Synthesis of 5‐tert‐butyl‐1‐(3‐tert‐butyldimethylsiloxy)phenyl‐4,4‐dimethyl‐2,6,7‐trioxabicyclo[3.2.0]heptanes and their fluoride‐induced chemiluminescent decomposition: effect of a phenolic electron donor on the CIEEL decay rate in aprotic polar solvent

Four bicyclic dioxetanes bearing a phenolic substituent, 3‐tert‐butyldimethylsiloxy‐4‐chlorophenyl ( 3a ), 5‐tert‐butyldimethylsiloxy‐4‐chloro‐2‐ethylphenyl ( 3b ), 5‐tert‐butyldimethylsiloxy‐2‐ethylphenyl ( 3c ), and 3‐tert‐butyldimethylsiloxy‐4‐ethylphenyl ( 3d ), were synthesized. All dioxetanes 3a – 3d gave intense blue light on treatment with tetrabutylammonium fluoride (TBAF) in DMSO or acetonitrile. Kinetic study on the fluoride‐induced CIEEL decay of these dioxetanes 3a – 3d and the parent dioxetane 2b revealed that the para‐substitution with chlorine on the phenolic moiety of dioxetane increases free energy of activation (ΔG?), while the para‐substitution with ethyl on the aryl decreases ΔG?. On the other hand, substitution with an ethyl at the ortho‐position instead of the para‐position was found to increase ΔG? and to suppress the CIEEL decay. This fact is attributed to the steric factor of the ortho‐ethyl group which would prevent the aromatic ring from rotating freely around the axis joined to the peroxide ring, and supports the suggestion for a CIEEL‐active dioxetane bearing a phenolic moiety that an intramolecular electron transfer occurs preferentially from the phenolic donor to O–O of the dioxetane ring, when the aromatic ring lies in a certain conformation(s). Copyright © 2002 John Wiley & Sons, Ltd.     

Application of NMR spectroscopy for assignment of the absolute configuration of 8‐tert‐butyl‐2‐hydroxy‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]dec‐6‐en‐10‐one

In order to assign the absolute configurations of 8‐tert‐butyl‐2‐hydroxy‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]dec‐6‐en‐10‐one ( 2a , 2b ), their esters ( 5a , 5b , 5c , 5d ) with (R)‐ or (S)‐2‐methoxyphenylacetic acid ( 4a , 4b ) have been synthesized. The absolute configurations of these compounds have been determined on the basis of NOESY correlations between the protons of the tert‐butyl group and the cyclopentane fragment of the molecules. The crucial part of this analysis was assignment of the absolute configuration at C‐5. Additionally, by calculation of the chemical shift anisotropy, δ^RS, for the relevant protons, it was also possible to confirm the absolute configurations at the C‐2 centres of compounds 2a , 2b and 5a , 5b , 5c , 5d . Chirality, 25:422–426, 2013.© 2013 Wiley Periodicals, Inc.     

Dodecyl α‐L‐Rhamnopyranosyl‐(1→2)‐β‐D‐fucopyranoside Derivatives from the Glandular Trichome Exudate of Erodium pelargoniflorum

Chemical investigation of the glandular trichome exudate of Erodium pelargoniflorum (Geraniaceae) led to the isolation of two dodecyl disaccharide derivatives, named pelargoside A1 and pelargoside B1 ( 1 and 2 , resp.). The structures of 1 and 2 were determined as dodecyl 4‐O‐acetyl‐α‐L ‐rhamnopyranosyl‐(1→2)‐4‐O‐acetyl‐β‐D ‐fucopyranoside and dodecyl 3,4‐di‐O‐acetyl‐α‐L ‐rhamnopyranosyl‐(1→2)‐4‐O‐acetyl‐β‐D ‐fucopyranoside, respectively, by spectroscopic studies, including 2D‐NMR, and chemical transformations. In addition, undecyl, tridecyl, and tetradecyl homologs of 1 and 2 , named pelargosides A2–A4 and pelargosides B2–B4, were also characterized as minor constituents of the exudate.     

