Discovery of carboxypeptidase Y as a catalyst for the incorporation of sterically demanding α-fluoroalkyl amino acids into peptides

The first example of a direct enzymatic coupling of two different, sterically demanding C^α-fluoroalkyl amino acids to amino acid nucleophiles is reported. N-Protected Ala methyl ester derivatives bearing a methyl-, difluoromethyl-, or trifluoromethyl group, respectively, instead of the α-proton were accepted as substrates by carboxypeptidase Y and could, therefore, be coupled directly to various nucleophiles.     

Heterocyclic Rearrangement of 4,5,6,7-Tetrahydro-6,6-dimethyl-benzo[c][1,2,5]oxadiazol-4-one (Z)-Arylhydrazones into Corresponding 2-Aryl-4,5,6,7-tetrahydro-2H-benzo[d][1,2,3]triazol-4-one Oximes

The thermal base-catalysed and photochemical transformation (Boulton-Katritzky rearrangement) of the title tetrahydrobenzo[c][1,2,5]oxadiazoles to tetrahydro-2H-benzo[d][1,2,3]triazoles is studied. Attempts to induce analogous rearrangement in tetrahydro-2H-benzo[d][1,2,3]triazol-4-one arylhydrazones or oximes failed. Some CNDO/2 calculation are also carried out.     

Mechanism of the reaction of 2-methoxybenzo[d][1,3,2]dioxaphosphinin-4-one with chloral by quantum-chemical calculations

Quantum-chemical calculations of various stereoisomers, intermediates, and transition states of the reaction of 2-methoxybenzo[d][1,3,2]dioxaphosphinin-4-one with chloral, leading to formation of 2-methoxy-3-(trichloromethyl)benzo[e[1,4,2 ⁵]dioxaphosphepin-2,5-dione, were carried out by the density functional theory (DFT) method with the PBE functional and Triple z basis, using the Priroda program. The first step of the reaction is [1+2] cycloaddition of phosphorus to the chloral C=O bond to form an intermediate with a five-coordinate phosphorus atom via a transition state in which the positive and negative charges are strongly localized on phosphorus and chloral oxygen, respectively. Calculations of the internal reaction coordinate from all transition states were carried out.     

Titanium isopropoxide complexes of a series of sterically demanding aryloxo based [N2O2]2- ligands as precatalysts for ethylene polymerization

Several titanium isopropoxide complexes [N,N'-bis(2-oxo-3-R(1)-5-R(2)-phenylmethyl)-N,N'-bis(methylene-p-R(3)-C(6)H(4))-ethylenediamine]Ti(O(i)Pr)(2) [R(1) = t-Bu, R(2) = Me, R(3) = H (1b); R(1) = R(2) = t-Bu, R(3) = H, (2b); R(1) = R(2) = Cl, R(3) = H, (3b), R(1) = t-Bu, R(2) = Me, R(3) = Cl (4b); R(1) = R(2) = t-Bu, R(3) = Cl, (5b); R(1) = R(2) = R(3) = Cl, (6b)] supported over sterically demanding aryloxy based [N(2)O(2)]H(2) ligands have been designed as precatalysts for the ethylene polymerization. Specifically, the 1b-6b complexes, when treated with methylaluminoxane (MAO) under 88 ± 0.5 psi of ethylene at 30 °C for 3 h, produced polyethylene polymers of high molecular weight (M(w) = ca. 7.2-8.3 × 10(5) g mol(-1)) having broad molecular weight distribution (PDI = ca. 13.1-14.6). The 1b-6b complexes were conveniently synthesized from the direct reaction of the [N(2)O(2)]H(2) ligands, 1a-6a, with Ti(O(i)Pr)(4) in 69-86% yield.     

Vanillin esters of aromatic carboxylic acids in the synthesis of benzo[a]acridine and benzo[b][4,7]phenanthroline derivatives

By condensation of vanillin esters of substituted benzoic acids with 2-naphthylamine and 6-quinolylamines and also with cyclic β-diketones (1,3-cyclohexanedione and dimedone) 2-methoxy-4-(11-oxo-7,8,9,10,11,12-hexahydrobenzo[a]acridin-12-yl)-and 2-methoxy-4-(11-oxo-7,8,9,10,11,12-hexahydrobenzo[b][4,7]-phenanthrolin-12-yl)phenyl benzoates were prepared.     

TiO2 nanoparticles as an effective catalyst for the synthesis of hexahydro-2-quinolinecarboxylic acids derivatives

The one-pot three-component reaction of arylmethylidenepyruvic acids,1,3-cyclohexandiones and ammonium acetate provides an economical and efficient synthetic route to 5-oxo-4-aryl-l,4,5,6,7,8-hexahydro-2-quinolinecarboxylic acid 4 under solvent-free conditions using a catalytic amount of TiO₂ nanoparticles（TiO₂ NPs） as an effective heterogeneous catalyst.     

