Dihydroxy Groups Research Articles

Cellulose based molecularly imprinted polymer by hydroxyl functional allocation strategy with dual selectivity of boric acid affinity and molecular structure limitation to bortezomib: Preparation strategy, selectivity exploration, and metabolism study

Bortezomib is widely recognized as an effective drug for the treatment of multiple myeloma, but its metabolism in vivo has not been reported. There are extremely high requirements for selectivity and enrichment ability of pretreatment methods due to the complex biological matrix and trace metabolites. Urgently, a novel magnetic porous cellulose molecularly imprinted polymers (B-MPCMIP) based on bortezomib was developed for the first time using the magnetic porous cellulose (MPC) as the both carrier and functional monomer by the hydroxyl functional allocation strategy of cellulose, which showed the dual selectivity towards bortezomib through the boric acid affinity and molecular structure limitation. Firstly, the cis dihydroxy groups of cellulose was occupied by phenylboronic acid; then, another hydroxyl group in cellulose was modified by silane reagent to introduce reaction site for grafting MIP; subsequently, the phenylboronic acid was removed to release the cis dihydroxy groups of cellulose as the functional monomer for MIP; finally, MIP was prepared on the surface of MPC with the MPC as the both carrier and functional monomer for obtaining B-MPCMIP, which can recognize the bortezomib through the boric acid affinity molecular structure limitation. A series of characterization studies showed that B-MPCMIP had a porous structure, good thermal stability, ultra-high magnetism, mesoporous structure, and superhydrophilicity. B-MPCMIP showed good adsorption capacity (Qmax: 4.4 mg/g) and fast adsorption effect (adsorption equilibrium time: 30 min). Adsorption capacity of B-MPCMIP were also inspected under different temperature and pH conditions. The strong pH adsorption dependence indicates that B-MPCMIP mainly adsorbs bortezomib through the boric acid affinity, as the affinity between the cis dihydroxy groups in B-MPCMIP and the boric acid group in bortezomib is strongest at pH 8.5. Furthermore, B-MPCMIP exhibited excellent selectivity towards bortezomib with the imprinting factor, selectivity coefficient, and relative selectivity coefficient up to 8.6, 17, and 14, respectively. B-MPCMIP had outstanding reusability and stability, which remained 96 % of adsorption capacity after multiple recycling. B-MPCMIP-HPLC and B-MPCMIP-UPLC-MS/MS methods were successfully applied to enrich and detect bortezomib and its metabolites in mouse plasma and liver. The methods showed good selectivity, sensitivity, and accuracy. The maximum concentration of bortezomib in plasma and liver was detected as 34.3 μg/mL and 84.2 μg/mL. And six metabolites of bortezomib through oxidative deboronation were triumphantly detected and identified by B-MPCMIP-UPLC-MS/MS method.

Mode of molecular interaction of triterpenoid saponin ginsenoside Rh2 with membrane lipids in liquid-disordered phases

Ginsenoside Rh2 (Rh2) is a ginseng saponin comprising a triterpene core and one unit of glucose and has attracted much attention due to its diverse biological activities. In the present study, we used small-angle X-ray diffraction, solid-state NMR, fluorescence microscopy, and MD simulations to investigate the molecular interaction of Rh2 with membrane lipids in the liquid-disordered (Ld) phase mainly composed of palmitoyloleoylphosphatidylcholine compared with those in liquid-ordered (Lo) phase mainly composed of sphingomyelin and cholesterol. The electron density profiles determined by X-ray diffraction patterns indicated that Rh2 tends to be present in the shallow interior of the bilayer in the Ld phase, while Rh2 accumulation was significantly smaller in the Lo phase. Order parameters at intermediate depths in the bilayer leaflet obtained from 2H NMR spectra and MD simulations indicated that Rh2 reduces the order of the acyl chains of lipids in the Ld phase. The dihydroxy group and glucose moiety at both ends of the hydrophobic triterpene core of Rh2 cause tilting of the molecular axis relative to the membrane normal, which may enhance membrane permeability by loosening the packing of lipid acyl chains. These features of Rh2 are distinct from steroidal saponins such as digitonin and dioscin, which exert strong membrane-disrupting activity.