Substituent effects on chiral resolutions of derivatized 1‐phenylalkylamines by heptakis(2,3‐di‐O‐methyl‐6‐O‐tert‐butyldimethylsilyl)‐β‐cyclodextrin GC stationary phase

Chiral resolutions of trifluoroacetyl‐derivatized 1‐phenylalkylamines with different type and position of substituent were investigated by capillary gas chromatography by using heptakis(2,3‐di‐O‐methyl‐6‐O‐tert‐butyldimethylsilyl)‐β‐cyclodextrin diluted in OV‐1701 as a chiral stationary phase. The influence of column temperature on retention and enantioselectivity was examined. All enantiomers of meta‐substituted analytes as well as fluoro‐substituted analytes could be resolved. Temperature had a favorable influence on enantioselectivity for small amines with substituents at the ortho‐position. The type of substituent at the stereogenic center of amines also had a crucial effect as the ethyl group led to poor enantioseparation. Among all analytes studied, trifluoroacetyl‐derivatized 1‐(2′‐fluorophenyl)ethylamine exhibited baseline resolution with the shortest analysis time.     

Tyrosinase‐Mediated Formation of a Reactive Quinone from the Depigmenting Agents, 4‐tert‐Butylphenol and 4‐tert‐Butylcatechol

Exposure of the skin to certain phenols or catechols such as 4‐tert‐butylphenol (TBP) and 4‐tert‐butylcatechol (TBC) may cause leukoderma. These substances are used in the polymer industry and numerous cases have been reported. Several theories of the mechanism for chemical leukoderma have been suggested. In the present study, TBP and TBC are shown to be oxidised by tyrosinase. The oxidation of TBC yields a quinone that is further investigated on its reactions with cysteine or glutathione (GSH). The products formed are isolated and identified by mass spectrometry and nuclear magnetic resonance as being 4‐tert‐butyl‐6‐S‐cysteinylcatechol (cys‐TBC) and 4‐tert‐butyl‐6‐S‐glutathionylcatechol (GS‐TBC). The reactive quinone is a strongly electrophilic substance that rapidly reacts with GSH. A depletion of the GSH defence system may give conditions where the quinone lives long enough to effect its toxic properties. The influence of the reactive tert‐butylquinone on enzymatic activities is demonstrated by the inhibition of glyceraldehyde‐3‐phosphate dehydrogenase.     

Vibrational circular dichroism as a probe of solid‐state organisation of derivatives of cyclic β‐amino acids: Cis‐ and trans‐2‐aminocyclobutane‐1‐carboxylic acid

Peptide models built from cis‐ and trans‐2‐aminocyclobutane‐1‐carboxylic acids (ACBCs) are studied in the solid phase by combining Fourier‐transform infrared spectroscopy (FTIR) absorption spectroscopy, vibrational circular dichroism (VCD), and quantum chemical calculations using density functional theory (DFT). The studied systems are N‐tert‐butyloxycarbonyl (Boc) derivatives of 2‐aminocyclobutanecarboxylic acid (ACBC) benzylamides, namely Boc?(cis‐ACBC)?NH?Bn and Boc?(trans‐ACBC)?NH?Bn. These two diastereomers show very different VCD signatures and intensities, which of the trans‐ACBC derivative being one order of magnitude larger in the region of the ν (CO) stretch. The spectral signature of the cis‐ACBC derivative is satisfactorily reproduced by that of the monomer extracted from the solid‐state geometry of related ACBC derivatives, which shows that no long‐range effects are implicated for this system. In terms of hydrogen bonds, the geometry of this monomer is intermediate between the C6 and C8 structures (exhibiting a 6‐ or 8‐membered cyclic NH?O hydrogen bond) previously evidenced in the gas phase. The benzyl group must be in an extended geometry to reproduce satisfactorily the shape of the VCD spectrum in the ν (CO) range, which qualifies VCD as a potential probe of dispersion interaction. In contrast, reproducing the IR and VCD spectrum of the trans‐ACBC derivative requires clusters larger than four units, exhibiting strong intermolecular H‐bonding patterns. A qualitative agreement is obtained for a tetramer, although the intensity enhancement is not reproduced. These results underline the sensitivity of VCD to the long‐range organisation in the crystal.     

