The system of agaroids and carrageenans from the soluble fraction of the tetrasporic stage of the red seaweed Iridaea undulosa

NMR spectroscopy for structural elucidation of sulfated polysaccharides from red seaweeds

Some sulfated polysaccharides from red seaweeds are used as hydrocolloids. In addition, it is well known that there are sulfated galactans (carrageenans and agarans) and sulfated mannans, with remarkable biological properties, as antiviral, antitumoral, immunomodulating, antiangiogenic, antioxidant, anticoagulant, and antithrombotic activities, and so on. Knowledge of the detailed structure of the active compound is essential and difficult to acquire. The substitution patterns of the polymer chain, as degree of sulfation and position of sulfate groups, as well as other substituents of the backbone, determine their biological behavior. NMR spectroscopy is a powerful and versatile tool for structural determination. It can be used for elucidation of structures of polysaccharides from new algal sources with novel substitutions or to detect the already known structures from different algal sources, and it could even help to monitor the quality of the active compound on a productive scale. In this review, the available information about NMR spectroscopy of sulfated polysaccharides from red seaweeds is revised and rationalized, to help other researchers working in different fields to study their structures. In addition, considerations about the effects of different structural features, as well as some recording conditions on the chemical shifts of the signals are analyzed.

To gel or not to gel: differential expression of carrageenan-related genes between the gametophyte and tetasporophyte life cycle stages of the red alga Chondrus crispus

Chondrus crispus is a marine red alga with sulfated galactans, called carrageenans, in its extracellular matrix. Chondrus has a complex haplodiplontic life cycle, alternating between male and female gametophytes (n) and tetrasporophytes (2n). The Chondrus life cycle stages are isomorphic; however, a major phenotypic difference is that carrageenan composition varies significantly between the tetrasporophytes (mainly lambda-carrageenan) and the gametophytes (mainly kappa/iota-carrageenans). The disparity in carrageenan structures, which confer different chemical properties, strongly suggests differential regulation of carrageenan-active genes between the phases of the Chondrus life cycles. We used a combination of taxonomy, biochemistry and molecular biology to characterize the tetrasporophytes and male and female gametophytes from Chondrus individuals isolated from the rocky seashore off the northern coast of France. Transcriptomic analyses reveal differential gene expression of genes encoding several galactose-sulfurylases, carbohydrate-sulfotransferases, glycosyltransferases, and one family 16 glycoside hydrolase. Differential expression of carrageenan-related genes was found primarily between gametophytes and tetrasporophytes, but also between the male and female gametophytes. The differential expression of these multigenic genes provides a rare glimpse into cell wall biosynthesis in algae. Furthermore, it strongly supports that carrageenan metabolism holds an important role in the physiological differentiation between the isomorphic life cycle stages of Chondrus.

Water-soluble polysaccharides from Pleurotus ostreatus var. florida mycelial biomass

Pleurotus ostreatus var. florida known as Hiratake has a high nutritional value, presents medicinal and nutraceutical properties and it is one of the consumed mushrooms in Brazil. Thus, the aim of this study was to characterize the chemical structure of polysaccharides found in mycelial biomass produced by submerged culture of P. ostreatus var. florida in order to compare with those found in P. ostreatus var. florida fruit bodies. Aqueous and alkali extracts obtained from mycelial biomass were purified, 13C NMR, GC-MS and chemical techniques were used to characterize three polysaccharide structures: a mannogalactan (MG-PfM) with α-D-Galp and 3-O-Me-α-D-Galp units, both (1→6)-linked, highly substituted at O-2 by D-Manp, a glycogen-like polymer (GLY-PfM) with α-D-Glp (1→4)-linked main chain, partially substituted at O-6 by α-D-Glcp side chains and a (1→3), (1→6) β-D-glucan (βGLC-PfM) with a main chain of β-D-Glcp (1→3)-linked units, partially substituted at O-6 by side chains of 6-O-substituted β-D-glucopyranosyl units, on an average of one to every two residues of the backbone. These results show the possibility to obtain similar and also different molecules from those found in the fruiting body of the same mushroom species, therefore the submerged culture of mushroom is a promising way to give raise molecules of interest.

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.