Revision of NMR assignment for Morin-3-O-glucoside and microbial production of Morin-2'-O-glucoside.

Morin is a flavonol having 2',4'-dihydroxy group on B-ring identified especially in Moraceae plants. While morin is widely known, its glycosides are relatively rare. To the best of our knowledge, morin-3-O-glucoside (1) was first reported in 2008. However, the reported chemical shift values of 1 were unsatisfactory with those of the aglycone, morin, which is rather similar to quercetin-3-O-glucoside (2). Therefore, we prepared morin-3-O-glucoside (1) by microbial transformation of morin with Cunninghamella sp., and the NMR assignment was reinvestigated. The microbial culture also produced another compound (3). The NMR and MS analyses of 3 revealed it as a novel compound, morin-2'-O-glucoside (3).In this study, the revision of the NMR assignment of morin-3-O-glucoside (1), and the preparation and structural elucidation of a novel compound, morin-2'-O-glucoside (3), were described.

Syntheses, crystal structures and properties of a series of isostructural lanthanide organic frameworks

We have successfully constructed nine isostructural Ln-MOFs with the formula Ln(L)1.5(H2O)2·H2O (1-Ce, 2-Dy, 3-Eu, 4-Gd, 5-Ho, 6-Nd, 7-Pr, 8-Sm, and 9-Tb) wherein the dihydroxy groups did not participate in coordination.

Synthesis and characterization of non-ionic flame-retardant waterborne polyurethane.

Waterborne polyurethane (WPU) offers many advantages and is widely used in coatings, leathers, adhesives, biomaterials, and other consumer products. However, WPU is highly flammable. Many reactive flame retardants have been developed, but their char formation efficiency is still unsatisfactory, and the melt dripping during combustion has not been effectively suppressed. In this paper, a novel phosphorus-containing flame retardant with dihydroxy groups, (6-((4-hydroxyphenyl)((4-hydroxyphenyl)amino)methyl) dibenzo[c,e][1,2]oxaphosphinine 6-oxide) (PHAD), was successfully synthesized and incorporated into WPU molecular chain as a chain extender, thereby synthesizing a series of non-ionic flame-retardant waterborne polyurethane (NFRWPU) emulsions. The chemical structure of NFRWPU was successfully characterized by Fourier transform infrared spectroscopy and nuclear magnetic resonance. With the help of a thermogravimetric analyzer, scanning electron microscope and other instruments, some key performance parameters of NFRWPU in applications were investigated, including: physical, mechanical, and thermal stability and flammability. Some important experimental results include: both the particle size and viscosity of the emulsion increase gradually with increasing PHAD content, and when the PHAD content reaches 12%, the average particle size of emulsion increases to 106.6 nm with a viscosity of 89 mPa s; with the addition of PHAD, the tensile strength of NFRWPU initially increased and then decreased, while the elongation at break showed a continuous downward trend. The maximum tensile strength reached 22.63 MPa, and the minimum elongation at break dropped to 1060%; the addition of PHAD improved the thermal stability and flame retardancy of the film, with the highest limiting oxygen index value reaching 25.6% and the maximum carbon residue increasing to 6.5%. All these results indicate that NFRWPU is a promising flame retardant WPU considering the comprehensive performance.

Turning damages into benefits: Corrosion-engineered cobalt foam for highly efficient biomass upgrading coupled with H2 generation

