2H‐Pyran‐2‐one and 2H‐Furan‐2‐one Derivatives from the Plant Endophytic Fungus Pestalotiopsis fici

Two new α‐pyrones (=2H‐pyran‐2‐ones), ficipyrones A and B ( 1 and 2 , resp.), and two new α‐furanones (=2H‐furan‐2‐ones), ficifuranones A and B ( 3 and 4 , resp.), together with three known metabolites, antibiotic F 0368 ( 5 ), hydroxyseiridin ( 6 ), and hydroxyisoseiridin ( 7 ), were isolated from solid cultures of the plant endophytic fungus Pestalotiopsis fici. Their structures were elucidated primarily by NMR spectroscopy, and the absolute configuration of 1 was deduced from the circular‐dichroism (CD) data. Compound 1 showed antifungal activity against the plant pathogen Gibberella zeae (CGMCC 3.2873) with an IC₅₀ value of 15.9 μM .     

Enantiopure 4‐oxazolin‐2‐ones and 4‐methylene‐2‐oxazolidinones as chiral building blocks in a divergent asymmetric synthesis of heterocycles

Enantiopure 3‐((R)‐ and 3‐((S)‐1‐phenylethyl)‐4‐oxazoline‐2‐ones were evaluated as chiral building blocks for the divergent construction of heterocycles with stereogenic quaternary centers. The N‐(R)‐ or N‐(S)‐1‐phenylethyl group of these compounds proved to be an efficient chiral auxiliary for the asymmetric induction of the 4‐ and 5‐positions of the 4‐oxazolin‐2‐one ring through thermal and MW‐promoted nucleophilic conjugated addition to Michael acceptors and alkyl halides. The resulting adducts were transformed via a cascade process into fused six‐membered carbo‐ and heterocycles. The structure of the reaction products depended on the electrophiles and reaction conditions used. Alternative isomeric 4‐methylene‐2‐oxazolidinones served as chiral precursors for a versatile and divergent approach to highly substituted cyclic carbamates. DFT quantum calculations showed that the formation of bicyclic pyranyl compounds was generated by a diastereoselective concerted hetero‐Diels‐Alder cycloaddition.     

Synthesis of 8‐Substituted 2′‐Deoxyisoguanosines via Unprotected 8‐Brominated 2‐Amino‐2′‐deoxyadenosine

A variety of applications of 8‐alkynylated nucleosides has prompted the synthesis of new purine analogues. Bromination of unprotected 2‐amino‐2′‐deoxyadenosine with Br₂/AcOH/AcONa gives 2‐amino‐8‐bromo‐2′‐deoxyadenosine (87%). The brominated derivative is converted to 8‐alkynylated 2‐amino‐2′‐deoxyadenosines by palladium‐catalyzed Sonogashira cross‐coupling reaction via microwave assistance (81 – 95%). The resulting compounds are further transformed to 8‐alkynylated 2′‐deoxyisoguanosines (52 – 70%). The physical properties of new compounds are investigated.     

Magnesium methoxide‐induced chemiluminescent decomposition of bicyclic dioxetanes bearing a 2′‐alkoxy‐2‐hydroxy‐1,1′‐binaphthyl‐7‐yl moiety

Bicyclic dioxetanes 2a–c bearing a 2′‐alkoxy‐2‐hydroxy‐1,1′‐binaphthyl‐7‐yl moiety were effectively synthesized and their base‐induced chemiluminescent decomposition was investigated by the use of alkaline metal (Na⁺ and K⁺) or Mg²⁺ alkoxide in MeOH. When 2a–c were treated with tetrabutylammonium fluoride (TBAF) in dimethyl sulfoxide (DMSO) as a reference system, they showed chemiluminescence as a flash of orange light (maximum wavelength λ_max^CL = 573–577 nm) with efficiency Φ^CL = 6–8 × 10^–2. On the other hand, for an alkaline metal (Na⁺ or K⁺) alkoxide/MeOH system, 2a–c decomposed slowly to emit a glow of chemiluminescence, the spectra of which were shifted slightly toward red from the TBAF/DMSO system, and Φ^CL (= 1.4–2.3 × 10^–3) was considerably decreased. In addition, Mg(OMe)₂ was found to play a characteristic role as a base for the chemiluminescent decomposition of 2a–c through coordination to the intermediary oxidoaryl‐substituted dioxetanes 13. Thus, Mg²⁺ increased Φ^CL to more than twice those with Na⁺ or K⁺, while it shifted λ_max^CL considerably toward blue (λ_max^CL = 550–566 nm). Copyright © 2012 John Wiley & Sons, Ltd.     

