Regioselective protection of xylose for efficient synthesis of arabino-α-1,3-xylosides

We reported here an efficient regioselective protection strategy for xylose with two-step successive protections on 4- and 2-OH. This method enables the expeditious preparation of various xylose building blocks (3a–c, 5, 6). The rapid selective 2,4-protection especially facilitates the synthesis of 3-substituted xyloside structures. By this approach, typical arabino-α-1,3-xyloside disaccharide and trisaccharide, as fragment structure units from arabinoxylans, have been successfully synthesized.     

A novel application of terminal alkynes as the homogeneous catalysts for acetalization and esterification

The theoretical study focused on the possible use of low-molecular-weight mono-as well as multifunctional terminal alkynes as catalysts for two reactions, which are known to be typically acid catalyzed - acetalization and esterification, is presented in this study. Multifunctional terminal alkynes [(diethynylbenzenes, triethynylbenzene, and tetrakis(4-ethynylphenyl)methane] were significantly more active than the monofunctional ones (cyclopropylacetylene, phenylacetylene, 3-cyclohexylprop-1-yne, 1-ethynyl-2-fluorobenzene, 1-ethynyl-4-fluorobenzene, 4-ethynyltoluene, 4-tert-butylphenylacetylene, and 2-ethynyl-α,α,α-trifluorotoluene), this fact can be partly explained by the higher amount of ethynyl groups per alkyne molecule. We confirmed that terminal ethynyl groups in low-molecular-weight alkynes can successfully act as acid catalytic centers for acetalization as well as for esterification.     

Selective Formation of Methyl α-Methylsulfanyl Dimethylphosphonothioacetate and Thiopropanoate by Phase Transfer Catalysis

The sulfanylation of methyl dimethylphosphonothioacetate was investigated by a phase transfer catalysis procedure which was shown to be superior to the noncatalytic method. The possibility of electrophilic substitution of the α-sulfanylated phosphonothioacetate to give a quaternary α-carbon atom is shown by the reaction with methyl iodide.

     

A FACILE APPROACH FOR THE SYNTHESIS OF α -HALOGENATED ALKYLIDENEDIPHOSPHONATES BY REACTION OF ALKYLLITHIUM WITH CHLOROPHOSPHATE AND HALOGEN REAGENT

Alkyllithium reacts with chlorophosphate to generate the α -lithio- alkylidenediphosphonate, which further reacts with halogen reagents to afford corresponding α -halogenated alkylidenediphosphonates.     

Lithium Perchlorate Diethyl Ether Solution: A Highly Efficient Media for the Abramov Reaction

The f -hydroxy phosphonates are readily prepared by treating aromatic or aliphatic aldehydes and ketones with trialkylphosphite in the presence of trimethylsilylchloride in a very short time and in almost quantitative yields.     

Statistical Characterization of Succinoylated Dextrin Degradation Behavior in Human α-Amylase

Dextrin is a biomedically well-established, water-soluble polymer that has recently attracted considerable interest for conjugation to bioactive payloads. Succinoylation functionalizes dextrin and alters the rate at which it is degraded by human amylase, providing the bases for a convenient, controlled drug release technology. To date, the choice of a succinoylated dextrin intermediate requires laborious physicochemical characterization of entire libraries of succinoylated dextrin intermediates. We report the governance of dextrin degradation as a function of initial polymer molecular weight and degree of succinoylation through statistical analysis of a library of succinoylated dextrins relevant to acute disease (parent-dextrin molecular weight: 8,100 to 28,900 g/mol; 0 to 14.5 mol% succinoylation) at a typical physiologic concentration of human amylase (100 IU/L). Within these parameters, the rate of degradation of all succinoylated dextrins was best predicted by logarithmic regression. The contribution of degree of succinoylation to the variance in the degradation rate increased progressively and substantially with decreasing initial polymer weight (4.19% to 21.33%). These results facilitate the choice of succinoylated dextrin intermediates in the construction of controlled-release constructs, increase relevance to clinical scenarios requiring specific controlled-release rates, and contribute to the adoption of succinoylated dextrin as a versatile polymer for conjugation in controlled-release therapeutics.     

α-NH2 Determination from Biological Infrared Spectra

The use of Mid-infrared spectroscopy for the analysis of food products has only recently developped with the advent of Fourier Transformed spectroscopy and other techniques like Attenuated Total Reflectance, diffused reflection combined to the use of powerful micro-computers. We have recently reported to use a combination of multidimensional statistical analysis and Mid-FTIR spectroscopy for the quantitative determination of sugars in a biological sample. In this paper we have evaluated the use of such a method for the quantitative measurement of α-amino groups from ammo-acids, peptides and proteins. The spectral region where the characteristic absorption bands of such groups are located, ranges between 1200 cm-1 and 1900 cm-1. Water features a major absorption band in this region (1500–1700 cm-1). This superimpose with amide I and II bands.

The standard deviation for each and every wavelength, calculated for all the spectra of the calibration set, show the existence of two absorption bands in the 1500–1900 cm-1 region which means that the observed variations in this zone are not only due to water but are also due to two peaks centered at 1650 cm-1 and 1540 cm-1 (with a hollow at 1600 cm-1) that are characteristic of protids.

The contribution of the first four axes of the PCA, axes 5, 1, 4 and 2, to the total inertia percentage are 2. 37%, 53. 36%, 3. 92% and 28. 82% respectively. The correlation coefficient between the major axis, axis 5, and the chemical values of α-NH₂ is 0. 311 and the second axis, axis 1, increases this value to 0. 541. The first 10 axes were used to establish the prediction equation; the correlation coefficient value is very high: 0. 978.

Good predictions were obtained; mean and standard deviation associated to the predicted concentrations of α-NH₂content, valued 0 g/ml and 0. 12 g/ml respectively. Hence, we have established the possibility of determining, from a MIR spectra, the α-NH₂ content.     

The Electronic Nature of the P=C Bond

Abstract

The influence of substituents at the carbon of the P=C bond of about 60 phosphaalkenes was investigated by ³¹P NMR spectroscopy. The P=C system is characterized as electronwithdrawing. All compounds were found to be configurationally stable.     

A facile one-pot highly chemo- and regioselective synthesis of the novel heterocyclic system indolo[1,2-c]azolo[1,5-a]quinazoline-8,10-dione

A series of novel indolo[1,2-c]azolo[1,5-a]quinazoline-8,10-diones was obtained by a multi-component reaction between cyclic 1,3-diketones, α-aminoazoles, and glyoxal. The unexpected cyclization process was established by NMR spectroscopy and X-ray diffraction measurements.     

Use of Derivative Spectrophotometry for the In Vitro Determination of Allopurinol and Uric Acid Mixtures

Abstract

Allopurinol and uric acid are successfully assayed either in laboratory made mixtures or in urine using derivative spectrophotometry. The former is determined through first - derivative signal (¹ D) measurement at 284 nm, and the latter through second - derivative signal (²D) measurement at 293 nm. The colinearity of these values versus concentration of both compounds in the range 0.2–1.2 mg% permits their determination with high accuracy and good reproducibility. The method is recommended to monitor the allopurinol therapy in treatment of chronic gouty patients.