Electrocatalysis using 5-hydroxylmethylfurfural (HMF) as a substrate to produce 2,5-furandicarboxylic (FDCA) is a potentially sustainable and mild route to harvest both value-added chemicals and clean energy hydrogen. However, the poor chemical and thermal stability of HMF has impeded its storage and industrialization. Additionally, the uncontrollability, scalability, and cost of catalyst preparation methods are rarely considered in this field. Herein, we capitalize on the spontaneous and harmful corrosion phenomenon occurring under natural conditions to prepare efficient Co-based catalysts for the electrooxidation 2,5-bis(hydroxymethyl)furan (BHMF) with more stable dihydroxy groups, coupled with hydrogen evolution. The preparation of electrocatalysts through corrosion engineering is a straightforward, cost-effective, highly feasible, and scalable approach, requiring minimal equipment. In the optimal concentration of 200 mM BHMF, an ultrahigh current density of 1981.7 mA cm−2 was achieved at 2.293 V vs. RHE, contributed by both BHMF oxidation and oxygen evolution reaction (OER). Chronoamperometric electrolysis realized efficient FDCA production with 95.4% yield and 96.5% faradaic efficiency (FE) at an ultralow potential of 1.4 V vs. RHE. Since it is etched and grown on the substrate itself, the catalyst prepared by corrosion engineering is very stable and undergoes ten successive chronoamperometric electrolysis without significant structural or performance failure. Moreover, kinetic analyses are investigated to explore the origin of catalytic activity and reaction energy barrier. Finally, to further realize the potential of FDCA and H2 production in practical application, we innovatively designed a device with a two-electrode electrolyzer and a solar cell in series to drive BHMF electrooxidation with outdoor sunlight. The complete conversion of BHMF only takes 90 min, achieving a 93.5% FDCA yield and nearly theoretical hydrogen evolution.

Reactive metal boride nanoparticles trap lipopolysaccharide and peptidoglycan for bacteria-infected wound healing

Bacteria and excessive inflammation are two main factors causing non-healing wounds. However, current studies have mainly focused on the inhibition of bacteria survival for wound healing while ignoring the excessive inflammation induced by dead bacteria-released lipopolysaccharide (LPS) or peptidoglycan (PGN). Herein, a boron-trapping strategy has been proposed to prevent both infection and excessive inflammation by synthesizing a class of reactive metal boride nanoparticles (MB NPs). Our results show that the MB NPs are gradually hydrolyzed to generate boron dihydroxy groups and metal cations while generating a local alkaline microenvironment. This microenvironment greatly enhances boron dihydroxy groups to trap LPS or PGN through an esterification reaction, which not only enhances metal cation-induced bacterial death but also inhibits dead bacteria-induced excessive inflammation both in vitro and in vivo, finally accelerating wound healing. Taken together, this boron-trapping strategy provides an approach to the treatment of bacterial infection and the accompanying inflammation.

GC-MS analysis of oxysterols and their formation in cultivated liver cells (HepG2).

Oxysterols play a key role in many (patho)physiological processes and they are potential biomarkers for oxidative stress in several diseases. Here we developed a rapid gas chromatographic-mass spectrometry-based method for the separation and quantification of 11 biologically relevant oxysterols bearing hydroxy, epoxy, and dihydroxy groups. Efficient chromatographic separation (resolution≥ 1.9) was achieved using a medium polarity 35%-diphenyl/65%-dimethyl polysiloxane stationary phase material (30 m × 0.25 mm inner diameter and 0.25 μm film thickness). Based on thorough analysis of the fragmentation during electron ionization we developed a strategy to deduce structural information of the oxysterols. Optimized sample preparation includes (i) extraction with a mixture of n-hexane/iso-propanol, (ii) removal of cholesterol by solid phase extraction with unmodified silica, and (iii) trimethylsilylation. The method was successfully applied on the analysis of brain samples, showing consistent results with previous studies and a good intra- and interday precision of ≤20%. Finally, we used the method for the investigation of oxysterol formation during oxidative stress in HepG2 cells. Incubation with tert-butyl hydroperoxide led to a massive increase in free radical formed oxysterols (7-keto-chol> 7β-OH-chol>> 7α-OH-chol), while 24 h incubation with the glutathione peroxidase 4 inhibitor RSL3 showed no increase in oxidative stress based on the oxysterol pattern. Overall, the new method described here enables the robust analysis of a biologically meaningful pattern of oxysterols with high sensitivity and precision allowing us to gain new insights in the biological formation and role of oxysterols.

