Cellulose synthase (CesA) genes in algae and seedless plants

Microfibril structure is determined largely by the organization of arrays of integral plasma membrane protein particles known as “terminal complexes”, which include cellulose synthase catalytic subunits encoded by CesA genes. Although the CesA genes of plants and bacteria share conserved regions, variations in terminal complex and microfibril structure presumably result from sequence differences. Thus, the CesA domains that influence terminal complex assembly may be revealed by examining the differences between CesA genes from green algae in which terminal complex structure ranges from rosettes (plant-like) to linear (bacteria-like). This report describes a second CesA gene that has been cloned from Mesotaenium caldariorum, a unicellular green alga from the order Zygnematales, which have rosette terminal complexes. Both McCesA1 and McCesA2 are similar to seed plant CesAs in domain structure and intron position. Seed plants have multiple CesAs and CesA-like (Csl) genes, some of which appear to be expressed specifically during cell expansion, secondary cell wall deposition in vascular tissue, or tip growth. Diversification of the CesA and Csl gene families can be explored by comparing these genes in mosses, which lack vascular tissue with secondary cell walls, and early divergent vascular plants such as ferns. Degenerate primers were used to amplify and clone five unique CesA and Csl fragments from genomic DNA isolated from Physcomitrella patens. Probes derived from the cloned fragments were used to isolate several clones from a Physcomitrella genomic library. One Csl fragment was amplified from genomic DNA isolated from the fern Ceratopteris richardii. Phylogenetic analysis supports the presence of CslD genes in both mosses and ferns, but does not support the presence of secondary cell wall specific CesA orthologs in mosses.     

Asymmetric nitrone cycloadditions and their application to the synthesis of enantiopure pyrrolidine and pyrrolizidine derivatives

The cycloaddition reactions of a pair of chiral pyrroline-N-oxides derived from d-ribose with some typical mono and disubstituted alkenes are reported. In all these reactions with monosubstituted alkenes as well as with dimethyl maleate the preferred stereochemical outcome of the cycloaddition step comes from a 5-exo-anti transition state whereas stereoisomers from the 5-exo-syn transition state are also present as minor adducts. In the reaction with dimethyl fumarate the major adduct comes from a 4-exo-5-endo-syn transition state. The further behavior of the obtained isoxazolidines upon reductive ring opening conditions depends on the kind and the geometry of the preexisting substituents and they are transformed to enantiomerically pure pyrrolidine or pyrrolizidinone derivatives.     

Enzymatic formation of an unnatural methylated triketide by plant type III polyketide synthases

Octaketide synthase, a novel plant-specific type III polyketide synthase from Aloe arborescens, efficiently accepted (2RS)-methylmalonyl-CoA as a sole substrate to produce 6-ethyl-4-hydroxy-3,5-dimethyl-2-pyrone. On the other hand, a tetraketide-producing chalcone synthase from Scutellaria baicalensis and a diketide-producing benzalacetone synthase from Rheum palmatum also yielded the unnatural methylated C₉ triketide pyrone as a single product by sequential decarboxylative condensations of three molecules of (2RS)-methylmalonyl-CoA.     

Separation of Flavonoids from the Leaves of Oroxylum indicum by HSCCC

A high-speed counter-current chromatography system (HPCCC) capable of rapid processing has been employed to separate seven flavonoids from a methanolic extract of the leaves of Oroxylum indicum by a one-step isocratic elution using a chloroform–methanol–water (9.5:10:5) two-phase system. LC, MS and NMR have identified the components from the extract as chrysin, baicalein, baicalein-7-O-glucoside, baicalein-7-O-diglucoside, chrysin-7-O-glucuronide, baicalein-7-O-glucuronide, and a chrysin-diglucoside. Baicalein-7-O-glucuronide and chrysin-7-O-glucuronide have been separated from this plant by HSCCC for the first time. The present study also reports a new chrysin-diglucoside from the leaf extract. The results demonstrate that HSCCC is a powerful separation tool and can contribute to identifying and quantifying plant ingredients.     

Acid-induced conformational alteration of cis-preferential aromatic amides bearing N-methyl-N-(2-pyridyl) moiety

A series of cis-preferential aromatic N-methyl amides was designed and synthesized, and acid-induced conformational alteration of these compounds was investigated by means of NMR measurements in solution and X-ray crystal structure analysis. Compounds with a terminal N-methyl-N-(2-pyridyl) amide unit showed acid-induced conformational change from cis to trans, while those with a terminal N-methyl-2-pyridinecarboxamide unit showed a change of the carbonyl orientation from anti to syn with retention of cis conformation.     