A 3-O-methylated mannogalactan from Pleurotus pulmonarius: structure and antinociceptive effect

A polysaccharide (Mw 2.39x10(4)g/mol) was extracted with cold water from the basidiomycete Pleurotus pulmonarius, and its antinociceptive and anti-inflammatory properties were evaluated. It was a mannogalactan (MG), whose structure was characterized using mono- and two-dimensional NMR spectroscopy, methylation analysis, and a controlled Smith degradation. It had a main chain of (1-->6)-linked alpha-D-galactopyranosyl and 3-O-methyl-alpha-D-galactopyranosyl units, both of which are partially substituted at O-2 by beta-D-mannopyranosyl non-reducing ends. The MG was tested for its effects on the acetic acid-induced writhing reaction in mice, a typical model for inflammatory pain, causing a marked and dose-dependent inhibition of the nociceptive response, with ID50 of 16.2 (14.7-17.7)mg/kg and inhibition of 93+/-3% at a dose of 30mg/kg. An inflammatory response was not inhibited.

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 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.

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.

Unusual structures in the polysaccharides from the red seaweed Pterocladiella capillacea (Gelidiaceae, Gelidiales)

Sequential extraction of tetrasporic Pterocladiella capillacea with water at room temperature and then at 50 degrees C led to the isolation of two products that were each fractionated with cetrimide to give a soluble fraction and a precipitate. The precipitates were then subjected to fractional solubilization in solutions of increasing sodium chloride concentration. The whole treatment yielded two major fractions in each case, one soluble in the cetrimide medium and the other soluble in 0.5 M NaCl, which were further fractionated by anion-exchange chromatography. Structural analysis, carried out by methylation, desulfation-methylation, 13C NMR spectroscopy and determination of the absolute configuration of the 2,6-di-O-methylgalactose units in the permethylated products, indicated the presence of xylogalactans, with low content of 3,6-anhydrogalactose and low molecular weight. These polysaccharides varied in the level of xylopyranosyl and sulfate substitution, primarily on the 6-position of the 3-linked beta-D-galactopyranosyl and on the 3-position of the 4-linked alpha-galactopyranosyl units. Moreover, herein we report, for the first time, the presence of 3-substituted, 4-linked D-galactopyranosyl residues in an alga belonging to the Gelidiales.

Fucoidans from the brown seaweed Adenocystis utricularis: extraction methods, antiviral activity and structural studies

The brown seaweed Adenocystis utricularis (family Adenocystaceae, order Ectocarpales sensu lato) was extracted in parallel with three solvents usually utilized for obtaining fucoidans: distilled water, 2% calcium chloride solution and diluted hydrochloric acid (pH 2) solution. In each case, the extraction was effected at room temperature and then at 70 degrees C. The extraction yields and characteristics of the products were similar in the three cases, with only minor differences. The analytical features of the products indicate that two different types of fucoidans are present in this seaweed. One of them, mostly extracted at room temperature, is composed mainly of L-fucose, D-galactose and ester sulfate (the 'galactofucan'). The other product (the 'uronofucoidan') is the major component of the extracts obtained at 70 degrees C. It is composed mainly of fucose, accompanied by other monosaccharides (mostly Man, but also Glc, Xyl, Rha and Gal), significant amounts of uronic acids and low proportions of sulfate ester. Fractionation with the cationic detergent cetrimide has allowed achieving a better separation of the galactofucan and uronofucoidan components. The galactofucans show a high inhibitory activity against herpes simplex virus 1 and 2, with no cytotoxicity, whereas the uronofucoidans carry no antiviral activity. Structural studies on the galactofucan fractions were carried out by methylation analysis, desulfation and NMR spectroscopy. The fucan constituent is mainly composed of 3-linked alpha-L-fucopyranosyl backbone, mostly sulfated at C-4, and branched at C-2 with non-sulfated fucofuranosyl and fucopyranosyl units, and 2-sulfated fucopyranosyl units. The galactan moiety is more heterogeneous, with predominant D-galactopyranose units linked on C-3 and C-6, and sulfation mostly on C-4, even in terminal non-reducing units. It may be inferred that at least some of these galactose units carry the alpha-configuration.

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.