Carrageenan and agaran structures from the red seaweed Gymnogongrus tenuis.

The galactan system biosynthesized by the red seaweed Gymnogongrus tenuis (Phyllophoraceae) is constituted by major amounts of κ/ι-carrageenans, with predominance of ι-structures, which were isolated by extraction with hot water in high yield (∼ 45%). A small amount of non-cyclized carrageenans mostly of the ν-type was also obtained. Besides, 12% of these galactans are agaran structures, which were present in major quantities in the room temperature water extracts, but they were also found in the hot water extract. They are constituted by 3-linked ß-D-galactose units partially substituted on C-6 with sulfate or single stubs of ß-D-xylose and 4-linked residues that comprise α-L-galactose units partially sulfated or methoxylated on C-3 or sulfated on C-3 and C-6 and 3,6-anhydro-α-L-galactose. Related structural patterns were previously found for agarans synthesized by other carrageenophytes. Results presented here show that these agarans are low molecular weight molecules independent of the carrageenan structures, with strong interactions between them.

Anticoagulant activity of a unique sulfated pyranosic (1->3)-ß-L-arabinan through direct interaction with thrombin.

A highly sulfated 3-linked ß-arabinan (Ab1) with arabinose in the pyranose form was obtained from green seaweed Codium vermilara (Bryopsidales). It comprised major amounts of units sulfated on C-2 and C-4 and constitutes the first polysaccharide of this type isolated in the pure form and fully characterized. Ab1 showed anticoagulant activity by global coagulation tests. Less sulfated arabinans obtained from the same seaweed have less or no activity. Ab1 exerts its activity through direct and indirect (antithrombin- and heparin cofactor II-mediated) inhibition of thrombin. Direct thrombin inhibition was studied in detail. By native PAGE, it was possible to detect formation of a complex between Ab1 and human thrombin (HT). Ab1 binding to HT was measured by fluorescence spectroscopy. CD spectra of the Ab1 complex suggested that ligand binding induced a small conformational change on HT. Ab1-thrombin interactions were studied by molecular dynamic simulations using the persulfated octasaccharide as model compound. Most carbohydrate-protein contacts would occur by interaction of sulfate groups with basic amino acid residues on the surface of the enzyme, more than 60% of them being performed by the exosite 2-composing residues. In these interactions, the sulfate groups on C-2 were shown to interact more intensely with the thrombin structure. In contrast, the disulfated oligosaccharide does not promote major conformational modifications at the catalytic site when complexed to exosite 1. These results show that this novel pyranosic sulfated arabinan Ab1 exerts its anticoagulant activity by a mechanism different from those found previously for other sulfated polysaccharides and glycosaminoglycans.

ß-D-(1→4), ß-D-(1→3) 'mixed linkage' xylans from red seaweeds of the order Nemaliales and Palmariales.

Xylans from five seaweeds belonging to the order Nemaliales (Galaxaura marginata, Galaxaura obtusata, Tricleocarpacylindrica, Tricleocarpa fragilis, and Scinaia halliae) and one of the order Palmariales (Palmaria palmata) collected on the Brazilian coasts were extracted with hot water and purified from acid xylomannans and/or xylogalactans through Cetavlon precipitation of the acid polysaccharides. The ß-D-(1→4), ß-D-(1→3) 'mixed linkage' structures were determined using methylation analysis and 1D and 2D NMR spectroscopy. The presence of large sequences of ß-(1→4)-linked units suggests transient aggregates of ribbon- or helical-ordered structures that would explain the low optical rotations.

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry analysis of oligosaccharides and oligosaccharide alditols obtained by hydrolysis of agaroses and carrageenans, two important types of red seaweed polysaccharides.

