Ester derivatives, calixarenes

McKervey [7] and Chang and Cho [9] carried out similar studies. They prepared various ester derivatives of calixarene and tested their ion carrying capacities (Scheme 1). 

Cuest-Induced Changes in Membrane Permeability. Calixarene derivatives are also used for sensing systems other than ISEs or optodes. Recently, a systematic investigation on the control of membrane permeability by use of oriented monolayers composed of calixarene esters was carried out. The hosts used were short alkyl chain esters of calix[6]arene [28 (R = Bu )] and calix[4]arene [26 (R = Bu ), 30 both cone conformers]. The permeabilities through the intermo-lecular voids of these monolayers were evaluated by cyclic voltammetry, as described earlier for oriented membranes of nucleobase derivatives. Cationic, anionic, and neutral electroactive compounds were used as the permeability markers. The voltammetric measurements were carried out either for a monolayer... 

Calixarene esters are easily available by alkylation with ethyl bromoacetate and are often used as starting materials for the introduction of chiral groups at the narrow rim. Their aminolysis by chiral amines led to chiral calixarene derivatives in high yields. Water soluble calix[4]arene amino acid derivatives 9a,b obtained in this way, were successfully used as a pseudostationary phase... 

The size of the calixarene macrocycle can govern the selectivity with regard to the different cations. For example, the ester derivative of calix[4]arene presents a high selectivity for the smaller cations Na" and However, the analogous ester derivative of calix[5]arene and calix[6]arene interact strongly with Cs =Rb >K. No selectivity with regard to cations is observed for the calix[7]arene and calix[8]arene ester derivatives. 

The interaction of thiacalixarene ester derivatives (Fig. lA) alkali metal cations, is strongly conformation of calixarene... 

For the preparation of multiply phosphorus bridged systems, we studied the pyrolytic behavior of calixarene dialkyl phosphate ester derivatives. These compounds are useful intermediates for the OH-depletion of the calixarenes [15, 16] and for the preparation of aminocalixarenes [17]. These esters can be prepared by treatment of the calixarenes with a dialkyl chlorophosphate in the presence of base [18]. In the case of 1, under mild conditions, the distal (i.e, 1,3-) bis(diethyl phosphate ester) derivative is obtained (2a) while under more drastic conditions (CH2Cl2/aq NaOH, phase transfer catalysis) the tetraphosphate 2b is formed [15a]. Calixarene mono diisopropyl phosphate ester and l,2-bis(diisopropyl phosphate ester) derivatives (2c and 2d) were prepared by mono- or dideprotonation by LDA of the monospirodienone derivative 3 followed by treatment with the corresponding dialkyl chlorophosphate [15e, 17b]. Aromatization of the spirodienone products was achieved by heating or by their treatment with HBr yielding the dialkylphos-phate esters derivatives 2c and 2d [15e, 17b]. 

Multiply bridged calixaienes can be easily obtained by pyrolysis of calixarene (dialkyl phosphate ester) derivatives. The multiple bridging of the calix[4]- and calix[6]arenes raises the barrier for ring inversion, but it does not completely freeze all possible dynamic processes. 

Chang and coworkers [10] have synthesized amide derivatives of calixarenes and examined their ion binding properties with Group I and Group II cations. They observed that although the amides are much less effective than the esters for the complexation of Group I cations they are more effective for Group II cations. 

Calixarenes, which are macrocyclic compounds, are one of the best building blocks to design molecular hosts in supramolecular chemistry [158]. Synthesis of calix[4]arenes, which have been adamantylated, has been reported [105, 109]. In calix[4]arenes, adamantane or its ester/carboxylic acid derivatives were introduced as substituents (Fig. 29). The purpose of this synthesis was to learn how to employ the flexible chemistry of adamantane in order to construct different kinds of molecular hosts. The X-ray structure analysis of p-(l-adamantyl)thiacalix[4]arene [109] demonstrated that it contained four CHCI3 molecules, one of which was located inside the host molecule cavity, and the host molecule assumed the cone-like conformational shape (Fig. 30). 

Several classes of synthesized calixarenes bearing several moieties (ether, ester, and amide derivatives), were tested for the extraction of strontium picrates (from aqueous solutions into dichloromethane).128 Only a few of them show appreciable extraction levels. The p-i-butyl calix[6]arene hexa(di-/V-ethyl)amide (CA4) shows a very high extraction level of alkaline earth cations with respect to alkali metal cations. Moreover, dealkylation of the calix[6]arene hcxa(di-/V-cthyl)amidc (CA5) decreases the extraction of both sodium and strontium. As this decrease is much more important for sodium than for strontium, the Sr/Na selectivity, which increases from 3.12 to 9.4, is better than that achieved for DC18 derivative under the same conditions (8.7). These results were confirmed by extraction of strontium (5 x 10 4 M) from 1 M HN03 solutions, where it was found that p-t-butyl calix[4]arene tetra(di-N-ethyl) amide (CA2) (10 2 M in NPOE) extracts only sodium (DNa = 12.3, DSl < 0.001). 

Recently the separation of enantiomers by RIfS and SPR using calixarenes with chiral amide residues was demonstrated [19]. Chirasil-Calix (Fig. 7) is well known from capillary GC as a stationary-phase material because of its good thermal and long-term stability. The separation of amino acid derivatives and lactic esters was widely studied [23]. 

Probably the first examples of chiral calixarene derivatives were esters with camphorsulfonic acid24 derived from t-butyl-calixfSjarene.25 Later ethers obtained with (S)-2-methylbutyl bromide were synthesized and studied with respect to their CD spectra and their chiral recognition ability.26... 

Chiral calix[4]arene podands were made using A-benzyl histidine methyl ester.33 These histidyl calixarenes 12a,b were studied in complexation experiments with Co(H), but no use was made of their chirality. The same is true for a chiral calix[4]arene capped tetraphenyl porphyrin which is C4-symmetrical due to the four L-alanine derived linkers.34... 

The partial 0-alkylation of larger calixarenes becomes more and more difficult due to the increasing number of possible products (16, 28 and 46 for calix[7 to 9]arenes). Nevertheless, various 1,3,5,7-tetraethers were obtained in yields up to 50% by alkylation of 2e in the presence of weak bases such as K2CO3 or CsF and 19 out of the 28 possible methyl ethers have been isolated and identified . The benzoylation of 2e could be optimized to furnish heptabenzoates (with a variety of p-substituents in the ester group) in yields of 40-80% , which can be used as protected calix[8]arenes for the synthesis of monosubstituted derivatives (for an example see Section Vin.A). Very recently, the first examples for the regioselective 0-substitution of 2d were reported . 

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). 

The lower rim tetraamido 47a, 47b and l -distal diamido 48 calix[4]arene derivatives having terminal 2-pyridyl groups in the pendant chains have been synthesized by aminol5 is of the corresponding calixarene and chloride/ester with an appropriate pyridyl amine. The binding properties of 47a, 47b and 48 toward alkali, alkaline earth metal ions and lanthanides have been determined (2006SC219, 2001TL3595). 

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. 

Widening the opposite side of a calixarene upon complexation of small cations to the oxygen atoms of a calixarene lower riin leads to the positive heterotropic allosteric effectin the inclusion o/[60]fullerene in a cage molecule 14 (Fig. 4) derived from two calix[3]aryl esters by complexation of their pyridine groups with Pd(II). " ... 

---