Nucleophilic acceleration of the cleavage of β-cyclodextrin trans-cinnamate by amines

The cleavage of β-cyclodextrin trans-cinnamate (1) was accelerated by amines such as quinuclidine and piperidine by 27- and 13-fold, respectively. The reaction involves complex formation of 1 with the amines, and proceeds via nucleophilic attack by the neutral amine, which was shown by the production of amide in the reaction of 1 with piperidine. Quinuclidine exhibited real catalysis of hydrolysis without production of amide. The present finding indicates that the rates of the rate-determining deacylation step in the cyclodextrin-accelerated hydrolyses of phenyl esters can be made larger than the rates of uncatalyzed hydrolyses by an amine such as quinuclidine, resulting in the use of cyclodextrin as a true catalyst and as a better enzyme model.     

Metal-ion-catalyzed hydrolysis of monomethyl and dimethyl esters of 3-(2-imidazoleazo)phthalic acid: Bifunctional catalysis by carboxyl group and the metal ion in the hydrolysis of an alkyl ester

The Cu(II) or Ni(II) ion-catalyzed hydrolysis of methyl 2-carboxy-6-(2-imidazoleazo)benzoate (1) and the corresponding dimethyl ester (2) was studied kinetically at various pH values. For 2, the ester group located at the o position to the azo substiuent was hydrolyzed. From the rate data obtained at various metal concentrations, the values of k_cat and K_f were estimated at each pH value. For the Ni(II)-catalyzed hydrolysis of 1 at pH < 4, k_cat increases as pH is lowered, indicating bifunctional catalysis by the carboxyl group and the metal ion. For most of the reactions investigated under other conditions, the ester hydrolysis was subjected to sole catalysis by the metal ions. Detailed analysis of kinetic data obtained for these reactions indicated that the metal-ion catalysis involves the rate-determining breakdown of the tetrahedral intermediates formed by the addition of a water molecule or hydroxide ion. The bifunctional catalysis by the carboxyl group and Ni(II) ion can be considered as a model for carboxypeptidase A. The kinetic data indicate that the bifunctional catalysis proceeds through the nucleophilic attack of the carboxylate ion at the Ni(II)-coordinated carbonyl group.     

Design,synthesis and biological evaluation of novel spiro-pentacylamides as acetyl-CoA carboxylase inhibitors

Acetyl-CoA carboxylase (ACC) catalyzes the rate-determining step in de novo lipogenesis and plays an important role in the regulation of fatty acid oxidation. Therefore, ACC inhibition offers a promising option for intervention in nonalcoholic fatty liver disease (NAFLD), type 2 diabetes (T2DM) and cancer. In this paper, a series of spiropentacylamide derivatives were synthesized and evaluated for their ACC1/2 inhibitory activities and anti-proliferation effects on A549, H1975, HCT116, SW620 and Caco-2 cell lines in vitro. Compound 6o displayed potent ACC1/2 inhibitory activity (ACC1 IC₅₀?=?0.527?μM, ACC2 IC₅₀?=?0.397?μM) and the most potent anti-proliferation activities against A549, H1975, HCT116, SW620 and Caco-2 cell lines, with IC₅₀ values of 1.92?μM, 0.38?μM, 1.22?μM, 2.05?μM and 5.42?μM respectively. Further molecular docking studies revealed that compound 6o maintained hydrogen bonds between the two carbonyls and protein backbone NHs (Glu-B2026 and Gly-B1958). These results indicate that compound 6o is a promising ACC1/2 inhibitor for the potent treatment of cancer.     

Kinetics of the reduction of C-9 substituted acridinium cations by 1,4-dihydronicotinamides