Synthesis, in vitro evaluation, and molecular docking studies of benzofuran based hydrazone a new inhibitors of urease

This work has described the synthesis of novel class (1 – 25) of benzofuran based hydrazone. The hybrid scaffolds (1 – 25) of benzofuran based hydrazone were evaluated in vitro , for their urease inhibition. All the newly synthesized analogues (1 – 25) were found to illustrate moderate to good urease inhibitory profile ranging from 0.20 ± 0.01 to 36.20 ± 0.70 µM. Among the series, compounds 2 2 (IC 50 = 0.20 ± 0.01 µM), 5 (IC 50 = 0.90 ± 0.01 µM), 23 (IC 50 = 1.10 ± 0.01 µM) and 25 (IC 50 = 1.60 ± 0.01 µM) were found to be the many folds more potent than thiourea as standard inhibitor (IC 50 = 21.86 ± 0.40 µM). The elevated inhibitory profile of these analogues might be due to presence of dihydroxy and flouro groups at different position of phenyl ring B attached to hydrazone skeleton. These dihydroxy and fluoro groups bearing compounds have shown many folds better inhibitory profile through involvement of oxygen of dihydroxy groups in hydrogen bonding with active site of enzymes. Various types of spectroscopic techniques such as 1 H-, 13 C- NMR and HREI-MS spectroscopy were used to confirm the structure of all the newly developed compounds. To find SAR, molecular docking studies were performed to understand, the binding mode of potent inhibitors with active site of enzymes and results supported the experimental data.

Antiinflammation Derived Suzuki-Coupled Fenbufens as COX-2 Inhibitors: Minilibrary Construction and Bioassay.

A small fenbufen library comprising 18 compounds was prepared via Suzuki Miyara coupling. The five-step preparations deliver 9–17% biphenyl compounds in total yield. These fenbufen analogs exert insignificant activity against the IL-1 release as well as inhibiting cyclooxygenase 2 considerably. Both the para-amino and para-hydroxy mono substituents display the most substantial COX-2 inhibition, particularly the latter one showing a comparable activity as celecoxib. The most COX-2 selective and bioactive disubstituted compound encompasses one electron-withdrawing methyl and one electron-donating fluoro groups in one arene. COX-2 is selective but not COX-2 to bioactive compounds that contain both two electron-withdrawing groups; disubstituted analogs with both resonance-formable electron-donating dihydroxy groups display high COX-2 activity but inferior COX-2 selectivity. In silico simulation and modeling for three COX-2 active—p-fluoro, p-hydroxy and p-amino—fenbufens show a preferable docking to COX-2 than COX-1. The most stabilization by the p-hydroxy fenbufen with COX-2 predicted by theoretical simulation is consistent with its prominent COX-2 inhibition resulting from experiments.

Antioxidant Activity of Natural Hydroquinones.

Secondary metabolites derived from hydroquinone are quite rare in nature despite the original simplicity of its structure, especially when compared to other derivatives with which it shares biosynthetic pathways. However, its presence in a prenylated form is somewhat relevant, especially in the marine environment, where it is found in different algae and invertebrates. Sometimes, more complex molecules have also been identified, as in the case of polycyclic diterpenes, such as those possessing an abietane skeleton. In every case, the presence of the dihydroxy group in the para position gives them antioxidant capacity, through its transformation into para-quinones.This review focuses on natural hydroquinones with antioxidant properties referenced in the last fifteen years. This activity, which has been generally demonstrated in vitro, should lead to relevant pharmacological properties, through its interaction with enzymes, transcription factors and other proteins, which may be particularly relevant for the prevention of degenerative diseases of the central nervous system, or also in cancer and metabolic or immune diseases. As a conclusion, this review has updated the pharmacological potential of hydroquinone derivatives, despite the fact that only a small number of molecules are known as active principles in established medicinal plants. The highlights of the present review are as follows: (a) sesquiterpenoid zonarol and analogs, whose activity is based on the stimulation of the Nrf2/ARE pathway, have a neuroprotective effect; (b) the research on pestalotioquinol and analogs (aromatic ene-ynes) in the pharmacology of atherosclerosis is of great value, due to their agonistic interaction with LXRα; and (c) prenylhydroquinones with a selective effect on tyrosine nitration or protein carbonylation may be of interest in the control of post-translational protein modifications, which usually appear in chronic inflammatory diseases.

