Separation and identification of O-acetyl-O-methyl-galactononitriles by gas-liquid chromatography and mass spectrometry

A novel substitution pattern in glucuronoarabinoxylans from woody bamboos

(1 → 4)-β-D-Xylans are the second most abundant plant biopolymers on Earth after cellulose. Although their structures have been extensively studied, and industrial applications have been found for them and their derivatives, they are still investigated due to the diversity of their structures and uses. In this work, hemicellulose fractions obtained previously with 1 M KOH from two species of woody bamboos, Phyllostachys aurea and Guadua chacoensis, were purified, and the structures of the glucuronoarabinoxylans (GAX) were studied by chemical and spectroscopic methods. In both cases, major amounts of α-L-arabinofuranose residues were linked to C3 of the xylose units of the backbone, and also α-D-glucuronic acid residues and their 4-O-methyl-derivatives were detected in minor quantities, linked to C2 of some xylose residues. Methylation analysis of the carboxyl-reduced derivative from GAX from P. aurea indicated the presence of terminal and 5-linked arabinofuranose units. NMR spectroscopy showed the presence of disaccharidic side chains of 5-O-α-l-arabinofuranosyl-L-arabinofuranose for the GAX from P. aurea, while for those of G. chacoensis, only single side chains were found. To the best of our knowledge, this disaccharide was not found before as side chain of xylans.

Complex sulfated galactans from hot water extracts of red seaweed Asparagopsis taxiformis comprise carrageenan and agaran structures

Hot water extraction from the red seaweed Asparagopsis taxiformis yielded three extracts which showed sulfated galactans with a D:L-galactose ratio non consistent with carrageenan or agaran backbones. The major extract was fractionated by cetrimide precipitation and redissolution with increasing sodium chloride concentrations due to their low solubility. Seven fractions were obtained, and studied by methylation analysis, desulfation-methylation, and NMR spectroscopy of the partially hydrolyzed and the native samples. Fractions with the highest yield were those obtained at high concentrations of NaCl. They comprised both agaran and crageenan structures in considerable amounts. The main agaran structures were β-D-galactose 4-sulfate and β-D-galactose 2-sulfate units linked to α-L-galactose 2,3-disulfate residues, and β-D-galactose linked to α-L-galactose 3-sulfate or 6-sulfate, or substituted with single stubs of β-D-xylose on C3, while the carrageenan structures comprised β-D-galactose (2-sulfate) linked to α-D-galactose 3-sulfate or 2,3-disulfate, and β-D-galactose 2,4-disulfate linked to α-D-galactose 2,3-disulfate. Between the less sulfated fractions, the one obtained by solubilization in 0.5 M NaCl was mainly constituted by agarans, which included 3,6-anhydro-α-L-galactose units. Anticoagulant activity was assayed by general coagulation tests (aPTT and TT), showing a moderate action compared with heparin. This is the first detailed study of the sulfated galactans from the order Bonnemaisoniales.

Determination of Substitution Patterns of Galactans from Green Seaweeds of the Bryopsidales

Sulfated and pyruvylated galactans are the major soluble polysaccharides produced by seaweeds of the Bryopsidales. Their backbones have a complex and variable pattern of substitution which, until now, has only been elucidated for a few species. Methods for determination of sulfate and pyruvic acid content, and chemical strategies to determine their position in the galactan chain are outlined here. These methods can also be applied to other sulfated and/or pyruvylated polysaccharides.

Chemical structure and anticoagulant activity of highly pyruvylated sulfated galactans from tropical green seaweeds of the order Bryopsidales

Sulfated and pyruvylated galactans were isolated from three tropical species of the Bryopsidales, Penicillus capitatus, Udotea flabellum, and Halimeda opuntia. They represent the only important sulfated polysaccharides present in the cell walls of these highly calcified seaweeds of the suborder Halimedineae. Their structural features were studied by chemical analyses and NMR spectroscopy. Their backbone comprises 3-, 6-, and 3,6-linkages, constituted by major amounts of 3-linked 4,6-O-(1'-carboxy)ethylidene-d-galactopyranose units in part sulfated on C-2. Sulfation on C-2 was not found in galactans from other seaweeds of this order. In addition, a complex sulfation pattern, comprising also 4-, 6-, and 4,6-disulfated galactose units was found. A fraction from P. capitatus, F1, showed a moderate anticoagulant activity, evaluated by general coagulation tests and also kinetics of fibrin formation was assayed. Besides, preliminary results suggest that one of the possible mechanisms involved is direct thrombin inhibition.

