Theoretical study of 1D and 2D fused magnesium porphine oligomers

The structural characteristics, energies, and spectroscopic properties of 1D linear chains and 2D planar sheets of (meso-meso, β-β, β-β)-linked magnesium porphines have been calculated by the density functional theory B3LYP method. The trends in the changes in the ionization potential, electron affinity, relative multiplet energies, and electron and spin density characteristics have been scrutinized as a function of the oligomer size and n in the range 0–8.     

Triterpene glycosides ofCaltha polypetala glycosides A,B, D,E, and F

Five individual triterpene glycosides — A, B, D, E, and F — which are hederagen-in mono- and biosides, have been isolated from the roots ofCaltha polypetala (Great Marsh Marigold), familyRanunculaceae. Glycosides E and F proved to be new compounds for which, on the basis of the results of acid and alkaline hydrolyses, methylation, methanolysis, and physicochemical methods of investigation, the following structures are proposed: E — hederagenin 3-0-D-glucopyranoside, 28-O-L-rhamnopyranoside; and F — heteragenin 28-O-[O-L-rhamnopyranosyl-(1→ 6)-D-glucopyranoside].     

Divergent Total Synthesis of Fornicin A,Fornicin D,and Ganodercin D,Meroterpenoids from Ganoderma Mushrooms

The meroterpenoids fornicin A, fornicin D, and ganodercin D, found in mushrooms of the Ganoderma genus, have been prepared in a concise and divergent synthesis route. The characteristic unsaturated γ-ketoacid moiety was obtained via an optimized step-wise aldol condensation between two readily accessible building blocks. THP-protection of a phenolic hydroxyl group under basic conditions was developed, a protocol that adds to the versatility of this protecting group.     

A manganese(II) coordination polymer with a 3D porous structure: Synthesis,structure, and spectroscopic and magnetic behaviour

A manganese(II) complex with N,N′-bis(carboxymethyl)dithiooxamide (H₄GLYDTO), [Mn(H₂GLYDTO)(H₂O)₂]_n, has been synthesized and characterized by elemental analysis and thermogravimetric analysis, as well as by infrared, electronic and EPR spectroscopy and magnetic susceptibility measurements. The crystal and molecular structure of this complex was determined by single-crystal X-ray structure analysis. The compound shows a 3D porous framework with alternate left- and right-handed helical channels where the manganese(II) ions have an octahedral environment. Variable temperature magnetic measurements reveal the existence of very weak antiferromagnetic interactions through the syn-anti carboxylate bridge, with an exchange parameter of J/k = −0.12 K.     

Stereostructures of leucothol B and D,diterpenoids of Leucothoe grayana

Two novel diterpenoids, leucothol B and D, have been isolated from the leaves of Leucothoe grayana (Ericaceae). Chemical and spectroscopic investigations have shown that leucothol B and D have stereostructures 2 and 3, respectively, and possess a unique carbon skeleton.     

Synthesis of diastereomeric,deoxy and ring-expanded sulfone analogues of aigialomycin D

Several analogues of the fungal natural product aigialomycin D (AmD) have been synthesised. These include the stereoisomer 5′R,6′S-AmD, 2,4-di-deoxyAmD, 1′,2′,7′,8′-tetrahydroAmD and a 15-membered macrocyclic sulfone. Growth inhibitory activities of these compounds against the HL-60 leukaemic cell line were measured. The ring-expanded sulfone and tetrahydro-analogue were found to have similar IC₅₀ values to the natural product, whereas the 5′R,6′S-stereoisomer was inactive. Energy minimisation of AmD and the synthesised analogues resulted in a range of lowest energy conformers, from planar, open arrangements of the macrocycle in AmD and tetrahydroAmD to bent, L-shaped structures for the sulfone. The synthesis of methyl orsellinate was investigated and optimised as part of this work. A stereodivergent route to both enantiomers of the diol fragment from d-ribose was also achieved.     