MALDI-TOF mass spectrometry analyses of several oligosaccharides (aldoses) and oligosaccharide alditols derived from agaroses, kappa- and iota-carrageenans using different matrices (2,5-dihydroxybenzoic acid, nor-harmane, ferulic acid, and the ionic liquid matrices 2,5-dihydroxybenzoic acid-n-butylamine and ferulic acid-n-butylamine) were conducted. These carbohydrates were selected as model compounds to study the MALDI prompt and post-source decay (PSD) fragmentation processes of both families of oligosaccharides. Sulfated alditols showed in the negative-ion mode the molecular ion as [M-Na](-) together with the species yielded by their prompt fragmentation (mainly desulfation) while the sulfated oligosaccharides (aldoses) showed mainly glycosidic prompt fragmentation (glycosidic C-cleavages and desulfation). Non-sulfated aldoses and alditols, which could only be analyzed in positive-ion mode ([M+Na](+)), did not suffer any prompt fragmentation. The former yielded cross-ring fragmentation in the PSD mode. Best results were obtained by using 2,5-dihydroxybenzoic acid and/or nor-harmane as matrices for all the compounds studied.

Galactans from Cryptonemia species. Part II: studies on the system of galactans of Cryptonemia seminervis (Halymeniales) and on the structure of major fractions.

Cryptonemia seminervis biosynthesizes a family of D,L-hybrid galactans based on the classical 3-linked beta-D-galactopyranosyl-->4-linked alpha-D- and alpha-L-galactopyranosyl alternating sequence (A-units-->B-units) with major amounts of alpha-D- and alpha-L-galactose and 3,6-anhydro-D- and L-galactose and lesser percentages of 3,6-anhydro-2-O-methyl-L-galactose, 2-O-methyl-, 4-O-methyl- and 6-O-methylgalactoses. The dispersion of structures in this family is based on five structural factors, namely: (a) the amount and position of substituent groups as sulfate (major), pyruvic acid ketals, methoxyl and glycosyl side-chain (4-O-methyl galactopyranosyl and/or xylosyl); (b) the ratio galactose/3,6-anhydrogalactose in the B-units; (c) the ratio D,L-galactoses and D,L-3,6-anhydrogalactoses also in the B-units, (d) the formation of diads and (e) the sequence of the diads in the linear backbone. Considering these variables it is not unexpected to find in the fractions studied at least 18 structural units producing highly complex structures. Structural studies carried out in two major fractions (S2S-3 and S2S-4) showed that these galactans were formed mainly by beta-D-galactopyranosyl 2-sulfate (20 and 11.9 mol%), beta-d-galactopyranosyl 2-sulfate 4,6-O-(1'-carboxyethylidene) (8.9 and 6.0 mol%) and beta-D-galactopyranosyl 2,6-sulfate (5.4 and 18.6 mol%), together with 3,6-anhydro-alpha-l-galactopyranosyl (11.4 and 7.3 mol%) and 3,6-anhydro-alpha-L-galactopyranosyl 2-sulfate (4.9 and 15.4 mol%) and minor quantities of 12-15 other structural units. Preparative alkaline treatment carried out on fraction (S2S-3) produced a quantitative formation of 3,6-anhydro alpha-L-galactopyranosyl units from precursor units (alpha-L-galactose 6-sulfate and alpha-L-galactose 2,6-sulfate). Kinetic studies on this 3,6-anhydro cyclization show a rate constant of 5.2 x 10(4)s(-1) indicating diads of the type G-->L6S/2,6S. Data from chemical, spectroscopic and kinetic studies suggest that, in S2S-3, the agaran block in the D,L-hybrid galactan is composed of the following diads: G(6R)-->L6S/2,6S and G2S(P)(2,6S)-->LA(2S)(2R)(2M) and the carrageenan block of G2S(P)-->D(2S)(2,3S)(3S)(3,6S) in a molar ratio of agaran to carrageenan structures of approximately 2:1.

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 ß-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.

Matrix-assisted ultraviolet laser desorption/ionization time-of-flight (UV-MALDI-TOF) mass spectra of N-acylated and N,O-acylated glycosylamines.

Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF-MS) has shown to be a very useful technique for the study of the non-volatile and thermally non-stable N-acylated glycopyranosyl- and glycofuranosyl-amines. Of the several matrices tested, 2,5-dihydroxybenzoic acid (DHB) was the most effective giving good spectra in the positive-ion mode. In the linear and reflectron modes, the [M+Na](+) ions appeared with high intensity. Their fragmentation patterns were investigated by post-source decay (PSD) UV-MALDI-TOF-MS showing mainly cross-ring cleavages. In addition, N,O-acylated glycopyranosyl- and glycofuranosyl-amines were also analyzed by this technique. PSD UV-MALDI-TOF-MS gave significant signals for several primary fragment ions, which were proposed but not detected, or observed with very low abundance, in electron ionization mass spectrometry (EI-MS) experiments.

Galactans from cystocarpic plants of the red seaweed Callophyllis variegata (Kallymeniaceae, Gigartinales).

The polysaccharide extracted from cystocarpic Callophyllis variegata was fractionated with potassium chloride yielding three small fractions that precipitated in the ranges of 0-0.05 M KCl, 1.20-1.25 M KCl, and 1.80-2.00 M KCl, and a main product soluble in 2.00 M KCl. These fractions were analyzed, and as the first one contained very high amounts of protein, it was not studied further. Structural analysis of the rest of the fractions (F1-F3) was carried out by methylation, desulfation-methylation, IR, and 13C NMR spectroscopy. The results are consistent for F1 with a carrageenan-type backbone mainly constituted by beta-D-galactose 2-sulfate linked to alpha-D-galactose 2,3,6-trisulfate and beta-D-galactose 2,4-disulfate linked to 3,6-anhydro-D-galactose 2-sulfate as dominant diads. In F2 these diads are present together with low amounts of beta-D-galactose 2-sulfate linked to 3,6-anhydro-D-galactose 2-sulfate, whose contribution becomes higher in F3. In addition, minor but significant amounts of L-galactose were detected. F1-F3 showed potent antiviral activity against herpes simplex types 1 and 2 and dengue type 2.

The system of galactans from Cryptonemia crenulata (Halymeniaceae, Halymeniales) and the structure of two major fractions. Kinetic studies on the alkaline cyclization of the unusual diad G2S-->D(L)6S.

Cryptonemia crenulata biosynthesizes a family of dl-hybrid galactans that are based on the classical 3-linked beta-d-galactopyranosyl-->4-linked alpha-galactopyranosyl alternating sequence (A-units-->B-units). The dispersion of structures in these galactans is based on four factors, namely: (a) the amount and position of substituent groups as sulfate (major), pyruvic acid ketals, methoxyl and side substituents of beta-D-xylose and/or beta-D-galactose; (b) the ratio galactose/3,6-anhydrogalactose in the B-units; (c) the ratio D-/L-galactoses and 3,6-anhydrogalactoses also in the B-units and (d) the sequence of the diads in the linear backbone. Alkali treatment carried out on the major fraction produced a nearly quantitative formation of 3,6-anhydrogalactose units from precursor units (alpha-galactose 6-sulfate (major) and alpha-galactose 2,6-sulfate, minor). Kinetic studies show a rate constant, for the diad G2S-D(L) 6-S, of 1.7 x 10(4)s(-1) indicating a reaction faster than in lambda-carrageenans but slower than in porphyrans.

Matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry of beta-(1 --> 3), beta-(1 --> 4)-xylans from Nothogenia fastigiata using nor-harmane as matrix.

