RESUMO
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.
Assuntos
Galactanos/química , Rodófitas/química , Ressonância Magnética Nuclear Biomolecular , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
Sulfated xylomannans were isolated from two species of genus Chondrophycus by aqueous extraction followed by KCl fractionation. Structural determination of the native, desulfated and Smith-degraded KCl-precipitated polysaccharides carried out by composition and methylation analysis and NMR spectroscopy (1D and 2D experiments) showed the following general structure: [see text] These xylomannans present different degrees of branching (15-25%) by beta-D-Xylp (70-80%) and beta-D-Manp-2-S (20-30%) and molecular weights (33-222kDa). This is the first report of the presence of a sulfated xylomannan in species of order Ceramiales.
Assuntos
Polissacarídeos/química , Polissacarídeos/isolamento & purificação , Rodófitas/química , Sulfatos/química , Brasil , Sequência de Carboidratos , Fracionamento Químico , Cromatografia em Gel , Espectroscopia de Ressonância Magnética , Metilação , Dados de Sequência Molecular , Monossacarídeos/análise , Óptica e FotônicaRESUMO
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.
Assuntos
Galactanos/química , Galactanos/isolamento & purificação , Hidróxidos/química , Rodófitas/química , Cromatografia por Troca Iônica , Ciclização , Cinética , Metilação , Ressonância Magnética Nuclear Biomolecular , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
This study presents the chemical composition and antiviral activity against herpes simplex virus type 1 (HSV-1) and 2 (HSV-2) of sulfated galactan crude extracts and main fractions obtained from two red seaweeds collected in Brazil, Gymnogongrus griffithsiae and Cryptonemia crenulata. Most of the eighteen tested products, including homogeneous kappa/iota/nu carrageenan and DL-galactan hybrid, exhibited antiherpetic activity with inhibitory concentration 50% (IC50) values in the range 0.5-5.6 microg/ml, as determined in a virus plaque reduction assay in Vero cells. The galactans lacked cytotoxic effects and showed a broad spectrum of antiviral activity against HSV-1 and HSV-2. No direct virus inactivation was observed after virion treatment with the galactans. The mode of action of these compounds could be mainly ascribed to an inhibitory effect on virus adsorption. Most importantly, a significant protection against a murine vaginal infection with HSV-2 was afforded by topical treatment with the sulfated galactans.