Production of theasinensins A and D, epigallocatechin gallate dimers of black tea, by oxidation-reduction dismutation of dehydrotheasinensin A

Theasinensins A and D are B,B′-linked dimers of (−)-epigallocatechin 3-O-gallate connected through R and S biphenyl bonds, respectively, and are major constituents of black tea. Enzymatic oxidation of epigallocatechin 3-O-gallate produced dehydrotheasinensin A, and the structure was shown to be equivalent to an o-quinone of theasinensin A. When the aqueous solution of dehydrotheasinensin A was heated, theasinensin D was produced along with galloyl oolongtheanin. On the other hand, dehydrotheasinensin A was converted to theasinensins A and D along with oxidation products in phosphate buffer at pH 6.8 at room temperature. The results strongly suggested that theasinensins in black tea were produced by oxidation-reduction dismutation of dehydrotheasinensin.     

Total synthesis of monocyclic β-lactam antibiotics,nocardicin A and D

The total synthesis of monocyclic β-lactam antibiotics, nocardicins A (1a) and D (1d), is described. 3-Aminonocardicinic acid (3-ANA, 2) was synthesized from p-hydroxyphenylglycine via an acid chloride-imine cyloaddition reaction. The side chain amino acid 13 was prepared via a key step of condensation of p-hydroxyacetophenone and α-phthalimidobutyrolactone. Acylation of 3-ANA with 13 gave nocardicin D, from which nocardicin A was obtained by oximation.     

Total synthesis and cytotoxic activity of dechlorogreensporones A and D

The first and convergent total syntheses of polyketide natural products dechlorogreensporones A and D have been accomplished in 17 longest linear steps with 2.8% and 5.4% overall yields, respectively, starting from known methyl 2-(2-formyl-3,5-dihydroxyphenyl)acetate and commercially available R-(+)-propylene oxide and 1,2-epoxy-5-hexene. Our synthesis exploited key Mitsunobu esterification and (E)-selective ring-closing metathesis (RCM) to assemble the macrocycles as well as a Jacobsen hydrolytic kinetic resolution to install the stereogenic centers. Both synthetic compounds were found to display significant cytotoxic activity against seven human cancer cell lines with the IC₅₀ ranges of 6.66–17.25?μM.     

Strain of 2D materials via substrate engineering

Two-dimensional(2D) materials have received extensive attention in the fields of electronics, optoelectronics, and magnetic devices attributed to their unique electronic structures and physical properties. The application of strain is a simple and effective strategy to change the lattice structure of 2D materials thus modulating their physical properties, which further facilitate their applications in carrier mobility transistor, magnetic sensor, single-photon emitter etc. In this short review, ...     

Studies on terpenoids and steroids—2 : Structures of two new tri- and tetra-oxygenated D:A-friedo-oleanan triterpenes from kokoona zeylanica

The two D:A-friedo-oleanane triterpenes kokzeylanol and kokzeylanonol isolated from the inner bark of Kokoona zeylanica have been characterized as 6β,27-dihydroxy-D:A -friedo-olean-3-one and 6β,27-dihydroxy-D:A-friedo-olean-3,21-dione, respectively, by the deoxygenation of their 27-acetoxy derivatives using lithium-ethylenediamine reduction coupled with spectroscopic and irradiation methods. Kokzeylanonol represents the first tetra-oxygenated D:A-friedo-oleanane triterpene obtained from a nautral source. Significance of some of these D:A-friedo-oleananes in the biosynthesis of quinonoid triterpenes in Celastraceae is discussed.     