HS‐SPME‐GC‐FID method for detection and quantification of Bacillus cereus ATCC 10702 mediated 2‐acetyl‐1‐pyrroline

A rapid micro‐scale solid‐phase micro‐extraction (SPME) procedure coupled with gas‐chromatography with flame ionized detector (GC‐FID) was used to extract parts per billion levels of a principle basmati aroma compound “2‐acetyl‐1‐pyrroline” (2‐AP) from bacterial samples. In present investigation, optimization parameters of bacterial incubation period, sample weight, pre‐incubation time, adsorption time, and temperature, precursors and their concentrations has been studied. In the optimized conditions, detection of 2‐AP produced by Bacillus cereus ATCC10702 using only 0.5 g of sample volume was 85 μg/kg. Along with 2‐AP, 15 other compounds produced by B. cereus were also reported out of which 14 were reported for the first time consisting mainly of (E)?2‐hexenal, pentadecanal, 4‐hydroxy‐2‐butanone, n‐hexanal, 2–6‐nonadienal, 3‐methoxy‐2(5H) furanone and 2‐acetyl‐1‐pyridine and octanal. High recovery of 2‐AP (87 %) from very less amount of B. cereus samples was observed. The method is reproducible fast and can be used for detection of 2‐AP production by B. cereus. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1356–1363, 2014     

Synthesis and Biological Activity of New 4‐tert‐Butylcyclohexanone Derivatives

In the synthesis performed in this study, derivatives of 4‐tert‐butylcyclohexanone 1 were obtained using typical reactions of organic synthesis. The bioactivity of the selected compounds was evaluated. 1‐(Bromomethyl)‐8‐tert‐butyl‐2‐oxaspiro[4.5]decan‐3‐one ( 5 ) was characterized by attractant properties against larvae and a weak feeding deterrent activity against adults of Alphitobius diaperinus Panzer . This bromolactone was a moderate antifeedant towards Myzus persicae Sulzer . In addition, ethyl (4‐tert‐butylcyclohexylidene)acetate ( 2 ) and bromolactone 5 displayed antibacterial activity. The strongest bacteriostatic effect was observed against Gram‐positive strains: Bacillus subtilis and Staphylococcus aureus. The bromolactone 5 also limited the growth of Escherichia coli strain.     

Trafficking of Acetyl‐C16‐Ceramide‐NBD with Long‐Term Stability and No Cytotoxicity into the Golgi Complex

The Golgi complex plays a prominent role in the modification and sorting of lipids and proteins, and is a highly dynamic organelle that is dispersed and rearranged before and after mitosis. Several reagents including 4‐nitrobenzo‐2‐oxa‐1,3‐diazole‐labeled C6‐ceramide (NBD‐C6‐ceramide, a ceramide having an NBD‐bound C6‐N‐acyl chain) and Golgi‐specific proteins that emit fluorescence are used as Golgi markers. In the present study, we synthesized a new ceramide analog, acetyl‐C16‐ceramide‐NBD (a ceramide having an acetylated C‐1 hydroxyl group, C16‐N‐acyl chain, and NBD‐bound C15‐sphingosine), and showed that it preferentially accumulated in the Golgi complex without cytotoxicity for over 24 h. Pathways for cellular uptake and interorganelle trafficking of acetyl‐C16‐ceramide‐NBD were investigated. Acetyl‐C16‐ceramide‐NBD was transported to the Golgi complex via ceramide transport proteins. In contrast to NBD‐C6‐ceramide, acetyl‐C16‐ceramide‐NBD was resistant to ceramide metabolic enzymes such as sphingomyelin synthase and glucosylceramide synthase. Because of its weaker cytotoxicity and resistance to ceramide metabolic enzymes, the localization of the Golgi complex could be observed in acetyl‐C16‐ceramide‐NBD‐labeled cells before and after mitosis.      