Second-order rate constants (k₂) are reported for the reduction of 9-R-10-methylacridinium cations (5:R = H, CH₃, CH₃CH₂, C₆H₅CH₂, (CH₃)₂CH, C₆H₅, 4-(CH₃)₂NC₆H₄) by 1-benzyl-1,4-dihydronicotinamide (2:R = C₆H₅CH₂) in 20% CH₃CN-80% H₂O at 25°C. All 5:R ≠ H are reduced in the range 20- to 140-fold more slowly than 5:R = H. However, there is no simple relationship between k₂ and the nature of R, nor between k₂ and the second-order rate constant for hydroxide ion attack at C-9 of these cations in pseudobase formation. Rates of reduction of 5 by 1-benzyl-4,4-dideuterio-1,4-dihydronicotinamide allow the calculation of the following kinetic isotope effects in this solvent medium: 5:R, $\text{k}{}^{\mathrm{<mtext>H</mtext>}}\text{k}{}^{\mathrm{<mtext>D</mtext>}}\text{:}\text{H}$, 1.56; C₆H₅CH₂, 2.7; C₆H₅, 5.4. Substituent effects upon k₂ were evaluated for the reduction of 5 by 1-(X-benzyl)-1,4-dihydronicotinamides, and lead to the following Hammett ? parameters: 5:R, ?: H, ?0.68; C₆H₅CH₂, ?0.92; C₆H₅, ?0.96. The latter two values require essentially complete unit positive charge generation on the nicotinamide moiety in the rate-determining transition state. It is shown that these Hammett ? values and the above isotope effects can only be rationalized by a two-step e^? + H^? mechanism for hydride transfer from 2 to 5 in this solvent system. This result contrasts with our earlier conclusion of direct, one-step hydride transfer in the reduction of isoquinolinium cations by 2, but is consistent with our observation that acridinium cations are reduced 37500-fold faster by 2 than predicted on the basis of the relative rates of nucleophilic attack (hydroxide ion) on acridinium and isoquinolinium cations. It is suggested that the availability of both Hammett ? values and primary kinetic isotope effects will generally allow the establishment of the mechanism of hydride transfer in these systems. Application of these ideas to literature data suggests that 5:R = H is reduced by direct hydride transfer in acetonitrile solution, in contrast to the above result in predominantly aqueous solution. The ready formation of acridanyl radicals by electron transfer to acridinium cations is demonstrated by the formation of Wurster's Blue radical cation upon mixing solutions of acridinium cations with N,N,N′,N′-tetramethyl-p-phenylenediamine.     

Nitric oxide diffusion to red blood cells limits extracellular,but not intraphagosomal,peroxynitrite formation by macrophages

Macrophage-derived nitric oxide (^•NO) participates in cytotoxic mechanisms against diverse microorganisms and tumor cells. These effects can be mediated by ^•NO itself or ^•NO-derived species such as peroxynitrite formed by its diffusion-controlled reaction with NADPH oxidase-derived superoxide radical anion (O₂^•−). In vivo, the facile extracellular diffusion of ^•NO as well as different competing consumption routes limit its bioavailability for the reaction with O₂^•− and, hence, peroxynitrite formation. In this work, we evaluated the extent by which ^•NO diffusion to red blood cells (RBC) can compete with activated macrophages-derived O₂^•− and affect peroxynitrite formation yields. Macrophage-dependent peroxynitrite production was determined by boron-based probes that react directly with peroxynitrite, namely, coumarin-7-boronic acid (CBA) and fluorescein-boronate (Fl-B). The influence of ^•NO diffusion to RBC on peroxynitrite formation was experimentally analyzed in co-incubations of ^•NO and O₂^•−-forming macrophages with erythrocytes. Additionally, we evaluated the permeation of ^•NO to RBC by measuring the intracellular oxidation of oxyhemoglobin to methemoglobin. Our results indicate that diluted RBC suspensions dose-dependently inhibit peroxynitrite formation, outcompeting the O₂^•− reaction. Computer-assisted kinetic studies evaluating peroxynitrite formation by its precursor radicals in the presence of RBC are in accordance with experimental results. Moreover, the presence of erythrocytes in the proximity of ^•NO and O₂^•--forming macrophages prevented intracellular Fl-B oxidation pre-loaded in L1210 cells co-cultured with activated macrophages. On the other hand, Fl-B-coated latex beads incorporated in the macrophage phagocytic vacuole indicated that intraphagosomal probe oxidation by peroxynitrite was not affected by nearby RBC. Our data support that in the proximity of a blood vessel, ^•NO consumption by RBC will limit the extracellular formation (and subsequent cytotoxic effects) of peroxynitrite by activated macrophages, while the intraphagosomal yield of peroxynitrite will remain unaffected.     

Compounds isolated from Euonymus spraguei Hayata induce ossification through multiple pathways

The process of bone metabolism includes catabolism of old or mature bone and anabolism of new bone, carried out by osteoclasts and osteoblasts respectively. Any imbalance in this process results in loss of bone mass or osteoporosis. Drugs available to combat osteoporosis have certain adverse effects and are unable to improve bone formation, hence identifying new agents to fulfil these therapeutic gaps is required. To expand the scope of potential agents that enhance bone formation, we identified Euonymus spraguei Hayata as a plant material that possesses robust osteogenic potential using human osteoblast cells. We isolated three compounds, syringaresinol (1), syringin (2), and (−)-epicatechin (3), from E. spraguei. Results demonstrated that syringin (2), and (−)-epicatechin (3), increased alkaline phosphatase activity significantly up to 131.01% and 130.67%, respectively; they also elevated mineral deposition with respective values of up to 139.39% and 138.33%. In addition, 2 and 3 modulated autophagy and the bone morphogenetic protein (BMP)-2 signaling pathway. Our findings demonstrated that 2 and 3 induced osteogenesis by targeting multiple pathways and therefore can be considered as potent multi-targeted drugs for bone formation against osteoporosis.     

