Enhancement of Acid‐Catalyzed Esterification by the Addition of Base

General acid‐catalyzed reaction can be enhanced by the addition of base. Self‐catalyzed esterification of benzoic acid and octan‐1‐ol was enhanced by the addition of certain base such as imidazole. The rate of the esterification was accelerated as the concentration of imidazole increased. Trans‐esterification of 4‐nitrophenyl acetate was promoted in chloroform by the mixture of benzoic acid and imidazole, but not by benzoic acid or imidazole alone.     

SYNTHESIS AND NMR SPECTROSCOPIC STUDY OF NEW 5-METHYLFURYL-CONTAINING SCHIFF BASES AND RELATED BIS(AMINOPHOSPHONATES)

The synthesis of three novel 5-methylfuryl-containing Schiff bases: N,N′-bis(5-methylfurfurylidene)-4,4′-diaminodiphenylmethane, N,N′-bis(5-methylfurfurylidene)-1,4-phenylenediamine, and N,N′-bis(5methylfurfurylidene)benzidine and the corresponding bis(aminophosphonates) derived from them, 4,4′-bis{N-methyl(diethoxyphosphonyl)-1-[(5-methyl)-2-furyl]} diaminodiphenylmethane, 1,4-bis { N-methyl(diethoxyphosphonyl)-1-[(5-methyl)-2-furyl]} diaminobenzene, and bis{N-methyl(diethoxyphosphonyl)-1-[(5-methyl)-2-furyl]}- benzidine, is reported. The compounds have been characterized by elemental analysis, TLC, IR, and NMR ( ¹ H, ¹³ C, and ³¹ P) spectra. For comparison, new ¹³ C and ³¹ P NMR data of three furyl-containing analogues of the above bis(aminophosphonates) are also regarded. The NMR studies of the two series of bis(aminophosphonates) reveal the presence of one diastereomer (meso or racemic form).     

One-bond 1J(15N,H) coupling constants at sp2-hybridized nitrogen of Schiff bases,enaminones and similar compounds: A theoretical study

¹J(¹⁵N,H) coupling constants for enaminones and NH-forms of intramolecularly hydrogen-bonded Schiff bases as model compounds for sp²-hybridized nitrogen atoms are evaluated using density functional theory (DFT) to find the optimal functionals and basis sets. Ammonia is used as a test molecule and its one-bond coupling constant is compared with experiment. A methylamine Schiff base of a truncated molecule of gossypol is used for checking the performance of selected B3LYP, O3LYP, PBE, BHandH, and APFD density functionals and standard, modified, and dedicated basis sets for coupling constants. Both in vacuum and in chloroform, modeled by the simple continuum model of solvent, the modified basis sets predict significantly better the ¹J(¹⁵N,H) value in ammonia and in the methylamine Schiff base of a truncated molecule of gossypol than the standard basis sets. This procure is then used on a broad set of intramolecularly hydrogen-bonded molecules, and a good correlation between calculated and experimental one-bond NH coupling constants is obtained. The ¹J(¹⁵N,H) couplings are slightly overestimated. The calculated data show for hydrogen-bonded NH interatomic distances that the calculated values depend on the NH bond lengths. The shorter the bond lengths, the larger the ¹J(¹⁵N,H). A useful correlation between ¹J(¹⁵N,H) and NH bond length is derived that enables realistic predictions of one-bond NH coupling constants. The calculations reproduce experimentally observed trends for the studied molecules.     

Synthesis,spectroscopic characterization,thermal behaviour,in vitro antimicrobial and anticancer activities of novel ruthenium tricarbonyl complexes containing monodentate V‐shaped Schiff bases

The interaction of Ru₃(CO)₁₂ with a novel family of monodentate V‐shaped Schiff base ligands (L^1–4; L¹: (E)‐1‐(4‐((4‐bromobenzylidene)amino)phenyl)ethanone, L²: (E)‐1‐(3‐(4‐(dimethylamino)benzylideneamino)phenyl)ethanone, L³: (E)‐1‐(4‐(4‐(dimethylamino)benzylideneamino)phenyl)ethanone, L⁴: (E)‐1‐(3‐(3,4‐dimethoxybenzylideneamino)phenyl)ethanone) in air under atmospheric pressure afforded the novel complexes [Ru(CO)₃(L^1–4)₂]. The parent ligands and their complexes were characterized using elemental analyses and spectroscopic techniques. In addition, the structure of the representative ligand L¹ was determined using single‐crystal X‐ray analysis. The stereochemistry and theoretical optimization of the three‐dimensional geometry of the ligands and their complexes were justified. In vitro antimicrobial screening against bacterial stains Escherichia coli and Staphylococcus aureus and fungus Candida albicans was conducted. Cytotoxicity of the compounds as anti‐tumour agents was evaluated against liver carcinoma (HepG2), breast carcinoma (MCF7) and colon carcinoma (HCT‐116) cell lines relative to cisplatin and doxorubicin. The complexes showed variable in vitro cytotoxic activities against the three studied cell lines, with IC₅₀ values less than those of cis‐platin, and thus appear to be building blocks for promising anti‐tumour agents.     

