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Amide proton transfer

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https://www.readbyqxmd.com/read/29623974/mechanistic-insights-into-pd-0-catalyzed-intermolecular-and-intramolecular-hydroamination-of-methylenecyclopropanes-a-computational-study
#1
Yuan Liu, Abosede Adejoke Ogunlana, Xiaoguang Bao
The mechanisms of transition metal-catalyzed methylenecyclopropanes (MCPs)-involved reactions are rather complicated due to the diverse pathways for the activation of MCPs. Herein, computational studies were carried out to investigate the detailed mechanisms of Pd(0)-catalyzed intermolecular and intramolecular hydroamination of MCPs. The initial activation of the three-membered ring of MCPs readily occurs via the insertion of Pd(0) into the distal C-C bond, leading to a metallacyclobutane intermediate. The commonly proposed oxidative addition of amine/amide nucleophile (Nu-H) onto the Pd(0) center to afford a hydrido-Pd(ii) complex, however, is less favorable in comparison with the Pd(0)-mediated cleavage of the distal C-C bond of MCPs...
April 6, 2018: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/29601193/mechanism-and-origins-of-stereoinduction-in-asymmetric-friedel-crafts-alkylation-reaction-of-chalcone-catalyzed-by-chiral-n-n-dioxide-sc-iii-complex
#2
Yini Zuo, Na Yang, Xunkun Huang, Changwei Hu, Zhishan Su
The mechanism and selectivity of asymmetric Friedel-Crafts (F-C) alkylation reaction between indole and chalcone catalyzed by chiral N, N'-dioxide-Sc(III) complexes were investigated at the M06/6-311+G(d,p)//M06/[LANL2DZ, 6-31G(d)](SMD,CH2Cl2) level. The reaction occurred via a three-step mechanism: (i) the C3-C bond formation by interacting the most mucleophilic C3 centre of indole with the most electrophilic C centre of chalcone; (ii) the abstraction of the proton at C3 atom of indole by counterion OTf-; (iii) proton transfer from HOTf to C atom of chalcone, generating F-C alkylation product...
March 30, 2018: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/29540619/amide-proton-transfer-imaging-of-cavernous-malformation-in-the-cavernous-sinus
#3
Manisha Bohara, Kiyohisa Kamimura, Masanori Nakajo, Tomohide Yoneyama, Takashi Yoshiura
No abstract text is available yet for this article.
March 13, 2018: Magnetic Resonance in Medical Sciences: MRMS
https://www.readbyqxmd.com/read/29528228/high-resolution-2d-nmr-of-disordered-proteins-enhanced-by-hyperpolarized-water
#4
Or Szekely, Gregory Lars Olsen, Isabella Caterina Felli, Lucio Frydman
This study demonstrates the usefulness derived from relying on hyperpolarized water obtained by dissolution DNP, for site-resolved biophysical NMR studies of intrinsically disordered proteins. Thanks to the facile amide-solvent exchange experienced by protons in these proteins, 2D NMR experiments that like HMQC rely on the polarization of the amide protons, can be enhanced using hyperpolarized water by several orders of magnitude over their conventional counterparts. Optimizations of the DNP procedure and of the subsequent injection into the protein sample are necessary to achieve these gains while preserving state-of-the-art resolution; procedures enabling this transfer of the hyperpolarized water and the achievement of foamless hyperpolarized protein solutions, are here demonstrated...
March 12, 2018: Analytical Chemistry
https://www.readbyqxmd.com/read/29504144/pro-quest-a-rapid-assessment-method-based-on-progressive-saturation-for-quantifying-exchange-rates-using-saturation-times-in-cest
#5
Eleni Demetriou, Mohamed Tachrount, Moritz Zaiss, Karin Shmueli, Xavier Golay
PURPOSE: To develop a new MRI technique to rapidly measure exchange rates in CEST MRI. METHODS: A novel pulse sequence for measuring chemical exchange rates through a progressive saturation recovery process, called PRO-QUEST (progressive saturation for quantifying exchange rates using saturation times), has been developed. Using this method, the water magnetization is sampled under non-steady-state conditions, and off-resonance saturation is interleaved with the acquisition of images obtained through a Look-Locker type of acquisition...
