keyword
MENU ▼
Read by QxMD icon Read
search

ring

keyword
https://www.readbyqxmd.com/read/28346939/a-b12-dependent-radical-sam-enzyme-involved-in-oxetanocin-a-biosynthesis
#1
Jennifer Bridwell-Rabb, Aoshu Zhong, He G Sun, Catherine L Drennan, Hung-Wen Liu
Oxetanocin A (OXT-A) is a potent antitumour, antiviral and antibacterial compound. Biosynthesis of OXT-A has been linked to a plasmid-borne Bacillus megaterium gene cluster that contains four genes: oxsA, oxsB, oxrA and oxrB. Here we show that both the oxsA and oxsB genes are required for the production of OXT-A. Biochemical analysis of the encoded proteins, a cobalamin (Cbl)-dependent S-adenosylmethionine (AdoMet) radical enzyme, OxsB, and an HD-domain phosphohydrolase, OxsA, reveals that OXT-A is derived from a 2'-deoxyadenosine phosphate in an OxsB-catalysed ring contraction reaction initiated by hydrogen atom abstraction from C2'...
March 27, 2017: Nature
https://www.readbyqxmd.com/read/28346791/hydroxy-directed-enantioselective-hydroxyalkylation-in-the-carbocyclic-ring-of-indoles
#2
Marc Montesinos-Magraner, Carlos Vila, Gonzalo Blay, Isabel Fernández, M Carmen Muñoz, José R Pedro
A Cinchona-derived squaramide catalyzes the reaction between hydroxyindoles and isatins leading to enantioenriched indoles substituted in the carbocyclic ring. The reaction proceeds efficiently with differently substituted isatins, yielding the desired products with excellent regioselectivity, good yields, and high enantiocontrol. Moreover, every position of the carbocyclic ring of the indole can be functionalized by using the appropriate starting hydroxyindole. The OH group was removed smoothly upon hydrogenolysis of the corresponding triflate...
March 27, 2017: Organic Letters
https://www.readbyqxmd.com/read/28346789/resolving-ultrafast-photoinduced-deactivations-in-water-solvated-pyrimidine-nucleosides
#3
Ana J Pepino, Javier Segarra-Martí, Artur Nenov, Roberto Improta, Marco Garavelli
For the first time, ultrafast deactivations of photo-excited water-solvated pyrimidine nucleosides are mapped employing hybrid QM(CASPT2)/MM(AMBER) optimizations that account for explicit solvation, sugar effects and dynamically correlated potential energy surfaces. Low energy S1/S0 ring-puckering and ring-opening conical intersections (CIs) are suggested to drive the ballistic coherent sub-ps (<200fs) decays observed in each pyrimidine, the energetics controlling this processes correlating with the lifetimes observed...
March 27, 2017: Journal of Physical Chemistry Letters
https://www.readbyqxmd.com/read/28346784/structure-determination-of-mycobacterium-tuberculosis-serine-protease-hip1-rv2224c
#4
Jacqueline Lara Naffin-Olivos, Andrew Daab, Andre White, Nathan Eric Goldfarb, Amy C Milne, Dali Liu, Jacqueline Baikovitz, Ben M Dunn, Jyothi Rengarajan, Gregory A Petsko, Dagmar Ringe
The Mycobacterium tuberculosis (Mtb) serine protease Hip1 (Hydrolase important for pathogenesis; Rv2224c) promotes tuberculosis (TB) pathogenesis by impairing host immune responses through proteolysis of a protein substrate, Mtb GroEL2. The cell surface localization of Hip1 and its immunomodulatory functions make Hip1 a good drug target for new adjunctive immune therapies for TB. Here we report the crystal structure of Hip1 to a resolution of 2.6 Å and the kinetic studies of the enzyme against model substrates and the protein GroEL2...
March 27, 2017: Biochemistry
https://www.readbyqxmd.com/read/28346614/crosstalk-between-transforming-growth-factor-beta-2-and-toll-like-receptor-4-in-the-trabecular-meshwork
#5
Humberto Hernandez, Wanda E Medina-Ortiz, Tomi Luan, Abbot F Clark, Colleen M McDowell
Purpose: The trabecular meshwork (TM) is involved in the outflow of aqueous humor and intraocular pressure (IOP) regulation. Regulation of the extracellular matrix (ECM) by TGFβ2 signaling pathways in the TM has been extensively studied. Recent evidence has implicated toll-like receptor 4 (TLR4) in the regulation of ECM and fibrogenesis in liver, kidney, lung, and skin. Here, we investigated the role of TGFβ2-TLR4 signaling crosstalk in the regulation of the ECM in the TM and ocular hypertension...
March 1, 2017: Investigative Ophthalmology & Visual Science
https://www.readbyqxmd.com/read/28346559/mechanism-of-degradation-of-a-nitrogenous-heterocycle-induced-by-a-reductive-radical-decomposition-of-a-sym-triazine-ring
#6
