Synthesis, characterization and solid-phase C NMR of naphtho-9-crown-3

The synthesis and characterization of naptho-9-crown-3, N9C3, as a novel 9-membered ring crown ether with greater lipophilicity than that of benzo-9-crown-3, B9C3, is reported. The solution AA′BB′ pattern of –CH₂O– protons in N9C3 is close to that of B9C3. The solid-phase ¹³C CPMAS NMR, as a tool for conformation prediction, reveals that the solid-phase conformation of the 9-membered ring crown cavity in N9C3 is different from B9C3, the two key C2O2CH₂ and C3O1CH₂ units are predicted to be out of naphthalene plane, and the two C1C2O2CH₂ and C4C3O1CH₂ torsion angles are close to each other.     

Synthesis and conformational analysis of a novel carbohydrate-fused bis-crown ether: crown-CyPLOS

A novel sugar-based macrocycle consisting of a phosphate-linked 12-membered disaccharide ring (cyclic phosphate-linked oligosaccharide, CyPLOS), fused to two 18-crown-6 ether residues, is here described. The synthesis of the target compound has been accomplished in 23% overall yield for 11 reaction steps, exploiting phosphoramidite chemistry for the dimerization and a classical phosphotriester methodology for the cyclization reaction. NMR-based conformational analysis studies have been carried out on the fully deprotected macrocycle, showing a characteristic arched-structure with C₂-symmetry.     

DDQ mediated regiospecific protection of primary alcohol and deprotection under neutral conditions: Application of new p-methoxy benzyl-pixyl ether as reagent of choice for nucleoside protection

A simple and efficient protocol is described for regiosepecific protection of primary hydroxyl group both in nucleosides and other molecules with p-methoxy-benzyl 2,7-dimethyl pixylether (MBDPE) in presence of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Furthermore, swift deprotection of 2, 7-dimethylpixyl (DMPx) is accomplished with DDQ in MeOH. Both procedures are successfully implemented on gram-scale synthesis of modified nucleosides. This protocol offers mild and neutral conditions for selective protection and deprotection of DMPx group while compatible in presence of other conventional protecting groups such as benzoyl, benzyl, THP, TBDPS and acetonide.     

Synthesis, variable temperature NMR investigations and solid state characterization of novel octafluorofluorene compounds

The preparation of a number of new 9-substituted octafluorofluorene derivatives, solution NMR studies, and the first examples of solid state structures of octafluorofluorenes [1,2,3,4,5,6,7,8-octafluorofluorene, C₁₃H₂F₈, 1; 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenylfluorene, C₁₉HF₁₃, 8; 1,1′,2,2′,3,3′,4,4′,5,5′,6,6′,7,7′,8,8′-hexadecafluoro-9,9′-bifluorenyl, C₂₆H₂F₁₆, 11] are reported. Variable temperature ¹⁹F NMR investigations have been performed on the 9-aryl substituted compounds 1,2,3,4,5,6,7,8-octafluoro-9-(pentafluoro)phenyl-9-hydroxyfluorene, C₁₉HF₁₃O, 4, 1,2,3,4,5,6,7,8-octafluoro-9-(nonafluoro-4′-biphenylyl)-9-hydroxyfluorene, C₂₅HF₁₇O, 5, and 8, and the energetic barriers to rotation of the aryl have been determined. A lower rotational barrier is observed for compound 4 with respect to compound 8, while 5 does not show fluxional behaviour below 338 K. The results of the variable temperature experiments performed on 8 have been rationalized by 2D NMR studies, and compared to the solid state data resulting from the X-ray structural analysis.     

Design and synthesis of novel imidazolium-based ionic liquids with a pseudo crown-ether moiety: diastereomeric interaction of a racemic ionic liquid with enantiopure europium complexes

A planar-chiral imidazolium salt with a tris(oxoethylene) bridge was synthesized, and its potential application as a room temperature ionic liquid with a molecular-recognition ability was demonstrated.     

Synthesis, structure, and cation complexation of a novel crown ether porphyrin

A new porphyrin appended with four crown ether units at meso-positions via an acetylene bridge was synthesized and structurally characterized, and its complexation with a variety of metal and diammonium cations was investigated.     

