Electrochemical nitric oxide sensor preparation: a comparison of two electrochemical methods of electrode surface modification

Platinum electrodes modified with Mn(II) 5-(N-(8-pyrrole-yl-3,6-dioxa-1-aminooctane)phenylamide-10,15,20-trimethoxyphenylporphyrin (Mn(II)triOMeTCPPyP) using multi-sweep cyclic voltammetry and differential pulse amperometry were evaluated as electrocatalytic surfaces for the oxidation of nitric oxide. The electrodes modified using the pulse amperometric approach were more sensitive towards the detection of nitric oxide. The increased sensitivity led to the attainment of a wider linear dynamic range for the quantification of nitric oxide.     

Michael-type addition of secondary phosphine oxides to (1,4-cyclohexadien-3-yl)phosphine oxides

Base-induced reaction between (1,4-cyclohexadien-3-yl)phosphine oxides and secondary phosphine oxides gives 3,4-bis(phosphinoyl)cyclohexenes and 2,3-bis(phosphinoyl)cyclohexenes through an in situ isomerization of one of the cyclohexadienyl double bonds and a subsequent Michael-type addition of the secondary phosphine oxide.     

An improved synthesis of 3,6-diamino-1,2,4,5-tetrazine. II. From triaminoguanidine and 2,4-pentanedione

A new synthesis for the title compound that gives an 80% overall yield was developed. Treatment of triaminoguanidine monohydrochloride ( 1 ) with 2,4-pentanedione ( 2 ) gave 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5-tetrazine ( 3 ) in 80–85% yield. Oxidation of 3 with nitric oxide or nitrogen dioxide to 3,6-bis(3,5-dimethyylpyrazol-1-yl)-1,2,4,5-tetrazine ( 4 ) followed by ammonolysis of 4 gave 3,6-diamino-1,2,4,5-tetrazine ( 5 ) in guantitatively yields.     

Synthesis of 1,2-dialkyl-3,6-dimethyl-1,2-dihydropyridazines from acetonylacetone

Condensation of acetonylacetone with symmetrical dimethyl- and diethylhydrazines leads to 1,2-dialkyl-3,6-dimethyl-1,2-dihydropyridazines and 2,3,5,6-tetraalkyl-1,4-dimethyl-2, 3,5,6-tetraazabicyclo[2.2.2]octanes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 400–403, March, 1971.     

Phthalocyanines and related compounds: XLVII. Nucleophilic replacement of chlorine atoms in tetrachlorophthalonitrile. Synthesis of phenyl(alkyl)amino-substituted phthalonitriles and some phthalocyanines based thereon

Nucleophilic replacement of chlorine atoms in tetrachlorophthalonitrile by the action of primary and secondary amines was studied. The reactions of tetrachlorophthalonitrile with amines at a ratio of 1: 10 gave with high yields and regioselectivity the corresponding 4,5-diamino-3,6-dichlorophthalonitriles from cyclic secondary amines and 4-amino-3,5,6-trichlorophthalonitriles from primary amines and acyclic secondary amines. 4-Amino-3,5,6-trichlorophthalonitriles were used to synthesize cobalt and zinc phthalocyanine complexes. It was shown that replacement of chlorine atoms in the pyrrolic β-positions of hexadecachlorophthalocyanines by amino groups is not accompanied by red shift of the long-wave absorption band in the electronic spectra.     

A two-directional approach to enantiopure 1,4-difluoro-cyclohexenes: synthesis of difluorinated cyclitol analogues

Enantiopure 1,4-difluoro-cyclohexenes were prepared from readily available acetonide-protected (3 S,4 S)-hexa-1,5-diene-3,4-diol. In a two-directional mode, a double cross-metathesis reaction using allyltrimethylsilane as the olefinic partner, followed by electrophilic fluorination, afforded diastereomeric acetonide-protected 3,6-difluoro-octa-1,7-diene-4,5-diols. These dienes were found to be suitable substrates for ring-closing metathesis, delivering cyclohexenes featuring fluorine atoms on the two allylic positions flanking the double bond. Upon dihydroxylation, novel difluorinated cyclitol analogues were formed.     

Synthesis of highly substituted 1,3-dienes, 1,3,5-trienes, and 3,6-disubstituted cyclohexenes by the palladium-catalyzed coupling of organic halides, internal alkynes or 1,3-cyclohexadienes, and organoboranes

A number of highly substituted 1,3-dienes and 1,3,5-trienes have been stereoselectively prepared in moderate to good yields by the coupling of vinylic iodides, internal alkynes, and organoboranes in the presence of a palladium catalyst. Optimal reaction conditions for different organoboron substrates have been developed. The analogous three-component coupling of aryl halides, 1,3-cyclohexadiene, and boronic acids provides a synthetically useful route to 3,6-disubstituted cyclohexenes. These methods are very efficient and provide an expeditious way to synthesize the indicated alkenes, dienes, and trienes, whose preparation would normally require multi-step synthesis.     

