Conversion of d‐Galactose to d‐threo‐Hexos‐2,3‐diulose by Fungal Pyranose Oxidase

Pyranose oxidase (pyranose:O₂ 2‐oxidoreductase, EC 1.1.3.10) purified from mycelia of the basidiomycete fungi Trametes versicolor and Oudemansiella mucida catalyzed oxidation of d‐galactose successively at C‐2 and C‐3 to d‐threo‐hexos‐2,3‐diulose (2,3‐dehydro‐d‐galactose, 2,3‐diketo‐d‐galactose) in the yields up to 80%. The sites of oxidation were deduced from structures of the N,N‐diphenylhydrazone derivatives of the reaction products. Under the reaction conditions used, the diulose was susceptible to non‐enzymatic oxidative decarboxylation to d‐threo‐pentos‐2‐ulose (2‐dehydro‐d‐xylose, 2‐keto‐d‐xylose) in yields of 5–10%.     

Crystal Structures of β‐1‐N‐Chloroacetamido Derivatives of d‐Glucose and d‐Galactose

Crystal structures of 1‐N‐(β‐d‐glucopyranosyl)chloroacetamide (1), an inhibitor of glycogen phosphorylase, and the corresponding galactopyranosyl amide (2) have been determined. Both crystals belong to P2₁2₁2₁ space group with 1 having the unit cell dimensions of a = 7.939(3), b = 9.547(3) and c = 14.157(2) Å, while those of 2 are, a = 7.636(10), b = 9.004(8) and c = 14.807(5) Å. The sugar ring takes a ⁴ C ₁ conformation and the amide linkage exists in Z‐anti conformation in both crystals. The torsion angle O5–C1–N1–C1′ is ? 93.9(5) for 1 and ? 111.5(3)° for 2. The conformational preference of Cl and N1 in 1 and 2 is found to be between anti and gauche. The molecular assembly in both 1 and 2 is stabilized by a finite chain of hydrogen bonds starting from N1H and ending at O1′, whereas a ten membered hydrogen‐bonded ring involving O4H and O5 is observed in 1.     

Practical One‐Pot Procedure for the Synthesis of 1,2,3,4‐Tetrahydroquinolines by the Imino‐Diels‐Alder Reaction

A novel‐one‐pot procedure for the synthesis of tetrahydroquinolines via the imino‐Diels‐Alder reaction is described. This procedure gives better yields and exhibits better versatility for alkene substrates than the existing hemi‐aminal based methodologies.     

Catalysis of the Reaction of Cholesteryl Acetate with 4‐Phenyl‐1,2,4‐triazoline‐3,5‐dione by Lithium Perchlorate

Abstract

The 3β‐acetoxy‐6β‐(3,5‐dioxo‐4‐phenyl‐[1,2,4]triazolidin‐1‐yl)cholest‐4‐ene structure has been assigned to a single product of the reaction of cholesteryl acetate with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione in Et₂O solution, mediated by LiClO₄.     

Solid‐Phase Synthesis of N‐Aryl‐N′‐Carboalkoxy Guanidines by the Mitsunobu Reaction of Fmoc‐Guanidines

Abstract

A new method for the solid‐phase synthesis of N‐aryl‐N′‐carboalkoxy guanidines is described. Aromatic amines were reacted with Fmoc‐isothiocyanate to provide Fmoc‐thioureas, which were coupled with Rink amide resin to provide the corresponding resin‐bound Fmoc‐guanidines. Subsequent Mitsunobu alkylation with a variety of alcohols delivered N‐aryl‐N′ carboalkoxy guanidines in good to high purity after resin cleavage.     

Sydnones as Masked Hydrazines for the Synthesis of 4‐Arylazo‐1,2‐dihydro‐pyrazol‐3‐one Derivatives

A simple and convenient one‐pot synthesis of 4‐(4‐chlorophenylazo)‐5‐methyl‐2‐aryl‐1,2‐dihydro‐pyrazol‐3‐ones (4a–j) has been carried out from 3‐arylsydnones (3a–j) by reaction with 2‐(4‐chlorophenyl)‐hydrazono‐3‐oxo‐butyric acid ethyl ester (2b). The 3‐arylsydnones are used as masked hydrazines in this reaction. Similarly, the 4‐arylazo‐2‐(7‐hydroxy‐4‐methyl‐2‐oxo‐2H‐chromen‐8‐ylmethyl)‐5‐methyl‐1,2‐dihydro‐pyrazol‐3‐ones (7a–j) were synthesized from 3‐[(7‐acetoxy‐4‐methyl‐8‐methylene)coumaryl]sydnone (5). All the newly synthesized compounds exhibited antimicrobial activity greater than the reference drugs used.     

