Adriana A. Kolender

Sulfated polysaccharides from the red seaweed Georgiella confluens.

The water-soluble polysaccharides from Georgiella confluens, collected in Antarctica, were fractionated with cetrimide. The complexed material was subjected to fractional solubilization in solutions of increasing sodium chloride concentration. The initially extracted polysaccharide and the major fraction isolated, soluble in 0.5 M NaCl, were studied. These are sulfated xylogalactans naturally rich in methylated sugar residues, comprising of 3,6-anhydro-2-O-methyl-L-galactose, 2-O-methyl-L-galactose and 6-O-methyl-D-galactose. Structural analysis was carried out by methylation, ethylation, desulfation-ethylation, desulfation-methylation, Smith degradation, 13C NMR spectroscopy and determination of the absolute configuration of monosaccharides by gas chromatography of diastereomeric derivatives produced by reductive amination. The results indicated the presence of an agaran backbone with an unusual substitution pattern: sulfation mainly at the 3-position of the alpha-L-galactose units and the presence of xylose side chains at the 4-position of the beta-D-galactose residues.

Structural analysis of antiviral sulfated α--(1 → 3)-linked mannans

Abstract The structures of two α-(1 → 3)-α- d -xylo- mannans were determined. The different antiviral activity of the xylo-mannans from Nothogenia fastigiata was explained on the basis of a flexible backbone, molecular size, content and distribution of sulfate groups and of the single stubs of β-(1 → 2)- linked d - xylose .

Matrix-assisted ultraviolet laser-desorption ionization time-of-flight mass spectrometry of sulfated mannans from the red seaweed Nothogenia fastigiata

Matrix-assisted ultraviolet laser-desorption ionization time-of-flight mass spectrometry (UV-MALDI-TOF-MS) was applied to sulfated xylo-mannan fractions from Nothogenia fastigiata in order to determine their molecular weights and distribution profiles. The number-average molecular weight calculated from the spectra was similar to that determined by chemical end-group analysis for the lower molecular weight fractions. For the other fractions, the number-average molecular weight was lower than that chemically determined; the increased difference may be attributed to higher desorption difficulties and, consequently, mass-dependent discrimination. A reconstructed spectrum, using the peaks obtained from all the fractions, suggested an unimodal distribution. The best results were obtained by using 2,5-dihydroxybenzoic acid as matrix doped with 1-hydroxyisoquinoline and with harmane and nor-harmane.

Synthesis and characterization of poly-O-methyl-[n]-polyurethane from a d-glucamine-based monomer.

Aminoalditol 1-amino-1-deoxy-D-sorbitol (1) was readily converted into 2,3,4,5-tetra-O-methyl derivative 5, a key precursor of a sugar-based [n]-polyurethane. For the polymerization, the free amino or primary hydroxyl groups of 5 were selectively activated and employed as starting monomers in two alternative procedures. Thus, the amino function of 5 was converted into the isocyanate derivative by treatment with di-tert-butyltricarbonate, and polymerized in situ in the presence of Zr(IV) acetylacetonate. The resulting poly(1-amino-1-deoxy-2,3,4,5-tetra-O-methyl-D-sorbitol)urethane (8) had a moderate molecular weight and showed the presence of urea units. The alternative synthesis of 8 involved the activation of the free hydroxyl group of 5 as the corresponding phenylcarbonate. The polymerization of this α-amino-ω-phenylcarbonate alditol monomer does not require a metal catalyst. The resulting material exhibited an improved molecular weight and higher purity than that obtained via the isocyanate. [n]-polyurethane 8 was highly soluble in water as well as in common organic solvents (chloroform, acetone, ethyl acetate, etc) and was obtained as an amorphous material which was characterized thermally and spectroscopically.

Synthesis and Applications of Carbohydrate-Based Polyurethanes

Polyurethanes are one of the most important and widespread type of polymers which display a wide range of industrial and biomedical applications. The recent approaches and advances in polyurethane research involve the replacement of petro-based polyols and isocyanates with biobased molecules. In this regard, carbohydrates offer a great promise due to their rich functionality, varied stereochemistry, and renewable production on an impressive scale. The carbohydrate-based polyurethanes are also prone to being biodegradable and biocompatible. These types of materials may be entirely derived from carbohydrates or contain carbohydrates as pendant groups or as constituents of the soft part of the polymer. Artificial polymers prepared by combination of polysaccharides with synthetic monomers or polymers are also included. The synthesis of these materials is described, and their actual or potential applications (mostly in biomedicine, as implants for tissue repair, as permanent or temporary prosthesis, or as drug delivery systems) are discussed.

A convenient synthesis of hexulosonic acids by IBX mediated oxidation of D-glucono-1,5-lactone derivatives

The oxidation of the free hydroxyl group of methyl 3,4:5,6-di-O-isopropylidene-D-gluconate 2 or its 2,3:5,6-di-O-isopropylidene analogue 3, the products of acetonation of D-glucono-1,5-lactone 1, has been attempted by alternative procedures. The oxidation of OH-2 in 2, or OH-4 in 3, with o-iodoxybenzoic acid (IBX) took place to afford the respective 2-keto 4 and 4-keto 7 derivatives in almost quantitative yields. In contrast, the oxidations with pyridinium dichromate were unsuccessful, and those using dimethylsulfoxide−acetic anhydride afforded low yields of 4 or 7. Selective removal of the isopropylidene groups in 4 or 7 with 88% aqueous acetic acid afforded, respectively, the methyl esters 5 or 8; whereas treatment with aqueous trifluoroacetic acid led to the free hexulosonic acids 6 or 9. The tautomeric preferences for the oxidation products 4 and 7, and their derivatives, have been established by C NMR spectroscopy.