metal ions, amines or phosphates, tubular molecules, in particular cyclodextrin, also recognize hydrophobic surfaces. Kemp acid derivatives finally provide a concave cavity with sizes up to about 10 A, in which dipole-dipole interactions are sufficient to bind molecules [5]. 

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