Synthesis and structural characterization of novel pyranoluteolinidin dyes

The synthesis and structural characterization by LC–MS and NMR of novel pyranoluteolinidin derivatives are reported. The compounds result from the reactions between luteolinidin and three different carboxylic acids in wine model-like solutions. The three pigments possess different substituents attached to the D ring (methyl, catechol and dimethylaminophenyl groups) and the same catechol group in the B ring, yielding a wide spectrum of colors from yellow to pink-purple.     

Synthesis and spectroscopic properties of a novel zinc phthalocyanine with four 17-membered crown ether voids

A novel zinc phthalocyanine containing four 17-crown-5 ether voids(17C5ZnPc) has been synthesized and characterized. UV-visible absorption and fluorescence emission spectra and as-sociated photophysical parameters have been determined. In contrast to most of the crown ether substituted phthalocyanines, no cofacial dimer formation is observed in the presence of alkali metal salts. In addition to the fluorescence at 710 nm from S1, a strong upper excited state (Soret 52) emission around 424 nm has been detected for the first time in the phthalocyanine series. Fluorescence decay of S1 and S2 emission can be analyzed by mono- and biexponential fits respectively. X-ray structure analysis showed that the crown ether unit is conformationally deformed and oblate that may account for the unusual spectroscopic properties.     

Chiral recognition in NMR spectroscopy using crown ethers and their ytterbium(III) complexes

Chiral crown ethers 1 and 5 are useful enantiomeric discriminating agents in ¹H NMR spectroscopy for neutral and protonated primary amines, amino acids, and amino alcohols. The presence of the carboxylic acid groups in 1 and 5 provide sites at which ytterbium(III) can bind. Adding ytterbium(III) nitrate to crown–substrate mixtures in methanol-d₄ causes shifts in the spectra of substrates and often enhances the chiral discrimination in the ¹H NMR spectrum. The enhancement in enantiomeric discrimination that occurs in the presence of ytterbium(III) allows lower concentrations of the crown ether to be used in chiral recognition studies. Several amide derivatives of 1 were prepared and evaluated as chiral NMR discriminating agents, although except for 1e, these were less effective than 1.     

Synthesis and characterization of novel ionophores of double-armed penta-crown ethers

Unique structures of novel ionophores of double-armed penta-crown ethers were successfully synthesized. Diaza 18-crown-6 was designed as the parent crown ring. The penta-crown ethers were prepared by the reaction of trimethylolpropane triacrylate (TMPTA) with diaza 18-crown-6 and further with 1-aza crown ethers through the Michael reaction. The newly synthesized penta-crown ethers were characterized by ¹H NMR, ¹³C NMR, FAB mass spectrum, IR and elemental analyses, respectively.     

Synthesis and characterization of novel substituted and cyclic benzoquinone derivatives

Novel substituted benzoquinone compounds were synthesized from the reactions of p-chloranil and p-fluoranil with some thiols, amines, and diols in different reaction media. Interesting cyclic compounds like crown ether structures were obtained. The structures of all compounds were characterized by spectroscopic methods and microanalysis.     

Synthesis of novel 6-substituted sulfur-containing derivatives of pyridoxine

An efficient synthesis of novel 6-substituted derivatives of pyridoxine was achieved. The reactions of various thiols with mono-, bis-, and tris(сhlorine) derivatives of 6-methyl-2,3,4-tris(hydroxymethyl)pyridin-5-ol (6-hydroxymethylpyridoxine) gave sulfur-containing derivatives of pyridoxine.     

NMR Studies of the Interaction of Catechol and Ascorbic Acid with the Crown Ether

Abstract

Various crown ethers have been electropolymerized onto a platinum electrode for the determination of catechol and catecholamines by static potentiometry and potentiometric-flow injection analysis(FIA). The response mechanism of this modified electrode was investigated by scanning electron microscopy (SEM), electron dispersive X-ray analysis (EDAX), and electron spectroscopy for chemical analysis(ESCA). However, these studies were not conclusive with respect to possible mechanisms, and, therefore, nuclear magnetic resonance (NMR) studies were carried out on similar soluble crown ethers to determine the mode of interaction. As the crown ether resonances were shifted to higher fields by the added catechol in D₂O but not d₆-DMSO, it is postulated that the crown ether and catechol associate via interactions between hydrophobic surfaces. Hydrophilic ascorbic acid showed no NMR shifts which is consistent with its lack of potentiometric response. The EDAX and ESCA results indicated that there was also an interaction of catechol with the crown itself but the NMR shows that this interaction is a secondary effect in the overall electrode response.