In Vitro Liver Metabolism of Six Flavonoid C-Glycosides.

Several medical plants belonging to the genera Passiflora, Viola, and Crataegus accumulate flavonoid C-glycosides, which likely contribute to their efficacy. Information regarding their phase I and II metabolism in the liver are lacking. Thus, in vitro liver metabolism of orientin, isoorientin, schaftoside, isoschaftoside, vitexin, and isovitexin, all of which accumulated in Passiflora incarnata L., was investigated by incubation in subcellular systems with human liver microsomes and human liver S9 fraction. All metabolite profiles were comprehensively characterized using HPLC-DAD and UHPLC–MS/MS analysis. Mono-glycosylic flavones of the luteolin-type orientin and isoorientin showed a broad range of mono-glucuronidated and mono-sulfated metabolites, whereas for mono-glycosylic flavones of the apigenin-type vitexin and isovitexin, only mono-glucuronidates could be detected. For di-glycosylic flavones of the apigenin-type schaftosid and isoschaftosid, no phase I or II metabolites were identified. The main metabolite of isoorientin was isolated using solid-phase extraction and prep. HPLC-DAD and identified as isoorientin-3′-O-α-glucuronide by NMR analysis. A second isolated glucuronide was assigned as isoorientin 4′-O-α-glucuronide. These findings indicate that vitexin and isovitexin are metabolized preferentially by uridine 5′-diphospho glucuronosyltransferases (UGTs) in the liver. As only orientin and isoorientin showed mono-sulfated and mono-glucuronidated metabolites, the dihydroxy group in 3′,4′-position may be essential for additional sulfation by sulfotransferases (SULTs) in the liver. The diglycosylic flavones schaftoside and isoschaftoside are likely not accepted as substrates of the used liver enzymes under the chosen conditions.

A halogen-free, flame retardant, waterborne polyurethane coating based on the synergistic effect of phosphorus and silicon

In this study, p-hydroxybenzaldehyde, 3-aminopropanol and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were used as raw materials, and a novel flame retardant with dihydroxy groups, namely 4-DOPO-((3-hydroxypropyl) imino) methyl) phenol (PHID), was synthesized. Then, a flame retardant, water-based polyurethane with phosphorus (P) and silicon (Si) units (FR/Si-WPU) was successfully prepared. Limited oxygen index (LOI), vertical burning tests, and cone calorimetry were employed to investigate the flammability characterizations of the WPU. In contrast to pure WPU, the LOI value of FR/Si-WPU was found to be increased from 18.2% to 28.6%, the UL 94 rating was upgraded to V-0. The peak heat release rate (pk-HRR) and peak smoke production rate (pk-SPR) were found to be decreased by 80.5% and 70.5%, respectively. In addition, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), thermogravimetric analysis-infrared spectrometry (TG-IR), laser Raman spectroscopy (LRS), and X-ray photoelectron spectroscopy (XPS) were employed to evaluate the synergistic mechanisms of P and Si. The results demonstrated that the synergistic effect of PHID with hydroxyl silicone oil (HO-Si) can generate a more compact char to protect the underlying polyurethane, the decomposition of PHID can produce PO· radicals that combine with H· and OH· radicals to interrupt the combustion reaction, and HO-Si can produce a special insulating SiO layer to improve the thermo oxidative stability. The synergistic effects of these factors contribute to the designable flammability of the WPU coating. Further investigation revealed that Si units can efficiently balance the other properties of the WPU, and the cold resistance and mechanical properties of FR/Si-WPU were found to increase instead of decrease. In this work, a flame retardant WPU coating with good comprehensive performance was fabricated via a simple and efficient method.