Polysaccharides of the red algae

Red algae (Rhodophyta) are known as the source of unique sulfated galactans, such as agar, agarose, and carrageenans. The wide practical uses of these polysaccharides are based on their ability to form strong gels in aqueous solutions. Gelling polysaccharides usually have molecules built up of repeating disaccharide units with a regular distribution of sulfate groups, but most of the red algal species contain more complex galactans devoid of gelling ability because of various deviations from the regular structure. Moreover, several red algae may contain sulfated mannans or neutral xylans instead of sulfated galactans as the main structural polysaccharides. This chapter is devoted to a description of the structural diversity of polysaccharides found in the red algae, with special emphasis on the methods of structural analysis of sulfated galactans. In addition to the structural information, some data on the possible use of red algal polysaccharides as biologically active polymers or as taxonomic markers are briefly discussed.

The system of sulfated galactans from the red seaweed Gymnogongrus torulosus (Phyllophoraceae, Rhodophyta): Location and structural analysis

Sulfated polysaccharides were localized in the cuticle, cortex and medulla of the gametophyte thallus, being more concentrated in the intercellular matrix than in the cell walls. During the water extraction sequence, a small percentage of galactan sulfates (5.1% of dry seaweed) with average low Mr (6-11.4kDa) were extracted at room temperature without disturbing the cellular arrangement, while sulfated galactans of average medium Mr (18-45kDa) were obtained by further hot-water extractions (52.4% of dry seaweed), with diorganization of the tissue. The residue (40.0% of dry seaweed) still contained carrageenan-type (major) and agaran-type (minor) galactans. Part of these galactans was extracted with 8.4% LiCl solution in DMSO, from which "pure" κ/ι-carrageenans were isolated. Carrageenans and agarans were extracted in a ratio 1:0.5, showing the highest amount of agaran-structures for a carrageenophyte. The galactans comprise alternating 4-sulfated (major) and non-sulfated (minor) 3-linked β-d-galactopyranose units, and 4-linked α-galactopyranose units with the following substitutions: (i) non-sulfated and 2-sulfated 3,6-anhydro-α-d-galactopyranose residues in the carrageenan-structures, which belong to the κ-family (κ/ι-carrageenans); (ii) 3-sulfated α-l-galactopyranose units and 2-sulfated 3,6-anhydro-α-l-galactopyranose residues in the agaran-structures. Alkaline treatment and alkaline dialysis of the main extracts gave "pure" κ/ι-carrageenans, showing that carrageenan molecules are extracted together with low Mr agarans or agaran-dl-hybrids.

The system of galactans of the red seaweed, Kappaphycus alvarezii, with emphasis on its minor constituents

The galactans extracted with hot water from Kappaphycus alvarezii, after previous extraction at room temperature, are mainly composed of kappa-carrageenans (approximately 74%) and micro-carrageenans (approximately 3%). However, a significant percentage of these galactans (at least 14%) is composed of sulfated agarans and, possibly, agaran-type sulfated DL-hybrid galactans. These agarans are partially substituted on C-2 or C-4 or disubstituted on both positions of the beta-D-galactose units and on C-3 or C-2 and C-3 of the alpha-L-galactose residues with sulfate groups or single stubs of beta-D-xylopyranose, D-glucopyranose, and galactose or with D-glucopyranosyl-(1-->4)-D-glucopyranose side chains. Significant quantities of 2-O-methyl- and 3-O-methyl-L-galactose units are also present. A great tendency to retain Ca2+ and Mg2+, in spite of massive treatments with Na+ and K+ salts, was observed. The complexation between agarans and agarans-kappa-carrageenans through divalent cations and the possible zipper-type carbohydrate-carbohydrate interactions would be two complementary mechanisms of interactions.

Determination of the configuration of 3,6-anhydrogalactose and cyclizable alpha-galactose 6-sulfate units in red seaweed galactans

A combination of two reported procedures was used in order to determine the configuration of the 3,6-anhydrogalactose present in red seaweed polysaccharides. A mild hydrolysis (to cleave only 3,6-anhydrogalactosyl linkages) was followed by a reductive amination with a chiral amine. Then, the total hydrolysis proceeded, followed by a new step of reductive amination. In this way, using (S)-alpha-methylbenzylamine as the chiral amine, it was possible to separate and quantitate both enantiomers of 3,6-AnGal and its 2-O-methyl ether as their diastereomeric acetylated aminoalditols. On the other hand, using (S)-1-amino-2-propanol, even though the derivatives of both enantiomers of 3,6-AnGal are not separated, the mixture can be safely quantitated with respect to galactose. Furthermore, a one-pot technique was developed to carry out an alkaline treatment of the polysaccharides, followed by the double hydrolysis-reductive amination procedure, which is useful to determine the proportions of both enantiomers of 6-sulfated 4-linked galactose units in the native polysaccharides. The unexpected presence of small amounts of units of this type belonging to the D-series in a porphyran sample is revealed by this novel procedure.