Synthesis and antibacterial activity of novel water-soluble nocathiacin analogs

Semi-synthetic water-soluble analogs were synthesized from nocathiacin I through the formation of a versatile intermediate nocathiacin amine 5, and subsequent transformation via reductive amination, acylation or urea formation. Several of the novel analogs displayed much improved aqueous solubility over 1, while retained antibacterial activity. Compound 15 and 16 from the amide series, demonstrated excellent in vitro and in vivo antibacterial activity.     

Synthesis and biological evaluation of scopoletin derivatives

A series of new scopoletin derivatives were designed and synthesized. Their anti-proliferative effect was initially evaluated against various human cancer cell lines. Among the tested compounds, A1, A2, and D6 showed significant anti-proliferative activities. Angiogenesis was detected by endothelial cell migration assay and tube formation study. The results showed that A1, A2, and D6 inhibited the vascular endothelial growth factor (VEGF)-stimulated proliferation, migration, and tube formation of human umbilical vein endothelial cells in vitro. Moreover, they inhibited the vessel growth in the chorioallantoic membrane in vivo. This inhibition was correlated with a significant decrease in the VEGF-triggered phosphorylated forms of ERK1/2 and Akt. In summary, these findings strongly suggested that these scopoletin derivatives might be structurally novel angiogenesis inhibitors.     

Nickel/zinc-catalyzed decarbonylative addition of anhydrides to alkynes: A DFT study

Density functional theory (DFT) was used to investigate the nickel- or nickel(0)/zinc- catalyzed decarbonylative addition of phthalic anhydrides to alkynes. All intermediates and transition states were optimized completely at the B3LYP/6-31+G(d,p) level. Calculated results indicated that the decarbonylative addition of phthalic anhydrides to alkynes was exergonic, and the total free energy released was ?87.6 kJ mol^?1. In the five-coordinated complexes M4a and M4b, the insertion reaction of alkynes into the Ni-C bond occurred prior to that into the Ni-O bond. The nickel(0)/zinc-catalyzed decarbonylative addition was much more dominant than the nickel-catalyzed one in whole catalytic decarbonylative addition. The reaction channel CA→M1'→T1'→M2'→T2'→M3a'→M4a'→T3a1'→M5a1' →T4a1'→M6a'→P was the most favorable among all reaction pathways of the nickel- or nickel(0)/zinc- catalyzed decarbonylative addition of phthalic anhydrides to alkynes. And the alkyne insertion reaction was the rate-determining step for this channel. The additive ZnCl₂ had a significant effect, and it might change greatly the electron and geometry structures of those intermediates and transition states. On the whole, the solvent effect decreased the free energy barriers.

Bicyclic brominated furanones: A new class of quorum sensing modulators that inhibit bacterial biofilm formation

Both natural and synthetic brominated furanones are known to inhibit biofilm formation by bacteria, but their toxicity to mammalian cells is often not reported. Here, we designed and synthesized a new class of brominated furanones (BBFs) that contained a bicyclic structure having one bromide group with well-defined regiochemistry. This class of molecules exhibited reduction in the toxicity to mammalian cells (human neuroblastoma SK-N-SH) and did not inhibit bacteria (Pseudomonas aeruginosa and Escherichia coli) growth, but retained the inhibitory activity towards biofilm formation of bacteria. In addition, all the BBFs inhibited the production of virulence factor elastase B in P. aeruginosa. To explore the effect of BBFs on quorum sensing, we used a reporter gene assay and found that 6-BBF and 7-BBF exhibited antagonistic activities for LasR protein in the lasI quorum sensing circuit, while 5-BBF showed agonistic activity for the rhlI quorum sensing circuit. This study suggests that structural variation of brominated furanones can be designed for targeted functions to control biofilm formation.     

