Preparation and Evaluation of 1,3-alternate 25,27-Bis-[p-nitrobenzyloxy]-26,28-bis-[3-propyloxy]-calix[4]arene-bonded Silica Gel Stationary Phase for LC

A novel 1,3-alternate 25,27-bis-[p-nitrobenzyloxy]-26,28-bis-[3-propyloxy]-calix[4]arene-bonded silica gel stationary phase has been prepared and used for separating various selected analytes by HPLC. The effect of organic modifier and pH of the mobile phase on retention and selectivity were studied using aromatic positional isomers as an example. Application examples have been provided for separation of alkylbenzenes, PAHs, xanthine derivatives, and purine and pyrimidine bases. A selectivity comparison of the novel phase versus CalixBz and Backerbond PhenylEthyl phases has been performed.

     

Preparation and evaluation of 1,3-alternate 25,27-bis-(pentafluorobenzyloxy)-26,28-bis-(3-propyloxy)-calix[4]arene-bonded silica gel high performance liquid chromatography stationary phase

A 1,3-alternate 25,27-bis-(pentafluorobenzyloxy)-26,28-bis-(3-propyloxy)-calix[4]arene-bonded silica gel stationary phase (CalixBzF₁₀) was synthesized, structurally characterized, and used as a selector in liquid chromatography. The selectivity study of this phase was done by using fluorine-containing compounds (fluorobenzenes, fluoro-pyrimidine bases), as well as non-fluorinated analytes (non-steroidal anti-inflammatory drugs, sulfonamides, xanthines and polynuclear aromatic hydrocarbons). The effects of organic modifiers on the retention of various compounds possessing basic, acidic and neutral characteristics were studied. It was shown that only basic analytes exhibit a “U-shaped” retention profile and that retention depends on the mobile phase pH. Selectivity comparisons of the novel phase vs. the 1,3-alternate 25,27-bis-(benzyloxy)-26,28-bis-(3-propyloxy)-calix[4]arene phase (CalixBz) were performed. The retention mechanism is also discussed. The results indicate that the fluorinated calixarene stationary phase behaves like reversed-phase packing material; however, fluorine–fluorine interactions seem to be involved in the separation process of fluorine-containing analytes.     

Synthesis of di-substituted calix[4]arene-based receptors for extraction of chromate and arsenate anions

The article describes the synthesis of a family of novel calix[4]arene ionophores, 25,27-bis-(2-aminomethylpyridine-propoxy)-26,28-dihydroxycalix[4]arene (5a), 25,27-bis-(3-aminomethylpyridine-propoxy)-26,28-dihydroxycalix[4]arene (5b) and two chromogenic calix[4]arenes, 5,17-dinitro-25,27-bis-(2-aminomethylpyridine-propoxy)-26,28-dihydroxycalix[4]arene (5c), 5,17-dinitro-25,27-bis-(3-aminomethylpyridine-propoxy)-26,28-dihydroxycalix[4]arene (5d) bearing pyridinium units. In the synthesis, the upper and lower rims of p-tert-butylcalix[4]arene were modified in order to acquire binding sites for the recognition of arsenate and dichromate anions. It has been observed that protonated alkylammonium forms of the ionophores showed high affinity toward dichromate and arsenate anions.     

Preparation of a new 1,3-alternate-calix[4]arene-bonded HPLC stationary phase for the separation of phenols, aromatic amines and drugs

We have synthesized the 1,3-alternate 25,27-dioctyloxy-26,28-bis-[3-aminopropyloxy]-calix[4]arene and then immobilized onto γ-chloropropylsilica gel (CPS). The high-performance liquid chromatographic behavior of some aromatic hydrocarbons, phenolic compounds, aromatic amines and drug compounds was studied on this 1,3-alternate-calix[4]arene-bonded silica gel stationary phase (CIMS). The effect of organic modifier content and pH of the mobile phase on retention and selectivity of these compounds were investigated. According to chromatographic data, it can be concluded that the selectivity of CIMS for analytes ascribes to various interactions between CIMS and the analytes, such as hydrophobic interaction, hydrogen bonding interaction, π-π interaction and inclusion interaction.     

