Separation and identification of Taxifolin 3-O-glucoside isomers from Chamaecyparis obtusa (Cupressaceae)

Taxifolin 3-O-glucoside isomers, [(2R, 3R)-, (2R, 3S)-, (2S, 3R)- and (2S, 3S)-] were isolated from leaves of Chamaecyparis obtuse (Cupressaceae). Their structures were elucidated on the basis of UV, MS, CD, 1H- and 13C-NMR spectral data, including 2D shift correlation. It was found that the compounds could be distinguished by the use of 1H- and 13C-NMR spectral data.     

Reaction of azole condensed quinoxaline N-oxides with acetic anhydride

The reaction of 7-chlorotetrazolo[1,5-α]quinoxaline 5-oxide 6a with acetic anhydride gave 7-chloro-5-(7-chlorotetrazolo[1,5-α]quinoxalin-4-yl)-4,5-dihydro-4-oxotetrazolo[1,5-α]quinoxaline 7a , while the reaction of 7-chloro-1,2,4-triazolo[4,3-α]quinoxaline 5-oxide 6b with acetic anhydride afforded 7-chloro-5-(7-chloro-1,2,4-triazolo[4,3-α]quinoxalin-4-yl)-4,5-dihydro-4-oxo-1,2,4-triazolo[4,3-α]quinoxaline 7b and 7-chloro-4,5-dihydro-4-oxo-1,2,4-triazolo[4,3-α]quinoxaline 8b . The reaction of compound 6a or 6b with acetic anhydride/acetic acid provided 7-chloro-4,5-dihydro-4-oxo-tetrazolo[1,5-α]quinoxaline 8a or compound 8b , respectively.     

Substituent effects on the tautomer ratios between the hydrazone imine and diazenyl enamine forms in side-chained quinoxalines

The 3-(arylhydrazono)methyl-2-oxo-1,2-dihydroquinoxalines 9–11 were synthesized by the reaction of the quinoxalines 6–8 with various p-substituted benzenediazonium salts. Compounds 9–11 showed the tautomeric equilibria between the hydrazone imine A and diazenyl enamine B forms in dimethyl sulfoxide media. The substituent effect on the tautomer ratios of A to B was studied by the nmr spectroscopy to clarify that the presence of the ester group R² on the hydrazone carbon and electron-donating p-substituent R¹ on the side chain benzene ring exhibited a tendency to increase the ratios of the tautomer A .     

Structures of 1,4-benzodioxane derivatives from the seeds of Phytolacca americana and their neuritogenic activity in primary cultured rat cortical neurons

The methanol extract of the seeds of Phytolacca americana was reinvestigated to yield three new 1,4-benzodioxane-type compounds, americanoic acid methyl ester (1), isoamericanoic acid A methyl ester (2), and 9'-O-methylamericanol A (3) along with the previously isolated neolignans 6-9. The structures of 1-3 were characterized by 2D NMR and long-range selective proton-decoupling (LSPD) techniques. The neuritogenic effects of compounds 1-3, and dicarboxilic acids 4 and 5, which had been previously synthesized with horseradish peroxidase-catalyzed oxidative coupling of caffeic acid, were examined in primary cultured rat cortical neurons. Americanoic acid A methyl ester (1) exhibited neurite outgrowth-promoting activity at concentration of 0.01-1.0 microM, whereas dicarboxilic acids 4 and 5 were found to induce neuritogenesis dose dependently at the concentrations from 0.1 microM to 10 microM.     

Synthesis of 1-beta-D-(5-deoxy-5-iodoarabinofuranosyl)-2-nitroimidazole (beta-IAZA): a novel marker of tissue hypoxia

The present work describes the synthesis of the beta-isomer of 1-alpha-D-(5-deoxy-5-iodoarabinofuranosyl)-2-nitroimidazole (IAZA). Radioiodinated IAZA ((123)I-IAZA) has been extensively studied as a radiopharmaceutical for the diagnosis of regional and/or focal tissue hypoxia in a variety of clinical pathologies. The beta-anomer of IAZA, 1-beta-D-(5-deoxy-5-iodoarabinofuranosyl)-2-nitroimidazole (beta-IAZA, 1), was synthesized via an unconventional route starting from 1-beta-D-(ribofuranosyl)-2-nitroimidazole (AZR), with a change of configuration at the C-2'-position to afford 1-beta-D-(arabinofuranosyl)-2-nitroimidazole (beta-AZA, 7). Nucleophilic iodination of the 5'-O-toluenesulfonyl-2',3'-di-O-acetyl precursor of beta-AZA, 9, followed by deprotection, afforded 1 in satisfactory yield. beta-IAZA (1) was also synthesized from 7 using molecular iodine and triphenylphosphine.     

