In a recent publication, Eleftheriou et al. proposed that inhibitors of dipeptidyl peptidase-4 (DPP-4) are functional inhibitors of the main protease (Mpro) of SARS-CoV-2. Their predictions prompted the authors to suggest linagliptin, a DPP-4 inhibitor and approved anti-diabetes drug, as a repurposed drug candidate against the ongoing COVID-19 pandemic. We used an enzymatic assay measuring the inhibition of Mpro catalytic activity in the presence of four different commercially available gliptins (linagliptin, sitagliptin, alogliptin and saxagliptin) and several structural analogues of linagliptin to study the binding of DPP-4 inhibitors to Mpro and their functional activity. We show here that DPP-4 inhibitors like linagliptin, other gliptins and structural analogues are inactive against Mpro. 相似文献
Isomers of 4‐amino‐1,3‐dinitrotriazol‐5‐one‐2‐oxide (ADNTONO) are of interest in the contest of insensitive explosives and were found to have true local energy minima at the DFT‐B3LYP/aug‐cc‐pVDZ level. The optimized structures, vibrational frequencies and thermodynamic values for triazol‐5‐one N‐oxides were obtained in their ground state. Kamlet‐Jacob equations were used to evaluate the performance properties. The detonation properties of ADNTONO (D=10.15 to 10.46 km s−1, P=50.86 to 54.25 GPa) are higher compared with those of 1,1‐diamino‐2,2‐dinitroethylene (D=8.87 km s−1, P=32.75 GPa), 5‐nitro‐1,2,4‐triazol‐3‐one (D=8.56 km s−1, P=31.12 GPa), 1,2,4,5‐tetrazine‐3,6‐diamine‐1,4‐dioxide (D=8.78 km s−1, P=31.0 GPa), 1‐amino‐3,4,5‐trinitropyrazole (D=9.31 km s−1, P=40.13 GPa), 4,4′‐dinitro‐3,3′‐bifurazan (D=8.80 km s−1, P=35.60 GPa) and 3,4‐bis(3‐nitrofurazan‐4‐yl)furoxan (D=9.25 km s−1, P=39.54 GPa). The NH2 group(s) appears to be particularly promising area for investigation since it may lead to two desirable consequences of higher stability (insensitivity), higher density, and thus detonation velocity and pressure. 相似文献
The forward (kon) and reverse (koff) rate constants of drug–target interactions have important implications for therapeutic efficacy. Hence, time-resolved assays capable of measuring these binding rate constants may be informative to drug discovery efforts. Here, we used an ion channel activation assay to estimate the kons and koffs of four dopamine D2 receptor (D2R) agonists; dopamine (DA), p-tyramine, (R)- and (S)-5-OH-dipropylaminotetralin (DPAT). We further probed the role of the conserved serine S1935.42 by mutagenesis, taking advantage of the preferential interaction of (S)-, but not (R)-5-OH-DPAT with this residue. Results suggested similar koffs for the two 5-OH-DPAT enantiomers at wild-type (WT) D2R, both being slower than the koffs of DA and p-tyramine. Conversely, the kon of (S)-5-OH-DPAT was estimated to be higher than that of (R)-5-OH-DPAT, in agreement with the higher potency of the (S)-enantiomer. Furthermore, S1935.42A mutation lowered the kon of (S)-5-OH-DPAT and reduced the potency difference between the two 5-OH-DPAT enantiomers. Kinetic Kds derived from the koff and kon estimates correlated well with EC50 values for all four compounds across four orders of magnitude, strengthening the notion that our assay captured meaningful information about binding kinetics. The approach presented here may thus prove valuable for characterizing D2R agonist candidate drugs. 相似文献
