A reinvestigation of the synthesis of arsonolipids (2,3-diacyloxypropylarsonic acids)

A reinvestigation of the reactions leading to arsonolipids (2,3-diacyloxypropylarsonic acids) has been carried out in order to understand why the yields of their preparation were only moderate, although they are better than those reported for 2,3-diacyloxypropylphosphonic acid (phosphotidic acid). Thus, the reaction of glycidol and of 3-chloro-1,2-propanediol with alkaline sodium arsenite, "Na3AsO3", gives the desired product, 2,3-dihydroxypropylarsonic acid, and approximately 10% of an arsenic-containing glycerol dimer which is removed during the preparation of these arsonolipids. The step which is mainly responsible for the diminished yields is due to the reaction of the -As(SPh)2 or -AsO3H- precursor with the activated acid chlorides or carboxylic acid anhydrides to give an intermediate which cyclizes with the primary hydroxy group of the 2,3-dihydroxypropyl moiety. This cyclization does not allow the primary hydroxy group to be acylated. Such cyclization could not be avoided with RCOCl/py, (RCO)2O/DMAP, or RCOOH/DCC/DMAP acylating systems.     

New method for quantitative determination of uronic acids

A new method for determination of uronic acids with meta-hydroxydiphenyl is introduced. It is simpler, quicker, more sensitive, and more specific than other methods, and it needs lesser amounts of fluid. It is recommended for determination of acid mucopolysaccharides in biological materials.     

Deuterium labelling at C-5 in uronic acids

The study of electrokinetic phenomena has found wide application, particularly for biological systems¹; these systems consist, for the most part, of lipids, proteins, and carbohydrates^2,3. Electrophoresis of Pyrex and ion-exchanger particles dispersed in alcohol-water has been conducted by various workers^{4 ? 6}. Electro-osmotic studies of cholesterol-carbohydrate systems have been reported in an earlier communication⁷. In order to supplement such researches, the electrophoresis of cholesterol particles dispersed in aqueous solutions of carbohydrates has been studied, and the results are reported herein.     

Measurement of uronic acids without interference from neutral sugars

Replacement of carbazole with meta-hydroxydiphenyl greatly improves the determination of uronic acids in the presence of neutral sugars by preventing substantially, but not completely, the browning that occurs during the heating of sugars in concentrated sulfuric acid and avoiding the formation of additional interference by the carbazole reagent (Blumenkrantz, N., and Asboe-Hansen, G. (1973) Anal. Biochem. 54, 484-489). However, interference is still substantial when uronic acids are determined in the presence of excess neutral sugar, particularly because of the browning that occurs during the first heating before addition of the diphenyl reagent. The browning can be essentially eliminated by addition of sulfamate to the reaction mixture (Galambos, J. T. (1967) Anal. Biochem. 19, 119-132). Although others have reported that sulfamate and the diphenyl reagent were incompatible, we find that a small amount of sulfamate suppresses color production by a 20-fold excess of some neutral sugars without substantial sacrifice of the sensitive detection of uronic acids by the diphenyl reagent. Sodium tetraborate is required for the detection of D-mannuronic acid and enhances color production by D-glucuronic acid. We propose this modified sulfamate/m-hydroxydiphenyl assay as a rapid and reliable means for the assay of uronic acids, particularly when present in much smaller amounts than neutral sugars.     

A short synthesis of Dronedarone

A modification of the Nenitzescu reaction was used to obtain Dronedarone from quinonimine 20 and 1,3-diketone 14 (R?=?CH₂CH₂CH₂NBu₂) in a two-stage process in almost 55% overall yield. Our results represent significant improvement over other state-of-the-art methods as no extra steps for the decoration of the benzofuran core are required.     

