Polar Metabolites of the Tropical Green Seaweed Caulerpa taxifolia Which Is Spreading in the Mediterranean Sea: Glycoglycerolipids and Stable Enols (α\=Keto Esters)

Examination of the polar components of the green seaweed Caulerpa taxifolia (Vahl ) C. Agardh , which is heavily spreading in the northeastern Mediterranean, led to two families of compounds. The new (2R)-3-O-β-D -galactopyranosyl-1-O-[(7Z,10Z,13Z)-hexadeca-7,10,13-trienoyl]-2-O-[(9Z,12Z,15Z)-octadeca-1,12,15-trienoyl]-sn-glycerol ( 2 ) was isolated in low abundance, like the analogues 1 and 3 already known from freshwater cyanobacteria. The acyl positions in 1 – 3 were determined by enzymatic methods and the absolute configuration from the O-galactosylglycerol obtained upon alcaline methanolysis. More abundant were the (4-hydroxyphenyl)- and (3,4-dihydroxyphenyl)pyruvic acid methyl esters, occurring in the enol (Z) forms 13a and 14a accompanied by very minor (E) forms 13b and 14b . The latter became predominant on UV irradiation of 13a or 14a , allowing the determination of the C=C configuration of these isolatable, stable enols from ¹H,¹³C NMR couplings (larger H−C(3)/C(1) coupling constant in the (E) than in the (Z) isomer). Contrary to literature implications, the O-galactosylglycerolipids 1 – 3 lack any cholinergic or histaminergic activity; similarly, enols (= α-keto esters) 13 and 14 or terpenoids of this seaweed were also devoid of such biological activities (see Table).     

Preparation,spectral, thermal,and biological properties of zinc(II) 4-chloro- and 5-chlorosalicylate complexes with methyl 3-pyridylcarbamate and phenazone

New zinc(II) 4-chloro- and 5-chlorosalicylate complex compounds of the general formula ((4- or 5-Cl)C₆H₃(2-OH)COO)₂Zn · L _n (where L = methyl 3-pyridylcarbamate, phenazone; n = 2, 4) were prepared and characterized by elemental analysis, thermal analysis (TG/DTG, DTA), and IR spectroscopy. During thermal decomposition, mpc, phen, chlorosalicylic acid, chlorophenol, carbon dioxide, and carbon monoxide were released. Volatile products of the thermal decomposition were confirmed by mass spectrometry. The final solid product of the thermal decomposition up to 700°C was zinc oxide or metallic zinc. Antimicrobial activity of the compounds prepared was tested against various strains of bacteria, yeasts and filamentous fungi. The highest antimicrobial effect was determined against the G⁺ bacteria S. aureus.     

Probing the internal environment of PVP networks generated by irradiation with different sources

Poly(N-vinyl-2-pyrrolidone) (PVP) hydrogels have been synthesised from the aqueous solutions of the same linear polymer by two different radiation sources: electron beams and UV rays. The present investigation couples conventional hydrogel characterisation techniques with the study of the partition equilibria, fluorescence behaviour and release of two different molecular probes, 1-anilino-8-naphthalene sulphonate (ANS) and Thioflavin T (ThT). The two probes have comparable molecular weight and different structural and optical properties. The ‘chemical’ networks produced upon irradiation in different experimental conditions presented quite distinctive mechanical spectra, yielded to different porous solids upon freeze-drying and showed specific rehydration ratios when ‘equilibrated’ in water. More interestingly, they offered ‘hydrophobic pockets’ to host the ANS molecules in a way that the probe is completely occluded from water, making it fluoresce. Conversely, the generated PVP networks did not show any specific affinity towards the hydrophilic ThT that was only barely untaken.     

N,N-Dialkylcarbamato Complexes of the d10 cations of copper,silver, and gold

The reaction of CuO'Bu with CO₂, and ⁱPr₂NH in the presence of PPh₃, gives the dialkylcarbamato complex [Cu(O₂CNⁱPr₂)(PPh₃)₂] ( 1 ). The CO₂/R₂NH system (R = Me, Et) in an appropriate organic medium reacts with Ag₂O giving the corresponding N,N-dialkylcarbamato complexes of analytical formula [Ag(C₂CNR₂)] (R = Me, 2 ; R = Et, 3 ). The methyl derivative 2 was characterized by X-ray diffraction methods. Crystal data of 2 : for [Ag₂(O₂CNMe₂)₂], C₆H₁₂Ag₂N₂O₄, mol. wt. 391.9; monoclinic, space group P2₁/c, a = 12.08(1), b = 3.797(2), c = 11.316(7) Å, β = 113.37(6)°, V = 476.3 ų, Z = 2, D_c = 2.732 g cm^?3; μ(MoK_α) = 40.64 cm^?1, F(000) = 376.0; R = 0.059, R_w = 0.067; g.o.f. 1.27. The structure consists of dinuclear [(Ag₂OCNMe₂)₂] units with slightly distorted linearly two-coordinated Ag-atoms containing bridging carbamato groups to form a substantially planar eight-membered ring with an intra-annular Ag? Ag distance of 2.837(2) Å; the dinuclear units are further joined by Ag? O bonds to form an infinite array. Compound 3 , which is presumably dinuclear, as suggested by cryoscopic measurements in benzene, undergoes a structural fission with PPh₃, giving the mononuclear triphenylphosphine derivative [Ag(O₂CNEt₂)(PPh₃)₂] ( 4 ). The amine-catalyzed conversion of Ag₂O into Ag₂CO₃, in the presence of the ⁱPr₂NH/CO₂ system, is also reported. Cl-Exchange from [AuCl(PPh₃)] with [Ag(O₂CNEt₂)] ( 3 ) gives the first N,N-dialkylcarbamato complex of gold, namely [Au(O₂CNEt₂)(PPh₃)] ( 5 ), which crystallizes in the monoclinic system: C₂₃H₂₅AuNO₂P · 0.5 C₇H₁₆, mol. wt. 625.5, space group P2₁/c; a = 13.212(5), b = 12.25(1), c = 16.795(6) Å, β = 109.09(2)°, V = 2568(2) Å₃, Z = 4, D_c, = 1.618 g cm^?3; μ(AgK_α) = 31.40 cm^?1, F(000) = 1236.0; R = 0.058; R_w = 0.064; g.o.f. 2.121. The compound contains two-coordinated Au-atom, namely to the P-atom and to the O-atom of the monodentate carbamato group, the P? Au? O bond angle being 174.7(3)°. The reaction with MeI showed these compounds to react predominantly at the carbamato O-atom giving the corresponding urethanes R₂NCO₂Me. Evidence was gathered for the transient coordination of CO to Ag in 3 .     

