Scaffolds calixarene

Cotton et al. showed the assembly of a very stable coordination cage formed by linking two calixarene scaffolds functionalized with four carboxylic acid groups via bimetal units, (DaniF)2Rli2 [21]. This capsule permanently includes an NEt4+ cation and has a BF4 counterion external to the cage, as shown by the X-ray crystal structure determination. 

Fig. 14 A glycodendrimer constructed on a calixarene scaffold (left) and the proposed binding mode (right) presented in [128]...

The calix[4]arene 34 and bis calix[4]arene 35 derivatives were generated by bridging their lower rim oxygen with one 2,6-lutidyl unit or two of these at 1,3-distal positions of calixarene scaffolds. The calixarenes 34 and 35 showed complexation toward alkali metal cations (2000T3121). 

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). 

On the basis of the catalytic roles of calix[4]arene derived model 18-[Zn"]2 (99JOC3896) and cis-diaqua Cu complexes for cleavage of phosphate diesters, Reinhoudt designed a calix[4]arene derivative 66-[Cu ]2 functionalized with two ds-diaqua Cu° centers at the distal positions of the upper rim as a model for dinuclear metalloenzymes that catalyze chemical transformations of phosphate esters. It was synthesized from Cu(C104)2 and 5,17-bis(bis(l-methylimidazol-2-yl)hydroxy-methyl)-25,26,27,28-tetrakis(2-ethoxyethoxy)calix[4]arene which was conveniently obtained from the precursor diester and lithiated 1-methyl-imidazole. In this model, the two Cu° centers are well organized on the calixarene scaffold for performing S5mergistic action. 

The conjugation of porphyrins with a calixarene scaffold at its upper rim has been used for evolving cofacial porphyrin pairs for enhancing... 

A calix[4]arene receptor featuring both a cation-binding site in the form of ether/amide functionality and an anionbinding site in the form of a bisthiourea together on the lower (narrow) rim of the calixarene scaffold was reported by Kilbum in 2003. ... 

The direct connection of an amino acid or a peptide to a calixarene scaffold at the upper rim requires the presence of an acid or an amino functionality in a calixarene. Such an approach has been widely studied in the group of Ungaro (for review see ref. [13]). For example, calix[4]arene di- or tetracarboxylic acids have been used to... 

The synthesis of 8 is a very rare example that utilizes diastereoselective pathways to achieve chiral calixarenes. In most cases chiral groups are simply attached to the macrocyclic ring. Here, the stereogenic centers were introduced on an imine-calixarene scaffold using a chiral auxiliary strategy. 

Control of the appropriate substitution pattern on the calixarene scaffold provides a convenient route to amphiphilic macrocycles. One application of these calixarene-based amphiphiles is their use as binding agents at the air-water interface. 

Conjugates of nucleic acid related compounds (nucleobases, nucleosides and nucleotides) and calixarene scaffolds are potential candidates for the formation of well-defined supramolecular structures. Nucleobases are structurally predetermined to mediate non-covalent interactions, e.g. base pairing via hydrogen bonds and r-stacking to aromatic moieties. The versatile nature of the cahxarene corpus provides a convenient entry to multiple pre-oriented functionahties. By this combination a broad range of supramolecular architectures becomes accessible. Over the years a number of calixarene DNA hybrids have been constructed and investigated in their complexation properties towards nucleic acid related compounds. A valuable summary on this topic is given by Kumar et al. in Advances in Heterocyclic Chemistry [38]. 

Hetero-calixarenes represent another interesting group of calixarene-related compounds that can be used for the interaction with nucleic acids and related compounds. Due to their constitutional variation their structural features significantly differ from the corresponding original calixarene scaffolds. Still there is a number of examples worth considering in the broad context of calixarenes and nucleic acids. 

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