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β-Galactosidase from Aspergillus oryzae, α-galactosidase from Aspergillus niger, β-mannosidase from Helix pomatia and β-glucosidase from almond were used to synthesise different glycosides by reverse hydrolysis: GlcβO(CH2)6OH 1 was obtained in 61% yield, β-D-Glc-O(CH2)3CH-CH2 2 in 50% yield, β-D-Glc-O(CH2)2Si(Me)3 3 in 11% yield, β-D-Gal-O(CH2)6OH 4 in 48% yield, β-D-Gal-O(CH2)3CH-CH2 5 in 22% yield, α-D-Gal-O(CH2)6OH 6 in 47% yield, α-D-GalO(CH2)3CH-CH2 7 in 37% yield and β-D-ManO(CH2)6OH 8 in 12% yield. Using the appropriate glycosides methyl O-(2,3,4,6-tetra-O-benzyl-α-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzoyl-1-O-α-D-galactopyranoside 11 and 6′-benzoylhexyl-O-(2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl)-(1→4)-2,3,6-tri-O-benzoyl-1-O-β-D-galactopyranoside 15 were synthesised. This chemoenzymatic approach avoided at least four chemical steps that would have been necessary in a conventional synthesis. |
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