The technique of simultaneous pulse radiolysis and photolysis, PRAP, has been utilized to study the reactions of various radicals with ground state ZnTPPS and the triplet state ZnTPPST in aqueous solutions. The radicals H and OH add to both states with k ∼ 1 × 1010 M−1 s−1. The CH2C(CH3)2OH radical from t-BuOH is relatively inert toward ZnTPPS but reacts rapidly (k = 1.8 × 109 M−1 s−1) with ZnTPPST to form an adduct. Electron transfer reactions are found to be about an order of magnitude faster with the triplet than with the ground state. The (CH3)2COH radical reduces both ZnTPPS (k = 1 × 108 M−1 s−1) and ZnTPPST (k = 3 × 109 M−1 s−1) to the anion radical (ZnTPPS)−. The radical Br−2 oxidizes both states to the cation radical (ZnTPPS)+ with k = 8 × 108 M−1 s−1 for the ground state and 5 × 109 M−1 s−1 for the triplet. The transient cation Cd+ reduces both states with a diffusion-controlled rate (k = 1 × 1010 M−1 s−1) to produce the anion radical. The above mechanisms of radical addition and electron transfer are also supported by the product spectra. 相似文献
The substrate scope of the flavoprotein alditol oxidase (AldO) from Streptomyces coelicolor A3(2), recombinantly produced in Escherichia coli, was explored. While it has been established that AldO efficiently oxidizes alditols to D ‐aldoses, this study revealed that the enzyme is also active with a broad range of aliphatic and aromatic alcohols. Alcohols containing hydroxy groups at the C‐1 and C‐2 positions like 1,2,4‐butanetriol (Km=170 mM, kcat=4.4 s−1), 1,2‐pentanediol (Km=52 mM, kcat=0.85 s−1) and 1,2‐hexanediol (Km=97 mM, kcat=2.0 s−1) were readily accepted by AldO. Furthermore, the enzyme was highly enantioselective for the oxidation of 1,2‐diols [e.g., for 1‐phenyl‐1,2‐ethanediol the (R)‐enantiomer was preferred with an E‐value of 74]. For several diols the oxidation products were determined by GC‐MS and NMR. Interestingly, for all tested 1,2‐diols the products were found to be the α‐hydroxy acids instead of the expected α‐hydroxy aldehydes. Incubation of (R)‐1‐phenyl‐1,2‐ethanediol with 18O‐labelled water (H218O) revealed that a second enzymatic oxidation step occurs via the hydrate product intermediate. The relaxed substrate specificity, excellent enantioselectivity, and independence of coenzymes make AldO an attractive enzyme for the preparation of optically pure 1,2‐diols and α‐hydroxy acids. 相似文献
An analytical solution for a two resistance mass transfer model explaining the adsorption of Astrazone Blue dye (Basic Blue 69) onto Sorbsil silica has been developed. The model includes a film mass transfer coefficient, kf1 = 80 × 10−6cm·s−1, and an internal effective diffusivity, Deff = 18×10−9cm2·s−1 which controls the internal mass transport processes based on a pore diffusion mechanism. 相似文献
The third‐generation peptide‐dendrimer B1 (AcES)8(BEA)4(K‐Amb‐Y)2BCD‐NH2 (B=branching (S)‐2,3‐diaminopropanoic acid, K=branching lysine, Amb=4‐aminomethyl‐benzoic acid) is the first synthetic model for cobalamin‐binding proteins and binds cobalamin strongly (Ka=5.0×106 M ?1) and rapidly (k2=346 M ?1 s?1) by coordination of cobalt to the cysteine residue at the dendrimer core. A structure–activity relationship study is reported concerning the role of negative charges in binding. Substituting glutamates (E) for glutamines (Q) in the outer branches of B1 to form N3 (AcQS)8(BQA)4(B‐Amb‐Y)2BCD‐NH2 leads to stronger (Ka=12.0×106 M ?1) but slower (k2=67 M ?1 s?1) cobalamin binding. CD and FTIR spectra show that the dendrimers and their cobalamin complexes exist as random‐coil structures without aggregation in solution. The hydrodynamic radii of the dendrimers determined by diffusion NMR either remains constant or slightly decreases upon binding to cobalamin; this indicates the formation of compact, presumably hydrophobically collapsed complexes.相似文献