March 5, 2018: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
https://www.readbyqxmd.com/read/29502224/detection-of-side-chain-proton-resonances-of-fully-protonated-biosolids-in-nano-litre-volumes-by-magic-angle-spinning-solid-state-nmr
#6
James Tolchard, Manoj Kumar Pandey, Mélanie Berbon, Abdelmajid Noubhani, Sven J Saupe, Yusuke Nishiyama, Birgit Habenstein, Antoine Loquet
We present a new solid-state NMR proton-detected three-dimensional experiment dedicated to the observation of protein proton side chain resonances in nano-liter volumes. The experiment takes advantage of very fast magic angle spinning and double quantum 13C-13C transfer to establish efficient (H)CCH correlations detected on side chain protons. Our approach is demonstrated on the HET-s prion domain in its functional amyloid fibrillar form, fully protonated, with a sample amount of less than 500 µg using a MAS frequency of 70 kHz...
March 3, 2018: Journal of Biomolecular NMR
https://www.readbyqxmd.com/read/29488086/amide-proton-transfer-imaging-seems-to-provide-higher-diagnostic-performance-in-post-treatment-high-grade-gliomas-than-methionine-positron-emission-tomography
#7
Ji Eun Park, Ji Ye Lee, Ho Sung Kim, Joo-Young Oh, Seung Chai Jung, Sang Joon Kim, Jochen Keupp, Minyoung Oh, Jae Seung Kim
OBJECTIVES: To compare the diagnostic performance of amide proton transfer (APT) imaging and 11-C methionine positron emission tomography (MET-PET) for in vivo molecular imaging of protein metabolism in post-treatment gliomas. MATERIALS AND METHODS: This study included 43 patients (12 low and 31 high grade) with post-treatment gliomas who underwent both APT and MET-PET imaging within 3 weeks. APT-weighted voxel values and semi-quantitative tumour-to-normal ratios (TNR) were obtained from tumour portions...
February 27, 2018: European Radiology
https://www.readbyqxmd.com/read/29481097/a-next-generation-synthesis-of-bace1-inhibitor-verubecestat-mk-8931
#8
David A Thaisrivongs, William J Morris, Lushi Tan, Zhiguo J Song, Thomas W Lyons, Jacob H Waldman, John R Naber, Wenyong Chen, Lu Chen, Baoyun Zhang, Jun Yang
The development of a commercial manufacturing route to verubecestat (MK-8931) is described, highlights of which include the application of a continuous processing step to outcompete fast proton transfer in a Mannich-type ketimine addition, a copper-catalyzed amidation reaction, and an optimized guanidinylation procedure to form the key iminothiadiazine dioxide core.
February 26, 2018: Organic Letters
https://www.readbyqxmd.com/read/29478081/hybrid-mr-pet-of-brain-tumours-using-amino-acid-pet-and-chemical-exchange-saturation-transfer-mri
#9
N A da Silva, P Lohmann, J Fairney, A W Magill, A-M Oros Peusquens, C-H Choi, R Stirnberg, G Stoffels, N Galldiks, X Golay, K-J Langen, N Jon Shah
PURPOSE: PET using radiolabelled amino acids has become a promising tool in the diagnostics of gliomas and brain metastasis. Current research is focused on the evaluation of amide proton transfer (APT) chemical exchange saturation transfer (CEST) MR imaging for brain tumour imaging. In this hybrid MR-PET study, brain tumours were compared using 3D data derived from APT-CEST MRI and amino acid PET using O-(2-18 F-fluoroethyl)-L-tyrosine (18 F-FET). METHODS: Eight patients with gliomas were investigated simultaneously with18 F-FET PET and APT-CEST MRI using a 3-T MR-BrainPET scanner...
February 24, 2018: European Journal of Nuclear Medicine and Molecular Imaging
https://www.readbyqxmd.com/read/29470156/journal-club-evaluation-of-diffusion-kurtosis-imaging-of-stroke-lesion-with-hemodynamic-and-metabolic-mri-in-a-rodent-model-of-acute-stroke
#10
Dongshuang Lu, Yinghua Jiang, Yang Ji, Iris Yuwen Zhou, Emiri Mandeville, Eng H Lo, Xiaoying Wang, Phillip Zhe Sun
OBJECTIVE: Diffusion kurtosis imaging (DKI) has emerged as a new acute stroke imaging approach, augmenting routine DWI. Although it has been shown that a diffusion lesion without kurtosis abnormality is more likely to recover after reperfusion, whereas a kurtosis lesion shows poor response, little is known about the underlying pathophysiologic profile of the kurtosis lesion versus the kurtosis lesion-diffusion lesion mismatch. MATERIALS AND METHODS: We performed multiparametric MRI, including arterial spin labeling, pH-sensitive amide proton transfer, and DKI, in a rodent model of acute stroke caused by embolic middle cerebral artery occlusion...
