- Synthesis of raffinose family oligosaccharides by regioselective de-O-benzylation with Co2(CO)8/Et3SiH/CO system
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A convenient approach for synthesis of raffinose, stachyose, and verbascose using sucrose as the starting material is presented. The key step is the regioselective de-O-benzylation with Co2(CO)8/Et 3SiH/CO system, followed by a high α-selective glycosylation. The newly developed de-O-benzylation system is efficient in removing the primary benzyl groups of sucrose and raffinose under mild condition and with high selectivity. Using thioglycoside as donor, NIS/AgOTf as promoter and DTBMP as additive, glycosylation of acid labile sucrose substrate is achieved in high yield.
- Zhao, Yue-Tao,Niu, Shan,Huang, Lu-Bai,Wang, Ji-Ming,Yin, Zhao-Jun,Li, Qing,Li, Zhong-Jun
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p. 5022 - 5028
(2013/06/27)
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- Aspergillus nidulans α-galactosidase of glycoside hydrolase family 36 catalyses the formation of α-galacto-oligosaccharides by transglycosylation
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The α-galactosidase from Aspergillus nidulans (AglC) belongs to a phylogenetic cluster containing eukaryotic α-galactosidases and -galacto-oligosaccharide synthases of glycoside hydrolase family 36 (GH36). The recombinant AglC, produced in high yield (0.65 g·L-1 culture) as His-tag fusion in Escherichia coli, catalysed efficient transglycosylation with α-(1→6) regioselectivity from 40 mm 4-nitrophenol -d-galactopyranoside, melibiose or raffinose, resulting in a 37-74% yield of 4-nitrophenol α-d-Galp-(1→6) α-d-Galp, α-d-Galp- (1→6) α- d-Galp-(1→6) α-d-Glcp and α-d-Galp- (1→6) α- d-Galp-(1→6) α-d-Glcp-(1→2) α-d-Fruf (stachyose), respectively. Furthermore, among 10 monosaccharide acceptor candidates (400 mm) and the donor 4-nitrophenol -d-galactopyranoside (40 mm), -(1→6) linked galactodisaccharides were also obtained with galactose, glucose and mannose in high yields of 39-58%. AglC did not transglycosylate monosaccharides without the 6-hydroxymethyl group, i.e. xylose, l-arabinose, l-fucose and l-rhamnose, or with axial 3-OH, i.e. gulose, allose, altrose and l-rhamnose. Structural modelling using Thermotoga maritima GH36 -galactosidase as the template and superimposition of melibiose from the complex with human GH27 α-galactosidase supported that recognition at subsite +1 in AglC presumably requires a hydrogen bond between 3-OH and Trp358 and a hydrophobic environment around the C-6 hydroxymethyl group. In addition, successful transglycosylation of eight of 10 disaccharides (400 mm), except xylobiose and arabinobiose, indicated broad specificity for interaction with the +2 subsite. AglC thus transferred -galactosyl to 6-OH of the terminal residue in the -linked melibiose, maltose, trehalose, sucrose and turanose in 6-46% yield and the -linked lactose, lactulose and cellobiose in 28-38% yield. The product structures were identified using NMR and ESI-MS and five of the 13 identified products were novel, i.e. α-d-Galp-(1→6) α-d-Manp; α-d-Galp-(1→6) α- d-Glcp-(1→4) α-d-Glcp; α-d-Galp-(1→6) α- d-Galp-(1→4) α-d-Fruf; α-d-Galp-(1→6) α-d-Glcp-(1→1) α-d-Glcp; and α-d-Galp-(1→6) α- d-Glcp-(1→3) α-d-Fruf.
- Nakai, Hiroyuki,Baumann, Martin J.,Petersen, Bent O.,Westphal, Yvonne,Hachem, Maher Abou,Dilokpimol, Adiphol,Duus, Jens .,Schols, Henk A.,Svensson, Birte
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experimental part
p. 3538 - 3551
(2011/11/05)
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- Isolation and Identification of Oligosaccharides Produced from Raffinose by Transgalactosylation Reaction of Thermostable α-Galactosidase from Pycnoporus cinnabarinus
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The thermostable α-galactosidase purified from Pycnoporus cinnabarinus catalyzed the galactosyltransfer reaction in the hydrolysis of raffinose and produced several kinds of transfer products.The main transfer products were isolated and the stuctures of the six kinds of transfer products (oligosaccharides A, B, C, D, E, and F) were investigated by acid and enzymatic hydrolysis, and methylation analysis.Oligosaccharides A, B, C, D, E, and F were identified as O-α-D-galactopyranosyl-(1->3)-O-α-D-glucopyranosyl-(1->2)-β-D-fructofuranoside, O-α-D-galactopyranosyl-(1->3)-O-α-D-galactopyranosyl-(1->6)-O-α-D-glucopyranosyl-(1->2)-β-D- fructofuranoside, stachyose, O-α-D-galactopyranosyl-(1->3)-O-α-D-galactopyranosyl-(1->6)-O-α-D-galactopyranosyl-(1->6)-O-α-D-glucopyranosyl-(1->2)-β-D-fructofuranoside, verbascose, and ajugose, respectively.
- Mitsutomi, Masaru,Ohtakara, Akira
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p. 2305 - 2312
(2007/10/02)
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