Andrea Pochini

The preparation and properties of a new lipophilic sodium selective ether ester ligand derived from p-t-butylcalix[4]arene

Abstract A new lipophilic cation ligand (2), which shows selectivity for sodium in extraction experiments, has been obtained by the reaction of p-t-butylcalix[4]arene and t-butyl bromoacetate. The X-ray crystal structure determination and 1H and 13C NMR studies show compound (2) in a fixed “cone” structure both in the solid state and in solution. Compound (2) in apolar media strongly encapsulates sodium cation with a 1:1 stoichiometry and is able to separate the tight sodium picrate ion pair in THF.

p-t-Butylcalix[4]arene tetra-acetamide: a new strong receptor for alkali cations [1]

From the reaction ofp-t-butylcalix[4]arene with α-chloro-N,N-diethyl acetamide a new lipophilic ether-amide ligand (2) has been obtained in high yield. Solution studies show (2) to be a very strong cation receptor for alkali cations, especially sodium and potassium. The X-ray crystal structure determination of the free ligand (2) and two potassium complexes (KI and KSCN) shows the calix[4]arene in a fixed ‘cone’ structure and the cation completely encapsulated in a polar cavity of eight oxygen atoms.

Chloromethylation of calixarenes and synthesis of new water soluble macrocyclic hosts

Abstract The chloromethylation of calix[4]arene 1a and of the methyl ethers of calix[6]arene 1b and calix[8]arene 1c , using chloromethyl n-octyl ether and SnCl 4 in chloroform at room temperature has been performed in good yield for the first time. The chloromethylated products 2a–c have been used as intermediates to introduce on calixarenes phosphonic acid groups which render these macrocycles water soluble and potentially useful in Host Guest Chemistry.

Synthesis, 1H NMR, 13C NMR spectra and conformational preference of open chain ligands on lipophilic macrocycles☆

Abstract Several open chain ligands (polypodands) 3 and 4 have been synthesized introducing short oligoethylene glycol units (-CH 2 CH 2 O) m CH 3 , (m = 1,2,) on lipophilic matrices represented by cyclic tetra- 1 and octa- 2 oligomers obtained from the base catalyzed reaction of p-butylphenol or p-octylphenol and formaldeyde. 1 H NMR and 13 C NMR spectral data have been used to establish the conformational freedon of the ligands, which is important for cation binding studies.

Syn-1,2-dialkylated calix[4]arenes: general intermediates in the NaH/DMF tetraalkylation of calix[4]arenes

In DMF or acetonitrile with NaH as a base at room temperature the tetraalkylation of calix[4]arenes 1a and 1b proceeds via the syn-1,2-disubstituted products to the tetraalkylated calix[4]arenes in the cone conformation. With KH as a base the tetraalkylated calix[4]arenes are predominantly formed in the partial cone conformation, and the reaction proceeds via both the syn-1,3-di and the syn-1,2-disubstituted products. Also the solvent influences the pathway via which tetraalkylation takes place. The syn-1,2-disubstituted calix[4]arenes 4-6 can be isolated in 15-55 % from the NaH/DMF or MeCN reactions when only 2.2 equiv of the electrophile are used.

Synthesis, antimicrobial activity and binding properties of calix[4]arene based vancomycin mimics

Abstract Biologically active Vancomycin antibiotic mimics have been synthesized by linking two opposite aromatic nuclei of a calix[4]arene derivative in the cone conformation with a polifunctional bridge containing D-or L-alanine units and diethylentriamine segment.

Synthesis and Structure of ChiralCone Calix[4]arenes Functionalized at the Upper Rim with L-Alanine Units

Synthetic routes were developed to link L-alanine methyl ester or L-alanyl-L-alanine methyl ester at the upper rim of calix[4]arenes blocked in the cone conformation. Several tetra- (3 and 6) and difunctionalized (11 and 12) amino acids containing macrocycles were obtained. Reaction of these compounds with hydrazine gave the corresponding hydrazido derivatives 4, 13, and 14, while the hydrolysis of 3 with LiOH produced the tetraacid 5 whose lithium salt is water soluble at neutral pH. The structural properties of all amino acids containing calix[4]arenes were studied by mono- and bidimensional 1H NMR experiments. The X-ray crystal structure of the difunctionalized receptor 11 shows three different conformations in the solid state, none of them having intrachain hydrogen bonding.

Synthesis of Monoalkylated Calix(4)arenes via Direct Alkylation

A new one-step procedure for the synthesis of monoalkylated calix[4]arenes is presented. Reaction of calix[4]arene 1a or 1b with 1.2 equivalent of a weak base (K2CO3 in MeCN or CsF in DMF) and excess of alkylating agent affords the monoalkylated calix[4]arenes in moderate to good yields

Bridged calix[6]arenes in the cone conformation: New receptors for quaternary ammonium cations

Abstract The synthesis of calix[6]arene crown ethers 3 and 4 has been accomplished for the first time by selective bridging of the parent macrocycles. The alkylation of 3 with α-chloro-N,N-diethyl acetamide produces a compound 6 whose conformational flexibility is strongly reduced and which assumes a cone conformation both in solution and in the solid state. Compound 6 represents a new type of ditopic receptor which binds tetramethylammonium cation in the polar region at the lower rim, showing an association constant Ka=750 M−1 in CDCl3.

Rigidified Calixarenes Bearing Four Carbamoylmethylphosphineoxide or Carbamoylmethylphosphoryl Functions at the Wide Rim

Conformationally rigidified tetraCMPO derivatives have been prepared from calix[4]arene bis(crown ether) 4a in which adjacent oxygens are bridged at the narrow rim by two diethylene glycol links. Acylation of the tetraamine 4c with the CMPO-active ester 5b gave the tetraphosphine oxide 6a, while the tetraphosphinate 6b and the tetraphosphonate 6c were obtained by Arbuzov reaction of tetrabromoacetamido derivative 7 with PhP(OEt)2 or P(OEt)3. The extraction ability of these CMPO derivatives was checked for selected lanthanides and actinides and compared with the analogous compounds 1b, 10b and 10d derived from calix[4]arene tetrapentyl ether. All rigidified bis(crown ether) ligands are more effective extractants than their pentyl ether counterparts and require only 1/10 of the concentration (cL= 10 4M) to obtain the same distribution coefficients, while with CMPO itself a 2,000-fold concentration is necessary. This could be a consequence of a better preorganisation of the ligating functions owing to the rigidity which on the other hand did not change the observed selectivity for americium (DAm/DEu=9-19) and for light lanthanides over heavy ones. NMR relaxivity titration curves show that the complex of Gd3+ with ligand 6a is highly oligomerised in anhydrous acetonitrile over a large range of ligand:metal concentration ratios. Nuclear magnetic relaxation dispersion (NMRD) profiles also showed that large oligomers were formed, and their mean tumbling times were deduced from the Solomon-Bloembergen-Morgan equations. The NMR spectra of dia- and paramagnetic lanthanide complexes with 6a agreed with the presence of two conformers with an elongated calix[4]arene skeleton in which the distances between opposite methylene groups are different. Contrary to what was observed with ligand 2a, the addition of nitrate ions does not labilize the metal complexes, presumably because of the rigidification effect of the ether bridges. Single-crystal X-ray structures were obtained for the active ester 5b and for diphenylphosphorylacetic acid 5a.