February 22, 2018: AJR. American Journal of Roentgenology
https://www.readbyqxmd.com/read/29424463/spin-lock-imaging-of-early-tissue-ph-changes-in-ischemic-rat-brain
#11
Zhongliang Zu, Aqeela Afzal, Hua Li, Jingping Xie, John C Gore
We have previously reported that the dispersion of spin-lattice relaxation rates in the rotating frame (R1ρ ) of tissue water protons at high field can be dominated by chemical exchange contributions. Ischemia in brain causes changes in tissue pH, which in turn may affect proton exchange rates. Amide proton transfer (APT, a form of chemical exchange saturation transfer) has been shown to be sensitive to chemical exchange rates and able to detect pH changes non-invasively following ischemic stroke. However, the specificity of APT to pH changes is decreased because of the influence of several other factors that affect magnetization transfer...
February 9, 2018: NMR in Biomedicine
https://www.readbyqxmd.com/read/29412653/inner-sphere-and-outer-sphere-water-interactions-in-co-ii-paracest-agents
#12
Samira M Abozeid, Eric M Snyder, Timothy Y Tittiris, Charles M Steuerwald, Alexander Y Nazarenko, Janet R Morrow
High-spin Co(II) complexes are promising for development as paraCEST agents (paraCEST = paramagnetic chemical exchange saturation transfer) for magnetic resonance imaging applications. The first examples of Co(II) paraCEST agents with bound water ligands are presented here. Four Co(II) macrocyclic complexes based on 1,4,7-triazacyclononane and containing either pendent alcohol or pendent amide groups were prepared. Two of the macrocycles encapsulate the Co(II) and contain no water ligands as shown by X-ray crystallographic studies, and two complexes have macrocycles with only five ligand donor groups to leave an open coordination site for bound water...
February 7, 2018: Inorganic Chemistry
https://www.readbyqxmd.com/read/29392952/effect-of-hydrogen-bonding-and-partial-deprotonation-on-the-oxidation-of-peptides
#13
Bun Chan, Christopher J Easton, Leo Radom
In a recent computational study, we found that hydrogen bonding/partial deprotonation facilitates subsequent electron transfer from amides to HO•. We have now analyzed these and related reactions with a glycine derivative as a model peptide, investigating not only reaction energies but also barriers for the individual steps. We find that partial deprotonation not only assists subsequent electron transfer (a sequential proton-loss electron-transfer (SPLET)-type reaction pathway) but also promotes sequential hydrogen-atom transfer (HAT, in a sequential proton-loss hydrogen-atom-transfer (SPLHAT)-type process), both being potential alternatives to direct HAT as routes for peptide oxidation...
February 2, 2018: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29385345/thermodynamic-acidity-studies-of-6-6-dihydroxy-2-2-bipyridine-a-combined-experimental-and-computational-approach
#14
Dalton B Burks, Monica Vasiliu, David A Dixon, Elizabeth T Papish
The organic ligand 6,6'-dihydroxy-2,2'-bipyridine (6,6'-dhbp) is frequently used to bind transition metals in order to form catalysts for many organic and inorganic transformations. 6,6'-dhbp exists in two tautomeric forms, the pyridinol tautomer and the amide (lactam) tautomer with each tautomer having two rotational conformers: cis or trans. Only the cis-pyridinol tautomer has the proper configuration to bind transition metals. The pendant OH (or O- groups when deprotonated) in 6,6'-dhbp typically do not bind the metal when forming the metal catalyst but can facilitate the proton transfer steps in the catalysis process...
January 31, 2018: Journal of Physical Chemistry. A
https://www.readbyqxmd.com/read/29326984/using-para-hydrogen-to-hyperpolarize-amines-amides-carboxylic-acids-alcohols-phosphates-and-carbonates
#15
Wissam Iali, Peter J Rayner, Simon B Duckett
Hyperpolarization turns weak nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) responses into strong signals, so normally impractical measurements are possible. We use para hydrogen to rapidly hyperpolarize appropriate 1 H, 13 C, 15 N, and 31 P responses of analytes (such as NH3 ) and important amines (such as phenylethylamine), amides (such as acetamide, urea, and methacrylamide), alcohols spanning methanol through octanol and glucose, the sodium salts of carboxylic acids (such as acetic acid and pyruvic acid), sodium phosphate, disodium adenosine 5'-triphosphate, and sodium hydrogen carbonate...