Three xylan fractions isolated from the red seaweed Nothogenia fastigiata (Nemaliales) were analyzed by ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOFMS). UV-MALDI-TOFMS was carried out in the linear and reflectron modes, and as routine in the positive and negative ion modes. Of the several matrices tested, nor-harmane was the only effective one giving good spectra in the positive ion mode. The number-average molar masses of two of the fractions, calculated from the distribution profiles, were lower than those determined previously by (1)H NMR analysis, suggesting a decrease in the ionization efficiency with increasing molecular weight; weight-average molar mass and polydispersity index were also determined. As the xylans retained small but significant quantities of calcium salts, the influence of added Ca(2+) as CaCl(2) on UV-MALDI-MS was investigated. The simultaneous addition of sodium chloride and calcium chloride was also analyzed. Addition of sodium chloride did not change the distribution profile of the native sample showing that the inhibitory effect is due to Ca(2+) and not to Cl(-). Addition of calcium chloride with 1:1 analyte/salt molar ratio gave spectra with less efficient desorption/ionization of oligomers; the signals of these oligomers were completely suppressed when the addition of the salt became massive (1:100 analyte/salt molar ratio).

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.

Sulfated seaweed polysaccharides as antiviral agents.

Several sulfated seaweed polysaccharides show high antiviral activity against enveloped viruses, including important human pathogens such as human immunodeficiency virus, herpes simplex virus, human cytomegalovirus, dengue virus and respiratory syncytial virus. They can be obtained in major amounts and at low costs, have low toxicity and in some cases, lack anticoagulant effects. Even if the systemic applications have many drawbacks, their structure and mode of action indicate potential for topical uses to prevent virus infection. The herpes simplex viruses attach to cells by an interaction between the envelope glycoprotein C and the cell surface heparan sulfate (HS). The virus-cell complex is formed by ionic interactions between the anionic (mainly sulfate) groups in the polysaccharide and basic amino acids of the glycoprotein, and non-ionic ones depending on hydrophobic amino acids interspersed between the basic ones in the glycoprotein-binding zone. Hypothesis are advanced of the corresponding hydrophobic structures in the polysaccharides. The antiviral activity of the sulfated seaweed polysaccharides is based on the formation of formally similar complexes that block the interaction of the viruses with the cells. Correlations are established between different structural parameters and antiviral activity. The minimal, ionic and hydrophobic, structures in the seaweed polysaccharides were hypothesized by comparison of the polysaccharides with the known minimal binding structure in HS/heparin, together with a correlation between those structures of the polysaccharides and their antiviral activity.

The structure of the agaran sulfate from Acanthophora spicifera (Rhodomelaceae, Ceramiales) and its antiviral activity. Relation between structure and antiviral activity in agarans.

The sulfated agaran isolated by water extraction from the red seaweed, Acanthophora spicifera (Rhodomelaceae, Ceramiales), is made up of A-units highly substituted with sulfate groups on C-2 (28-30%), sulfates on C-2 and 4,6-O-(1'-carboxyethylidene) groups (9-15%), and only the C-2 sulfate groups (5-8%) with small amounts of C-6 sulfate, 6-O-methyl, and nonsubstituted residues. B-units are formed mainly by 3,6-anhydro-alpha-L-galactose (15-16%) and its precursor, alpha-L-galactose 6-sulfate (10-17%), together with lesser amounts of 3,6-anhydro-alpha-L-galactose 2-sulfate, alpha-L-galactose 2,6-disulfate, alpha-L-galactose 2,3,6-tri-sulfate, alpha-L-galactose 2,6-disulfate 3-xylose, 2-O-methyl-alpha-L-galactose, and unsubstituted alpha-L-galactose. Small, but significant quantities of beta-D-xylose were found in all the fractions, together with small amounts to traces of D-glucose. Some of the fractions have high antiviral activity. Attempts to correlate structure and antiviral activity in agarans are presented.

MM3 potential energy surfaces of trisaccharides. II. Carrageenan models containing 3,6-anhydro-D-galactose.