Gengxin Lyu, Guosheng Shi, Liang Tang, Haiping Fang, Minghong Wu
Cyanuric acid is a major component of many materials and chemicals, and is the most important intermediate in the degradation processes of sym-triazine compounds in the natural environment, as well as being used for water treatment. However, the degradation mechanism of cyanuric acid is still unclear in various advanced oxidation processes (AOPs), where ˙OH is usually regarded as the dominant radical. Here, using a combination of density functional theory calculations and experimental observations, we unexpectedly show that the sym-triazine ring structure is broken efficiently by reductive free radicals - hydrogen radicals (˙H), rather than traditional ˙OH...
March 27, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28346465/sept12-phosphorylation-results-in-loss-of-the-septin-ring-sperm-annulus-defective-sperm-motility-and-poor-male-fertility
#7
Yi-Ru Shen, Han-Yu Wang, Yung-Che Kuo, Shih-Chuan Shih, Chun-Hua Hsu, Yet-Ran Chen, Shang-Rung Wu, Chia-Yih Wang, Pao-Lin Kuo
Septins are critical for numerous cellular processes through the formation of heteromeric filaments and rings indicating the importance of structural regulators in septin assembly. Several posttranslational modifications (PTMs) mediate the dynamics of septin filaments in yeast. However, little is known about the role of PTMs in regulating mammalian septin assembly, and the in vivo significance of PTMs on mammalian septin assembly and function remains unknown. Here, we showed that SEPT12 was phosphorylated on Ser198 using mass spectrometry, and we generated SEPT12 phosphomimetic knock-in (KI) mice to study its biological significance...
March 27, 2017: PLoS Genetics
https://www.readbyqxmd.com/read/28346393/choerosponins-a-and-b-two-new-cytotoxic-bridged-ring-ketones-and-the-determination-of-their-absolute-configurations
#8
Chang-Wei Li, Bing Han, Bing Cai, Cheng-Bin Cui
Bioactivity-directed fractionation of antitumor compounds from the stem barks of Choerospondias axillaries (Roxb.) Burtt et Hill (Anacardiaceae) afforded two new cytotoxic bridged-ring ketones, choerosponins A (1) and B (2), and their structures were elucidated by spectroscopic methods; their stereochemistry was determined by NOE difference experiments, CD spectra and the modified Mosher's method. Compound 1 has a rare dioxatricyclo skeleton. Flow cytometry and SRB methods were employed to evaluate the antitumor activity of the two compounds against tsFT210, HCT-15, HeLa, A2780 and MCF-7 cell lines, and both of them showed strong cytotoxicity...
March 27, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/28346359/new-acorane-type-sesquiterpene-from-acorus-calamus-l
#9
Juan Li, Jianping Zhao, Wei Wang, Lin Li, Lan Zhang, Xiao-Fang Zhao, Qing-Ru Liu, Fang Liu, Min Yang, Ikhlas A Khan, Shun-Xiang Li
A new sesquiterpene, named neo-acorane A (1), and two known ones, acoric acid (2) and calamusin D (3), were isolated from a 95% ethanol extract of the rhizome parts of Acorus calamus L. Their structures were elucidated by spectroscopic methods, and the absolute configurations were determined by single-crystal X-ray diffraction analysis. Compounds 1 and 2 are nonisoprenoid sesquiterpenoids, likely biosynthesized from an acorane-type sesquiterpene by oxidative fission of the six- or five-membered ring. Moreover, compounds 1 (10 μM), 2 (5 μM and 10 μM) and 3 (10 μM) showed cell proliferation activity on the SK-N-BE (2) cell line...
March 26, 2017: Molecules: a Journal of Synthetic Chemistry and Natural Product Chemistry
https://www.readbyqxmd.com/read/28346143/action-of-cmg-with-strand-specific-dna-blocks-supports-an-internal-unwinding-mode-for-the-eukaryotic-replicative-helicase
#10
Lance D Langston, Mike E O'Donnell
Replicative helicases are ring-shaped hexamers that encircle DNA for duplex unwinding. The currently accepted view of hexameric helicase function is by steric exclusion, where the helicase encircles one DNA strand and excludes the other, acting as a wedge with an external DNA unwinding point during translocation. Accordingly, strand specific blocks only affect these helicases when placed on the tracking strand, not the excluded strand. We examined the effect of blocks on the eukaryotic CMG and, contrary to expectations, blocks on either strand inhibit CMG unwinding...
March 27, 2017: ELife
https://www.readbyqxmd.com/read/28345888/influence-of-ring-strain-and-bond-polarization-on-the-ring-expansion-of-phosphorus-homocycles