Parallel kinetic resolution of D‐labelled 2‐aryl‐propionic and butanoic acids using quasi‐enantiomeric combinations of oxazolidin‐2‐ones

The parallel kinetic resolution of racemic 2‐aryl‐2‐deuterio‐propionic and butanoic acids using an equimolar combination of quasi‐enantiomeric oxazolidin‐2‐ones is discussed. The levels of diastereoselectivity were high leading to enantiomerically pure D ‐labeled products in good yield. Chirality, 2010. © 2009 Wiley‐Liss, Inc.     

Dual labeling with 5‐bromo‐2'‐deoxyuridine and 5‐ethynyl‐2'‐deoxyuridine for estimation of cell migration rate in the small intestinal epithelium

Small intestinal epithelium is a self‐renewing system in which the entire sequence of cell proliferation, differentiation, and removal is coupled to cell migration along the crypt‐villus axis. We examined whether dual labeling with different thymidine analogues, 5‐bromo‐2'‐deoxyuridine (BrdU) and 5‐ethynyl‐2'‐deoxyuridine (EdU), can be used to estimate cell migration rates on the villi of small intestines in rats. Rats received a single intraperitoneal injection of BrdU and EdU within a time interval, and signals in tissue sections were examined by immunohistochemistry and the “click” reaction, respectively. We successfully observed BrdU‐ and EdU‐positive cells on the epithelium with no cross‐reaction. In addition, we observed an almost complete overlapping of BrdU‐ and EdU‐positive cells in rats administered simultaneously with BrdU and EdU. By calculating the cell migration rate by dividing the distance between the median cell positions of the distribution of BrdU‐ and EdU‐positive cells by the time between the injection of BrdU and EdU, we estimated approximately 9 and 5 μm/h for the cell migration rates on the villi in the jejunum and ileum, respectively. We propose that dual labeling with BrdU and EdU within a time interval, followed by detecting with immunohistochemistry and the click reaction, respectively, is useful to estimate accurately the cell migration rate in the intestinal epithelium in a single animal.     

Spectrofluorimetric determination of aluminium using 2‐hydroxy‐1‐naphthylidene‐(8‐aminoquinoline)

A sensitive and selective spectrofluorimetric method has been developed for the rapid determination of aluminium. This method is based on the complex formation between aluminium and 2‐hydroxy‐1‐naphthylidene‐(8‐aminoquinoline) (HNAQ). The optimum conditions for the complex formation were a metal‐to‐ligand (M : L) stoichiometric ratio of 1:1, a pH of 5.5 and a 0.20 m acetate buffer. The fluorescence of the complex was monitored at an emission wavelength of 502 nm with excitation at 438 nm. Under these conditions, linear calibration curves were obtained in the ranges 0.05–1 and 1–5 ppm. The detection limit was 3.4 ppb for the former and 13.5 ppb for the latter. The maximum relative standard deviation of the method for an aluminium standard of 200 ppb was 1.5% (n = 5). This method was successfully applied for the determination of aluminium in drinking water, pharmaceutical antacid tablets and suspension samples. Copyright © 2010 John Wiley & Sons, Ltd.     

