(S)-(+)-N-acetylphenylglycineboronic acid: a chiral derivatizing agent for Ee determination of 1,2-diols

A new chiral derivatizing agent for ee determination of 1,2-diols via (1)H NMR is described. (S)-(+)-N-acetylphenylglycineboronic acid (1) is synthesized in enantiomerically pure form; its reaction with chiral diols quantitatively yields cyclic boronic esters 5a-g. The latter show a remarkably high diastereodifferentiation of proton NMR signals useful for de determination. [reaction: see text]     

Cinchona alkaloids in the asymmetric synthesis of 2-(phenylsulfanyl)aziridines

Enantioselective aza-Michael initiated ring closure (MIRC) additions of ethyl nosyloxycarbamate to 2-(phenylsulfanyl)-2-cycloalkenones catalysed by Cinchona alkaloids were studied. The results suggest that the enantioselectivity obtained is influenced by the structure of the catalyst and the different amination conditions. Substrate ring size also plays an important role.     

Electrode surface modification by a spirobifluorene derivative. An XPS and electrochemical investigation

Ordered thin layers of a spirobifluorene derivative containing an amino group were formed by grafting them onto a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) on gold. Either physical (H-bonding) or chemical bonding (activated by EDCl) was investigated. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy confirmed that both methods can be used to effectively graft 2-amino-9,9'-spirobifluorene molecules onto the SAM surface, giving high surface coverages, with a significantly higher packing in the case of chemisorbed films. EIS measurements also showed that the covalently bonded spirobifluorene SAMs act as an effective barrier to both ion penetration and heterogeneous electron transfer.     

Solution calorimetry to monitor swelling and dissolution of polymers and polymer blends

The observed rate of drug release from a polymeric drug delivery system is governed by a combination of diffusion, swelling and erosion. It is thus not a simple task to determine the effects of the polymer on the observed drug release rate, because the swelling characteristics of the polymer are inferred from the drug release profile. Here we propose to use solution calorimetry to monitor swelling. Powdered polymer samples (HPMC E4M, K4M, K15M and NaCMC, both alone and in a blend) were dispersed into water or buffer (pH 2.2 and 6.8 McIlvaine citrate buffers) in a calorimeter and the heat associated with the swelling phenomena (hydration, swelling, gelation and dissolution) was recorded. Plots of normalised cumulative heat (i.e. q_t/Q, where q_t is the heat released up to time t and Q the total amount of heat released) versus time were analysed by the power law model, in which a fitting parameter, n, imparts information on the mechanism of swelling.

For all systems the values of n were greater than 1, which indicated that dissolution occurred immediately following hydration of the polymer. However, while not suitable for determining reaction mechanism, the values of n for each polymer were significantly different and, moreover, were observed to vary both as a function of particle size and dissolution medium pH. Thus, the values of n may serve as comparative parameters. Properties of the polymer blends were observed to be different from those of either constituent and correlated with the behaviour seen for polymer tablets during dissolution experiments. The data imply that solution calorimetry could be used to construct quantitative structure–activity relationships (QSARs) and hence to optimise selection of polymer blends for specific applications.     

Capillary electrophoresis studies on the aggregation process of beta-amyloid 1-42 and 1-40 peptides

The possibility to monitor, in solution, the steps of beta-amyloid (Abeta) nucleation and therefore to describe this dynamic process by using capillary electrophoresis and under optimized experimental conditions is described. Striking differences in the electrophoretic patterns of Abeta 1-42 and Abeta 1-40 over time are here shown, and different aggregation states are elucidated, which reflect the very diverse oligomerization behavior of two very similar peptides. The isolation of one aggregated species of high molecular weight by ultracentrifugation allowed us to assess its role as toxic oligomer. The perturbation of the existing equilibrium among the identified species by the addition of small molecules can in principle interfere with the aggregation process of the peptides and ultimately prevent the plaque formation in vitro.     

Unusual Friedel-Crafts reactions,IX. One-step ortho-acylation of phenols with α,β-unsaturated acyl chlorides. Synthesis of 2'-hydroxychalcones and sorbicillin analogues

The reaction of bromomagnesium phenolates 1 in toluene with α, β-unsaturated acyl chlorides 2 at room temperature provides a straightforward highly selective synthesis of α,β-unsaturated 2-hydroxyarylketones 3. 2'-Hydroxychalcones, ortho-sorbylphenols including sorbicillin 3g, and ortho-propiolylphenols were usefully synthesized by this way. This reaction provides a further example of the synthetic versatility of the chelation-controlled approach in the elaboration of phenol derivatives.     

Design and photochemical characterization of a biomimetic light-driven Z/E switcher

Protonated Schiff bases (PSBs) of polyenals constitute a class of light-driven switchers selected by biological evolution that provide model compounds for the development of artificial light-driven molecular devices or motors. In the present paper, our primary target is to show, through combined computational and experimental studies, that it is possible to approach the design of artificial PSBs suitable for such applications. Below, we use the methods of computational photochemistry to design and characterize the prototype biomimetic molecular switchers 4-cyclopenten-2'-enylidene-3,4-dihydro-2H-pyrrolinium and its 5,5'-dimethyl derivative both containing the penta-2,4-dieniminium chromophore. To find support for the predicted behavior, we also report the photochemical reaction path of the synthetically accessible compound 4-benzylidene-3,4-dihydro-2H-pyrrolinium. We show that the preparation and photochemical characterization of this compound (together with three different N-methyl derivatives) provide both support for the predicted photoisomerization mechanism and information on its sensitivity to the molecular environment.     

PEG-supported pyridylthioesters for racemization-free amide synthesis: a reagent that allows simultaneous product formation and removal from the polymer

Pyridylthioesters anchored to a modified poly(ethylene glycol) of M_w 5000 Da have been prepared in high yields. The thioesters were employed as a convenient starting material for the liquid-phase synthesis of various enantiomerically pure amides. This new methodology allowed to perform simultaneously the reaction with the poly(ethylene glycol)-supported reagent and the traceless removal of the final product from the polymer support in a single step. The products were obtained in high yield and purity.     

Efficient, solventless N-Boc protection of amines carried out at room temperature using sulfamic acid as recyclable catalyst

A simple, rapid, and efficient protocol for the chemoselective N-Boc protection of amines using sulfamic acid as catalyst is described. N-Boc protection of various structurally diverse aliphatic, aromatic, alicyclic, and heterocyclic amines (1°, 2°, 3°) was carried out with (Boc)₂O using sulfamic acid as catalyst (5 mol %) at room temperature under solventless conditions. The advantages of this method are simplicity, shorter reaction times (1-15 min), a cost-effective catalyst, and excellent isolated yields (90-100%); it is also environmentally benign. Moreover, the combined use of ultrasound and sulfamic acid achieves a synergic effect that is especially marked in the N-Boc protection of deactivated (sterically hindered and electron-deficient) amines. The catalyst possesses distinct advantages: ease of handling, cleaner reactions, high activity, and excellent chemoselectivity.     

Evidence for two geminate rebinding states following laser photolysis of R state hemoglobin encapsulated in wet silica gels

In this letter we report the first experimental evidence for CO rebinding to human hemoglobin from multiple geminate states. The analysis of the rebinding kinetics using a maximum entropy method allowed the identification of two distinct rebinding states within the protein matrix, which become populated under conditions of increased viscosity in a silica gel at high glycerol concentration. Our findings suggest the presence of at least two distinct docking sites for the photolyzed ligand. Assuming a minimal four-state model, we estimate the microscopic rates and the activation energies for the elementary processes.