A potent seven-membered cyclic BTK (Bruton's tyrosine Kinase) chiral inhibitor conceived by structure-based drug design to lock its bioactive conformation

A seven-membered cyclic chiral analog of potent lead BTK inhibitor 1 was envisioned by structure-based design to lock the molecule into its bioactive conformation. For the elaboration of the seven-membered ring, compound 1 pyridone 6-position was substituted with the purpose to prevent formation of reactive metabolites. Eventually, the cyclic chiral compound 3 maintained the high potency of 1, and most importantly showed no activity at either GSH or TDI assays suggesting no formation of reactive metabolites. The anticipated bound conformation of 3 to BTK was confirmed by X-ray crystallography. Synthetically, the crucial seven-membered ring formation was obtained by using TosMIC as a connective reagent.     

Coordinated nitroxyl anion is produced and released as nitrous oxide by the decomposition of iridium-coordinated nitrosothiols

The aqueous decomposition of the iridium coordinated nitrosothiols (RSNOs) trans-K[IrCl₄(CH₃CN)NOSPh] (1), and K₂[IrCl₅(NOECyS)] (2, ECyS = cysteine ethyl ester), was studied by MS analysis of the gaseous products, ESI-MS, NMR, and UV-Vis spectroscopy. Bent NO (NO⁻, nitroxyl anion), sulfenic acids and nitrite were observed as coordinated products in solution, while nitrous oxide (N₂O) and nitrogen were detected in the gas phase. The formation of coordinated NO⁻ and N₂O, a nitroxyl dimerization product, allows us to propose the formation of free nitroxyl (HNO) as an intermediate. Complex 1 decomposes 300 times slower than free PhSNO does. In both cases (1 and 2) kinetic results show a first order decomposition behavior and a very negative ΔS^≠, which strongly indicates an associative rate-determining step. A proposed decomposition mechanism, supported by the experimental data and DFT calculations, involves, as the first step, nucleophilic attack of H₂O on to the sulfur atom of the coordinated RSNO, producing an NO⁻ complex and free sulfenic acid, followed by two competing reactions: a ligand exchange reaction of this NO⁻ with the sulfenic acid or, to a minor extent, coordination of N₂O to produce an NO⁻/N₂O complex which finally renders free N₂ and coordinated NO₂⁻. Some of the produced NO⁻ is likely to be released from the metal center producing nitroxyl by protonation and finally N₂O by dimerization and loss of H₂O. In conclusion, the decomposition of these coordinated RSNOs occurs through a different mechanism than for the decomposition of free RSNOs. It involves the formation of sulfenic acids and coordinated NO⁻, which is released from the complexes and protonated at the reaction pH producing nitroxyl (HNO), and ultimately N₂O.     

Metal ion induced reaction specificity in vitamin B6 model systems: The effects of Zn2+ and Cu2+ on the 5-deoxypyridoxal catalyzed reactions of α-phenyl-α-aminomalonic acid

In the absence of metal ions, the reaction of 5-deoxypyridoxal (III) with α-phenyl-α-aminomalonic acid, (II; R=C₆H₅) leads to the formation of two 5-deoxypyridoxal-derived products, 5-deoxypyridoxamine (VII) and a dimer-like product (VIII) formed from the condensation of a molecule of III and a molecule of VII (J. W. Thanassi, Biochemistry12, 5109 (1973)). The addition of excess Zn²⁺ ions or limiting Cu²⁺ ions leads to the formation of VII only. Addition of excess Cu²⁺ ions results in an entirely different 5-deoxypyridoxal-derived product, VI, which is a peptide of 5-deoxypyridoxic acid and d,l-α-phenylglycine (V), and which is formed in an oxidative reaction. Mechanisms for the formation of these compounds are discussed in relation to reaction selectivity in vitamin B₆ catalysis.     

Functional mimics of catechol oxidase by mononuclear copper complexes of sterically demanding [NNO] ligands

Several mononuclear copper complexes 1(a-b) and 2(a-b) supported over sterically demanding [NNO] ligands namely, N-(aryl)-2-[(pyridin-2-ylmethyl)amino]acetamide [aryl = 2,6-diethylphenyl (1) and mesityl (2)], exhibit catecholase-like activity in performing the aerial oxidation of 3,5-di-t-butylcatehol (3,5-DTBC) to 3,5-di-t-butyl-catequinone (3,5-DTBQ) under ambient conditions. The 1(a-b) and 2(a-b) complexes were directly synthesized from the reaction of the respective ligands 1-2 with CuX₂·nH₂O (X = Cl, NO₃, n = 2, 3) in 55-85% yield. Mechanistic insights on the catalytic cycle as obtained by density functional theory studies for a representative complex 1a suggest that an intramolecular hydrogen transfer, from a catechol-OH moiety to a copper bound superoxo moiety, form the rate-determining step of the oxidation process, displaying an activation barrier of 18.3 kcal/mol (ΔG^‡) [6.9 kcal/mol in Δ(PE + ZPE)^‡ scale].     