Efficient biofuel production by MTV-UiO-66 based catalysts

In this study, highly defected and functionalized metal-organic framework (MOF) structures are developed and exploited as catalysts for an esterification reaction for biofuel production. Two systems of multivariate UiO-66 series, namely MTV-UiO-66(COOH)2 and MTV-UiO-66(OH)2 incorporating dicarboxylate and dihydroxy groups, respectively, along with the single component structures, are thus explored for butyl butyrate production. Ratios of functionalized linkers to terephthalic acid are varied and a modulation synthesis approach is employed allowing for high levels of structural defects. The synthesized MOF structures are fully characterized using Powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), proton nuclear magnetic resonance (1H NMR), Brunauer–Emmett–Teller (BET), and scanning electron microscopy (SEM), and the results confirmed the homogeneous incorporation of the functionalized linkers in the structures. The combination of multivariate approach along with modulation synthesis yields structures with catalytic activity higher than those of highly defective fully functionalized structures and close to the homogeneous conventional catalyst used in esterification reactions. Moreover, the ratio of functionalized linkers to terephthalic acid is shown to be very important since not all MTV-UiO-66 performed better than the single-component structure which can be attributed to a combination of factors related to the density of active sites and their accessibility. The most active MTV-UiO-66(OH)2 member, incorporating 52% of functionalized linkers, a defects number of 1.9, and a surface area of 761 m2/g, yielded 92% conversion to butyl butyrate, compared to 95% for H2SO4, and its activity and stability is maintained over 4 consecutive cycles. Furthermore, by using the data of 33 different UiO-66 based catalysts for butyl butyrate production, a weighted linear regression model is suggested to predict the conversion based on the parameters that are concluded to mostly govern the catalytic activity of MOF catalysts. These parameters include the surface area, the catalytic loading, the defects number, and the level of incorporation of BDC, and the functionalized linkers. The weights calculated for each of these parameters indicate that there is a more pronounced effect of active sites density on the conversion when compared to the surface area or the catalyst loading. These conclusions help pave the way for the engineering of MOF-based catalysts in the path of bridging the gap between homogeneous and heterogeneous catalysis for efficient biofuel production.

One pot synthesis of nano Ag in calcium alginate beads and its catalytic application in p‐Nitrophenol reduction with kinetic parameter estimation and model fitting

AbstractIn this work, one step process of synthesis of silver nanoparticles (Agnp) embedded in insitu formed calcium alginate (CA) beads is stated. CA, formed from the reaction between sodium alginate and calcium hydroxide, acts as reducing and stabilizing agent as well as support for nanoparticles. The reaction mechanism for the formation and stabilization of Agnp is proposed where the vicinal dihydroxy groups of alginate are assumed to act as the reducing agent for Ag+ to Ag°. Transmission electron microscopy (TEM), x‐ray diffraction (XRD), UV‐vis spectroscopy, field emission scanning electron microscopy (FESEM), and atomic absorption spectroscopy (AAS) were used to characterize the Agnp. The formation of spherical nanoparticles with average size range of 4‐5 nm was confirmed by TEM. Catalytic activity of this nano silver‐calcium alginate (Agnp‐CA) composite was evaluated in the reduction of p‐nitrophenol. Concentrations of sodium alginate, calcium hydroxide, and AgNO3 are found to be the parameters that critically affect the synthesis of Agnp. The efficacy of the catalyst is expressed on the basis of suitable reaction parameters. Both pseudo‐homogeneous and heterogeneous kinetic models are proposed for the reaction to find the best model and the Eley‐Riedel model is found to fit well with the experimental data. The novelty of this work is that the tandem process of CA bead formation, Agnp formation, and Agnp entrapment in CA have been transformed into a single‐step process. Moreover, elaborations of each step of the ionic mechanisms of Agnp formation and p‐NP reduction with Agnp and the establishment of a heterogeneous kinetic model for the reaction are reported for the first time here.

Direct Observation of the Interplay of Catechol Binding and Polymer Hydrophobicity in a Mussel-Inspired Elastomeric Adhesive.