Mannopeptimycin, a potent drug lead, has superior activity against difficult‐to‐treat multidrug‐resistant Gram‐positive pathogens such as methicillin‐resistant Staphylococcus aureus (MRSA). (2S,3S)‐β‐Methylphenylalanine is a residue in the cyclic hexapeptide core of mannopeptimycin, but the synthesis of this residue is far from clear. We report here on the reaction order and the stereochemical course of reaction in the formation of (2S,3S)‐β‐methylphenylalanine. The reaction is executed by the enzymes MppJ and TyrB, an S‐adenosyl methionine (SAM)‐dependent methyltransferase and an (S)‐aromatic‐amino‐acid aminotransferase, respectively. Phenylpyruvic acid is methylated by MppJ at its benzylic position at the expense of one equivalent of SAM. The resulting β‐methyl phenylpyruvic acid is then converted to (2S,3S)‐β‐methylphenylalanine by TyrB. MppJ was further determined to be regioselective and stereoselective in its catalysis of the formation of (3S)‐β‐methylphenylpyruvic acid. The binding constant (KD) of MppJ versus SAM is 26 μM . The kinetic constants with respect to kcat Ppy and KM Ppy, and kcat SAM and KM SAM are 0.8 s?1 and 2.5 mM , and 8.15 s?1 and 0.014 mM , respectively. These results suggest SAM has higher binding affinity for MppJ than Ppy, and the C? C bond formation in βmPpy might be the rate‐limiting step, as opposed to the C? S bond breakage in SAM.相似文献
The branched-pore adsorption model, expressed by an external mass transfer coefficient kf, a solid diffusivity Ds, a lumped micropore diffusion rate parameter kb, and the fraction of macropores f, describes kinetic data from initial contact of adsorbent-adsorbate to the long-term ( > 24 hours) adsorption stages with reasonable accuracy.In this work the model is applied for three basic dye systems, namely Basic Red 22, Basic Yellow 21 and Basic Blue 69, all on carbon. A single value of each parameter describes each dye system. The kf values are 0.18 × 10−2±28%, 0.3 × 10−2±17% and 0.2 × 10−2 ± 20% cm s−1, the Ds values are 0.33 × 10−9 21%, 0.72 × 10−9 ± 9% and 0.72 × 10−9 ± 9% cm2 s−1, the kb values are 0.65 × 10−6 ± 7.7%, 1.8 × 10−6 0.2 × 10−6 1% s−1, while the f values are 0.55 ± 9%, 0.60 ± 10 % and 0.18 ± 11%, each for Basic Red 22, Basic Yellow 21 and Basic Blue 69 respectively.The model is based on the internal structure of the carbon particle being divided into a macropore and a micropore region. The latter has an upper-bound capacity of 241, 245 and 656 mg g−1 for Basic Red 22, Basic Yellow 21 and Basic Blue 69 respectively. A sensitivity analysis for each parameter has been carried out. 相似文献
Reactions of H atoms with COS, CS2, and H2S were studied behind reflected shock waves at temperatures between 1170 K and 1830 K and pressures around 1.0 bar by applying atomic resonance absorption spectroscopy (ARAS) for time-resolved measurements of H atoms at Lα. The thermal decomposition of a few ppm ethyl iodide (C2H5I) was used as a H-atom source. In the presence of a large excess of the molecular reactant COS, CS2, or H2S, a consumption of H was observed which follows a pseudo first-order rate law. Rate coefficients for the reactions: were determined to be: k1 = 2.4 × 1014exp(–3415 K/T) cm3mol−1s−1k2 = 1.4 × 1015exp(–9250 K/T) cm3mol−1s−1k3 = 2.5 × 1014exp(–2890 K/T) cm3mol−1s−1相似文献