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     

Enantioselective resolution of 4‐chloromandelic acid by liquid–liquid extraction using 2‐chloro‐N‐carbobenzyloxy‐L‐amino acid

A liquid–liquid extraction resolution of 4‐chloro‐mandelic acid (4‐ClMA) was studied by using 2‐chloro‐N‐carbobenzyloxy‐L‐amino acid (2‐Cl‐Z‐AA) as a chiral extractant. Important factors affecting the extraction efficiency were investigated, including the type of chiral extractant, pH value of aqueous phase, initial concentration of chiral extractant in organic phase, initial concentration of 4‐ClMA in aqueous phase, and resolution temperature. It was observed that the concentration of (R)‐4‐ClMA was much higher than that of (S)‐4‐ClMA in organic phase due to a higher stability of the complex formed between (R)‐4‐ClMA and 2‐Cl‐Z‐AA. A separation factor (α) of 3.05 was obtained at 0.02 mol/L 2‐Cl‐Z‐Valine dissolved in dichloromethane, pH of 2.0, concentration of 4‐ClMA of 0.11 mmol/Land T of 296.7K.     

In vitro effects of 2‐methoxyestradiol‐bis‐sulphamate on the non‐tumorigenic MCF‐12A cell line

A priority in recent anti‐cancer drug development has been attaining better side‐effect profiles for potential compounds. To produce highly specific cancer therapies it is necessary to understand both the effects of the proposed compound on cancer and on normal cells comprising the rest of the human body. Thus in vitro evaluation of these compounds against non‐carcinogenic cell lines is of critical importance. One of the most recent developments in experimental anti‐cancer agents is 2‐methoxyestradiol‐bis‐sulphamate (2ME‐BM), a sulphamoylated derivative of 2‐methoxyestradiol. The aim of this study was to evaluate the in vitro effects of 2ME‐BM on cell proliferation, morphology and mechanisms of cell death in the non‐carcinogenic MCF‐12A breast epithelial cell line. The study revealed changes in proliferative capacity, morphology and cell death induction in response to 2ME‐BM exposure (24 h at 0.4 µM). Microscopy showed decreased cell density and cell death‐associated morphology (increased apoptotic characteristics), a slight increase in acidic intracellular vesicles and insignificant ultra‐structural aberrations. Mitotic indices revealed a G₂M‐phase cell cycle block. This was confirmed by flow cytometry, where an increased fraction of abnormal cells and a decrease in cyclin B1 levels were observed. These results evidently demonstrate that the non‐carcinogenic MCF‐12A cell line is less susceptible when compared to 2ME‐BM‐exposed cancer cell lines previously tested. Further in vitro research into the mechanism of this potentially useful compound is warranted. Copyright © 2010 John Wiley & Sons, Ltd.     

Unexpected Loss of Stereoselectivity in Ring‐Opening Reaction of 2‐Alkoxy‐2‐Thio‐1,3,2‐Oxathiaphospholanes With a Pyrophosphate Anion

A reaction of DBU promoted ring opening in nucleoside‐3'‐O‐ and nucleoside‐5'‐O‐(2‐thio‐4,4‐pentamethylene‐1,3,2‐oxathiaphospholane) monomers with a pyrophosphate or a methylenediphosphonate anion proceeds with substantial loss of stereoselectivity. Depending on the absolute configuration of the phosphorus atom, so far widely accepted the stereoretentive mechanism of condensation is accompanied by a stereoinvertive one, most likely employing an intramolecular ligand–ligand exchange in an uncharged intermediate. Chirality 27:155–122, 2015. © 2014 Wiley Periodicals, Inc     

Homo‐C‐nucleoside analogs IV. Synthesis of 4‐(2,5‐anhydro‐D‐altro‐pentitol‐1‐yl)‐2‐phenyl‐2H‐1,2,3‐triazole homo‐C‐nucleoside. CD assignment of the absolute configuration of the carbon bridge

Dehydrative cyclization of 4‐(D‐altro ‐pentitol‐1‐yl)2‐phenyl‐2H ‐1,2,3‐triazole in basic medium with one moler equivalent of p‐toluene sulfonyl chloride in pyridine solution gave the homo‐C‐ nucleoside 4‐(2,5‐anhydro‐D‐altro ‐1‐yl)‐2‐phenyl‐2H ‐1,2,3‐triazole. The structure and anomeric configuration was determined by acylation, nuclear magnetic resonance (NMR), and mass spectroscopy. The stereochemistry at the carbon bridge of homo‐C‐ nucleoside 2‐phenyl‐2H ‐1,2,3‐triazoles was determined by circular dichroism (CD) spectroscopy.     