The adiabatic potential energy surfaces (PES) of six trisaccharides-namely 3,6-An-alpha-D-Galp-(1-->3)-beta-D-Galp-(1-->4)-3,6-An-alpha-D-Galp, beta-D-Galp-(1-->4)-3,6-An-alpha-D-Galp-(1-->3)-beta-D-Galp, and their derivatives sulfated on positions 2 and 4 of the beta-galactose unit-were obtained using the MM3 force field. Each PES was described by a single contour map for which the energy is plotted against the two psi glycosidic angles, given the small variations of the phi glycosidic torsional angle in the low-energy regions of disaccharide maps. In five of the six examples, the surfaces are those expected from the maps of the disaccharidic repeating units of carrageenans, with less important factors altering the additive effect of both linkages. However, when a sulfate group is present on C2 of a beta-galactose reducing end, a new low-energy minimum in a different region is produced, originated in a hydrogen bond between the first and third monosaccharidic moieties of the trisaccharide. The flexibility of the beta-linkages is nearly identical to that in their disaccharide counterparts, while that of the alpha-linkages is slightly reduced, independent of their presence closer or further away from the reducing end. A fair agreement is observed between the x-ray fiber diffraction analysis for a kappa-carrageenan double helix and the surfaces obtained for the trisaccharide analogs of that polymer.

MM3 potential energy surfaces of the 2-linked glucosyl trisaccharides alpha-kojitriose and beta-sophorotriose.

The adiabatic potential energy surfaces (PES) of two trisaccharides with 2-linkages (alpha-kojitriose and beta-sophorotriose) were obtained using the MM3 force field, and are represented by a single 3D contour map for which the energy is plotted against the two psi glycosidic angles. In spite of the proximity of the positions where the two monosaccharidic units are linked to the central monosaccharide, an almost independent behavior of both linkages was found for the alpha-linked trisaccharide alpha-kojitriose, i.e., the surfaces are those expected from the maps of the disaccharide containing the same linkage. A slight shift of the position of the global minimum is found to occur, due to a hydrogen bond between the third and first monosaccharide units, which also leads to an increase in flexibility. On the other hand, for the beta-linked trisaccharide beta-sophorotriose, the surface is sharply different from that expected by observation of the disaccharide map. Some of the expected minima cannot appear unless a serious deformation of the phi and/or psi angles is produced. Furthermore, the global minimum corresponds to a combination of different conformations for each of the linkages, whereas another minimum with only slightly higher energy has both glycosidic linkages in a conformation less favored for the disaccharide, though close to that predicted in crystal diffraction studies.

Depicting the MM3 potential energy surfaces of trisaccharides by single contour maps: application to beta-cellotriose and alpha-maltotriose.

The adiabatic potential energy surfaces (PES) of two trisaccharides (beta-cellotriose and alpha-maltotriose) were obtained using the MM3 force field. Each PES can be described by a single 3D contour map for which the energy is plotted against the two psi glycosidic angles. Given the usually small variations of the phi glycosidic torsional angle in the low-energy regions of disaccharide maps (at least with MM3), it is valid to leave both phi glycosidic angles to relax in the process of building the conformational map of trisaccharides. The surfaces are those expected from the map of disaccharides containing the same linkages and monosaccharide units (i.e., beta-cellobiose and alpha-maltose), with second-order factors altering the 'symmetry' of both linkages. A large low-energy region appears for beta-cellotriose, comprising four minima in close proximity, with barriers between them below 0.6 kcal/mol. On the other hand, for alpha-maltotriose a main global minimum is observed, with several surrounding local minima. The surfaces obtained agree with single-crystal X-ray data on these trisaccharides and derivatives. A reduction of the linkage flexibilities is observed when passing from the disaccharides to the trisaccharides. Furthermore, the linkage closer to the reducing end appears to be less flexible than the linkage closer to the non-reducing end.

Disaccharide conformational maps: 3D contours or 2D plots?