Marine organisms such as mussels have mastered the challenges in underwater adhesion by incorporating post-translationally modified amino acids like l-3,4-dihydroxyphenylalanine (DOPA) in adhesive proteins. Here we designed a catechol containing elastomer adhesive to identify the role of catechol in interfacial adhesion in both dry and wet conditions. To decouple the adhesive contribution of catechol to the overall adhesion, the elastomer was designed to be cross-linked through [2 + 2] photo-cycloaddition of coumarin. The elastomer with catechol moieties displayed a higher adhesion strength than the catechol-protected elastomer. The contact interface was probed using interface-sensitive sum frequency generation spectroscopy to explore the question of whether catechol can displace water and bond with hydrophilic surfaces. The spectroscopy measurements reveal that the maximum binding energy of the catechol and protected-catechol elastomers to sapphire substrate is 7.0 ± 0.1 kJ/(mole of surface O–H), which is equivalent to 0.10 J/m2. The higher dry and wet adhesion observed in the macroscopic adhesion measurements for the catechol containing elastomer originates from multiple hydrogen bonds of the catechol dihydroxy groups to the surface. In addition, our results show that catechol by itself does not remove the confined interstitial water. In these elastomers, it is the hydrophobic groups that help in partially removing interstitial water. The observation of the synergy between catechol binding and hydrophobicity in enabling the mussel-inspired soft adhesive elastomer to stick underwater provides a framework for designing materials for applications in tissue adhesion and moist-skin wearable electronics.

Rhodium(I)‐Catalyzed Cycloisomerization of Homopropargylallene‐Alkynes through C(sp3)−C(sp) Bond Activation

AbstractUpon exposure to a catalytic amount of [RhCl(CO)2]2 in 1,4‐dioxane, homopropargylallene‐alkynes underwent a novel cycloisomerization accompanied by the migration of the alkyne moiety of the homopropargyl functional group to produce six/five/five tricyclic compounds in good yields. A plausible mechanism was proposed on the basis of an experiment with 13C‐labeled substrate. The resulting tricyclic derivatives were further converted into the corresponding bicyclo[3.3.0] skeletons with vicinal cis dihydroxy groups.

Rhodium(I)-Catalyzed Cycloisomerization of Homopropargylallene-Alkynes through C(sp3 )-C(sp) Bond Activation.

Upon exposure to a catalytic amount of [RhCl(CO)2 ]2 in 1,4-dioxane, homopropargylallene-alkynes underwent a novel cycloisomerization accompanied by the migration of the alkyne moiety of the homopropargyl functional group to produce six/five/five tricyclic compounds in good yields. A plausible mechanism was proposed on the basis of an experiment with 13 C-labeled substrate. The resulting tricyclic derivatives were further converted into the corresponding bicyclo[3.3.0] skeletons with vicinal cis dihydroxy groups.

Controllable assembly of rectangular macrocycles bearing different numbers of unsaturated sites based on half-sandwich iridium fragments.

A series of hexanuclear rectangular macrocycles were designed and synthesized by utilizing multifunctional pyrazine-derived (pyrazine-2,3-diamine (H4L1)) and quinoxaline-derived ligands (2,3-dihydroxy-quinoxaline (H2L2)) featuring two monodentate sites and one pair of chelating sites. X-ray crystallography in combination with 1H NMR spectroscopy elucidated that both half-sandwich iridium diimine and dihydroxy moieties are located on either side of the rectangular macrocycles, making them centrosymmetric. Thereby, the prepared diimine-functionalised complexes were found to have unsaturated metal sites on account of their strongly bound Ir-N-C-C-N arrangement. However, all the iridium atoms in the rectangular macrocycles containing dihydroxy groups were found to adopt an 18-electron coordination configuration, indicating that the O,O'-bonded iridium centers had bound additional ligands, such as Cl-, MeOH, MeCN, etc. Notably, a rare rectangular macrocycle containing a single coordinatively unsaturated metal site was achieved when the ligands H2L12- and L22- were introduced simultaneously.