Exploring the resistance mechanism of imipenem in carbapenem hydrolysing class D beta-lactamases OXA-143 and its variant OXA-231 (D224A) expressing Acinetobacter baumannii: An in-silico approach

Acinetobacter baumannii (A. baumannii), is a Gram negative, coccobacilli and is associated with nosocomial infections. The bacterium has developed resistance to all known classes of antibiotics. Multi-drug resistant A. baumannii infections have been treated with the carbapenem group of antibiotics like imipenem and meropenem. Recent reports indicate that A. baumannii has acquired resistance to imipenem due to the secretion of carbapenem hydrolysing class D beta-lactamases (CHDLs). Such CHDLs found in carbapenem resistant A. baumannii belongs to OXA-143 and its variant OXA-231, which has Alanine (A) in place of Aspartic acid (D) at sequence position 224. The mutation of the OXA-231 CHDL alters the catalytic activity of the enzyme. Hence, the present study was carried out to find the probable mechanism of imipenem resistance in OXA-143 and OXA-231 (D224A) CHDLs expressing A. baumannii by employing molecular docking and dynamics. Methods Our study reveals that OXA-143 CHDL-imipenem complex has more binding affinity than OXA-231 (D224A) CHDL-imipenem complex. Our results indicate that there is a strong binding affinity of OXA-143 with imipenem when compared with OXA-243 and this mechanism might be the probable reason for imipenem resistance in OXA-143 expressing A. baumannii strains.     

Novel bioactive vic-dioxime ligand containing piperazine moiety: Synthesis,X-ray crystallographic studies, 2D NMR applications and complexation with Ni(II)

A new vic-dioxime ligand bearing an important pharmacophore substituent, anti-1-(4-benzylpiperazine-1-yl) phenylglyoxime (LH₂) (Scheme 1), has been synthesized and its nickel(II) complex was obtained by the reaction of NiCl₂·6H₂O and the ligand. The characterization of the newly formed compounds was performed by elemental analysis, FT-IR, 1D NMR (¹H, ¹³C, DEPT), 2D NMR (HMBC), ESI mass-spectrometry, TG/DTA, X-ray crystallography. The antibacterial activity was also studied against Staphylococcus aureus ATCC 25923, Streptococcus mutans RSHM 676, Enterococcus faecalis ATCC 29212, Lactobacillus acidophilus RSHM 06029, Escherichia coli ATCC 25922, E. coli ATCC 35218, Pseudomonasaeruginosa ATCC 27853. The antimicrobial test results indicated that all the compounds have mild antibacterial activity against both Gram negative and Gram positive bacterial species.     

3D crumbled MXene for high-performance supercapacitors

MXene materials have recently attracted considerable attention in energy storage application owing to their metallic conductivity, 2D structure and tunable surface terminations. However, the restacking of 2D MXene nanosheets hinders the ion transport and accessibility to the surface, resulting in adverse effect on their electrochemical performances. Here, with the assistance of hexamethylenetetramine (C₆H₁₂N₄), 2D Ti₃C₂T_x MXene nanosheets were fabricated into a 3D architecture with crumbled and porous structure through an electrostatic self-assembly followed by annealing. The resultant 3D structure can expose massive active sites and facilitates the ion transport, which is beneficial for sufficient utilization of the outstanding superiorities of the MXene. Therefore, as a pseudocapacitive material, the 3D crumpled and porous Ti₃C₂T_x MXene shows a gravimetric capacitance of 333 F/g at 1 A/g, and maintains 261 F/g and 132 F/g at ultrahigh current densities of 100 A/g and 1000 A/g, respectively, revealing promising potential for application in supercapacitors.     

Synthesis and specific solvatochromism of D–π–A type pyridinium dye

Donor–π–acceptor (D–π–A) type pyridinium dye bearing an iodide ion as the counter anion that has been newly synthesized showed specific solvatochromism, leading to large bathochromic shift of absorption band in halogenated solvents: the bathochromic shifts of the D–π–A type pyridinium dye in halogenated solvents are larger than those of the non-halogenated solvents of low ?_r values. Investigation of absorption spectral measurement, ¹H NMR measurements, and semi-empirical molecular calculations (AM1 and INDO/S using the SCRF Onsager Model) revealed that the intramolecular charge transfer (ICT) characteristics of the D–π–A type pyridinium dye became stronger in the halogenated solvents. On the basis of the experimental results and the theoretical calculations, the influences of halogenated solvent on the large bathochromic shift of D–π–A type pyridinium dye are discussed. ^©2012 Elsevier Science. All rights reserved.     