Stereoselective Synthesis of β‐Lactams by Using D‐Mannitol‐Derived Oxazolidin‐2‐one as a Chiral Auxiliary

Abstract

Chiral oxazolidin‐2‐ones containing isopropylidene and cyclohexylidene functionalities, readily available from D‐mannitol, have been demonstrated to undergo highly diastereoselective β‐lactam synthesis via the Staudinger reaction with Mukaiyama reagent. Stereoselectivity for cis‐β‐lactam was the result of the [2?+?2] cycloaddition reaction of ketene to trans imines, and cyclohexylidene showed better yield and stereoselectivity than the isopropylidene auxiliary.     

P‐Dimethyl Amino Benzaldehyde as a New Chromogenic Reagent for the Determination of Nonsteroidal Anti‐Inflammatory Drug by First‐Order Derivative Spectrophotometry

Abstract

Mefenamic acid reacts with P‐dimethylamino benzaldehyde to give a bluish‐green complex in acidic media after heating for 90 s at 90°C, having maximum absorbance at 597.5 nm. The reaction is selective for mefenamic acid with 0.02 mg/10 mL as visual limit of quantitation and provides a basis for a new spectrophotometric determination. The reaction obeys Beer's Law from 0.02 mg to 2.5 mg/10 mL of mefenamic acid and the relative standard deviation is 0.50%. The quantitative assessment of tolerable amounts of other drugs not interfering has also been studied. First‐order derivative spectrophotometric procedure was applied for the determination of mefenamic acid in pharmaceutical preparations.     

Recent Advances in One-Electron-Oxidized CuII–Diphenoxide Complexes as Models of Galactose Oxidase: Importance of the Structural Flexibility in the Active Site

The phenoxyl radical plays important roles in biological systems as cofactors in some metalloenzymes, such as galactose oxidase (GO) catalyzing oxidation of primary alcohols to give the corresponding aldehydes. Many metal(II)–phenoxyl radical complexes have hitherto been studied for understanding the detailed properties and reactivities of GO, and thus the nature of GO has gradually become clearer. However, the effects of the subtle geometric and electronic structural changes at the active site of GO, especially the structural change in the catalytic cycle and the effect of the second coordination sphere, have not been fully discussed yet. In this Review, we focus on further details of the model studies of GO and discuss the importance of the structural change at the active site of GO.     

Evaluation of the (Allyl alcohol 1,2‐butoxylate‐block‐etoxylate)‐b‐PMMA Copolymers Composition by the Dielectric Measurements

Redox initiated free‐radical polymerization of methyl methacrylate (MMA) with allyl alcohol 1,2‐butoxylate‐block‐etoxylate (AABE) was carried out to yield AABE‐b‐PMMA copolymers at elevated temperatures. The composition of the copolymers depending on the polymerization temperature was qualitatively estimated by the dielectric measurements. It has been seen that AABE segment quantity decreased and PMMA segment quantity increased with increasing the polymerization temperature. The dielectric constant and the dissipation factor of the copolymers were investigated as a function of frequency and temperature. The dielectric constant and the dissipation factor were found to be strongly affected by the polymerization temperature. The highest dielectric constant in all studied temperatures and frequencies was obtained in the case of the copolymer which was prepared at 313 K. The dipolar C‐O and OH groups of the AABE segment have the primary effect on the dielectric constant. The copolymer which was prepared at 323 K, showed the highest dissipation factor near the relaxation temperature of PMMA.     

Novel Procedure for the Synthesis of 1‐Hydroxy‐1,1‐bisphosphonic Acids using Phenols as Medium

A facile synthetic route for the synthesis of bisphosphonates in phenols is described. Preparations of some of bisphosphonates, which are presently in clinical use such as risedronic acid and alendronate sodium, are synthesized following this new, simple method. This procedure can be useful for the synthesis of this class of bone‐resorptive inhibitors in bulk quantities.     

One‐Pot Preparation of Fluorinated α‐Aminoalkyl Phosphonates under Microwave Irradiation and Solvent‐Free Conditions

A facile one‐pot method has been developed for the synthesis of fluorine‐containing α‐amino phosphonates in good yields by a three‐component reaction of fluorinated aromatic aldehydes, anilines, and diethyl phosphate in the presence of a silica‐gel support under microwave irradiation within 10 min. All new compounds are fully characterized by spectral methods and elemental analysis.     

Study of Spectrophotometric Determination of Amoxicillin Using Sodium 1,2‐Naphthoquinone‐4‐Sulfonate as the Chemical Derivative Chromogenic Reagent

Abstract

A simple and sensitive spectrophotometric method is described for determination of amoxicillin. The method is based on a nucleophilic substitution reaction to measure the pink compound produced by the reaction of amoxicillin with sodium 1,2‐naphthoquinone‐4‐sulfonate in pH 9.00 buffer solution. The stoichiometric ratio of the compound is 1:1, and its maximum absorption wavelength is at 468 nm, ε=3.91×10³ L · mol^?1 · cm^?1. The Beer's law is obeyed in the range of 0.8–120 µg · mL^?1 of amoxicillin. The linear regression equation is A=0.041239+0.22128 C, with 0.9994 of a linear regression correlation coefficient. The detection limit is 2.0 µg · mL^?1, and average recovery is over 98.5%. This paper further optimizes the determination of amoxcillin compared to the previous methods, and the kinetic property and reaction mechanism are studied intensively. This proposed method has been successfully applied to the determination of amoxicillin in tablets and capsules. The results obtained by this method agreed well with those by the official method high pressure liquid chromatography (HPLC).     