DL-Galactan hybrids and agarans from gametophytes of the red seaweed gymnogongrus torulosus

Seaweeds from the genus Gymnogongrus are known to be carrageenophytes; nevertheless, fractionation techniques used previously for the separation of gel-forming and 'soluble' carrageenans, applied to the galactans of Gymnogongrus torulosus together with enantiomeric analysis of the sugar components and (when possible) of the structural units, suggested that the system of galactans biosynthesized by the seaweed was formed by DL-galactan hybrids having major amounts of carrageenan-type or agaran-type chains, with minor quantities of agarans with unusual structural details.

The system of low-molecular-weight carrageenans and agaroids from the room-temperature-extracted fraction of Kappaphycus alvarezii

The room-temperature-extracted fraction from the red seaweed Kappaphycus alvarezii consists mainly of low-molecular-weight carrageenans, with structural dispersion around a basic kappa-pattern. This dispersion results from: (a) low percentages of 3,6-anhydrogalactose and the presence of precursor units; (b) important quantities of 6-O-methyl beta-D-galactose (4-sulfate) residues; (c) significant amounts of iota-repeating structure, and (d) small amounts of non-sulfated and disulfated beta-D-galactose residues. Significant quantities of alpha-L-galactose units suggest the presence of agaroids, as it has been reported in several other carrageenophytes.

Structural analysis of antiviral sulfated alpha-D-(1-->3)-linked mannans

The structures of two alpha-(1-->3)-alpha-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 beta-(1-->2)-linked D-xylose.

Cold water-soluble polysaccharides from tetrasporic Pterocladia capillacea

Cold water extraction of tetrasporic Pterocladia capillacea led to the isolation of a product which was characterized and further treated with Cetrimide. The complexed material was subjected to fractional solubilization in solutions of increasing sodium chloride concentration and six fractions were separated. The two major products obtained, one soluble in Cetrimide solution, the other soluble in 0.5 M sodium chloride, were subjected to structural studies, carried out by methylation analysis and 13C NMR spectroscopy. The results obtained indicated for the former a backbone mainly constituted by alternating 3-linked beta-D-galactose units and 4-linked 3,6-anhydro-alpha-L-galactose residues, but with other structural features probably responsible for its non-gelling properties. The acidic fraction is a complex polysaccharide sulphated mainly on C-6 of the beta-D-galactose units and on C-3 of the alpha-L-galactose residues.

Structure of the 'corallinans'--sulfated xylogalactans from Corallina officinalis

The structure of the main polysaccharides extracted from the red seaweed Corallina officinalis was characterized by methylation, desulfation-methylation, and ethylation analysis. The backbone has an alternating-->4)-alpha-L-Gal-(1-->3)-beta-D-Gal-(1-->structure. The C6 position of 3-linked units is substituted mainly by beta-D-xylosyl side stubs but also by sulfate ester groups and minor amounts of 4-O-methylgalactosyl side stubs. Positions C2 and C3 of 4-linked units also carry sulfate or methoxyl as substituents, but never both together in the same unit. Minor fractions modulate this structure with other irregularities, such as higher branching or, possibly, unusual (1-->2) or (1-->6) linkages.

Glucuronoxylomannan of Cryptococcus neoformans serotype B: structural analysis by gas-liquid chromatography-mass spectrometry and 13C-nuclear magnetic resonance spectroscopy

The major extracellular polysaccharide (glucuronoxylomannan, GXM) from six strains of Cryptococcus neoformans serotype B was characterized by gas-liquid chromatography (g.l.c.), g.l.c.-mass spectrometry (g.l.c.-m.s.), and nuclear magnetic resonance (n.m.r.) spectroscopy. Ultrasonic irradiation (u.i.) was used to reduce the mol.wt. of native GXM from 9.75 x 10(5) to 1.15 x 10(5) without apparent change in its composition (GXM-S). The Xylp:Manp:GlcpA molar ratio of the GXM and GXM-S from the six strains of C. neoformans serotype B is approximately 3.5:3.0:0.6. GXM-S was O-deacetylated (GXM-D) by treatment with NH4OH. The 13C-n.m.r. analysis of GXM-D gave spectra that served as characteristic fingerprints of the structure and also facilitated the assignment of the anomeric carbon resonances to specific structural moieties present in GXM-D. The GXM-D from each serotype B strain was found to be similar by 13C-n.m.r. spectroscopy. The structure contains a linear (1----3)-alpha-D-Manp backbone substituted with 2-O-beta-GlcpA and 2-O-beta-Xylp. beta-Xylp is also O-4 linked to the Manp substituted with GlcpA. In addition, a model for the disposition of the Xylp and GlcpA side chain substituents along the mannopyranan backbone is proposed, based upon results from the combination of g.l.c.-m.s. and 13C-n.m.r. spectroscopy.