Identification of vitamins A, D and E by particle beam liquid chromatography-mass spectrometry

Particle beam (PB) high performance liquid chromatography (HPLC)-mass spectrometry (MS) has been studied to investigate its suitability for the analysis of fat-soluble vitamins, as an example of thermally labile substances. The PB LC-MS system has been used to detect and identify vitamins A, D and E in foods and multi-vitamin preparations. The qualitative performance of the PB interface has been evaluated by an examination of the working parameters. A rapid elution of the vitamins was obtained on a C8 reversed-phase column using an aqueous methanol mobile phase. Analyses have been carried out using both, electron (EI) and chemical (CI) ionization. Positive and negative-ion CI spectra of the compounds are discussed. When PB-MS conditions are optimized, the detection limits for the fat-soluble vitamins tested have been typically in the 0.6–25 ng range when using the selected-ion monitoring technique.     

Syntheses,structures and magnetic properties of Mn(II) containing 3D polymeric networks

Two novel 3D coordination polymers {[Mn(aip)(DMF)]}_n, CPO-9, and {[Mn₃(Hatp)₂(atp)₂](H₂O)₂(DEF)₄}_n CPO-10 (aip = 5-aminoisophthalate, atp = 2-aminoterephthalate, DMF = dimethylformamide, DEF = diethylformamide) have been synthesized by solvothermal methods. Their properties have been studied by single-crystal X-ray diffraction, thermogravimetric analysis, high-temperature powder X-ray diffraction and magnetic susceptibility measurements. The crystal structure of CPO-9 is based on infinite chains of carboxylato-bridged five-coordinated Mn(II) ions that are crosslinked via the aip ligands to form a 3D structure. CPO-10 is based on linear trinuclear building units of carboxylato-bridged octahedral Mn(II) ions that are crosslinked by the atp ligands into a 3D structure. Both compounds have 1D channels that contain solvent molecules. The solvent accessible void volume for CPO-10 is 51.9% of the unit cell volume. For both compounds, however, the solvent molecules cannot be removed without the collapse of the structures into amorphous phases at 250 °C. The magnetic susceptibility measurements indicate antiferromagnetic couplings between the Mn(II) ions in both compounds. The magnetic data have been fitted using theoretical approaches.     

The first total synthesis of trichostatin D

Trichostatin D and 6-epi-trichostatin D have been stereoselectively synthesized through a remote stereoinduction with a chiral vinylketene silyl N,O-acetal and glycosylation of hydroxyimide under Mitsunobu conditions.     

Synthesis,Characterization, and Properties of a 1D Zinc(II) Complex from Substituted Imidazole Dicarboxylate

A one-dimensional zinc(II) polymer, {[Zn₂((p-FPhHIDC)(p-FPhH₂IDC)₂)(Phen)₂] · H₂O} _n (I) (p-FPhH₃IDC = 2-(p-fluorophenyl)-1H-imidazole-4,5-dicarboxylicacid (Phen = 1,10-phenanthroline), has been solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction (CIF file CCDC no. 1063532), elemental analyses, and IR spectra. In polymer I, these 1D wave chains were joined through the π–π interactions and intermolecular hydrogen bonds to give a 2D architecture. The thermal properties of I have been determined in air.     

Concise total syntheses of heliannuols B and D

Concise and efficient enantioselective total syntheses of heliannuols B and D have been accomplished using chirality transfer through a Lewis acid-promoted Claisen rearrangement for the construction of the C7 tertiary stereogenic center and a relay ring-closing metathesis for assembling the dihydrobenzo[b]oxepine backbone of the natural products as the key steps.