January 2018: Science Advances
https://www.readbyqxmd.com/read/29313159/improved-differentiation-of-low-grade-and-high-grade-gliomas-and-detection-of-tumor-proliferation-using-apt-contrast-fitted-from-z-spectrum
#16
Jiaxuan Zhang, Wenzhen Zhu, Rongwen Tain, Xiaohong Joe Zhou, Kejia Cai
PURPOSE: The purpose of the study is to demonstrate the value of quantitative amide proton transfer (APT) imaging for differentiating glioma grades and detecting tumor proliferation. PROCEDURES: This study included 32 subjects with 16 low-grade gliomas (LGG) and 16 high-grade gliomas (HGG) confirmed by histopathology. Chemical exchange saturation transfer (CEST) magnetic resonance imaging with APT weighting was performed on a 3 T scanner. After B0 correction, Z-spectra were fitted with Lorentzian functions corresponding to the upfield semi-solid magnetization transfer and nuclear overhauser enhancement (MT&NOE) effect, the direct saturation (DS) effect, and the downfield APT effect centered at around - 1...
January 8, 2018: Molecular Imaging and Biology: MIB: the Official Publication of the Academy of Molecular Imaging
https://www.readbyqxmd.com/read/29301781/addition-of-amide-proton-transfer-imaging-to-fdg-pet-ct-improves-diagnostic-accuracy-in-glioma-grading-a-preliminary-study-using-the-continuous-net-reclassification-analysis
#17
A Sakata, T Okada, Y Yamamoto, Y Fushimi, T Dodo, Y Arakawa, Y Mineharu, B Schmitt, S Miyamoto, K Togashi
BACKGROUND AND PURPOSE: Amide proton transfer imaging has been successfully applied to brain tumors, however, the relationships between amide proton transfer and other quantitative imaging values have yet to be investigated. The aim was to examine the additive value of amide proton transfer imaging alongside [18 F] FDG-PET and DWI for preoperative grading of gliomas. MATERIALS AND METHODS: Forty-nine patients with newly diagnosed gliomas were included in this retrospective study...
February 2018: AJNR. American Journal of Neuroradiology
https://www.readbyqxmd.com/read/29234914/discriminating-mgmt-promoter-methylation-status-in-patients-with-glioblastoma-employing-amide-proton-transfer-weighted-mri-metrics
#18
Shanshan Jiang, Qihong Rui, Yu Wang, Hye-Young Heo, Tianyu Zou, Hao Yu, Yi Zhang, Xianlong Wang, Yongxing Du, Xinrui Wen, Fangyao Chen, Jihong Wang, Charles G Eberhart, Jinyuan Zhou, Zhibo Wen
OBJECTIVES: To explore the feasibility of using amide proton transfer-weighted (APTw) MRI metrics as surrogate biomarkers to identify the O6-methylguanine-DNA methyltransferase (MGMT) promoter methylation status in glioblastoma (GBM). METHODS: Eighteen newly diagnosed GBM patients, who were previously scanned at 3T and had a confirmed MGMT methylation status, were retrospectively analysed. For each case, a histogram analysis in the tumour mass was performed to evaluate several quantitative APTw MRI metrics...
December 12, 2017: European Radiology
https://www.readbyqxmd.com/read/29193448/increased-cest-specificity-for-amide-and-fast-exchanging-amine-protons-using-exchange-dependent-relaxation-rate
#19
Xiao-Yong Zhang, Feng Wang, Junzhong Xu, Daniel F Gochberg, John C Gore, Zhongliang Zu
Chemical exchange saturation transfer (CEST) imaging of amides at 3.5 ppm and fast-exchanging amines at 3 ppm provides a unique means to enhance the sensitivity of detection of, for example, proteins/peptides and neurotransmitters, respectively, and hence can provide important information on molecular composition. However, despite the high sensitivity relative to conventional magnetic resonance spectroscopy (MRS), in practice, CEST often has relatively poor specificity. For example, CEST signals are typically influenced by several confounding effects, including direct water saturation (DS), semi-solid non-specific magnetization transfer (MT), the influence of water relaxation times (T1w ) and nearby overlapping CEST signals...
February 2018: NMR in Biomedicine
https://www.readbyqxmd.com/read/29154463/establishing-upper-limits-on-neuronal-activity-evoked-ph-changes-with-apt-cest-mri-at-7-t
#20
Vitaliy Khlebnikov, Jeroen C W Siero, Alex A Bhogal, Peter R Luijten, Dennis W J Klomp, Hans Hoogduin
PURPOSE: To detect neuronal activity-evoked pH changes by amide proton transfer-chemical exchange saturation transfer (APT-CEST) MRI at 7 T. METHODS: Three healthy subjects participated in the study. A low-power 3-dimensional APT-CEST sequence was optimized through the Bloch-McConnell equations. pH sensitivity of the sequence was estimated both in phantoms and in vivo. The feasibility of pH-functional MRI was tested in Bloch-McConnell-simulated data using the optimized sequence...
November 20, 2017: Magnetic Resonance in Medicine: Official Journal of the Society of Magnetic Resonance in Medicine
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