Architecture and self‐assembly of the SARS‐CoV‐2 nucleocapsid protein

The COVID‐2019 pandemic is the most severe acute public health threat of the twenty‐first century. To properly address this crisis with both robust testing and novel treatments, we require a deep understanding of the life cycle of the causative agent, the SARS‐CoV‐2 coronavirus. Here, we examine the architecture and self‐assembly properties of the SARS‐CoV‐2 nucleocapsid protein, which packages viral RNA into new virions. We determined a 1.4 Å resolution crystal structure of this protein's N2b domain, revealing a compact, intertwined dimer similar to that of related coronaviruses including SARS‐CoV. While the N2b domain forms a dimer in solution, addition of the C‐terminal spacer B/N3 domain mediates formation of a homotetramer. Using hydrogen‐deuterium exchange mass spectrometry, we find evidence that at least part of this putatively disordered domain is structured, potentially forming an α‐helix that self‐associates and cooperates with the N2b domain to mediate tetramer formation. Finally, we map the locations of amino acid substitutions in the N protein from over 38,000 SARS‐CoV‐2 genome sequences. We find that these substitutions are strongly clustered in the protein's N2a linker domain, and that substitutions within the N1b and N2b domains cluster away from their functional RNA binding and dimerization interfaces. Overall, this work reveals the architecture and self‐assembly properties of a key protein in the SARS‐CoV‐2 life cycle, with implications for both drug design and antibody‐based testing.     

VCD studies on cyclic peptides assembled from L‐α‐amino acids and a trans‐2‐aminocyclopentane‐ or trans‐2‐aminocyclohexane carboxylic acid

The increasing interest in peptidomimetics of biological relevance prompted us to synthesize a series of cyclic peptides comprising trans‐2‐aminocyclohexane carboxylic acid (Achc) or trans‐2‐aminocyclopentane carboxylic acid (Acpc). NMR experiments in combination with MD calculations were performed to investigate the three‐dimensional structure of the cyclic peptides. These data were compared to the conformational information obtained by electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopy. Experimental VCD spectra were compared to theoretical VCD spectra computed quantum chemically at B3LYP/6‐31G(d) density functional theory (DFT) level. The good agreement between the structural features derived from the VCD spectra and the NMR‐based structures underlines the applicability of VCD in studying the conformation of small cyclic peptides. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Resolution of 1‐n‐Butyl‐3‐Methyl‐3‐Phospholene 1‐Oxide With TADDOL Derivatives and Calcium Salts of O,O'‐Dibenzoyl‐(2R,3R)‐ or O,O'‐di‐p‐Toluoyl‐(2R,3R)‐tartaric Acid

The resolution methods applying (?)‐(4R,5R)‐4,5‐bis(diphenylhydroxymethyl)‐2,2‐dimethyldioxolane (“TADDOL”), (?)‐(2R,3R)‐α,α,α',α'‐tetraphenyl‐1,4‐dioxaspiro[4.5]decan‐2,3‐dimethanol (“spiro‐TADDOL”), as well as the acidic and neutral Ca²⁺ salts of (?)‐O,O'‐dibenzoyl‐ and (?)‐O,O'‐di‐p‐toluoyl‐(2R,3R)‐tartaric acid were extended for the preparation of 1‐n‐butyl‐3‐methyl‐3‐phospholene 1‐oxide in optically active form. In one case, the intermediate diastereomeric complex could be identified by single‐crystal X‐ray analysis. The absolute P‐configuration of the enantiomers of the phospholene oxide was also determined by comparing the experimentally obtained and calculated CD spectra. Chirality 26:174–182, 2014. © 2014 Wiley Periodicals, Inc.     