     

Synthesis of novel macrocyclic crown ethers from D-glucose

A simple and efficient synthetic protocol for an easy access of carbohydrate-linked crown ethers from cheap and readily available D-glucose in good yields has been devised. The base-mediated cyclization of sugar-linked bis-iodo podands in CH₃CN with amines, including ethylamine and furfurylamine afforded the novel chiral monoaza-15-crown-5-type macrocyclic crown ethers anellated to 3-O-benzyl-1,2-O-isopropylidene-α-D-glucofuranose and 3-O-benzyl-1,2-O-isopropylidene-α-D-allofuranose. The glucose-based crown ethers have been characterized by spectroscopy techniques including IR, ¹H NMR, and ¹³C NMR.     

Synthesis of selenium- and tellurium-containing nucleosides derived from uridine

The synthesis of selenium- and tellurium-containing nucleosides, derived from uridine is described herein. These compounds were prepared in a concise and short synthetic route in good yields, by nucleophilic substitution of a tosylate group by organoselenium nucleophiles.     

Synthesis and NMR characterization of a novel class of thienomorphinans

[formula: see text] Synthesis of four novel thieno derivatives 4-7 featuring the codeine skeletal backbone is reported. Characterization by 1H and 13C NMR is also discussed, along with binding profile for opioid receptors.     

Synthesis and NMR elucidation of novel penta-cycloundecane amine derivatives as potential antituberculosis agents

The synthesis and NMR elucidation of five novel penta-cycloundecane amine derivatives are reported. These compounds are potential antituberculosis agents. The (1)H and (13)C spectra showed major overlapping of methine signals of the cage skeleton making it extremely difficult to elucidate these compounds. The overlapping occurs as a result of the additions made to the carbonyl carbon (C-8/C-11) of the cage. The two-dimensional NMR technique proved to be a useful tool in overcoming this problem. All compounds reported are meso compounds thereby not only simplifying the NMR structure elucidation, but also making it indeed possible.     

Synthesis and characterization of sulphonated PEES copolymers by NMR spectroscopy

Two sulphonated PEES copolymers were synthesized by reacting 75 or 60 mol% silylated hydroquinone sulphonic acid and 25 or 40 mol% of hydroquinone with 4,4′-difluorodiphenyl sulphone. The number average molecular weights determined by GPC were 13.250 and 12.050 g/mol. In the FTIR spectra, in addition to the characteristic absorption bands due to aromatic skeleton, absorption bands associated with sulphonic acid groups were observed at ∼3500, 1172, 1080, 1026, and 706 cm⁻¹. In ¹H NMR, the aromatic proton resonance signals were observed between δ = 6.99 and 7.96 ppm. ¹³C{¹H} NMR spectra of these copolymers were complex and in order to resolve this, two-dimensional (2D) NMR techniques were utilized. Heteronuclear single quantum coherence (HSQC), total correlated spectroscopy (TOCSY), and heteronuclear multiple bond correlation (HMBC) were used for assigning the structure of the copolymers.     

Synthesis and NMR elucidation of novel amino acid cavitand derivatives

The synthesis of seven novel protected amino acid cavitands is reported. All have four pendant n-undecyl chains and ‘headgroups’ connected by a two-carbon spacer at four positions on the aromatic rings. The amino acids employed are glycine, alanine, phenylalanine, leucine, proline, tryptophan, serine, glutamine and lysine. The structures of the compounds were elucidated using one- and two-dimensional NMR techniques, which verified that all tetra-substituted cavitands have symmetrical C_4v conformation. This is the first example of a complete study for amino acid cavitand derivatives.     

Synthesis and NMR spectral assignments of novel nitrogen and sulfur heterocyclic compounds

Synthesis and NMR spectral studies of multidentate N and S heterocycles, 1,3,5-tris(N-methylbenzimidazolyl)benzene, 1,3,5-tris(benzimidazolyl)benzene,1,3,5-tris(benzothiazolyl) benzene, 2,2'-bipyridine 3,3'-bis(benzothiazolyl)benzene and 1,2,4,5-tetrakis(benzothiazolyl) benzene have been carried out. 2D (1)H-(1)H PFG-COSY as well as (1)H-(13)C single and multiple bond correlated (2D GRASP-HSQC and GRASP-HMBC) experiments have been employed to characterize the compounds. 1D NOE experiments have been useful in understanding the structure of 1,3,5-tris(N-methylenzimidazolyl)benzene.