O‐Glycosylated 24 kDa human growth hormone has a mucin‐like biantennary disialylated tetrasaccharide attached at Thr‐60

MS was used to characterize the 24 kDa human growth hormone (hGH) glycoprotein isoform and determine the locus of O‐linked oligosaccharide attachment, the oligosaccharide branching topology, and the monosaccharide sequence. MALDI‐TOF/MS and ESI‐MS/MS analyses of glycosylated 24 kDa hGH tryptic peptides showed that this hGH isoform is a product of the hGH normal gene. Analysis of the glycoprotein hydrolysate by high‐performance anion‐exchange chromatography with pulsed amperometric detection and HPLC with fluorescent detection for N‐acetyl neuraminic acid (NeuAc) yielded the oligosaccharide composition (NeuAc₂, N‐acetyl galactosamine₁, Gal₁). After β‐elimination to release the oligosaccharide from glycosylated 24 kDa hGH, collision‐induced dissociation of tryptic glycopeptide T6 indicated that there had been an O‐linked oligosaccharide attached to Thr‐60. The sequence and branching structure of the oligosaccharide were determined by ESI‐MS/MS analysis of tryptic glycopeptide T6. The mucin‐like O‐oligosaccharide sequence linked to Thr‐60 begins with N‐acetyl galactosamine and branches in a bifurcated topology with one appendage consisting of galactose followed by NeuAc and the other consisting of a single NeuAc. The oligosaccharide moiety lies in the high‐affinity binding site 1 structural epitope of hGH that interfaces with both the growth hormone and the prolactin receptors and is predicted to sterically affect receptor interactions and alter the biological actions of hGH.     

A Simple Method for Resolution of Endo‐/Exo‐Monoesters of Trans‐Norborn‐5‐Ene‐2,3‐Dicarboxylic Acids Into Their Enantiomers

Separation of optical isomers obtainable from trans‐norborn‐5‐ene‐2,3‐dicarboxylic acid methyl and tert‐butyl monoesters was performed by crystallization of the respective salts prepared with (R)‐ and (S)‐1‐phenylethylamine. Starting from racemic endo‐monomethyl ester of trans‐norborn‐5‐ene‐2,3‐dicarboxylic acid, prepared by partial hydrolysis of the cyclopentadiene‐dimethyl fumarate adduct, the corresponding (2R,3R)‐endo‐monoester was isolated in 97% enantiomeric excess (ee) yield after seven repeated crystallizations from tetrachloromethane. Starting from exo‐mono‐tert‐butyl ester of the same acid, prepared by alcoholysis of the cyclopentadiene‐maleic anhydride adduct followed by isomerization, (2R,3R)‐exo‐monoester was isolated in >98% ee yield after four repeated crystallizations from ethanol. Crystallization of the acids from the mother liquor containing (S)‐1‐phenylethylamine yielded products with inverse stereochemical configuration. Chirality 27:151–155, 2015. © 2014 Wiley Periodicals, Inc.     

Solvent‐dependent conformation of a regioselective amylose carbamate: Amylose‐2‐acetyl‐3,6‐bis(phenylcarbamate)

Six amylose‐2‐acetyl‐3,6‐bis(phenylcarbamate) (AAPC) samples ranging in weight‐average molar mass M_w from 1.8 × 10⁴ g mol^?1 to 1.1 × 10⁶ g mol^?1 have been prepared from enzymatically synthesized amylose samples. Static light scattering, small‐angle X‐ray scattering, sedimentation equilibrium, and viscosity measurements were made for the samples in 1,4‐dioxane (DIOX), 2‐ethoxyethanol (2EE), and 2‐butanone (MEK) all at 25°C to determine particle scattering functions, z‐average radii of gyration, intrinsic viscosities, as well as M_w. The data were analyzed in terms of the wormlike cylinder model mainly to yield the helix pitch per residue h and the Kuhn segment length λ^?1, which corresponds to twice of the persistence length. The latter parameters (λ^?1) in 2EE (11 nm) and MEK (12 nm) are quite smaller than those for amylose tris(phenylcarbamate) (ATPC) in the same solvent (16 nm in 2EE and 18 nm in MEK) whereas those for AAPC (21 nm) and ATPC (22 nm) in DIOX are essentially the same as each other. This indicates that the chain stiffness of AAPC is more strongly influenced by the solvents since the number of intramolecular H‐bonds of AAPC is more changeable than that for ATPC. © 2012 Wiley Periodicals, Inc. Biopolymers 97:1010–1017, 2012.     