Influence of Chemical Structure of Some Flavonols on Their Electrochemical Behaviour

The electrochemical behaviour of three structurally related flavonols, quercetin, morin, and rutin was studied by cyclic, differential pulse, and square-wave voltammetry methods. The study reveals that their electrochemical behaviour strongly depends on their chemical structure and electronic properties, particularly on the presence of electron- donating -OH groups, i.e. their numbers and position on rings A, B, and C in the structure of these flavonols. The important factors of the electrochemical oxidation behaviour of flavonols are as follows. (i) The presence of two electron-donating -OH groups on the B ring in the ortho-position. (ii). The 2, 3- double bond in conjugation with a 4-oxo group on the C ring. (iii) The electron donating 3-OH group on the C ring, and (iv) the electron-donating 5-OH and 7-OH groups on A ring. Quercetin satisfies all of the requirements mentioned above and therefore has the best electron-donating properties of all investigated flavonols. The first oxidation peak of quercetin (peak A1) corresponds to the reversible oxidation of 3', 4'-OH groups (catechol moiety) at the B ring to the ortho- quinone structure by two-electron- two-proton (2e- -2H+ ) process. This electrochemically active and unstable ortho-quinone species then undergoes chemical rearrangements or addition reactions, indicates an electrochemical- chemical (EC) reaction mechanism. At higher anodic potential the -OH group at position 3 of ring C was oxidized (peak A2), by the reversible one- electron-oneproton reaction. In this study, it was for the first time observed that the second reduction peak of quercetin (peak C2) corresponds to the 3-OH group on ring C. The hydroxyl groups at position 5 and 7 at ring A have significantly smaller electron- donating effect than -OH groups at ring B, and therefore were oxidized at higher anodic potentials (peak A3). This oxidation is an irreversible process. Morin with meta-2', 4’- dihydroxyl groups (resorcinol moiety) shows the higher value of oxidation potential of peak A1 than quercetin, indicating that oxidation of 2', 4'-OH groups on ring B of morin to quinone structure is more difficult in comparison to that of quercetin. This fact clearly shows the importance of the presence of two hydroxyl groups in the ortho-diphenolic arrangement on the ring B of flavonols. The first oxidation process of morin is an one- electron-one-proton reversible reaction, which proceeds in an EC mechanism. The oxidation peak of morin A3 should be associated with the oxidation of 5, 7- dihydroxyl moiety of ring A, which oxidation occurs at very high oxidation potentials. This oxidation is an irreversible process because no reduction peak was observed. The absence of oxidation peak A2 could be explained possibly by the formation of hydrogen bond between the 3-OH group and the oxygen at position C-4 on the ring C. Rutin (quercetin-3-O- rutinose) shows the highest oxidationpotential of peak A1 of all investigated flavonols. Such behaviour reflects the influence of glycosylation with rutinose on position 3 of the C ring. Therefore, an oxidation process was blocked, what significantly decreases the strength of delocalization of electrons from B ring, in comparison to that of quercetin. In concordance with this fact, the oxidation of B ring of rutin was observed at significantly higher potentials. This result shows how important is the role of 3-OH group in the C ring on the electrochemical properties of flavonols. The first redox couple of rutin (peaks A1 and C1) corresponds (as in the case of quercetin) to the oxidation of 3’, 4’-dihydroxy groups on the B ring of rutin and the reduction of the 3’, 4’-quinone, respectively. This reaction is a reversible process proceeds through EC reaction mechanism. The oxidation peak of rutin A3 should be associated with oxidation of 5, 7- dihydroxyl moiety of ring A. This oxidation is an irreversible process because no reduction peak was observed. The absence of oxidation peak A2 could be explained by the presence of rutinoside group without electrochemical activity, at position 3 of C ring of rutin. The results of present study give some new information about the electrochemical oxidation/reduction processes of investigated flavonols. (i) For the first time was observed the presence of cathodic reduction peak of quercetin (peak C2) which corresponds to 3-OH group at C ring. (ii) The reversibility of the first oxidation process of morin (peaks A1 and C1) was clearly demonstrated. (iii) It was clearly shown how important is the role of -OH groups (i.e. their number and their position on rings A, B, and C) on the electrochemical behaviour of investigated flavonols.