Regioisomers Salviprolin A and B,Unprecedented Rosmarinic Acid Conjugated Dinorditerpenoids from Salvia przewalskii Maxim

Salvia przewalskii Maxim is a perennial plant from the genus Salvia (family Lamiaceae). The roots of S. przewalskii were long used as a traditional herb to treat blood circulation related illnesses in China. As part of our continuing interest in polycyclic natural products from medicinal plants, two unprecedented adducts comprised of a dinor-diterpenoid and a 9′-nor-rosmarinic acid derivative, linked by a 1,4-benzodioxane motif (1 and 2), were isolated from the roots of S. przewalskii. Their structures were established by extensive spectroscopic approaches including 1D, 2D NMR, and HRFABMS. Their cytotoxic activities against five human tumor cell lines were evaluated.     

Titanium-mediated syntheses of cyclopropylamines

The transformations of N,N-dialkylcarboxamides and nitriles with 1,2-dicarbanionic organometallics in situ generated from organomagnesium (Grignard) as well as organozinc reagents in the presence of stoichiometric or substoichiometric (semi-catalytic) quantities of a titanium alkoxide derivative of type XTi(OR)₃ with X=OR, Cl, Me and OR=OiPr, OEt are described. The key step in the transformation of a monocarbanionic into a 1,2-dicarbanionic organotitanium species is a disproportionation of a dialkyltitanium intermediate to form an alkane and a titanium alkene complex which has the reactivity of a titanacyclopropane derivative. The latter are able to undergo insertion of the carbonyl group of an N,N-dialkylcarboxamide or a cyano group to furnish, after ring contraction and hydrolysis, dialkylcyclopropylamines or cyclopropylamines, respectively. The titanium alkene complexes can also undergo ligand exchange with alkenes to afford new titanacyclopropanes, which subsequently react as 1,2-dicarbanionic equivalents. In many cases, these titanium-mediated formations of a wide range of synthetically and/or pharmacologically important cyclopropylamines proceed in good to very good yields (from 20% to 98% for dialkylcyclopropylamines from N,N-dialkylcarboxamides and from 27% to 73% for primary cyclopropylamines from nitriles) and with high chemo- and stereoselectivity. These circumstances in conjunction with the simplicity of the experimental handling and inexpensiveness of the reagents favor these reactions for an ever increasing range of applications in organic synthesis.     

Intramolecular 1,3-dipolar nitrone and nitrile oxide cycloaddition of 2- and 4-O-allyl and propargyl glucose derivatives: a versatile approach to chiral cyclic ether fused isoxazolidines, isoxazolines and isoxazoles

2-O- and 4-O-Allyl and -propargyl glucose and the corresponding oxime derivatives were prepared from readily available glucose dithioacetals. Intramolecular 1,3-dipolar cycloaddition of the N-benzyl and N-methyl nitrones of the above acyclic 2-O-allyl glucose derivatives led to the diastereoselective formation of chiral isoxazolidines incorporating the tetrahydrofuran ring. The EI mass spectra revealed a characteristic cleavage of the C-alkyl group adjacent to the furan oxygen atom. An enantiopure trisubstituted tetrahydrofuran was obtained by the reductive cleavage of the isoxazolidine ring of one of the cycloadducts. In contrast, the nitrile oxide cycloaddition of the 2-O-allyl derivatives afforded diastereomeric mixtures of the corresponding dihydroisoxazolines, the stereochemistry of which was tentatively assigned on the basis of the principle of optical superposition. The exclusive formation of a tetrahydrofuran ring from pentaallyl nitrone or nitrile oxide demonstrated the preferred formation of a five-membered ring to that of six or seven-membered rings. The nitrile oxide generated from a 3,4,5,6,7-pentaallyloxy-1-nitroheptane derivative obtained from pentaallylglucose underwent diastereoselective cycloaddition to give an isoxazoline fused to a pyran ring. Enantiopure isoxazoles containing tetrahydrofuran and oxepane rings were also prepared in good yields by the nitrile oxide cycloaddition of the 2-O- and 4-O-propargyl derivatives.     

Extraction,Isolation and Characterization of Bioactive Compounds from Artemisia and Their Biological Significance: A Review

Diverse medicinal plants such as those from the genus Artemisia have been employed globally for centuries by individuals belonging to different cultures. Universally, Artemisia species have been used to remedy various maladies that range from simple fevers to malaria. A survey conducted by the World Health Organization (WHO) demonstrated that 80% of the global population is highly reliant on herbal medicine for their primary healthcare. WHO recommends artemisinin-based combination therapies (ACT) for the treatment of global diseases such as malaria. Artemisinin is a bioactive compound derived from Artemisia annua leaves. It is a sesquiterpene endoperoxide with potent antimalarial properties. This review strives to instill natural products to chemists and others in diverse fields with a heterogeneous set of knowledge compiled from multifaceted researchers and organizations in literature. In particular, the various Artemisia species and effective extraction, isolation, and characterization methodologies are discussed in detail. An in-depth investigation into the literature reveals that divergent species of Artemisia exhibit a vast array of biological activities such as antimalarial, antitumor, and anti-inflammatory activities. There is substantial potential for bioactive compounds from Artemisia to provide significant relief from differing human ailments, but more meticulous research in this field is needed.     