Synthesis of 2,5-bis(2-aminothiazol-5-yl)-3,6-dichloro-1,4-benzoquinones

A series of 2-(2-aminothiazol-5-yl)-3,6-dichloro-5-diethylaminoethenyl-1,4-benzoquinones was synthesized from 2-(2-aminothiazol-5-yl)-3,5,6-trichloro-1,4-benzoquinones using acetaldehyde and diethylamine in toluene solution. Refluxing these compounds with substituted thioureas in acetonitrile in the presence of hydrochloric acid gives the corresponding 2,5-bis(2-aminothiazol-5-yl)-3,6-dichlorohydroquinones which can be oxidized to the target products with ferric chloride in aqueous DMF.Riga Technical University, Riga LV-1048, LatviaTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 835–839, June, 2000     

Electrochemical Reduction of Pyridinic Herbicides Picloram and Clopyralid on a Mercury Pool Electrode

This paper presents the identification by GC/MS of the products obtained after the total reduction of picloram and clopyralid on a mercury pool electrode. The products found in the strongly acidic media reduction of picloram are 4‐amino‐3,5,6‐trichloro‐2‐pyridinecarboxaldehyde, 4‐amino‐3,5,6‐trichloro‐2‐pyridinecarbinol and 4‐amino‐3,5‐dichloro‐2‐pyridinecarboxylic acid; at pH 3–4 the first compound is substituted by 4‐amino‐3,5‐dichloro‐2‐pyridinecarboxaldehyde. For clopyralid 3,6‐dichloro‐2‐pyridinecarbinol was detected. Under the light of such products the overall reduction processes are discussed showing the partial reductive cleavage of chlorine atoms in both cases.     

Acyl Derivatives of 2-Aminobenzimidazole and Their Fungicide Activity

Procedures have been developed for the preparation of methyl 2-benzimidazolylcarbamate, 2-acetylaminobenzimidazole, 2-benzoylaminobenzimidazole, 2-(3,5-dibromo-2-hydroxybenzoylamino)benzimidazole, 1-(3,6-dichloro-2-methoxybenzoyl)-2-aminobenzimidazole, 2-(3,5-dichloro-2-hydroxybenzoylamino)benzimidazole, 2-(3,5-dichloro-2-methoxybenzoylamino)benzimidazole, and 1-(3,5,6-trichloro-2-methoxybenzoyl)-2-aminobenzimidazole. The synthesized compounds have been tested for fungicide activity.     

Lucidin type anthraquinone glycosides from Putoria calabrica

Two new lucidin type anthraquinone glycosides, putorinoside A (1) and putorinoside B (2) were isolated from Putoria calabrica, in addition to two known anthraquinone glycosides, lucidin 3-O-beta-glucopyranoside (3) and lucidin 3-O-primeveroside (4). Based on spectroscopic data, putorinosides A and B were identified as 2-hydroxymethyl-1-methoxy-3,5,6-trihydroxyanthraquinone 3-O-beta-glucopyranoside and 2-hydroxymethyl-1-methoxy-3,6-dihydroxyanthraquinone 3-O-beta-glucopyranoside, respectively.     

Gas chromatographic determination of nitric oxide at sub-ppm levels

The highly sensitive procedure involves the reaction of nitric oxide with various aromatic amines in the presence of copper (II) halide at room temperature and the gas chromatographic measurement of the aryl halide formed with an electron capture detector. The conversion yield of nitric oxide and the sensitivity of the detector to each product were studied. The system containing 3,4-dichloroaniline and copper(II) bromide is the most sensitive; the detection limit is 0.01 ppm, which indicates the possibility of determining nitric oxide in air samples without preconcentration. Gases commonly encountered in polluted air do not interfere, except for nitrogen dioxide, which can be removed by the Saltzman method.     

Concise formal total synthesis of hybocarpone and related naturally occurring naphthazarins

A concise formal total synthesis of the cytotoxic bisnaphthazarin derivative hybocarpone has been completed through the development of routes to the synthetic precursor, 3-ethyl-2-hydroxy-5,7,8-trimethoxy-6-methyl-1,4-naphthoquinone. The oxidation of 3-ethyl-1,2,4,5,7,8-hexamethoxy-6-methylnaphthalene under Rapoport conditions gave 3-ethyl-2-hydroxy-5,7,8-trimethoxy-6-methyl-1,4-naphthoquinone in modest yields after basic hydrolysis. In addition, treatment of 3-ethyl-1,2,4,5,7,8-hexamethoxy-6-methylnaphthalene with boron tribromide provided access to the naturally occurring naphthazarin, boryquinone. The analogous oxidative demethylation of 3,6-dimethyl-1,2,4,5,7,8-hexamethoxynaphthalene and 3-ethyl-1,2,4,5,7,8-hexamethoxynaphthalene resulted in the synthesis of 2,5,7,8-tetrahydroxy-3,6-dimethyl-1,4-naphthoquinone (aureoquinone) and 3-ethyl-2,5,7,8-tetrahydroxy-1,4-naphthoquinone, respectively. An alternative selective synthetic route to 3-ethyl-2-hydroxy-5,7,8-trimethoxy-6-methyl-1,4-naphthoquinone was also developed utilizing an intramolecular Claisen condensation of methyl 2-butyryl-3,5,6-trimethoxy-4-methylphenylacetate with concomitant in situ aerial oxidation.     