Ammounium acetate as a catalyst of the condensation of sterically hindered functionalized hydroxylamines with ketones

Ammonium acetate was found to be a catalyst of the condensation of α-hydroxylamino oximes and α-hydroxylamino alcohols with ketones. This condensation leads to sterically hindered heterocyclic hydroxylamines, which are precursors of stable nitroxides.     

FTIR investigation of the O-H[middle dot][middle dot][middle dot]Xe interaction in simple carboxylic acids in solid xenon

The O-H stretching region of the infrared spectra of a series of carboxylic acids in Xe matrices was investigated as a function of temperature. Upon increasing the temperature, the νO-H band site-components undergo reversible frequency blue-shifts, which are larger for the lowest-frequency components. This unprecedented observation indicates both that different types of O-H[middle dot][middle dot][middle dot]Xe specific interactions occur, depending on different trapping sites, and the prevalence of stronger interactions of this type for molecules trapped in sites corresponding to lower frequency νO-H band site-components. These results are in agreement with previous investigations pointing to an increased stabilization and larger νO-H frequency red-shifts in carboxylic acid∕Xe complexes bearing a specific H-bond like O-H[middle dot][middle dot][middle dot]Xe interaction. O-H[middle dot][middle dot][middle dot]Xe interaction energies were obtained theoretically and also estimated from the spectroscopic data. Changes in the interaction energies upon temperature variation were also evaluated.     

[Bmim]N3 as an efficient reagent for the Schmidt reactions of ketones,arylaldehydes and aromatic carboxylic acids

Schmidt reaction of arylaldehydes, ketones and aromatic carboxylic acids using task-specific ionic liquid, [bmim]N₃ in the presence of AcOH/H₂SO₄ proceeds at 50–60 °C within 2–4 h to give the corresponding products. Benzaldehydes containing electron releasing groups afforded to the related benzamide derivatives. Benzonitrile derivatives were formed from the reaction of benzaldehydes containing electron withdrawing groups under these conditions. High yields of the related amides and anilines were obtained from the reaction of a variety of ketones and aromatic carboxylic acids, respectively, utilizing this procedure.     

Structural and functional mimic of galactose oxidase by a copper complex of a sterically demanding [N2O2] ligand

A structural and functional mimic of the galactose oxidase (GOase) enzyme active-site by a copper complex supported over a sterically demanding ligand having [N2O2] donor sites is reported. Specifically, the binding of the histidine (496 and 581) and tyrosine (272 and 495) residues to the copper center in a square-pyramidal fashion in the active-site of galactose oxidase (GOase) enzyme has been modeled in a copper complex, ([(3-tert-butyl-5-methyl-2-hydoxybenzyl)(3'-tert-butyl-5'-methyl-2'-oxobenzyl)(2-pyridylmethyl)]amine)Cu(OAc)) (1b), stabilized over a sterically demanding ligand in which the two phenolate-O atoms mimicked the tyrosine binding while an amine-N and pyridyl-N atoms emulated the histidine binding to the metal center, similar to that in the enzyme active-site. Furthermore, the copper complex 1b is found to be an effective functional model of the enzyme as it efficiently catalyzed the chemoselective oxidation of primary alcohols to aldehydes in high turnover numbers under ambient conditions. An insight into the nature of the active-species was obtained by EPR and CV studies, which in conjunction with the DFT studies, revealed that the active-species is an anti-ferromagnetically coupled diamagnetic radical cation, (1)1b+, obtained by one electron oxidation at the equatorial phenolate-O atom of the ligand in the 1b complex.     

Protic ionic liquid [TMG][Ac] as an efficient,homogeneous and recyclable catalyst for Boc protection of amines

An efficient and practical protocol for the chemoselective N-Boc protection of various structurally different aryl, aliphatic and heterocyclic amines was carried out with (Boc)₂O using protic 1, 1, 3, 3-tetra-methylguanidinium acetate (10 mol%) as recyclable catalyst under solvent free condition at ambient temperature. No competitive side reactions (isocyanate, urea and N, N-di-Boc) were observed. α-Amino alcohols afforded the N-Boc-derivative without oxazolidinone formation.     