Highly efficient bromination of aromatic compounds using 3-methylimidazolium tribromide as reagent/solvent

3-Methylimidazolium tribromide proves to be an alternative highly efficient reagent/solvent for the halogenation of non-activated aromatic compounds.     

N-H insertion reactions of primary ureas: the synthesis of highly substituted imidazolones and imidazoles from diazocarbonyls

Primary ureas have been used as substrates in rhodium-catalyzed N-H insertion reactions with an array of diazocarbonyls. The insertion reaction is efficient and gives excellent selectivity and yields. The products from the insertion reaction with diazoketones cyclize readily in the presence of acid to yield the corresponding imidazolones that can be further derivatized by N-alkylation with alkyl, allyl, and benzyl halides. Alternatively, the imidazolones were treated with phosphorus oxybromide to form the corresponding 2-bromoimidazoles that were further functionalized using a Suzuki coupling reaction.     

Oxime-based methods for synthesis of stereodefined acyclic polyfunctionalized δ-azido-nitriles and 5-substituted isoxazoles from carbohydrate derivatives

Hydroxylamine-mediated syntheses of stereodefined acyclic polyfunctionalized δ-azido-nitriles and 5-substituted isoxazoles, bearing a differentially protected glycerol moiety, from 2-deoxysugars and glycals are described.     

Nitrosyl induces phosphorous-acid dissociation in ruthenium(II)

The trans-[Ru(NO)(NH(3))(4)(P(OH)(3))]Cl(3) complex was synthesized by reacting [Ru(H(2)O)(NH(3))(5)](2+) with H(3)PO(3) and characterized by spectroscopic ((31)P-NMR, δ = 68 ppm) and spectrophotometric techniques (λ = 525 nm, ε = 20 L mol(-1) cm(-1); λ = 319 nm, ε = 773 L mol(-1) cm(-1); λ = 241 nm, ε = 1385 L mol(-1) cm(-1); ν(NO(+)) = 1879 cm(-1)). A pK(a) of 0.74 was determined from infrared measurements as a function of pH for the reaction: trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) + H(2)O ? trans-[Ru(NO)(NH(3))(4)(P(O(-))(OH)(2))](2+) + H(3)O(+). According to (31)P-NMR, IR, UV-vis, cyclic voltammetry and ab initio calculation data, upon deprotonation, trans-[Ru(NO)(NH(3))(4)(P(OH)(3))](3+) yields the O-bonded linkage isomer trans- [Ru(NO)(NH(3))(4)(OP(OH)(2))](2+), then the trans-[Ru(NO)(NH(3))(4)(OP(H)(OH)(2))](3+) decays to give the final products H(3)PO(3) and trans-[Ru(NO)(NH(3))(4)(H(2)O)](3+). The dissociation of phosphorous acid from the [Ru(NO)(NH(3))(4)](3+) moiety is pH dependent (k(obs) = 2.1 × 10(-4) s(-1) at pH 3.0, 25 °C).     

Design, synthesis and characterisation of guanosine-based amphiphiles

A small library of sugar-modified guanosine derivatives has been prepared, starting from a common intermediate, fully protected on the nucleobase. Insertion of myristoyl chains and of diverse hydrophilic groups, such as an oligoethylene glycol, an amino acid or a disaccharide chain, connected through in vivo reversible ester linkages, or of a charged functional group provided different examples of amphiphilic guanosine analogues, named G1-G7 herein. All of the sugar-modified derivatives were positive in the potassium picrate test, showing an ability to form G-tetrads. CD spectra demonstrated that, as dilute solutions in CHCl(3), distinctive G-quadruplex systems may be formed, with spatial organisations dependent upon the structural modifications. Two compounds, G1 and G2, proved to be good low-molecular-weight organogelators in polar organic solvents, such as methanol, ethanol and acetonitrile. Ion transportation experiments through phospholipid bilayers were carried out to evaluate their ability to mediate H(+) transportation, with G5 showing the highest activity within the investigated series. Moreover, G3 and G5 exhibited a significant cytotoxic profile against human MCF-7 cancer cells in in vitro bioassays.