Synthesis of 5-(5-amino-3,6-dichloro-1,4-benzoquinon-2-yl)-2-dimethylaminothiazoles and their properties

In the reaction of 2-dimethylamino-5-(3,5,6-trichloro-1,4-benzoquinon-2-yl)thiazole with primary and secondary amines, the chlorine atom at the 5-position of the benzoquinone ring is substituted, according to the ¹³C NMR spectroscopy data, by an amino group. The chemical, spectroscopic, and electrochemical properties of 5-(5-amino-3,6-dichloro-1,4-benzoquinon-2-yl)-2-dimethylaminothiazoles were revealed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 410–415, March, 1991.     

Brønsted Base Catalyzed One‐Pot Synthesis of Stereodefined Six‐Member Carbocycles Featuring Transient Trienolates and a Key Intramolecular 1,6‐Addition

A catalyst‐driven one‐pot reaction sequence is developed for the enantio‐ and diastereoselective synthesis of tetrasubstituted cyclohexenes from simple unsaturated ketones or thioesters. The method involves a tertiary amine/squaramide‐catalyzed α‐selective addition of transiently generated trienolates to nitroolefins, subsequent base‐catalyzed double bond isomerization, and an intramolecular (vinylogous) 1,6‐addition reaction, a rare key carbocyclization step that proceeded with essentially perfect stereocontrol.     

A Diels-Alder approach to the enantioselective construction of fluoromethylated stereogenic carbon centers

Highly enantioselective Diels-Alder reactions of β-fluoromethylacrylates were carried out in the presence of a Lewis acid activated chiral oxazaborolidine catalyst. These reactions yielded fluoromethylated cyclohexenes, including trifluoromethyl-, difluoromethyl-, and monofluoromethyl cyclohexenes, as nearly pure enantiomers. The resulting fluoromethyl cyclohexenes were converted into potential synthetic intermediates for bioactive compounds.     

The vinylogous intramolecular Morita-Baylis-Hillman reaction: synthesis of functionalized cyclopentenes and cyclohexenes with trialkylphosphines as nucleophilic catalysts

The development of the vinylogous intramolecular Morita-Baylis-Hillman reaction for the synthesis of functionalized cyclopentenes and cyclohexenes is described. The reaction involves the trialkyphosphine-catalyzed cyclization of 1,6- or 1,7-diactivated 1,5-hexadienes or 1,6-heptadienes, containing carboxyaldehyde, methyl ketone, or methoxycarbonyl as the olefin activating groups. A representative example of this reaction is the Me(3)P-catalyzed cyclization of 1a in tert-amyl alcohol, which provides the substituted cyclopentene 2a in 95% yield and with 97:3 regioselectivity.     

Syntheses and spectral characteristics of 6-mono-, 3,6-di- and 3,5,6-trisubstituted-1,2,4-triazines

The reaction of acidhydrazides with α-substituted carbonyl compounds in the presence of metal acetates gives substituted 1,2,4-triazines. These cyclisations could be effected without any added acetate by refluxing in dimethyl formamide, pyridine/acetic acid or dimethyl sulfoxide Sixty five 3,5,6-tri-3,6-di and 6 monosubstituted-1,2,4-triazines (in 50–90% yields) with a wide variation in the C₃ substituent (alkyl, aryl or heteryl) and the C₆-substituent (aryl or heteryl) are reported. The mechanistic path followed in the formation of these compounds is discussed.     

1H and 13C NMR assignments of new methoxylated furanoflavonoids from Lonchocarpus araripensis

Two new polymethoxylated flavonoids, 2',5',6'-trimethoxy-[2',3' : 3',4']furano dihydrochalcone and 2,4',4,5-tetramethoxy-[2',3' : 6,7]-furanodihydroaurone, were isolated from the root barks of Lonchocarpus araripensis, along with the known compounds 3,4,5,6-tetramethoxy-[2',3' : 7,8]-furanoflavan, 3,6-dimethoxy-1',1'-dimethylcromene-[2',3' : 7,8]-flavone, 3',4'-methylenodioxy-5,6-dimethoxy-[2',3' : 7,8]-furanoflavone, 3,5,6-trimethoxy-[2',3' : 7,8]-furanoflavanone, 3,5,6-trimethoxy-[2',3' : 7,8]-furanoflavone, and 6alpha-hydroxy-medicarpin. The complete (1)H and (13)C NMR assignments of the new furan flavonoids were performed using 1D and 2D pulse sequences, including COSY, HSQC, and HMBC experiments, and comparison with spectral data for analog compounds from the literature, particularly for the new furanodihydroaurone because of several inconsistencies on the carbonyl chemical shifts from the literature.     

Synthesis of a new phosphorus-containing macrocycle

Conclusions We synthesized a 15-membered organophosphorus macrocycle with twophosphine oxide groupings and polyether units, and specifically 1,2,7,8-dibenzo-3,6-diphospha-3,6-dioxo-3,6-diphenyl-15-crown-5.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1930–1932, August, 1978.