1,3-Alternate 25,27-dibenzoiloxy-26,28-bis-[3-propyloxy]-calix[4]arene-bonded silica gel as a new type of HPLC stationary phase

A new 1,3-alternate 25,27-dibenzoiloxy-26,28-bis-[3-propyloxy]-calix[4]arene-bonded silica gel stationary phase (1,3-Alt CalixBn) has been prepared and used for the separation of aromatic positional isomers by high-performance liquid chromatography (HPLC). The effect of organic modifier content and pH of the mobile phase on retention and selectivity of these compounds were studied. Application examples were provided for separation of purine and pyrimidine bases and non-steroidal anti-inflammatory drugs.     

Preparation and HPLC evaluation of a new 1,3-alternate 25,27-bis-[p-chlorobenzyloxy]-26,28-bis-[3-propyloxy]-calix[4]arene silica bonded stationary phase

The 1,3-alternate 25,27-bis-[p-chlorobenzyloxy]-26,28-bis-[3-propyloxy]-calix[4]arene-bonded silica gel stationary phase was synthesized, structurally characterized, and used as a selector in high performance liquid chromatography. Selectivity studies on that phase used aromatic positional isomers, alkylbenzenes, polynuclear aromatic hydrocarbons, sulfonamides, and non-steroidal anti-inflammatory drugs as analytes. The effects of organic modifier content and pH of the mobile phase on retention and selectivity of selected aromatic positional isomers were studied. Selectivity comparisons of the novel phase vs. 1,3-alternate 25,27-di-[benzyloxy]-26,28-bis-[3-propyloxy]-calix[4]arene phase and commercially available RP-Phenyl phases were performed. The retention mechanism was also discussed. The results indicated that the calixarene stationary phase behaves like a reversed-phase packing; however, other retention mechanisms seem to be involved in the separation process.     

Synthesis and spectroscopic characterization of novel 2-amino-4,5,6,7-tetrahydro-3H-cyclopenta[d]pyrimidine and pyrimido[1,2-a]pyrimidine derivatives

2-Aminocyclopenta[d]pyrimidines 3a-c were achieved via a one-pot, three-component reactions of cyclopentanone 1, aromatic aldehyde and guanidine hydrochloride (1:2:1 molar ratio). Also, cyclization of 2,5-bis-(arylmethylidene)cyclopentanones 2 with guanidine hydrochloride (1:1 molar ratio) in methanol in the presence of sodiummethoxide afforded cyclopenta-[d]pyrimidines 3. Compound 3a has been shown to be a useful building block for the synthesis of some novel pyrimido[1,2-a]pyrimidines 5, 7 and 12. The structures of the newly synthesized compounds were confirmed on the basis of analytical and spectral data.     

Synthesis and photoreactivity of aryl substituted 4,5-dithienyl[1,3]dithiol-2-ones

UV irradiation of hitherto unknown 4,5-bis-benzo[b]thiophen-3-yl-[1,3]dithiol-2-one gave 3-(3-benzo[b]thienyl)-thieno[3,4-c]benzo[e][1,2]dithiine by loss of carbon monoxide and rearrangement, whereas 4,5-bis-(2-bromo-phenyl)-[1,3]dithiol-2-one gave a polymeric material containing S-S bridges. The structures of both photoproducts were demonstrated on the basis of chemical behaviour and/or X-ray diffraction.     

Synthesis and extraction studies of polymeric phthalimido functionalized calix[4]arene

The article comprises synthesis and extraction studies of polymeric calix[4]arene having phthalimide groups at the lower rim. The polymeric phthalimido functionalized calix[4]arene was synthesized via radical initiated reactions involving a vinylic monomer 5,11,17,23-tetra-tert-butyl-25-[4-(acrylamido)benzyloxy]-26,28-bis-(2-phthalimido-ethoxy)-27-hydroxycalix[4]arene (5) with styrene. A five atom spacer group was incorporated between the bulky calixarene core and the acrylate moiety in order to minimize steric interactions which proved to impede the polymerization. From the liquid–liquid and solid–liquid extraction studies it has been concluded that the precursor 3 (5,11,17,23-tetra-tert-butyl-25-(4-nitro benzyloxy)-26,28-bis-(3-phthalimidoethoxy)-27-hydroxy-calix[4]arene) is selective for metal cations. The order of extractability of metal cations by the ligand 3 decreases in the sequence: Hg²⁺ > Cd²⁺ > Cu²⁺ > K⁺ > Co²⁺ whereas its polymeric derivative is selective in the sequence: Hg²⁺ > Cd²⁺ > K⁺ > Co²⁺ > Cu²⁺ for the metal cations used in the experiments.     