NMR study on the tautomeric equilibria between the hydrazone imine and diazenyl enamine forms in side chained quinoxalines: Solvent effects and temperature dependence

The reaction of 7-chloro-4-ethoxycarbonylmethylene-4,5-dihydro-1,2,4-triazolo[4,3-a]quinoxaline 6 with 4-ethoxycarbonyl-1-methyl-1H-pyrazole-5-diazonium chloride or 4-cyano-1,3-dimethyl-1H-pyrazole-5-diazonium chloride gave 7-chloro-4-[α-(4-ethoxycarbonyl-1-methyl-1H-pyrazol-5-ylhydrazono)-ethoxycarbonylmethyl]-1,2,4-triazolo[4,3-a]quinoxaline 8a or 7-chloro-4-[α-(4-cyano-1,3-dimethyl-1H-pyrazol-5-ylhydrazono)ethoxycarbonylmethyl]-1,2,4-triazolo[4,3-a]quinoxaline 8b , respectively, while the reaction of 7-chloro-4-ethoxycarbonylmethylene-4,5-dihydrotetrazolo[1,5-a]quinoxaline 7 with 4-ethoxycarbonyl-1-methyl-1H-pyrazole-5-diazonium chloride or 4-cyano-1,3-dimethyl-1H-pyrazole-5-diazomum chloride provided 7-chloro-4-[α-(4-ethoxycarbonyl-1-methyl-1H-pyrazol-5-ylhydrazono)ethoxycarbonylmethyl]tetrazolo[1,5-a]quinoxaline 9a or 7-chloro-4-[α-(4-cyano-1,3-dimethyl-1H-pyrazol-5-ylhydrazono)ethoxycarbonylmethyl]tetrazolo[1,5-a]quinoxaline 9b , respectively. Compounds 8a,b and 9a,b showed the tautomeric equilibria between the hydrazone imine C and diazenyl enamine D forms in dimethyl sulfoxide and/or trifluoroacetic acid, and the effects of solvent and temperature on the tautomer ratios of C to D were studied by the nmr measurements in a series of mixed trifluoroacetic acid/dimethyl sulfoxide media (compounds 8a,b and 9a,b ) and at various temperatures (compounds 8a,b ).     

Determination of bithionol, bromophen, nitroxynil, oxyclozanide, and tribromsalan in milk with liquid chromatography coupled with tandem mass spectrometry

LC/MS/MS was developed to determine the residues of bithionol (BTN), bromofen (BMF), nitroxynil (NTX), oxyclozanide (OCZ), and tribromsalan (TBS) in milk. Samples were extracted with ethyl acetate and cleaned up by liquid-liquid separation with acetonitrile and n-hexane. The compounds were determined by RP-LC using a C18 column with 0.1% formic acid-methanol. Mass spectral acquisition was performed in the negative mode by applying selected-reaction monitoring. The method was validated in milk spiked with these compounds at 5-600 microg/kg; average recoveries were in the range 83.8-97.1%, with RSD values of 1.4-8.0%. The interassay RSDs were less than 11%. The LODs of these compounds in milk were 0.1 microg/kg. The method was applied to 24 raw milk samples. The concentration of these compounds in all samples was lower than the Japanese maximum residue limits. The method is rapid, sensitive, and specific for monitoring residues of BTN, BMF, NTX, OCZ, and TBS in milk.     

Photochemical intramolecular nitrene insertion of 6-azidouridine derivatives

A highly efficient intramolecular nitrene insertion was observed upon irradiation of 6-azidouridine derivatives. The N⁶,2′-cyclo structure of the product was determined unequivocally by X-ray crystallography.     

Formation of double helix self-assembled monolayers of ethynylhelicene oligomer disulfides on gold surfaces

Optically active ethynylhelicene pentamers and hexamers linked by disulfide bonds were synthesized. They formed self-assembled monolayers (SAMs) with double helix structure on gold surfaces, which were analyzed by infrared reflection-absorption spectroscopy (IR-RAS), quartz crystal microbalance (QCM), surface plasmon resonance (SPR), and circular dichroism (CD). Double helix SAMs could be formed on gold surfaces either from double helices or random coils in solution. The double helices on the surface were more stable than in solution. This result suggested the presence of strong intercomplex interactions between double helix complexes on the surface.     

Rapid determination of fumagillin residues in honey by liquid chromatography-tandem mass spectrometry using the QuEChERS method

A new, rapid, and efficient method for determining the fumagillin residues in honey was developed. The samples extracted were analyzed using LC/MS/MS. Chromatographic separation of fumagillin was performed in gradient mode on a C8 column (100 x 2.0 mm, 5 microm) at 40 degrees C. The mobile phase consisted of a mixture of 2 mM ammonium formate-0.01% formic acid solution and methanol; the flow rate was set to 0.2 mL/min. Under these conditions, it was possible to measure fumagillin and its isomers as a single peak. The sample preparation procedure used is based on the QuEChERS (quick, easy, cheap, effective, rugged, and safe) method, which is fast (approximately 30 min) and uses less organic solvent. The fumagillin was extracted with acetonitrile containing 0.1% formic acid, then purified using a solid-phase extraction method with an Oasis mixed-mode weak anion-exchange cartridge. The overall recovery of fumagillin ranged from 88.1 to 99.4%; the intra- and interassay CVs were <4.5% and <4.9%, respectively. The LOQ was 0.1 microg/kg. LC/MS/MS coupled with the QuEChERS method showed strong potential as a method for determining fumagillin residues in honey.