Antiproliferative Evaluation of Some 2‐[2‐(2‐Phenylethenyl)‐cyclopent‐3‐en‐1‐yl]‐1,3‐benzothiazoles: DFT and Molecular Docking Study

The 2‐[2‐(2‐phenylethenyl)cyclopent‐3‐en‐1‐yl]‐1,3‐benzothiazoles were synthesized from the reactions of 7‐benzylidenebicyclo[3.2.0]hept‐2‐en‐6‐ones with 2‐aminobenzenethiol. The antiproliferative activities of 2‐[2‐(2‐phenylethenyl)cyclopent‐3‐en‐1‐yl]‐1,3‐benzothiazoles were determined against C6 (rat brain tumor) and HeLa (human cervical carcinoma cells) cell lines using BrdU cell proliferation ELISA assay. Cisplatin and 5‐fluorouracil (5‐FU) were used as standards. The most active compound was 2‐{(1S,2S)‐2‐[(E)‐2‐(4‐methylphenyl)ethenyl]cyclopent‐3‐en‐1‐yl}‐1,3‐benzothiazole against C6 cell lines with IC₅₀=5.89 μm value (cisplatin, IC₅₀=14.46 μm and 5‐FU, IC₅₀=76.74 μm ). Furthermore, the most active compound was 2‐{(1S,2S)‐2‐[(E)‐2‐(2‐methoxyphenyl)ethenyl]cyclopent‐3‐en‐1‐yl}‐1,3‐benzothiazole against HeLa cell lines with IC₅₀=3.98 μm (cisplatin, IC₅₀=37.95 μm and 5‐FU, IC₅₀=46.32 μm ). Additionally, computational studies of related molecules were performed by using B3LYP/6‐31G+(d,p) level in the gas phase. Experimental IR and NMR data were compared with the calculated results and were found to be compatible with each other. Molecular electrostatic potential (MEP) maps of the most active 2‐{(1S,2S)‐2‐[(E)‐2‐(2‐methoxyphenyl)ethenyl]cyclopent‐3‐en‐1‐yl}‐1,3‐benzothiazole against HeLa and the most active 2‐{(1S,2S)‐2‐[(E)‐2‐(4‐methylphenyl)ethenyl]cyclopent‐3‐en‐1‐yl}‐1,3‐benzothiazole against C6 were investigated, aiming to determine the region that the molecule is biologically active. Biological activities of mentioned molecules were investigated with molecular docking analyses. The appropriate target protein (PDB codes: 1 M17 for the HeLa cells and 1JQH for the C6 cells) was used for 2‐{(1S,2S)‐2‐[(E)‐2‐(2‐methoxyphenyl)ethenyl]cyclopent‐3‐en‐1‐yl}‐1,3‐benzothiazole and 2‐{(1S,2S)‐2‐[(E)‐2‐(4‐methylphenyl)ethenyl]cyclopent‐3‐en‐1‐yl}‐1,3‐benzothiazole molecules exhibiting the highest biological activity against HeLa and C6 cells in the docking studies. As a result, it was determined that these molecules are the best candidates for the anticancer drug.     

A cytotoxicity,optical spectroscopy and computational binding analysis of 4‐[3‐acetyl‐5‐(acetylamino)‐2‐methyl‐2,3‐dihydro‐1,3,4‐thiadiazole‐2‐yl]phenyl benzoate in calf thymus DNA

