- Synthesis of N-[4-(2'-[18F]fluoroalkoxybenzoyl)]- And N-(3-[123I]iodo-4-methoxybenzoyl)pyrrolidin-2-ones as potential brain imaging agents
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– The microfluidic synthesis of promising brain imaging PET agents N-[4-(2’-[18F]fluoroalkyloxybenzoyl)]pyrrolidin-2-ones 13a-c was accomplished by nucleophilic radiofluorination of the corresponding tosylate precursors 9a-c with Kryptofix-pota
- Akula, Murthy,Blevins, David,Kabalka, George W.,Osborne, Dustin
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p. 1226 - 1236
(2019/07/31)
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- Synthesis of trimethylsilyl carboxylates by HMDS under solvent-free conditions
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A broad set of structurally different carboxylic acids were transformed into their trimethylsilyl esters with HMDS in a practically completely solvent-free process, while a catalytic amount of iodine was required in some cases. The process has several advantages over the known methods: untreated reactants, air atmosphere, mild and neutral conditions, no evolution of hydrogen halide, no need of an additional base, low amount of waste, completely without chromatography, low consumption of energy, and operational simplicity.
- Jereb, Marjan,Lakner, Janja
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p. 5713 - 5723
(2016/08/23)
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- Investigation of the substrate range of CYP199A4: Modification of the partition between hydroxylation and desaturation activities by substrate and protein engineering
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The cytochrome P450 enzyme CYP199A4, from Rhodopseudomonas palustris HaA2, can efficiently demethylate 4-methoxybenzoic acid. It is also capable of oxidising a range of other related substrates. By investigating substrates with different substituents and ring systems we have been able to show that the carboxylate group and the nature of the ring system and the substituent are all important for optimal substrate binding and activity. The structures of the veratric acid, 2-naphthoic acid and indole-6-carboxylic acid substrate-bound CYP199A4 complexes reveal the substrate binding modes and the side-chain conformational changes of the active site residues to accommodate these larger substrates. They also provide a rationale for the selectivity of product oxidation. The oxidation of alkyl substituted benzoic acids by CYP199A4 is more complex, with desaturation reactions competing with hydroxylation activity. The structure of 4-ethylbenzoic acid-bound CYP199A4 revealed that the substrate is held in a similar position to 4-methoxybenzoic acid, and that the C β C-H bonds of the ethyl group are closer to the heme iron than those of the Cα (3.5 vs. 4.8 A?). This observation, when coupled to the relative energies of the reaction intermediates, indicates that the positioning of the alkyl group relative to the heme iron may be critical in determining the amount of desaturation that is observed. By mutating a single residue in the active site of CYP199A4 (Phe185) we were able to convert the enzyme into a 4-ethylbenzoic acid desaturase. Engineering a P450 desaturase: The substrate range of CYP199A4 from Rhodopseudomonas palustris was investigated. The partition between the hydroxylation and desaturation activities of 4-ethylbenzoic acid was studied by changing the substrate and by mutation. The activity of CYP199A4 with 4-ethylbenzoic acid was changed to a desaturase by a single mutation at F185. Copyright
- Bell, Stephen G.,Zhou, Ruimin,Yang, Wen,Tan, Adrian B. H.,Gentleman, Alexander S.,Wong, Luet-Lok,Zhou, Weihong
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p. 16677 - 16688
(2013/03/28)
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- Partition coefficients of ketones, phenols, aliphatic and aromatic acids, and esters in n-hexane/nitromethane
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Liquid-liquid partition is used in sample preparation and in countercurrent and liquid-liquid chromatographic separations. Partition coefficients are widely used in toxicology, environmental, and analytical chemistry. The K hn determination procedure for the n-hexane/ nitromethane system was optimized and partition coefficients for 99 ketones, esters and trimethylsilyl derivatives of phenols, aliphatic and aromatic acids were determined. For 130 compounds, Khn values were predicted using mathematical relationships between Khn and other physicochemical and structural parameters. Versita Sp. z o.o.