Synthesis and oxidation of thioglicosides underlain by neomenthanethiol,D-glucose,and D-fructose

Synthesis of sulfides proceeding from neomenthanethiol, 1,2-O-isopropylidene-α-D-glucofuranose and 2,3:4,5-di-O-isopropylidene-β-D-fructopyranose was performed to get 65 and 54% yield respectively. Oxidation of the sulfides afforded diastereomeric sulfoxides in the yields from 40 to 53%, and diastereomeric excess (de) up to 36%. After removing the isopropylidene protection from 1-deoxy-1-[(1S,2S,5R)-2-isopropyl-5-methylcyclohexylsulfanyl]-2,3:4,5-di-O-isopropylidene-β-D-fructopyranose a water-soluble sulfide was obtained.     

Synthesis of rigid photoswitchable hemithioindigo ω-amino acids

The synthesis of novel N-Boc- and N-Fmoc protected hemithioindigo-based ω-amino acids is described. An approach to modulate the thermal stability of a hemithioindigo subunit is presented. Placing the amino-group in the stilbene part from the para- to meta-position leads to an increase of the half-life of the thermally labile E-form from 19 h to 47 h.     

Evolving trends in the dereplication of natural product extracts. 3: further lasiodiplodins from Lasiodiplodia theobromae, an endophyte from Mapania kurzii

Two further lasiodiplodins, (3R,4R)-4-hydroxy-de-O-methyl-lasiodiplodin and (E)-9-etheno-de-O-methyl-lasiodiplodin, together with three known lasiodiplodins from a cytotoxic extract obtained from a culture of Lasiodiplodia theobromae, an endophyte from the root tissues of Mapania kurzii (Cyperaceae) from the Malaysian rain forest, were characterized on microgram scale.     

Hydro-amination/-amidation of 1,3-diynes with indoles/azoles/amides under modified Ullmann conditions: stereo- and regio-selective synthesis of N-alkenynes via N-H bond activation

An efficient strategy for the stereo- and regio-selective synthesis of N-alkenynes has been described. The salient feature of the reaction involves hydro-amination/amidation of 1,3-diynes with indoles/azoles/amides via transition-metal catalyzed activation of N-H bond. The resulting N-alkenynes derived from N-heterocycles and cyclic amides were obtained as a mixture of Z/E isomers with Z-stereoselectivity ranging from 60% to 95%. In contrast, acyclic amides afforded N-alkenynes with exclusive E-stereoselectivity, albeit in reduced yield ranging from ∼10% to 41%.     

Bioactive Molecules for Discriminating Robinia and Helianthus Honey: High-Performance Liquid Chromatography–Electron Spray Ionization–Mass Spectrometry Polyphenolic Profile and Physicochemical Determinations

Bioactive molecules from the class of polyphenols are secondary metabolites from plants. They are present in honey from nectar and pollen of flowers from where honeybees collect the “raw material” to produce honey. Robinia pseudoacacia and Helianthus annuus are important sources of nectar for production of two monofloral honeys with specific characteristics and important biological activity. A high-performance liquid chromatography–electro spray ionization–mass spectrometry (HPLC–ESI–MS) separation method was used to determine polyphenolic profile from the two types of Romanian unifloral honeys. Robinia and Helianthus honey showed a common flavonoid profile, where pinobanksin (1.61 and 1.94 mg/kg), pinocembrin (0.97 and 1.78 mg/kg) and chrysin (0.96 and 1.08 mg/kg) were identified in both honey types; a characteristic flavonoid profile in which acacetin (1.20 mg/kg), specific only for Robinia honey, was shown; and quercetin (1.85 mg/kg), luteolin (21.03 mg/kg), kaempferol (0.96 mg/kg) and galangin (1.89 mg/kg), specific for Helianthus honey, were shown. In addition, different phenolic acids were found in Robinia and Helianthus honey, while abscisic acid was found only in Robinia honey. Abscisic acid was correlated with geographical location; the samples collected from the south part of Romania had higher amounts, due to climatic conditions. Acacetin was proposed as a biochemical marker for Romanian Robinia honey and quercetin for Helianthus honey.     

Production of Polyhydroxyalkanoates (PHAs) by Vibrio alginolyticus Strains Isolated from Salt Fields

Vibrio alginolyticus is a halophilic organism usually found in marine environments. It has attracted attention as an opportunistic pathogen of aquatic animals and humans, but there are very few reports on polyhydroxyalkanoate (PHA) production using V. alginolyticus as the host. In this study, two V. alginolyticus strains, LHF01 and LHF02, isolated from water samples collected from salt fields were found to produce poly(3-hydroxybutyrate) (PHB) from a variety of sugars and organic acids. Glycerol was the best carbon source and yielded the highest PHB titer in both strains. Further optimization of the NaCl concentration and culture temperature improved the PHB titer from 1.87 to 5.08 g/L in V. alginolyticus LHF01. In addition, the use of propionate as a secondary carbon source resulted in the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). V. alginolyticus LHF01 may be a promising host for PHA production using cheap waste glycerol from biodiesel refining.     