In this study the interaction mechanism between newly synthesized 4‐(3‐acetyl‐5‐(acetylamino)‐2‐methyl‐2, 3‐dihydro‐1,3,4‐thiadiazole‐2‐yl) phenyl benzoate (thiadiazole derivative) anticancer active drug with calf thymus DNA was investigated by using various optical spectroscopy techniques along with computational technique. The absorption spectrum shows a clear shift in the lower wavelength region, which may be due to strong hypochromic effect in the ctDNA and the drug. The results of steady state fluorescence spectroscopy show that there is static quenching occurring while increasing the thiadiazole drug concentration in the ethidium bromide‐ctDNA system. Also the binding constant (K), thermo dynamical parameters of enthalpy change (ΔH°), entropy change (ΔS°) Gibbs free energy change (ΔG°) were calculated at different temperature (293 K, 298 K) and the results are in good agreement with theoretically calculated MMGBSA binding analysis. Time resolved emission spectroscopy analysis clearly explains the thiadiazole derivative competitive intercalation in the ethidium bromide‐ctDNA system. Further, molecular docking studies was carried out to understand the hydrogen bonding and hydrophobic interaction between ctDNA and thiadiazole derivative molecule. In addition the docking and molecular dynamics charge distribution analysis was done to understand the internal stability of thiadiazole derivative drug binding sites of ctDNA. The global reactivity of thiadiazole derivative such as electronegativity, electrophilicity and chemical hardness has been calculated.     

One‐pot synthesis of (R)‐1‐(pyridin‐4‐yl)ethyl acetate using tandem catalyst prepared by co‐immobilization of palladium and lipase on mesoporous foam: Optimization and kinetic modeling

The synthesis of (R )‐1‐(pyridin‐4‐yl)ethyl acetate was achieved over tandem palladium‐lipase catalyst with 100% selectivity using 4‐acetyl pyridine as a reactant. The 2% w /w palladium and lipase catalyst was successfully co‐immobilized in the microenvironment of the mesocellular foam and characterized by various techniques. The palladium metal from catalyst hydrogenated 4‐acetyl pyridine to form 1‐(pyridin‐4‐yl)ethanol. The generated intermediate product then underwent kinetic resolution over lipase and selectively gave (R )‐1‐(pyridin‐4‐ yl)ethyl acetate. The catalytic conditions were then studied for optimal performance of both steps. The reaction conditions were optimized to 50 °C and toluene as a solvent. Both chemical and enzymatic kinetic models of the reaction were developed for a given set of reaction conditions and kinetic parameters were predicted. At optimal conditions, the obtained selectivity of intermediate (1‐(pyridin‐4‐yl)ethanol) was 51.38%. The final product yield of ((R )‐1‐(pyridin‐4‐yl)ethyl acetate) was 48.62%.     

Synthesis,crystal structure and fluorescence properties of terbium complexes with phenoxyacetic acid and 2,4,6‐tris‐(2‐pyridyl)‐s–triazine

Two complexes of Tb³⁺, Gd³⁺/Tb³⁺ and one heteronuclear crystal Gd³⁺/Tb³⁺ with phenoxyacetic acid (HPOA) and 2,4,6‐tris‐(2‐pyridyl)‐s–triazine (TPTZ) have been synthesized. Elemental analysis, rare earth coordination titration, inductively coupled plasma atomic emission spectrometry (ICP‐AES) and thermogravimetric analysis‐differential scanning calorimetry (TG‐DSC) analysis show that the two complexes are Tb₂(POA)₆(TPTZ)₂·6H₂O and TbGd(POA)₆(TPTZ)₂·6H₂O, respectively. The crystal structure of TbGd(POA)₆(TPTZ)₂·2CH₃OH was determined using single‐crystal X‐ray diffraction. The monocrystal belongs to the triclinic system with the P‐1 space group. In particular, each metal ion is coordinately bonded to three nitrogen atoms of one TPTZ and seven oxygen atoms of three phenoxyacetic ions. Furthermore, there exist two coordinate forms between C₆H₅OCH₂COO^– and the metal ions in the crystal. One is a chelating bidentate, the other is chelating and bridge coordinating. Fluorescence determination shows that the two complexes possess strong fluorescence emissions. Furthermore, the fluorescence intensity of the Gd³⁺/Tb³⁺ complex is much stronger than that of the undoped complex, which may result from a decrease in the concentration quench of Tb³⁺ ions, and intramolecular energy transfer from the ligands coordinated with Gd³⁺ ions to Tb³⁺ ions. Copyright © 2015 John Wiley & Sons, Ltd.     