- Kotowska, Urszula,Isidorov, Valery A.
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scheme or table
p. 813 - 824
(2012/03/27)
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- Characterization of phenolic compounds in rooibos tea
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Polyphenols present in rooibos, a popular herbal tea from Aspalathus linearis, were isolated in two steps. First, phenolic ingredients were separated by multilayer countercurrent chromatography (MLCCC). Preparative high-performance liquid chromatography (HPLC) was then applied to obtain pure flavonoids. The purity and identity of isolated compounds was confirmed by different NMR experiments, HPLC-diode array detector (DAD), or gas chromatography-mass spectrometry (GC-MS) analysis. This strategy proved to be valid to isolate material in up to gram quantities and to verify known and previously not published polyphenol structures. In addition the chemistry of dihydrochalcones and related intermediates was studied. The dihydrochalcone aspalathin was oxidized to the corresponding flavanone-C-glycosides ((R)/(S)-eriodictyol-6-C-β-D-glucopyranoside and (R)/(S)-eriodictyol-8-C- β-D-glucopyranoside). Flavanone-6-C-β-D-glucopyranosides were further degraded to flavones isoorientin and orientin.
- Krafczyk, Nicole,Glomb, Marcus A.
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p. 3368 - 3376
(2008/09/20)
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- SYNTHESIS OF SEGMENTAL THERMOTROPIC LIQUID-CRYSTALLINE COPOLYESTERS
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A method of functionalization of a tetramer of α-methylstyrene with 4-hydroxybenzoyl groups has been proposed α,ω-(4-hydroxybenzoyl)-tetra-α-methylstyrene and α,ω-(4-hydroxybenzoyl-4-oxybenzoyl)-tetra-α-methylstyrene were obtained and characterized.Their
- Skorokhodov, S. S.,Korshun, A. M.,Asinovskaja, D. N.
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p. 179 - 188
(2007/10/02)
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- ESR and ENDOR Investigations of Spin Exchange in Mixed Galvinoxyl/Nitroxide Biradicals. Syntheses
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The synthesis of a variety of mixed biradicals consisting of galvinoxyl and nitroxide moieties is given.For the first time successful fluid solution ENDOR experiments on mixed biradicals could be performed.The magnetic properties of these systems are significantly dependent (a) on the relative magnitudes of the exchange integral J as compared to the hyperfine interactions, (b) on the sign of J, and (c) on the difference of the g values of the constituent monoradical fragments.It is demonstrated that the ENDOR technique allows direct determination of the hyperfine coupling constants even in cases where is comparable in magnitude to the hyperfine coupling constants.Moreover, the sign of the exchange integral can be deduced from these measurements.It is shown that the ENDOR spectroscopy in combination with spin labeling to obtain "weakly coupled biradicals" may serve as a technique to measure signs of hyperfine coupling constants.
- Kirste, B.,Krueger, A.,Kurreck, H.
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p. 3850 - 3858
(2007/10/02)
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- Syntheses and Reactions of (Trimethylsiloxy)benzoyl Chlorides
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The (trimethylsiloxy)benzoyl chlorides 1-7 are easily to obtain under mild conditions from silylated hydroxybenzoic acids by means of thionyl chloride.Whereas these acid chlorides are stable at room temperature, they undergo condensation polymerisation at temperatures above 100 deg C.Reactions with various nucleophils, such as thioalcohols, phenols, amines, N,O-bis(silylated)amino acids and N-silylated lactams were investigated.With hexamethyldisilazane and thionyl chloride the (trimethylsiloxy)benzonitriles 21, 22 are accessible, and by means of trimethylsilylazide the (trimethylsiloxy)phenyl isocyanates 23-25 were obtained.Conversion with phenyl carbazate and subsequent silylation lead to the 2-(trimethylsiloxy)phenyl-1,3,4-oxadiazol-5-ones 27a-c.
- Schwarz, Gerd,Alberts, Heinrich,Kricheldorf, Hans R.
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p. 1257 - 1270
(2007/10/02)
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