Mannopyranosyl uronic acid donor reactivity

The reactivity of a variety of mannopyranosyl uronic acid donors was assessed in a set of competition experiments, in which two (S)-tolyl mannosyl donors were made to compete for a limited amount of promoter (NIS/TfOH). These experiments revealed that the reactivity of mannuronic acid donors is significantly higher than expected based on the electron-withdrawing capacity of the C-5 carboxylic acid ester function. A 4-O-acetyl-β-(S)-tolyl mannuronic acid donor was found to have similar reactivity as per-O-benzyl-α-(S)-tolyl mannose.     

Stereoselective glycosidations of uronic acids

Stereoselective glycosidation and disaccharide formation of uronic acids were performed with silver perchlorate in acetonitrile. The course of the reaction is controlled by intermediate nitrilium acetonitrile conjugates, which are generated in situ.     

Automated chromatography of uronic acids on anion-exchange resins

An automatic system is described for the determination of various uronic and biouronic acids after chromatographic separation on an anion-exchange column. Elution is carried out with sodium acetate or acetic acid, and the colors developed with carbazole and after oxidation with chromic acid are determined in a multichannel photometer and recorded continuously.     

Interactions between polysaccharides uronic acid sequences and lipid molecules

Homogalacturonic and homoglucuronic acid sequences, with various molecular weights and corresponding monomer, were mixed with cholesterol or linolenic acid in controlled conditions (pH, temperature, concentration), then studied by ¹H and ¹³C NMR. The variation of ¹³C NMR chemical shifts showed the formation of interactions between cholesterol or linolenic acid and carbohydrate sequences depending the molecular weight. Galacturonic acid sequences revealed to be more suitable than glucuronic acid sequences to entrap cholesterol or linolenic acid molecules probably due to the difference of conformation of the two molecules.     

Studies on uronic acid materials : The simultaneous determination of uronic acid and alkoxyl groups in polysaccharides by reflux with hydriodic acid

A reaction period of 2.5 h is required for the decarboxylation of uronic acid groups with 19% (w/w) hydrochloric acid, but 55% (w/w) hydriodic acid gives complete decarboxylation in 1.5 h. This rapid reaction can be carried out in a standard Zeisel reaction flask and condenser. Vapour phase infra-red spectroscopy gives a specific determination of the carbon dioxide evolved, and facilitates simultaneous determinations of any alkoxyl groups present. The proposed method is particularly useful for pectins and plant gums; it gives greater sensitivity and reproducibility than previous methods.     

Studies on uronic acid materials : Part VIII1. a comparative study of some colorimetric methods of estimating the uronic acid contents of polysaccharides

Values for the uronic acid content of a variety of polysaccharide materials were obtained by colorimetric methods and by acidic decarboxylation ; very large differences were found, particularly for heterogeneous biological materials. Colorimetric methods are useful for “screening” many samples rapidly, and for routine or comparative measurements on characterised products. For materials of unknown structure, however, colorimetric results should be interpreted with caution, especially when shortage of material does not permit corroborative decarboxylation or titration values to be obtained.     

Determination of uronic acids in natural materials by the decarboxylation method

Summary A preferred variant of the decarboxylation method for the determination of uronic acids is proposed which uses 57% hydriodic acid and the direct nonaqueous titration of the CO₂ formed. The range of concentrations of uronic acids that can be determined is from 2 to 100 µM. The sensitivity of the method is 1.5 µM, its reproducibility 0.6%, and the time of one determination 40–50 min. The proposed variant of the method is applicable to the study of various polysaccharides and other carbohy drate-containing biopolymers.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center of the Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 10–13, January–February, 1976.     

Accessing C-1 phosphonylated 2-acylamino uronic acids via 2-nitro-glycals

Two approaches are described for the synthesis of 2-acylamino uronic acid glycosyl phosphonates from readily accessible D-glucal. The first approach that entailed oxidation of the C-6 hydroxyl group followed by phosphonylation of the uronate 2-nitro-glycal, resulted in the formation of the β-L-gulo-configured phosphonate. Reversing the reaction order resulted in the exclusive formation of the β-D-gluco-configured phosphonate. In both cases the thermodynamic 1,2-trans-di-equatorial phosphonylation product is obtained.     

Benzoylated uronic acid building blocks and synthesis of N-uronate conjugates of lamotrigine

A chemoenzymatic approach towards benzoylated uronic acid building blocks has been investigated starting with benzoylated hexapyranosides using regioselective C-6 enzymatic hydrolysis as the key step. Two of the building blocks were reacted with the antiepileptic drug lamotrigine. Glucuronidation of lamotrigine using methyl (2,3,4-tri-O-benzoyl-α-D-glycopyranosyl bromide)uronate proceeded to give the N2-conjugate. However, lamotrigine-N2-glucuronide was most efficiently synthesised from methyl (2,3,4-tri-O-acetyl-α-D-glucopyranosyl bromide)uronate. Employing nitromethane as solvent with CdCO(3) as a base lamotrigine-N2 glucuronide was prepared in a high yield (41%). Also methyl (2,3-di-O-benzoyl-4-deoxy-4-fluoro-α-D-glucosyl bromide)uronate underwent N-glucuronidation, but the product was unstable, eliminating hydrogen fluoride to give the corresponding enoate conjugate.     

A uronic acid analogue of isofagomine lactam as a nanomolar glucuronidase inhibitor

The synthesis of (3S,4R,5R)-3,4-dihydroxypiperidin-2-one-5-carboxylic acid (‘isofagomine lactam uronate’) from d-arabinose is reported. The product is a potent inhibitor in the low nanomolar range (K_i 36 nM) for bovine liver β-glucuronidase.     

Preparation of 1-thio uronic acid lactones and their use in oligosaccharide synthesis

The chemo- and regioselective TEMPO/BAIB-mediated oxidation of 2,6- and 3,6-dihydroxy 1-thio glycopyranosides to the corresponding 1-thio uronic acid lactones is described. These locked 1-thio glycuronides can directly be used as donors in glycosidation reactions using the Ph(2)SO/Tf(2)O reagent system. Alternatively, selective opening of the lactone bridge liberates a hydroxyl function for ensuing glycosylations.