A new 2D cadmium coordination polymer based on hydroxyl-substituted benzenedicarboxylic acid as an effective heterogeneous catalyst for Knoevenagel condensation

A self-assembled new 2D cadmium network, [Cd (BDC-OH)(DMF)₂·DMF]_n (Cd-BDC-OH), was synthesized based on 2-hydroxyterephthalic acid (BDC-OH) ligand and utilized as a heterogeneous catalyst for Knoevenagel condensation. The structure was fully elucidated by single-crystal X-ray diffraction, Hirshfeld surface analysis, powder X-ray diffraction, field emission-scanning electron microscopy, Fourier transform-infrared spectroscopy and thermogravimetric analysis. The fabricated coordination polymer exhibited high catalytic activity under ambient conditions, and was used without significant drop in product yield in further cycles.     

1,3-Benzothiazole-2-selenenyl chloride in the synthesis of 2,3-dihydrobenzo[d][1,3]selenazolo[2,3-b][1,3]thiazolium-4 derivatives

Cycloaddition of 1,3-benzothiazole-2-selenenyl chloride to alkenes leads to 2,3-dihydrobenzo[d][1,3]selenazolo[2,3-b][1,3]thiazolium-4 derivatives.     

Triethylamine as an effective catalyst for the reaction of CO2 with epichlorohydrin

Tertiary amines were shown to catalyze efficiently the reaction of CO₂ with epichlorohydrin at 60°C and atmospheric pressure. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1442‐1444, July, 1998.     

Reaction of 2,2,2-trichlorobenzo[d]-1,3,2-dioxaphosphole-5-carbonylchloride with phenylacetylene: predominant formation of 2-(2-chloro-2-phenylethenyl)-2,2-dichlorobenzo[d]-1,3,2-dioxaphosphole-5-carbonylchloride

The reaction of 2,2,2-trichlorobenzo[d]-1,3,2-dioxaphosphole-5-carbonylchloride with phenylacetylene in benzene (80 °C) afforded 2-(2-chloro-2-phenylethenyl)-2,2-dichlorobenzo[d]-1,3,2-dioxaphosphole-5-carbonylchloride (yield >95%) as a result of the electrophilic cis-addition of the phosphorus(v) derivative at the triple bond of acetylene with retention of coordination of the P atom. Hydrolysis of this compound affords predominantly 2-hydroxy-5-(hydroxycarbonyl)phenyl (2-chloro-2-phenylethenyl)phosphonate. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 377–379, February, 2006.     

Synthesis and antimicrobial of some new substituted tetrazolomethylbenzo[d]-[1,2,3]triazole derivatives using 1H-benzo[d][1,2,3]triazole as starting material

A series of tetrazolomethylbenzo[d][1,2,3]triazole derivatives (2–14) have been synthesized and evaluated as antimicrobial agents from 1H-benzo[d][1,2,3]triazole (1) as starting material. The reaction of benzotriazole 1 with chloroacetonitrile afforded 2-(1H-benzo[d][1,2,3]-triazol-1-yl)acetonitrile 2, which was reacted with sodium azide to give tetrazole derivative 3. Esterification of benzotriazole 1 with ethyl bromoacetate in the presence of anhydrous potassium carbonate afforded ester 4, which was treated with hydrazine hydrate to afford the corresponding hydrazide 5. Reaction of 3 with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide afforded the nitro-glycoside derivative 6, which was deacetylated using methanolic ammonia to deprotected nitroglycoside 7. The hydrazide 5 was reacted with 4,5,6,7-tetrachlorophthalic anhydride or 1,2,4,5-benzenetetracarboxylic dianhydride in refluxing glacial acetic acid to give the corresponding imides 8 and 9, respectively. Also, the hydrazide 5 was reacted with carbon disulphide in ethanol to give potassium salt 10, which was reacted with hydrazine hydrate to afford aminotriazole derivative 11. The latter compound was reacted with carbon disulphide to afford thiadiazole derivative 12, which was treated with 2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl bromide to give the thioglycoside derivative 13. Deacetylation of the thioglycoside 13 using methanolic ammonia solution at room temperature afforded the deprotected thioglycoside 14. The antimicrobial screening of some synthesized compounds showed that many of these compounds have good antimicrobial activities comparable to streptomycin and fusidic acid as reference drugs.     

2-Hydroxy-1,2,2-triphenylethanone as an efficient photolabile protecting group for carboxylic acids

The synthesis is reported of 2-hydroxy-1,2,2-triphenylethanone esters of carboxylic acids by the reaction between 2-chloro-1,2,2-triphenylethanone and a carboxylic acid in the presence of silver carbonate and silver tetrafluoroborate. Photolysis of the esters occurs rapidly on irradiation with a medium-pressure mercury lamp through quartz or Pyrex to return the carboxylic acid. The side product of the photolysis is benzo[b]phenanthro[9,10-d]furan, formed through a tandem process involving initial generation of 2,3-diphenylbenzofuran, photochemical cyclisation and re-aromatisation by aerial oxidation.