A facile one-pot regioselective synthesis of functionalized novel benzo[f]chromeno[4,3-b][1,7]naphthyridines and benzo[f][1,7]naphthyridines via an imino Diels-Alder reaction

A novel series of functionalized 13H-benzo[f]chromeno[4,3-b][1,7]naphthyridines and 1,3-diphenylbenzo[f][1,7]naphthyridines have been synthesized by an efficient regioselective one-pot multicomponent synthesis through intra and intermolecular imino Diels-Alder reaction. In this method, we have achieved complete regioselectivity and atom economy with polysubstituted core motifs in moderate to good yields. The proposed mechanism of this reaction has also discussed.     

Synthesis of conformationally diverse tetrathiacalix[4]arene(amido)crowns and tetrathiacalix[4]arene amides with pendant amine functions

A series of conformationally diverse novel tetrathiacalix[4]arene(amido)crowns and amides from tetrakis((ethoxycarbonyl)methoxy)p-tert-butyl tetrathiacalix[4]arene and its debutylated analog have been prepared by their reaction with diamines [H₂N(CH₂)_nNH₂; n=2,3,4, and 6] and polyamines. It has been determined that the length of the alkyl spacer in diamines is pivotal for the formation of either the tetrathiacalix[4]arene bis(amido)crowns or tetrathiacalix[4]arene amides with pendant amine functions. The synthesized compounds represent potential building blocks for achieving sophisticated molecular assemblies for molecular organization and recognition. Single crystal X-ray analysis of tetrathiacalix[4]arene bis(amido)crown 6a revealed that it has a 1,3-alternate conformation, which forms supramolecular complexes with chloroform.     

Oxidative azacyclization of 1-monosubstituted thioureas in reaction with [bis(acyloxy)iodo]arenes to form 1,2,4-thiadiazole derivatives

For the first time, derivatives of 1,2,4-thiadiazoles have been obtained by the reaction of [bis(acyloxy)iodo]arenes with 1-monosubstituted thioureas. 1-Acetylthiourea is subject to intermolecular azacyclization to form 3,5-bis-(acetylamino)-1,2,4-thiadiazole in reaction with [bis(acyloxy)iodo]benzene. 1-Phenylthiourea forms 3,5-bis-(phenylamino)-1,2,4-thiadiazole in a single-stage reaction with (diacetoxyiodo)benzene. The reaction of 1-phenylthiourea with [bis(trifluoroacetoxy)iodo]benzene leads to the formation of 5-imino-4-phenyl-3-phenylamino-4H-1,2,4-thiadiazoline.     

Efficient route to benzo[4,5]imidazo[2,1-a]phthalazines

Benzo[4,5]imidazo[2,1-a]phthalazines have been obtained from various o-nitrophenylhydrazines through different 2-(2-nitrophenyl)-1,2-dihydro-1-phthalazinones as intermediates using an elaborated advanced procedure. An activated chlorine atom in 2-nitrophenyl moiety of the latter is able to undergo nucleophilic substitution for secondary alicyclic amines yielding novel substituted phthalazinones. Their one-pot reduction and cyclodehydration yield a series of novel substituted benzo[4,5]imidazo[2,1-a]phthalazines.     

Interaction between cucurbit[6]uril and bispyridinecarboxamide

The interaction between cucurbit[6]uril and N,N′-(m-bispyridinecarboxamide)-1,n-alkane (m = 2, 3, 4; n = 4, 6, 8) has been investigated by ¹H-NMR, ESI-MS and single crystal X-ray diffraction method. The results show that cucurbit[6]uril can form pseudorotaxanes with N,N′-(m-bispyridinecarboxamide)-1,6-hexane (m = 2, 3, 4) easily. When the alkyl chain length increases (n = 8), the binding mode is identical, but the binding ability of the host towards guest decreases. In both two cases cucurbit[6]uril shows no selectivity towards positional isomers. However, in the case of n = 4, the binding mode is different, having relations with positional substitution of the guest. Only N,N′-(m-bispyridinecarboxamide)-1,4-butane (m = 2) can form pseudorotaxane with cucurbit[6]uril, while the other two (m = 3, m = 4) form external complex with cucurbit[6]uril. The possible reason for the difference has been discussed.     