#11
Saurabh S Chitnis, Rebecca A Musgrave, Hazel A Sparkes, Natalie E Pridmore, Vincent T Annibale, Ian Manners
Heterolytic cleavage of homoatomic bonds is a challenge, as it requires separation of opposite charges. Even highly strained homoatomic rings (e.g., cyclopropane and cyclobutane) are kinetically stable and do not react with nucleophiles or electrophiles. In contrast, cycloalkanes bearing electron-donating/withdrawing substituents on adjacent carbons have polarized C-C bonds and undergo numerous heterolytic ring-opening and expansion reactions. Here we show that upon electrophile activation phosphorus homocycles exhibit analogous reactivity, which is modulated by the amount of ring strain and extent of bond polarization...
March 27, 2017: Inorganic Chemistry
https://www.readbyqxmd.com/read/28345726/structural-analyses-of-isolated-cyclic-tetrapeptides-with-varying-amino-acid-residues
#12
A Stamm, D Maué, A Schaly, S Schlicher, J Bartl, S Kubik, M Gerhards
Cyclic peptides represent a large class of substances that occur in nature with important biological and medical functions. Synthetic cyclic peptides are used as artificial receptors due to a series of advantages over conventional receptors. In order to optimize their binding abilities, investigations of their intrinsic structural properties especially with regard to the influence of different amino acid residues are fundamental. Here we report the structural analysis of two synthetic cyclic tetrapeptides cyclo[l-Tyr(Me)-d-Pro-l-Ala-d-Pro] (CPAla) and cyclo[l-Tyr(Me)-d-Pro-l-Glu(Me)-d-Pro] (CPGlu) in a molecular beam by means of combined IR/UV spectroscopic techniques...
March 27, 2017: Physical Chemistry Chemical Physics: PCCP
https://www.readbyqxmd.com/read/28345631/structure-of-the-cyanuric-acid-hydrolase-trzd-reveals-product-exit-channel
#13
Asim K Bera, Kelly G Aukema, Mikael Elias, Lawrence P Wackett
Cyanuric acid hydrolases are of industrial importance because of their use in aquatic recreational facilities to remove cyanuric acid, a stabilizer for the chlorine. Degradation of excess cyanuric acid is necessary to maintain chlorine disinfection in the waters. Cyanuric acid hydrolase opens the cyanuric acid ring hydrolytically and subsequent decarboxylation produces carbon dioxide and biuret. In the present study, we report the X-ray structure of TrzD, a cyanuric acid hydrolase from Acidovorax citrulli. The crystal structure at 2...
March 27, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28345614/prognosis-and-value-of-preoperative-radiotherapy-in-locally-advanced-rectal-signet-ring-cell-carcinoma
#14
Chun-Run Ling, Rui Wang, Mo-Jin Wang, Jie Ping, Wen Zhuang
As well known, signet-ring cell carcinoma (SRCC) is a rare histological subtype of colorectal adenocarcinoma, which has been associated with poor prognosis and resistant to non-surgery therapy compared with common adenocarcinoma. In this study, we assessed the effect of preoperative radiotherapy (PRT) for locally advanced rectal SRCC in a large patient group from the Surveillance, Epidemiology, and End Results program (SEER, 1988-2011) database. SRCC was found in 0.9% (n = 622) rectal cancer (RC) patients in our study...
March 27, 2017: Scientific Reports
https://www.readbyqxmd.com/read/28345342/the-role-of-strain-in-the-homoaromatization-of-semibullvalenes
#15
Richard Vaughan Williams, Abdullah G Al-Sehemi, Amanda K Meier, Zachary Z Brown, John R Armantrout
The low activation barrier to the Cope rearrangement of semibullvalenes has been attributed to the inherent ring-strain of this nucleus. Appropriate, Dewar-Hoffmann, substitution of semibullvalene results in the stabilization of the transition state and a further lowering of the Cope barrier. An alternative proposal for lowering/eliminating this barrier is the use of strain to destabilize the localized semibullvalene. Using density functional and Hartree Fock calculations, we predict that additionally straining the semibullvalene nucleus, by small ring annelations, will lead to a lowering of the Cope barrier and ultimately to ground state neutral homoaromatics...
March 27, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28345339/synthesis-of-positional-isomeric-phenylphenalenones
#16
Felipe Ospina, Adrian Ramirez, Marisol Cano, William Hidalgo, Bernd Schneider, Felipe Otálvaro
