Regioselective enzymatic acylation of methyl shikimate. Influence of acyl chain length and solvent polarity on enzyme specificity

Candida antarctica lipase A (CAL-A) selectively catalyzes the acylation at the secondary C-4 hydroxyl group of methyl shikimate (2), which possesses three secondary hydroxyl groups, the C-3 allylic one being chemically more reactive. The effect both of the acyl group of the acylating agents and of the solvent polarity has been studied. The selectivity of CAL-A is almost complete with acyl donors that possess short chains. However, when acyl donors have longer chains, better results are obtained by C. antarctica lipase B (CAL-B).     

First synthesis of beta-keto sulfoxides by a palladium-catalyzed carbonylative Suzuki reaction

[reaction: see text] An unprecedented palladium-catalyzed three-component cross-coupling reaction between alpha-bromo sulfoxide, carbon monoxide, and aromatic boronic acids provides a new and efficient approach to the synthesis of beta-ketosulfoxides. The reaction takes place under mild conditions with a wide range of variously substituted aryl and heteroaryl boronic acids. The carbonylative cross-coupling reaction is strongly favored over competing direct cross-coupling and homocoupling processes, except with boronic acids carrying strong electron-withdrawing substituents.     

Novel fused D-A dyad and A-D-A triad incorporating tetrathiafulvalene and p-benzoquinone

Novel fused donor-acceptor dyad (TTF-Q or D-A) and acceptor-donor-acceptor triad (Q-TTF-Q or A-D-A) incorporating the donor tetrathiafulvalene (TTF) and the acceptor p-benzoquinone (Q) have been synthesized. The solution UV-vis spectra of these molecules display a low-energy absorption band that is attributed to an intramolecular charge transfer between both antagonistic units. The presence of reversible oxidation and reduction waves for the donor and acceptor moieties was shown by cyclic voltammetry, in agreement with the ratio TTF/quinone(s) units. The successive generation from these compounds of the cation radical and anion radical obtained upon (electro)chemical oxidation and reduction, respectively, was monitored by optical and ESR spectroscopies. The anion radical Q-TTF-Q(-.) triad was demonstrated to be a class II mixed-valence system with the existence of a temperature-dependent intramolecular electron transfer. The crystallographic tendency of these fused systems to overlap in mixed stacks of alternating A-D-A units is also discussed.     

Methylmercury and dimethylthallium complexes of 5-(4′-dimethylaminobenzylidene)-2-thiohydantoin (HDABTd): The crystal and molecular structures of HDABTd and [TlMe2(DABTd)(DMSO)]

The ligand 5-(4′-dimethylaminobenzylidene)-2-thiohydantoin (HDABTd) was prepared and its structure determined by X-ray diffraction. In the crystal, ligand molecules are linked in chains along the [110] direction by intermolecular N(3)–H(3)O(1)^I and N(1)–H(1)Sⁱⁱ hydrogen bonds. The complexes [HgMe(DABTd)] and [TlMe₂(DABTd)] were prepared by reaction of the ligand with methylmercury acetate or dimethylthallium hydroxide, and were characterized in the solid state by IR spectroscopy and in solution by conductivity measurements and ¹H, ¹³C, ¹⁹⁹Hg and ²⁰⁵Tl NMR spectroscopy. The dimethylthallium complex crystallized in DMSO solution as [TlMe₂(DABTd)(DMSO)], an X-ray diffraction study of which showed its thallium atoms to be coordinated to the two methyl C atoms, the oxygen atom of a DMSO molecule, the S and N(1) atoms of one DABTd ligand and, more weakly, to the oxygen atom of a neighbouring DABTd. This last interaction links the molecules of the complex in chains parallel to the b axis. Crystals of the methylmercury(II) complex contain three [HgMe(DABTd)]·DMSO structures per asymmetric unit, but poor data quality prevented complete refinement.     

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).     

Facile solid-phase synthesis of biotinylated alkyl thiols

Biotinylated alkyl thiols with the capacity to graft avidin proteins are in increasing demand for the development of self-assembled monolayers on gold. Here we propose 2-Chlorotrityl Chloride solid-phase resin as a new platform to produce these functionalized alkyl thiols. Biotinylated alkyl thiols of non-obvious solution synthesis were obtained rapidly using this method and without previous purification steps.     

Electrochemical synthesis and crystal structure of cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes with 2-pyridinecarbaldehyde-(2′-aminosulfonylbenzoyl)hydrazone

A new hydrazonic Schiff base ligand, 2-pyridinecarbaldehyde-(2′-aminosulfonylbenzoyl)hydrazone (HL), has been prepared and characterized, and its coordinative properties were studied. [ML₂] complexes, M = Co, Ni, Cu, Zn or Cd have been synthesised by electrochemical oxidation of the anodic metal in a cell containing an acetonitrile solution of the ligand. The compounds obtained have been characterized by microanalysis, IR, NMR and UV–Vis spectroscopy, mass spectrometry and also by X-ray diffraction. The structural studies show that the metal is in a distorted octahedral environment with the monoanionic ligand acting as a meridional tridentate (N,N,O) chelate system.     

Relating high-energy Lepton-Hadron, proton-nucleus, and nucleus-nucleus collisions through geometric scaling

A characteristic feature of small-x lepton-proton data from HERA is geometric scaling: the fact that in the region of small Bjorken variable x, x less, similar 0.01, all data can be described by a single variable Q(2)/Q(2)(s,p)(x), with all x dependence encoded in the so-called saturation momentum Q(s,p)(x). Here, we observe that the same scaling ansatz accounts for nuclear photoabsorption cross sections and favors the nuclear dependence Q(2)(s,A) proportional, variant A(alpha)Q(2)(s,p), alpha approximately 4/9. We then make the empirical finding that the same A dependence accounts for the centrality evolution of the multiplicities measured in Au+Au collisions at RHIC. It also allows one to parametrize the high-p(t) particle suppression in d+Au collisions at forward rapidities. If these geometric scaling properties have a common dynamical origin, then this A dependence of Q(2)(s,A) should emerge as a consequence of the underlying dynamical model.