Di-ionizable p-tert-butylcalix[4]arene-1,3-crown-4 ligands: synthesis and alkaline earth metal cation extraction

A series of di-ionizable calix[4]arene-1,3-crown-4 compounds has been synthesized. The ionizable groups are oxyacetic acid and N-(X)sulfonyl oxyacetamide groups with X=methyl, phenyl, 4-nitrophenyl and trifluoromethyl, which ‘tunes’ the acidity of the latter. The efficiency and selectivity of these novel ligands are assessed with competitive solvent extractions of alkaline earth metal cations from aqueous solutions into chloroform. The results are compared with those reported previously for calix[4]arene-crown analogues with crown-6 and crown-5 rings.     

An efficient synthesis of 9H-pyrrolo[1,2-a]indoles

A novel and effective method has been developed for the synthesis of 9H-pyrrolo[1,2-a]indoles by treatment of 3-substituted-4,6-dimethoxyindoles with chalcones in the presence of hydrochloric acid.     

A novel three-component method for the synthesis of spiro[chromeno [4′,3′:4,5] pyrimido[1,2-b] indazole-7,3′-indoline]-2′,6(9H)-dione

A green, efficient, and rapid procedure for the synthesis of novel spiro[chromeno[4′,3′:4,5] pyrimido[1,2-b]indazole-7,3′-indoline]-2′,6(9 H)-dione derivatives has been developed by one-pot condensation of 4-hydroxy-2H-chromen-2-one, isatin, and 1H-indazole-3-amine, in the presence of acetic acid in EtOH. This method has the advantages of operational simplicity, and high yield of products via a simple experimental and work-up procedure as compared to the conventional methods. The reaction mechanism and substrate scope of this novel reaction is briefly discussed.     

Synthesis and structure of a chiral areno-bridged [2.4]metacyclophane

The reductive coupling reaction of 1,4-bis(3-acetyl-5-tert-butyl-2-methoxyphenyl)butane 3 was carried out using TiCl₄-Zn in pyridine followed by a McMurry coupling reaction to afford the compounds anti and syn 1,2-dimethyl[2.4]MCP-1-ene 4. Bromination of 4 with BTMA-Br₃ in dry CH₂Cl₂ afforded the interesting compound 1,2-bis-(bromomethyl)-5,15-di-tert-butyl-8,18-dimethoxy[2.4]MCP-1-ene 6 and consecutive debromination with Zn and AcOH in CH₂Cl₂ solution afforded the stable solid 5,15-di-tert-butyl-8,18-dimethoxy-1,2-dimethylene[2.4]MCP 7 in 89% yield. Compound 7 was conveniently employed in a Diels–Alder reaction with dimethyl acetylenedicarboxylate (DMAD) to provide 2-(3′,6′-dihydrobenzo)-5,15-di-tert-butyl-8,18-dimethoxy[2.4]MCP-4′,5′-dimethylcarboxylate 8 in good yield. Diels–Alder adduct 8 was converted into a novel and inherently chiral areno-bridged compound [2.4]MCP 9 by aromatization. The chirality of the two conformers was characterized by circular dichroism (CD) spectra of the separated enantiomer which are perfect mirror images of each other.     

Regioselective synthesis of C-prenylated flavonoids via intramolecular [1,3] or [1,5] shift reaction catalyzed by acidic clays

Prenyl side chain and dihydropyrano skeleton exists in many natural and synthetic biologically active flavonoids. A highly efficient and regioselective method for the synthesis of C-prenylated flavonoids via intramolecular [1,3] or [1,5] shift reaction of 5-O-prenylflavonoids catalyzed by Florisil or Montmorillonite clays is described. Florisil catalyzes intramolecular [1,5] shift reaction of 5-O-prenylflavonoids to obtain 8-C-prenylated flavonoids exclusively, Montmorillonite K10 exhibits the superior selectivity to promote intramolecular [1,3] shift reaction to obtain 6-C-prenylated flavonoids compared with Florisil and Montmorillonite KSF. This method provides a practical process to regioselective synthesize biologically important C-prenylated flavonoids in good yields using commercially available and inexpensive catalyst under mild conditions.     

Mercury(II) and silver(I) receptors based on tetrathiacalix[4]arene hydrazones

The extraction ability of phenyl hydrazone derivatives of cone- and 1,3-alternate tetrathiacalix[4]arenes towards to some alkali, alkaline earth, transition and heavy metal ions has been investigated by picrate extraction method. The synthesized cone-tetrathiacalix[4]arene hydrazones show a high efficiency coupled with an excellent selectivity towards for Ag⁺ and Hg²⁺ ions. The stoichiometry of complexes and the extraction constants have been determined. The influence of calix[4]arene platform’s structure and the electron donor substituents in phenyl fragments on the extraction efficiency has been discussed.