A series of isomeric phenylphenalenones in which the phenyl ring is located at all possible peripheral positions of the phenalenone nuclei was synthesized. The structural characteristics of the series, in which topological variation is permitted with minimal electronic disturbance, could, in principle, allow for easy pharmacophore recognition when the compounds are aligned in steroidomimetic conformations.
March 27, 2017: Journal of Organic Chemistry
https://www.readbyqxmd.com/read/28345254/direct-functionalization-of-poly-spirophosphazene-s-via-the-regioselective-lithiation-of-the-aromatic-rings-using-a-cooperative-superbase
#17
Raquel de la Campa, Diego García, Sandra Rodríguez, Gabino A Carriedo, Alejandro Presa Soto
The direct chemical functionalization of poly(spirophosphazene) [NP(O2 C12 H8 )]n (1) can be performed by the lithiation of the aromatic rings at low temperature using Schlosser's base (Li(t) Bu/KO(t) Bu or "superbase"), and the subsequent reaction with various electrophiles such as ClSiMe3 , ClPPh2 , or MeOB(O2 C6 H12 ) (MeOBpin). The functionalized polymers, isolated in very high yields (>90%) and without degradation of the polymeric chains, have an average degree of substitution per repeat unit ranging from 0...
March 27, 2017: Macromolecular Rapid Communications
https://www.readbyqxmd.com/read/28345168/cardinal-and-anti-cardinal-points-equalities-and-chromatic-dependence
#18
Tanya Evans, William F Harris
PURPOSE: Cardinal points are used for ray tracing through Gaussian systems. Anti-principal and anti-nodal points (which we shall refer to as the anti-cardinal points), along with the six familiar cardinal points, belong to a much larger set of special points. The purpose of this paper is to obtain a set of relationships and resulting equalities among the cardinal and anti-cardinal points and to illustrate them using Pascal's ring. METHODS: The methodology used relies on Gaussian optics and the transference T...
March 27, 2017: Ophthalmic & Physiological Optics: the Journal of the British College of Ophthalmic Opticians (Optometrists)
https://www.readbyqxmd.com/read/28345086/selective-c-c-coupling-at-a-pt-iv-centre-100-preference-for-sp-2-sp-3-over-sp-3-sp-3
#19
Paul A Shaw, Jonathan P Rourke
The oxidative addition of three different organic halides RX to the non-symmetric platinum(ii) mer coordinated dicyclometallated C^N^C complex 1 yielded short-lived six-coordinate platinum(iv) complexes 2(R) (R = Me, allyl, Bn), with the incoming groups trans across the platinum centre. A spontaneous reductive coupling reaction then occurred with, in each case, a completely chemoselective sp(2)-sp(3) coupling, and exclusively gave R-3, with the newly introduced R group bonded to the previously cyclometallated aryl ring...
March 27, 2017: Dalton Transactions: An International Journal of Inorganic Chemistry
https://www.readbyqxmd.com/read/28345082/construction-of-the-septahydroxylated-abc-ring-system-of-dihydro-%C3%AE-agarofurans-application-of-6-exo-dig-radical-cyclization
#20
Hiroki Fujisawa, Tomochika Ishiyama, Daisuke Urabe, Masayuki Inoue
A synthetic route to the septahydroxylated ABC-ring system of dihydro-β-agarofurans was established. The B-ring was formed by a base-promoted diastereoselective Diels-Alder reaction between 3-hydroxy-2-pyrone and a d-glyceraldehyde-derived dienophile, while the C-ring was cyclized by PhSeCl-mediated etherification. The remaining A-ring was constructed via a 6-exo-dig radical reaction. Selective transformations gave rise to the ABC-ring system 1 with nine contiguous stereocenters. The thus obtained 1 corresponded to the enantiomer of the densely oxygenated core structure of dihydro-β-agarofurans...
March 27, 2017: Chemical Communications: Chem Comm
keyword
keyword
31947
1
2
Fetch more papers »
Fetching more papers... Fetching...
Read by QxMD. Sign in or create an account to discover new knowledge that matter to you.
Remove bar
Read by QxMD icon Read
×

Search Tips

Use Boolean operators: AND/OR

diabetic AND foot
diabetes OR diabetic

Exclude a word using the 'minus' sign

Virchow -triad

Use Parentheses

water AND (cup OR glass)

Add an asterisk (*) at end of a word to include word stems

Neuro* will search for Neurology, Neuroscientist, Neurological, and so on

Use quotes to search for an exact phrase

"primary prevention of cancer"
(heart or cardiac or cardio*) AND arrest -"American Heart Association"