The combi-CLEA approach: enzymatic cascade synthesis of enantiomerically pure (S)-mandelic acid

Enantiomerically pure (S)-mandelic acid was synthesised from benzaldehyde by sequential hydrocyanation and hydrolysis in a bienzymatic cascade at starting concentrations up to 0.25 M. A cross-linked enzyme aggregate (CLEA) composed of the (S)-selective oxynitrilase from Manihot esculenta and the non-selective nitrilase from Pseudomonas fluorescens EBC 191 was employed as the biocatalyst. The nitrilase produces approx. equal amounts of (S)-mandelic acid and (S)-mandelic amide from (S)-mandelonitrile under standard conditions, but we surprisingly found that high (up to 0.5 M) concentrations of HCN induced a marked drift towards amide production. By including the amidase from Rhodococcus erythopolis in the CLEA we obtained (S)-mandelic acid as the sole product in 90% yield and >99% enantiomeric purity.     

Biocatalytic reduction system for the production of chiral methyl (R)/(S)-4-bromo-3-hydroxybutyrate

An effective method for producing methyl 4-bromo-3-hydroxybutyrate enantiomers was developed using an engineered protein. Escherichia coli transformant cells containing a mutant β-keto ester reductase (KER-L54Q) from Penicillium citrinum and a cofactor-regeneration enzyme such as glucose dehydrogenase (GDH) or Leifsonia sp. alcohol dehydrogenase (LSADH) were used to produce methyl (S)-4-bromo-3-hydroxybutyrate from methyl 4-bromo-3-oxobutyrate. On the other hand, the production of methyl (R)-4-bromo-3-hydroxybutyrate was achieved by asymmetric reduction of methyl 4-bromo-3-oxobutyrate with a mutant phenylacetaldehyde reductase (PAR-HAR1) from Rhodococcus sp. ST-10.     

Asymmetric copper-catalyzed Diels–Alder reaction revisited: control of the structure of bis(oxazoline) ligands

Synthesis of 1,4-bis(oxazoline) ligands bearing a bicyclo[2,2,2]backbone derived from 9,10-dihydro-9,10-ethanoanthacene trans-dicarboxylic acid was revisited. Starting from l- or d-amino alcohols and either (S,S) or (R,R)-dihydroethano trans-dicarboxylic acid, a complete series of ligands was evaluated in the copper-catalyzed Diels–Alder reaction. The most efficient ligands with a phenyl substituent on the oxazoline ring afforded enantiomeric excess up to 98%. This is different from previous results indicating that the best enantioselectivity involved a diastereomeric ligand with the meso-backbone.     

Palladium-catalyzed α,β-dehydrogenation of acyclic ester equivalents promoted by a novel electron deficient phosphinooxazoline ligand

A unique example of Pd-catalyzed decarboxylative dehydrogenation of fully substituted N-acyl allyl enol carbonates is enabled by a new electron deficient phosphinooxazoline (PHOX) ligand. The reaction proceeds from the Z-enol carbonate to provide dehydrogenation products exclusively in high E/Z selectivity, while the E-enol carbonate provides the α-allylation product with only minor dehydrogenation. The reaction proceeds with a broad scope of Z-enol carbonates derived from N-acyl indoles to furnish acyclic formal α,β-unsaturated ester equivalents.     

The pressure–volume–temperature relationship of cellulose

Pressure–volume–temperature (PVT) measurements of α-cellulose with different water contents, were performed at temperatures from 25 to 180 °C and pressures from 19.6 to 196 MPa. PVT measurements allowed observation of the combined effects of pressure and temperature on the specific volume during cellulose thermo-compression. All isobars showed a decrease in cellulose specific volume with temperature. This densification is associated with a transition process of the cellulose, occurring at a temperature defined by the inflection point T _t of the isobar curve. T _t decreases from 110 to 40 °C with pressure and is lower as moisture content increases. For isobars obtained at high pressures and high moisture contents, after attaining a minimum, an increase in volume is observed with temperature that may be related to free water evaporation. PVT α-cellulose experimental data was compared with predicted values from a regression analysis of the Tait equations of state, usually applied to synthetic polymers. Good correlations were observed at low temperatures and low pressures. The densification observed from the PVT experimental data, at a temperature that decreases with pressure, could result from a sintering phenomenon, but more research is needed to actually understand the cohesion mechanism under these conditions.