A micromethod for the determination of 5-(adenosine 5'-pyrophosphoryl)-D-ribose (adenosine diphosphoribose-(5)) in biological extracts

The complex formation of Polysaccharide 13140 (1) or 13127 (2) [curdlan-type polysaccharides: gel-forming bacterial (1→3)-β-D-glucans] with dyes in aqueous solution was investigated. The (1→3)-β-D-glucans reacted specifically with Aniline Blue (water soluble) (3) to form stable color complexes. The rate of interaction between 1 or 2 and 3 in aqueous solutions was shown to be proportional to both concentration and gel-forming ability of 1 and 2. This complex formation is to be applied to the quantitative analysis and the determination of gel-forming ability of curdlan-type polysaccharides.     

Synthesis and evaluation of novel 2,3,5-triaryl-4H,2,3,3a,5,6,6a-hexahydropyrrolo[3,4-d]isoxazole-4,6-diones for advanced glycation end product formation inhibitory activity

The synthesis of some biologically interesting pyrrolo-isoxazolidine derivatives was accomplished by the 1,3-dipolar cycloaddition reaction of substituted azomethine N-oxides 1 with substituted N-aryl maleimides 2 leading to the formation of new stereoisomeric 2,3,5-triaryl-4H,2,3,3a,5,6,6a-hexahydropyrrolo[3,4-d]isoxazole-4,6-dione derivatives 3 in excellent yields. The synthesized compounds have been screened for their advanced glycation end (AGE) product formation inhibitory activity on the basis of their ability to inhibit the formation of AGEs in the bovine serum albumin (BSA)-glucose assay. All the synthesized compounds have been found to exhibit significant activity against AGE formation.     

Activity of caffeic acid derivatives against Candida albicans biofilm

The aim of this study was to evaluate the caffeic acid (1) and ester derivatives (2–10) against Candida albicans biofilm and to investigate whether these compounds are able to inhibit the biofilm formation or destroy pre-formed biofilm.Caffeic acid ester 7, cinnamic acid ester 8 and 3,4-dihydroxybenzoic acid ester 10 are more active than fluconazole, used as reference drug, both on biofilm in formation with MIC₅₀ values of 32, 32 and 16 μg/mL, respectively, and in the early stage of biofilm formation (4 h) with MIC₅₀ values of 64, 32 and 64 μg/mL, respectively. These esters result also more active than fluconazole on mature biofilm (24 h), especially 8 and 10 with MIC₅₀ values of 64 μg/mL.     

Deuterium-isotope effect in the biotransformation of 4-ethynylbiphenyls to 4-biphenylylacetic acids by rat hepatic microsomes

$\text{In vitro}$ studies using hepatic microsomal homogenate and 4-(1-deuteroethynyl) biphenyls have shown that there is an isotope effect in conversion of 4-ethynylbiphenyls to 4-biphenylylacetic acids. This effect is consistent with mechanisms involving either (1) direct hydroxylation of the ethynyl moiety or (2) oxirene formation followed by a rate-determining hydride shift to form the intermediate ketene.     

Rate-adjusted cross-linking reaction by photoresponsive α-bromoaldehyde (PBA)-conjugated ODN

We developed a photoresponsive α-bromoaldehyde-conjugated oligonucleotide (PBA-ODN). The PBA-ODN selectively reacted and formed covalent bonds with target oligonucleotides having adenine or cytosine at the frontal position of the aldehyde derivative. Kinetic studies revealed that PBA-ODN has increased kinetic rates for the formation of cross-linked duplexes compared with the corresponding α-chloroaldehyde-conjugated oligonucleotide (PCA-ODN).     

A thiol-inducible and quick-response DNA cross-linking agent

Three new 2,4-dinitrobenzenesulfonyl derivatives 1–3 were successfully prepared for the first time using a simple process. They were efficiently triggered by thiols (glutathione and l-cysteine) to release the corresponding phenol derivatives (4–6) within 5?min. The quick response of 1–3 toward thiols was determined by ¹H NMR and HPLC. Moreover, our results indicated that 1 could induce DNA cross-linking in the presence of glutathione, probably due to the quinone methide formation of phenol intermediate 4 followed by departure of 2,4-dinitrobenzenesulfonyl group.