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Chemical characterization of the immunomodulating polysaccharide of Aloe vera L.

2005; Elsevier BV; Volume: 340; Issue: 6 Linguagem: Inglês

10.1016/j.carres.2005.02.016

1873-426X

Jimmy T. Chow, David A. Williamson, Kenneth M. Yates, Warren J. Goux,

Natural Compound Pharmacology Studies

The polysaccharide isolated by alcohol precipitation of Aloe vera mucilaginous gel was found to have a Man:Glc:Gal:GalA:Fuc:Ara:Xyl ratio of 120:9:6:3:2:2:1 with traces of Rha and GlcA. Linkage analysis of the endo-(1→4)-β-d-mannanase-treated sample yielded Manp-(1→ (∼26%), 4-Manp (∼53%), 2,4-Manp (∼3%), 3,4-Manp (∼1%), 4,6-Manp (∼1%), 4-Glcp (∼5%), 4-Xylp (∼1%), Xylp-(1→ (∼2%), Galp-(1→ (∼5%), and traces of 4,6-Galp and 3,6-Galp. Hydrolysis with strong acids produced a mixture of short oligosaccharides and an acid-resistant fraction containing greater relative fractions of Manp-(1→, Araf-(1→, Xylp-(1→, and 4-Xylp than the bulk polysaccharide. NMR analysis of oligosaccharides generated by endo-(1→4)-β-d-mannanase and acid hydrolysis showed the presence of di-, tri-, and tetrasaccharides of 4-β-Manp, β-Glcp-(1→4)-Man, β-Glcp-(1→4)-β-Manp-(1→4)-Man, and β-Manp-(1→4)-[α-Galp-(1→6)]-Man, consistent with a backbone containing alternating →4)-β-Manp-(1→ and →4)-β-Glcp-(1→ residues in a ∼15:1 ratio. Analysis of the sample treated sequentially with endo-(1→4)-β-d-mannanase and α-d-galactosidase showed that the majority of α-Galp-(1→ residues were linked to O-2, O-3, or O-6 of →4)-β-Manp-(1→ residues, with ∼16 →4)-β-Manp-(1→ residues between side chains. Our data provide direct evidence of a previously proposed glucomannan backbone, but draw into question previously proposed side-chain structures.