Quorum quenching lactonases are enzymes capable of hydrolyzing lactones, including N-acyl homoserine lactones (AHLs). AHLs are molecules known as signals in bacterial communication dubbed quorum sensing. Bacterial signal disruption by lactonases was previously reported to inhibit behavior regulated by quorum sensing, such as the expression of virulence factors and the formation of biofilms. Herein, we report the enzymatic and structural characterization of a novel lactonase representative from the metallo-β-lactamase superfamily, dubbed GcL. GcL is a broad spectrum and highly proficient lactonase, with kcat/KM values in the range of 104 to 106 m −1 s−1. Analysis of free GcL structures and in complex with AHL substrates of different acyl chain length, namely, C4-AHL and 3-oxo-C12-AHL, allowed their respective binding modes to be elucidated. Structures reveal three subsites in the binding crevice: 1) the small subsite where chemistry is performed on the lactone ring; 2) a hydrophobic ring that accommodates the amide group of AHLs and small acyl chains; and 3) the outer, hydrophilic subsite that extends to the protein surface. Unexpectedly, the absence of structural accommodation for long substrate acyl chains seems to relate to the broad substrate specificity of the enzyme. 相似文献
Specific inhibition of the copper‐containing peptidylglycine α‐hydroxylating monooxygenase (PHM), which catalyzes the post‐translational modification of peptides involved in carcinogenesis and tumor progression, constitutes a new approach for combating cancer. We carried out a structure–activity study of new compounds derived from a well‐known PHM substrate analogue, the olefinic compound 4‐phenyl‐3‐butenoic acid (PBA). We designed, synthesized, and tested various PBA derivatives both in vitro and in silico. We show that it is possible to increase PBA affinity for PHM by appropriate functionalization of its aromatic nucleus. Compound 2 d , for example, bears a meta‐benzyloxy substituent, and exhibits better inhibition features (Ki=3.9 μM , kinact/Ki=427 M ?1 s?1) than the parent PBA (Ki=19 μM , kinact/Ki=82 M ?1 s?1). Docking calculations also suggest two different binding modes for PBA derivatives; these results will aid in the development of further PHM inhibitors with improved features.相似文献
Theory and experiments on the (non-equilibrium) stripping potentiostatic method for evaluation of the diffusion coefficient and desorption isotherms of hydrogen in α-Pd are discussed. Diffusion coefficient of hydrogen D can be evaluated either under transient conditions, from the anodic stripping current (Ia) or under steady-state condition, from the anodic charge corresponding to the stripping of hydrogen held initially in Pd membrane (Qa). Following data are reported: D = (3.60±0.06) × 10−7 cm2 s−1 (transient) and D = 3.41 × 10−7 cm2 s− (steady-state) at 20°C in 0.1 N H2SO4. Equilibrium concentration and equivalent pressure of hydrogen at the entrance side of Pd membrane can be calculated from the steady-state permeation current (I∞a or the anodic stripping charge (Qa) and its open-circuit potential just after stopping hydrogen generation, E0c. Reliable Sieverts' constants (Ks) have been calculated within 15 and 60°C, and the following thermodynamic values obtained: ΔHo = −(2.6±0.1) kcal (mol H)−1 and ΔSo = −(14.5±0.4) cal K−1 (mol H)−1. These data agree well with those obtained in gas phase measurements. 相似文献
Baeyer-Villiger monooxygenases (BVMOs) are remarkable biocatalysts for the Baeyer-Villiger oxidation of ketones to generate esters or lactones. The regioselectivity of BVMOs is essential for determining the ratio of the two regioisomeric products (“normal” and “abnormal”) when catalyzing asymmetric ketone substrates. Starting from a known normal-preferring BVMO sequence from Pseudomonas putida KT2440 (PpBVMO), a novel BVMO from Gordonia sihwensis (GsBVMO) with higher normal regioselectivity (up to 97/3) was identified. Furthermore, protein engineering increased the specificity constant (kcat/KM) 8.9-fold to 484 s−1 mM−1 for 10-ketostearic acid derived from oleic acid. Consequently, by using the variant GsBVMOC308L as an efficient biocatalyst, 10-ketostearic acid was efficiently transformed into 9-(nonanoyloxy)nonanoic acid, with a space-time yield of 60.5 g L−1 d−1. This study showed that the mutant with higher regioselectivity and catalytic efficiency could be applied to prepare medium-chain ω-hydroxy fatty acids through biotransformation of long-chain aliphatic keto acids derived from renewable plant oils. 相似文献