Use of Di‐tert‐butyl‐dicarbonate Both as a Protecting and Activating Group in the Synthesis of Dipeptides

Amide formation from amino acids was achieved in an easy and convenient one‐pot procedure using di‐tert‐butyl dicarbonate both as a protecting and an activating agent. A number of dipeptides have been synthesized in good yields.     

Aromatic Foldamer Helices as α-Helix Extended Surface Mimetics

Helically folded aromatic oligoamide foldamers have a size and geometrical parameters very distinct from those of α-helices and are not obvious candidates for α-helix mimicry. Nevertheless, they offer multiple sites for attaching side chains. It was found that some arrays of side chains at the surface of an aromatic helix make it possible to mimic extended α-helical surfaces. Synthetic methods were developed to produce quinoline monomers suitably functionalized for solid phase synthesis. A dodecamer was prepared. Its crystal structure validated the initial design and showed helix bundling involving the α-helix-like interface. These results open up new uses of aromatic helices to recognize protein surfaces and to program helix bundling in water.     

Synthesis of 1‐Indanones via Intramolecular Cyclodehydration of 3‐Arylpropionic Acids Catalyzed by Heteropoly Acid as Heterogeneous Catalyst

Intramolecular cyclodehydration of 3‐arylpropionic acids catalyzed by heteropoly acids was investigated for the first time. Several 3‐arylpropionic acids were refluxed and dehydrated in chlorobenzene in the presence of 0.2 equivalent of heteropoly acids, and 1‐indanones were obtained in good yield. At the same time, intermolecular Friedel–Crafts acylation were observed in this experiment.     

Preparation of 2‐Amino‐1,3‐butadienes as N‐Pyridine Derivatives

2‐Amino‐1,3‐butadienes as pyridine derivatives have been prepared from corresponding dihydrothiazolo[3,2‐a]pyridinium salts in reactions with a strong base. The pyridinium salts were prepared from pyridine‐2(1H)‐thiones and trans‐1,4‐dibromo‐2‐butene by a vicinal and chemoselective formation of 3‐vinyldihydrothiazolo[3,2‐a]pyridinium salts. A strong base was used for selective proton removal from the vinyl‐substituted 3‐position. A subsequent ring opening provided 2‐substituted 1,3‐butadienes with the azine appended at the annular nitrogen. Simple S‐alkylation yielded a corresponding azinium salt, thereby introducing electrophilic character to the 1,3‐butadiene system. Hydrolysis of the sulfide function provided the corresponding pyridin-2(1H)‐one attached to the 1,3‐butadiene in the 2‐position.     

One‐Pot Synthesis of 2‐Arylthio‐2‐cyclohexenone Derivatives by the Diels–Alder Reaction of 4‐Arylthio‐3‐hydroxy‐2‐pyrones

The base‐catalyzed Diels–Alder reactions of 4‐arylthio‐3‐hydroxy‐2‐pyrones are reported. Treatment of 4‐arylthio‐3‐hydroxy‐2‐pyrones and dienophiles with triethylamine gave 2‐arylthio‐2‐cyclohexenone derivatives by the Diels–Alder reaction involving a decarboxylation in excellent to reasonable yields.     

Post‐chemiluminescence Method of the Determination of Loperamide Hydrochloride in Human Plasma and Pharmaceutical by Using Dichlorofluorescein as Chemiluminescence Reagent

Abstract

A post‐chemiluminescence (PCL) was observed when loperamide hydrochloride solution was injected into the reaction mixture after the finish of CL reaction of alkaline N‐Chlorosuccinimide (NCS) and dichlorofluorescein. Based on this phenomenon, a simple, sensitive and fast flow injection PCL method was established for the determination of loperamide hydrochloride. The possible mechanism for the PCL reaction was discussed via the investigation of the CL kinetic characteristics, the CL spectra, the fluorescence spectra. The PCL intensity responded linearly to the concentration of loperamide hydrochloride in the range 8.0×10^?10 to 6.0×10^?7 g · ml^?1 with a linear correlation of 0.9995. The detection limit was 4×10^?10 g · ml^?1. The relative standard deviation was 2.4% for 4.0×10^?8 g · ml^?1 loperamide hydrochloride (n=11). This method has been applied to the determination of loperamide hydrochloride in human plasma and pharmaceutical samples with satisfactory results.     

CAN Catalyzed One‐Pot Synthesis of α‐Amino Phosphonates from Carbonyl Compounds

Abstract

α‐Amino phosphonates are synthesized by three component condensation of aldehydes, amines, and diethyl phosphite using ceric ammonium nitrate at room temperature to afford the corresponding α‐amino phosphonates in high yields.