Metabolism of uronic acids in plant tissues: partial purification and properties of uronic Acid oxidase from citrus leaves

A new enzyme, named uronic acid oxidase, was extracted and purified 67-fold by (NH(4))(2)SO(4) fractionation and CM-Sephadex column chromatography from ethylene-treated Shamouti orange (Citrus sinensis L. Osbeck) leaves. The enzyme catalyzes the oxidation of d-galacturonic acid and d-glucuronic acid to the corresponding hexaric acids in the presence of molecular oxygen with the production of H(2)O(2). The pH optimum for the oxidation of d-galacturonic acid and d-glucuronic acid is between 7 and 8. The enzyme is highly specific for d-galacturonic acid and d-glucuronic acid. It also oxidizes polygalacturonic acid. The apparent Michaelis constant values of the enzyme for d-galacturonic acid and d-glucuronic acid are 0.13 and 0.5 mm, respectively. The molecular weight of the enzyme, as determined by gel filtration, is about 98,000. The enzyme is inhibited by sodium hydrosulfite and other sulfites, indicating that it contains a flavin prosthetic group.     

Separation of meso and racemic 2,3-butanediol by aqueous liquid chromatography

Fermentation of xylose by Klebsiella pneumoniae (ATCC 8724) producers meso and nonmeso 2,3-butaneodiol. The enzyme Kinetic of 2,3-butanediol stereoisomer formation from acetone is currently under study in our laboratory. Modeling of these kinetics requires resolution of meso and racemic 2,3-butanediol and positive identification of these resolved components. We report their resolution by aqueous liquid chromatography on both an analytical and a preparative scale. The resolved stereoisomer were identified by a combination of gas chromatography, gas chromatography/mass spectroscopy, ¹³C-NMR spectroscopy, optical activity, and, melting points of the m-dinitrobenzoyl eaters of meso and racemic 2,3-butanediol. An aqueous liquid chromatographic technique for resolving and qualifying major components of a butanediol fermentation mixture in 40 min is presented.     

A short synthesis of antimalarial peroxides

A concise and efficient synthesis of two simplified diastereomeric analogues of a natural peroxide is presented. Both compounds could be isolated in high purity and fully identified. They exhibited moderate antimalarial activity.     

alpha-t-butyl- and alpha-i-propyl-ortho-hydroxybenzylamines: racemic synthesis/resolution and asymmetric synthesis

Efficient routes to alpha-tert-butyl- and alpha-iso-propyl-ortho-hydroxybenzylamines 1a and 1b are described. Highly enantioenriched 1a and 1b were obtained by resolution of the methoxy derivatives 2 by recrystallization of the salts formed with mandelic acid followed by Lewis acid mediated demethylation. The chiral 1,3-amino alcohol 1a has also been obtained in an asymmetric synthesis with the key step a diastereoselective alkylation of the imine obtained by condensation of o-anisaldehyde with phenyl glycinol. The absolute stereochemistry of these 1,3-aminophenols was determined by CD spectroscopy of the salicylideneamines 12 and by an X-ray structure analysis of the salt formed between (R)-mandelic acid and (S)-alpha-tert-butyl-ortho-methoxybenzylamine ((S)-2a).     

Microbial transformation of racemic hydantoins to D-amino acids

It has been shown that resting cells of Agrobacterium radiobacter catalyze a sequence of two stereospecific hydrolytic reactions leading to the complete transformation of racemic hydantoins to D -amino acids. This report describes some properties of this new biocatalyst and its potential application for the production of some D -amino acids, which are used as intermediates in the preparation of semisynthetic penicillin and cephalosporins.     

Synthesis of N-(fluoren-9-ylmethoxycarbonyl)glycopyranosylamine uronic acids

The synthesis of 10 N-(fluoren-9-ylmethoxycarbonyl)glycopyranosylamine uronic acids that are amenable to solid-phase synthesis is described. The general synthetic strategy involves initial incorporation of the protected amine, followed by selective TEMPO oxidation of C-6 hydroxyl groups to give the corresponding Fmoc-protected sugar amino acids. Amine incorporation may be accomplished from aminolysis of the free sugar or from glycosyl azide reduction. The reactions can be carried out on multigram scale, providing access to unique monomer units for future incorporation into combinatorial library syntheses.