Rates of hydrogen atom attack on o-fluorotoluene (o-FTOL) and m-fluorotoluene (m-FTOL) at temperatures of 988–1144 K and pressures of 2–2.5 bar have been determined in a single-pulse shock tube study. Hydrogen atoms, generated from the decomposition of hexamethylethane, were allowed to react with the substrates and the characteristic products observed. Rate constants for two reaction channels, displacement of fluorine or methyl, were determined relative to displacement of methyl from 1, 3,5-trimethylbenzene (135TMB). Evidence is presented that abstraction of F is unimportant over the studied temperature range. With k(H + 135TMB → m-xylene + CH3) = 6.7 × 1013 exp(–3255/T) cm3 mol−1s−1, the following rate expressions have been derived: k(H + o-FTOL → C6H5CH3 + F) = 8.38 × 1013 exp(–6041/T) cm3 mol−1s−1; (1012–1142 K) k(H + o-FTOL → C6H5F + CH3) = 2.37 × 1013 exp(–2938/T) cm3 mol−1s−1; (988–1142 K) k(H + m-FTOL → C6H5CH3 + F) = 1.33 × 1014 exp(–6810/T) cm3 mol−1s−1; (1046–1144 K) k(H + m-FTOL → C6H5F + CH3) = 2.04 × 1013 exp(–3104/T) cm3 mol−1s−1; (1008–1144 K) Uncertainties in the relative rate constants are estimated to be factors of about 1.1, while the above absolute values have estimated expanded uncertainties of about a factor of 1.4 in rate, 10 kJ mol−1 in the activation energy, and a factor of 3 in the A-factor. The present data are compared with relevant literature data. From our data and the thermochemistry, a model of the elementary steps comprising displacement of F is developed. On the basis of the model fit to our data, rate constants for the addition of atomic fluorine to toluene at 1100 K are derived. Rate expressions for fluorination reactions of toluene are also determined. The significance of the present results is discussed in the context of the formation of fluorinated byproducts in high-temperature systems. 相似文献
Expressions for the kinetics of grafting chains from a pure end-functional polymer melt to a reactive interface are derived under the assumption that the free energy of reaction is very large and negative. Two cases are considered: a case where the grafting is controlled by diffusion of free end-functional chains through the “brush” of previously grafted chains and a case where the grafting is controlled by the kinetics of the interface reaction itself. Both cases lead to the same form of the grafting kinetics, but with different characteristic times τD = Rga/D, where Rg is radius of gyration, a is the statistical segment length, and D is the diffusion coefficient of the end-functional polymer; and τR = Rg/(akf[B]) where kf is a forward rate constant and [B] is the concentration of groups at the interface that react with the end-function of the polymer chains. The grafting density Σ approaches a practical limit after long times for each value of the degree of polymerization N, and this limit decreases strongly with N. These predictions are compared with the results of recent experiments in which deuterated polystyrene chains with carboxylic acid end groups were grafted to either epoxy- or amine-rich cross-linked epoxy networks. The reaction-controlled grafting model fits the data best and permits us to extract forward rate constants of ˜0.18 kg s−1 mol−1 for the epoxy-rich networks and ˜5 × 10−3 kg s−1 mol−1 for the amine-rich ones. 相似文献