New Pyran‐2‐ones from Alkalophilic Actinomycete,Nocardiopsis alkaliphila sp. Nov. YIM‐80379

Two new pyran‐2‐ones, nocardiopyrones A and B ( 1 and 2 , resp.), along with four known compounds, pyridinols 3 – 5 , and 1‐acetyl‐β‐carboline ( 6 ) were isolated from the alkalophilic actinomycete Nocardiopsis alkaliphila sp. nov. YIM‐80379. Their structures were established on the basis of spectroscopic analysis, CD spectra, and the quantum‐chemical ECD calculation. Pyridinols 3 – 5 were isolated from a natural source for the first time. Compounds 1 and 2 showed weak antibacterial activities against Pseudomonas aeruginosa, Enterobacter aerogenes, and Escherichia coli with MIC values of 20–48 μM . Compound 2 showed weak antimicrobial activities against Candida albicans and Staphylococcus aureus with MIC values of 24 and 48 μM , respectively.     

A β1‐6/β1‐3 galactosidase from Bifidobacterium animalis subsp. lactis Bl‐04 gives insight into sub‐specificities of β‐galactoside catabolism within Bifidobacterium

The Bifidobacterium genus harbours several health promoting members of the gut microbiota. Bifidobacteria display metabolic specialization by preferentially utilizing dietary or host‐derived β‐galactosides. This study investigates the biochemistry and structure of a glycoside hydrolase family 42 (GH42) β‐galactosidase from the probiotic Bifidobacterium animalis subsp. lactis Bl‐04 (BlGal42A). BlGal42A displays a preference for undecorated β1‐6 and β1‐3 linked galactosides and populates a phylogenetic cluster with close bifidobacterial homologues implicated in the utilization of N‐acetyl substituted β1‐3 galactosides from human milk and mucin. A long loop containing an invariant tryptophan in GH42, proposed to bind substrate at subsite + 1, is identified here as specificity signature within this clade of bifidobacterial enzymes. Galactose binding at the subsite ? 1 of the active site induced conformational changes resulting in an extra polar interaction and the ordering of a flexible loop that narrows the active site. The amino acid sequence of this loop provides an additional specificity signature within this GH42 clade. The phylogenetic relatedness of enzymes targeting β1‐6 and β1‐3 galactosides likely reflects structural differences between these substrates and β1‐4 galactosides, containing an axial galactosidic bond. These data advance our molecular understanding of the evolution of sub‐specificities that support metabolic specialization in the gut niche.     

Synthesis and in Vitro Antimicrobial Activity Screening of New 3‐Acetyl‐2,5‐disubstituted‐1,3,4‐oxadiazoline Derivatives

Thirteen new 3‐acetyl‐2,5‐disubstituted‐1,3,4‐oxadiazoline derivatives were synthesized from corresponding hydrazide‐hydrazones of isonicotinic acid in the reaction with acetic anhydride. The obtained compounds were identified with the use of spectral methods (IR, ¹H‐NMR, ¹³C‐NMR, MS). In vitro antimicrobial activity screening of synthesized compounds against a panel of bacteria and fungi revealed interesting antibacterial and antifungal activity of tested 1,3,4‐oxadiazoline derivatives, which is comparable to that of commonly used antimicrobial agents.     

Bimolecular fluorescence quenching reactions of the biologically active coumarin composite 2‐acetyl‐3H‐benzo[f]chromen‐3‐one in different solvents

A study on fluorescence quenching was carried out for the coumarin derivative 2‐acetyl‐3H‐benzo[f]chromen‐3‐one (2AHBC) with aniline at room temperature. Efficient fluorescence quenching was observed and Stern–Volmer (S–V) plots showed upward curves from linearity in all solvents of different polarities. For the solute 2AHBC, ground state complex formation does not hold in our study. The kinetic distance (r) value was found to be greater than the encounter distance (R) and indicated that the quenching reaction was held within the sphere of action. Diffusion‐limited reactions were found to be more prominent in high polarity solvents, namely dimethyl sulfoxide (DMSO), DMF, ACN, methanol, ethanol, propanol and DCM. The relationships between quenching constant (K_SV) and dielectric constants (ε) of the different solvents were studied.