Preparation,characterizations and biological evaluations of new copper(II) complexes containing ONO pincer type ligands

A new heterocyclic Schiff bases, 6‐methyl/8methyl‐2‐oxo‐1,2‐dihydroquinoline‐3‐carboxaldehyde semicarbazones (H₂‐6MOQsc‐H) ( H ₂ L ¹ ) and (H₂‐8MOQsc‐H) ( H ₂ L ² ) and their corresponding copper(II) complexes [CuCl₂(H₂‐6MOQsc‐H)].3H₂O ( 1 ), [CuCl₂(H₂‐8MOQsc‐H)].3H₂O ( 2 ), [CuNO₃(H₂‐6MOQsc‐H)(H₂O)].NO₃ ( 3 ) and [CuNO₃(H₂‐8MOQsc‐H)(H₂O)].NO₃ ( 4 ) have been synthesized and characterized by various physicochemical techniques. The single crystal X‐ray diffraction and spectral data revealed that all of the complexes ( 1‐4 ), the ligands coordinated to the Cu(II) ion in a neutral manner via ONO donor atoms and all the complexes exhibited distorted squarepyramidal geometry. The consequence of electronegativity and ring size of nitrogen heterocyclic moiety of ONO donor type of copper(II) chelates on nucleic acid interaction and albumin binding was investigated by in vitro experiments. The interaction of compounds with calf‐thymus DNA (CT‐DNA) has been explored by absorption and emission titration, which exposed those ligands/complexes, could bind with CT‐DNA through electrostatic interaction. The results of gel electrophoresis proved the ability of complexes ( 1‐4 ) to cleave the pBR322 plasmid DNA. The interaction of serum albumin (BSA) was investigated by UV‐Vis, fluorescence, synchronous and three dimensional fluorescence spectra. In addition, radical scavenging activity, antifungal activity and cytotoxicity of the newly synthesized compounds were also evaluated. From the results of in vitro studies, it is seen that complex 3 has more potential as compared with other complexes and ligands.     

Tributyltin(IV) Schiff base complexes with amino acid derivatives: synthesis,characterization and biological activity

The synthesis in one‐pot reactions and structural characterization of six new tri‐n‐butyltin(IV) derivatives of Schiff bases are reported. The compounds are derived from a condensation reaction between l ‐alanine, l ‐valine, l ‐isoleucine, l ‐methionine, l ‐phenylalanine or l ‐tryptophan and 3,5‐di‐tert‐butyl‐2‐hydroxybenzaldehyde. Characterization was completed using elemental analysis, infrared spectroscopy, mass spectrometry, one‐ and two‐dimensional solution NMR (¹H, ¹³C and ¹¹⁹Sn) as well as solid‐state ¹¹⁹Sn NMR. In addition, the crystal structures of three of the compounds were confirmed using single‐crystal X‐ray diffraction. Although five‐coordinated and polymeric in the solid state, the tin compounds are four‐coordinated and monomeric in solution. The coordination environment around the triorganotin units comprises three carbon atoms and two oxygen atoms from two ligands in a trigonal bipyramidal geometry. The anti‐proliferative effect of these compounds on the cervical carcinoma cell lines HeLa, CaSki and ViBo was screened in vitro, the compounds showing cytotoxic activity against all three strains and null or low cytotoxic activity (necrotic) as well. Copyright © 2016 John Wiley & Sons, Ltd.     

Development of chiral heteroleptic magnesium amides; asymmetric deprotonations mediated by six-membered metallocyclic amidomagnesium naphtholates

A series of enantioenriched six-membered metallocyclic amidomagnesium naphtholates were prepared and used to probe the structure–reactivity/selectivity relationships of heteroleptic magnesium base complexes within asymmetric deprotonation reactions. An effective complex was identified and applied within enantioselective enolisation processes, delivering good levels of enantioselectivity and also revealing key structural requirements for achieving such selectivity.     

Preparation of Chiral Amino Esters by Asymmetric Phase‐Transfer Catalyzed Alkylations of Schiff Bases in a Ball Mill

The asymmetric alkylation of Schiff bases under basic conditions in a ball mill was performed. The starting Schiff bases of glycine were prepared beforehand by milling protected glycine hydrochloride and benzophenone imine, in the absence of solvent. The Schiff base was then reacted with a halogenated derivative in a ball mill in the presence of KOH. By adding a chiral ammonium salt derived from cinchonidine, the reaction proceeded asymmetrically under phase‐transfer catalysis conditions, giving excellent yields and enantiomeric excesses up to 75 %. Because an equimolar amount of starting material was used, purification was greatly simplified.