CD‐sensitive Zn‐porphyrin tweezer host‐guest complexes,part 2: Cis‐ and trans‐3‐hydroxy‐4‐aryl/alkyl‐β‐lactams. A case study

This article describes an application of the host‐guest chiral recognition approach called tweezer methodology for the determination of the absolute configuration of 3‐hydroxy‐β‐lactams. These substrates represent challenging cases due to their chemical reactivity, the presence of multiple stereogenic centers and several functional groups which offer various possibilities of binding to the Zn‐porphyrin host. OPLS‐2005, the force field used in this work to predict the interporphyrin twist, modeled correctly the host‐guest complexation mechanism and revealed conformational details of the bound substrates. The computational study also suggested that in cases where an increase in the magnitude of the stereodifferentiation and an intense experimental CD are observed, the bound conformation of the conjugates are hydrogen bonded. The present investigation provides evidence that when the tweezer method is assisted by the OPLS‐2005 based computational approach, it can be successfully applied to the configurational and conformational elucidation of multi‐functional compounds with multiple stereogenic centers. Chirality, 2010. © 2009 Wiley‐Liss, Inc.     

Asymmetrically simultaneous synthesis of L‐homophenylalanine and N6‐protected‐2‐oxo‐6‐amino‐hexanoic acid by engineered Escherichia coli aspartate aminotransferase

L ‐Homophenylalanine (L ‐HPA) and N⁶‐protected‐2‐oxo‐6‐amino‐hexanoic acid (N⁶‐protected‐OAHA) can be used as building blocks for the manufacture of angiotensin‐converting enzyme inhibitors. To synthesize L ‐HPA and N⁶‐protected‐OAHA simultaneously from 2‐oxo‐4‐phenylbutanoic acid (OPBA) and N⁶‐protected‐L ‐lysine, several variants of Escherichia coli aspartate aminotransferase (AAT) were developed by site‐directed mutagenesis and their catalytic activities were investigated. Three kinds of N⁶‐protected‐L ‐lysine were tested as potential amino donors for the bioconversion process. AAT variants of R292E/L18H and R292E/L18T exhibited specific activities of 0.70±0.01 U/mg protein and 0.67±0.02 U/mg protein to 2‐amino‐6‐tert‐butoxycarbonylamino‐hexanoic acid (BOC‐lysine) and 2‐amino‐6‐(2,2,2‐trifluoro‐acetylamino)‐hexanoic acid, respectively. E. coli cells expressing R292E/L18H variant were able to convert OPBA and BOC‐lysine to L ‐HPA and 2‐oxo‐6‐tert‐butoxycarbonylamino‐hexanoic acid (BOC‐OAHA) with 96.2% yield in 8 h. This is the first report demonstrating a process for the simultaneous production of two useful building blocks, L ‐HPA and BOC‐OAHA. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009     

Synthesis and Biological Evaluation of Novel 1‐(4‐(Hydroxy(1‐oxo‐1,3‐dihydro‐2H‐inden‐2‐ylidene)methyl)phenyl)‐3‐phenylurea Derivatives

A series of novel phenylurea containing 2‐benzoylindan‐1‐one derivatives 3a  –  3j were synthesized from the reaction of phenylurea‐substituted acetophenones 1a  –  1j with phthalaldehyde 2 under mild reaction conditions in good yields. All synthesized compounds were characterized by spectroscopic methods. The obtained compounds ( 3a  –  3j ) were evaluated for anticancer activity against HeLa and C6 cell lines. Antiproliferative activity was determined by the BrdU proliferation ELISA assay, 3f and 3g were found to be most active compounds. The compounds were also screened for antimicrobial activity and all compounds showed remarkable activity against used microorganisms.