Efficient heterogeneous synthesis of nucleophilic carboxymethyl hydrazides of polysaccharides.

Nucleophilic moieties in polysaccharides (PS) with distinct higher reactivity compared with the hydroxy group are interesting for sustainable applications in chemistry, medicine, and pharmacy. An efficient heterogeneous method for the formation of such nucleophilic PS is described. Employing alcohols as slurry medium, protonated carboxymethyl (CM) PS and hydrazine hydrate are allowed to react at elevated temperatures. The CM derivatives of starch and pullulan can be transformed almost quantitatively to the corresponding hydrazides. The reaction is less efficient for CM dextrans and CM xylans. As slurry media, 2-propanol and ethanol were probed, and the results are compared with a homogeneous procedure performed in water. Overall, the heterogeneous procedure is superior compared with the homogeneous route. 2-Propanol is the best slurry medium investigated yielding PS hydrazides with the highest nitrogen content.

Synthesis and characterization of nucleophilic polysaccharide carbazates.

A simple synthesis of amino polysaccharides (PS) could be developed. Phenyl carbonates (PC) of xylan, dextran, and cellulose were easily transferred into PS carbazates by conversion with hydrazine hydrate. The degree of substitution could be adjusted by varying the molar ratio of hydrazine to PS repeating unit, enabling the preparation of both pure PS carbazates and derivatives with bifunctional reactivity containing the reactive PC and the amino group of the carbazate moiety. Further functionalization of the derivatives is feasible with carbonyl compounds like aldehydes at the carbazate groups. The reactivity of carbazate groups is shown by the reaction with 4-fluorobenzaldehyde, resulting in the formation of Schiff base conjugates.

Efficient heterogeneous synthesis of reactive polygalacturonic acid hydrazides.

Low-methoxy ammonium pectinate (APC) and polygalacturonic acid (PG) could be transformed heterogeneously in a catalyst-free system very efficiently to the corresponding polysaccharide (PS) hydrazides. The hydrazide formation proceeds even at room temperature efficiently and is almost independent of the reaction temperature in the range from 25 of up to 80°C. In contrast to a homogeneous reaction, the heterogeneous path is efficient considering the amount of hydrazine hydrate employed. The PS hydrazides obtained show no signs of degradation or side reactions that might occur due to the basicity of the hydrazine reagent used. The polygalacturonic acid hydrazide (PGH) obtained is nontoxic as revealed by a chicken egg test. Furthermore, preliminary studies indicate that the PS hydrazides synthesized possess good metal chelating abilities, especially high amount of lead (II) can be bound from an aqueous solution.

Non-aqueous solvent for efficient dissolution of polygalacturonic acid.

The ionic liquid 1-n-butyl-3-methylimidazolium chloride (BMIMCl) was found to be a non-aqueous solvent for the fast and efficient dissolution of polygalacturonic acid. Up to 5.3 wt% biopolymer could be dissolved by heating the mixture of biopolymer/BMIMCl to 140 °C. About 50% of the polygalacturonic acid groups form the corresponding imidazolium salt at elevated temperature with the solvent, this leads to the solubility of the biopolymer in the surplus of BMIMCl. The salt formation was investigated with nuclear magnetic resonance (NMR)- and Fourier transform infrared (FTIR) spectroscopy as well as by X-ray diffraction (XRD) and is considered to be the driving force for the dissolution of the biopolymer.

A small azide-modified thiazole-based reporter molecule for fluorescence and mass spectrometric detection.

Molecular probes are widely used tools in chemical biology that allow tracing of bioactive metabolites and selective labeling of proteins and other biomacromolecules. A common structural motif for such probes consists of a reporter that can be attached by copper(I)-catalyzed 1,2,3-triazole formation between terminal alkynes and azides to a reactive headgroup. Here we introduce the synthesis and application of the new thiazole-based, azide-tagged reporter 4-(3-azidopropoxy)-5-(4-bromophenyl)-2-(pyridin-2-yl)thiazole for fluorescence, UV and mass spectrometry (MS) detection. This small fluorescent reporter bears a bromine functionalization facilitating the automated data mining of electrospray ionization MS runs by monitoring for its characteristic isotope signature. We demonstrate the universal utility of the reporter for the detection of an alkyne-modified small molecule by LC-MS and for the visualization of a model protein by in-gel fluorescence. The novel probe advantageously compares with commercially available azide-modified fluorophores and a brominated one. The ease of synthesis, small size, stability, and the universal detection possibilities make it an ideal reporter for activity-based protein profiling and functional metabolic profiling.

2-Isopropyl-2-(6-meth-oxy-1,3-benzo-thia-zol-2-yl)-5,5-dimethyl-1,3-thia-zolidin-4-one.

The title compound, C16H20N2O2S2, crystallizes with two enanti-omers (A and B) in the asymmetric unit. The most noticeable difference between these two mol-ecules is the relative orientation of the benzo-thia-zole rings, with S-C-C-S torsion angles of -19.4 (2) (mol-ecule A) and 100.6 (1)° (mol-ecule B). The amide structure of the thia-zolidinone rings leads to inter-molecular hydrogen-bonded dimers of the R and S enanti-omers.

2-(6-Bromo-benzo[d]thia-zol-2-yl)-5,5-di-methyl-thia-zol-4(5H)-one.

The title compound, C12H9BrN2OS2, was obtained by reacting 6-bromo-benzo[d]thia-zole-2-carbo-nitrile in iso-propanol with ethyl 2-mercapto-2-methyl-propano-ate at reflux temperature for several hours. The resulting di-methyl-oxyluciferin derivative shows partial double-bond character of the carbon-carbon bond between the two heterocyclic moieties [C-C = 1.461 (3) Å]. This double bond restricts rotation around this C-C axis, therefore leading to an almost planar mol-ecular structure [N-C-C-S torsion angle = 9.7 (3)°]. The five-membered thiazoline ring is not completely planar as a result of the bulky S atom [C-S-C-C torsion angle = 5.17 (12)°].