The potential energy surfaces of several alpha-(1-->3)- and beta-(1-->4)-linked disaccharides were obtained and plotted in terms of energy versus psi glycosidic angle. These plots were compared to those obtained previously in the way of the usual 3D contour maps, which relate the energy with the two glycosidic angles (phi and psi). Given the usually small variations of the phi angle in the low-energy regions (at least using MM3), both kinds of graphs lead to similar conclusions concerning flexibility measurements by two different methods and assessment of the effects of sulfation and/or hydroxyl group orientation. Only second-order effects were found with some sulfated disaccharides, not changing the general conclusions. The computational efforts required to produce those plots are smaller, and the plots are easier to interpret. Besides, the conversion of a 3D map into a 2D plot leaves the possibility of constructing 3D maps of carbohydrates including a second variable different to phi, e.g., the second psi angle of a trisaccharide or the omega angle of a 6-linked disaccharide.

Matrix-assisted ultraviolet laser-desorption ionization and electrospray-ionization time-of-flight mass spectrometry of sulfated neocarrabiose oligosaccharides.

Several commercial sulfated neocarrabiose oligosaccharides were analyzed by matrix-assisted ultraviolet laser-desorption ionization time-of-flight mass spectrometry (UV-MALDI-TOF-MS). UV-MALDI-TOF-MS was carried out in the linear and reflectron modes and, as routine, in both the positive- and negative-ion modes. 2,5-Dihydroxybenzoic acid and nor-harmane were used as matrices. In the positive- and negative-ion modes, with both matrices, peaks corresponding to (M+Na)(+) and (M-Na)(-) ions, respectively, were obtained, with only some signals due to glycosidic linkage cleavages (prompt fragmentation). With 2,5-dihydroxybenzoic acid abundant matrix signals were observed; nor-harmane afforded very few matrix signals in both ion modes, but more desulfation (prompt fragmentation) of the compounds occurred. When the desorption/ionization process was highly efficient, the post-source decay (PSD) fragmentation patterns were also investigated; most of the fragments detected derived from glycosidic linkage cleavages. Electrospray-ionization time-of-flight mass spectrometry (ESI-TOF-MS) in the negative-ion mode confirmed, with the observation of the (M-Na)(-) and the multiply charged anions, the identity and the purity of the samples.

The structure of a galactan sulfate from the red seaweed Bostrychia montagnei.

The sulfated, methylated galactan isolated from the red seaweed Bostrychia montagnei, showed an unusually narrow structural dispersion. This agaran has the defining linear backbone of alternating 3-linked beta-D-galactopyranosyl units and 4-linked alpha-L-galactopyranosyl and 3,6-anhydrogalactopyranosyl residues. The D-units have C-6 methylation, C-6 single stubs of xylopyranosyl and minor to trace amounts of (possible) C-6 linked single stubs of galactopyranosyl. These units are mainly sulfated on C-4 with lesser sulfation at C-6 and minor at C-2. The L-residues are mainly methylated on C-2 of the 3,6-anhydrogalactopyranosyl and sulfated on C-3 of the L-galactopyranosyl; minor amounts of 2,3- and 3,6-disulfated and 2-O-methyl or 2-O-glycosyl 3-sulfated L-galactopyranosyl were also found.

NMR spectroscopy and chemical studies of an arabinan-rich system from the endosperm of the seed of Gleditsia triacanthos.

Exhaustive extraction of the endosperm from the seed of Gleditsia triacanthos using water at room temperature and 50 degrees C left a residue, which was further extracted at 95 degrees C. Precipitation of this extract with 2-propanol yielded major amounts of galactomannan components, while the supernatant was mainly composed of arabinose-rich constituents. Two fractions were obtained by anion-exchange chromatography. The fraction that eluted with water is an arabinan with (1-->5) alpha-L linkages and branching mainly on C-2, accompanied with equal amounts of a low-galactose galactomannan oligosaccharide, and a small proportion of a beta-(1-->4)-galactan. The fraction eluted with an increased ionic strength consists mainly of a similar arabinan, and lower proportions of a high-galactose galactomannan, galactan, and protein. The arabinan moiety in both fractions was characterized by chemical analysis and 1D and 2D NMR spectroscopic techniques.