- Method of preparing lacitol monohydrate and dihydrate
-
The invention relates to the new product lactitol monohydrate and to a method for the production of crystalline lactitol. The crystalline lactitol monohydrate can be obtained bij seeding an aqueous lactitol solution of a special concentration under special conditions causing the lactitol monohydrate to crystallize and recovering the product. From the mother liquor a further amount of lactitol dihydrate can be recovered. Crystalline lactitol dihydrate can be obtained using different special conditions. Lactitolmonohydrate can further be obtained by mixing one part bij weight of an aqueous lactitol solution of a suited concentration with 1 tot 3 parts bij weight of methanol or ethanol and cooling the mixture to 15° tot 25° C.
- -
-
-
- Sequential removal of monosaccharides from the reducing end of oligosaccharides and uses thereof
-
Methods are provided for the sequential removal of monosaccharides from the reducing end of oligosaccharides. The present invention also discloses the use of such methods for structural determinations of oligosaccharides and to enable new structures to be generated from pre-existing oligosaccharides. In addition, the methods of the present invention may be automated by the incorporation into systems.
- -
-
-
- Hydrolysis of Substrate Analogues Catalysed by β-D-Glucosidase from Aspergillus niger. Part III. Alkyl and Aryl β-D-Glucopyranosides
-
The hydrolysis of eighteen alkyl and aryl β-D-glucopyranosides and the disaccharides methyl β-cellobioside (reference substrate), cellobitol, methyl β-gentiobioside, and methyl α-C-gentiobioside catalysed by β-D-glucosidase from Aspergillus niger has been studied using 1H NMR spectroscopy and progress-curve enzyme kinetics in both single-substrate and competition experiments.The influence of chain length and stereochemistry of alkyl groups and substitutions of phenyl groups revealed that this enzyme has evolved preferentially to hydrolyse cellobiose despite low aglycone specificity.The implications of steric and polar or non-polar effects, which were shown to be important for the active site interactions on the energetics of the enzymatic activity as inferred from the kinetic experiments, are discussed.
- Sigurskjold, Bent W.,Haunstrup, Ib,Bock, Klaus
-
p. 451 - 458
(2007/10/02)
-
- SYNTHESIS OF A CLOSE ANALOG OF THE REPEATING UNIT OF THE ANTIFREEZE GLYCOPROTEINS OF POLAR FISH
-
The protected glycopeptide N-(benzyloxycarbonyl)-L-alanyl-3)-O-(2,4,6-tri-O-benzyl-α-D-galactopyranosyl)-(1->3)>-L-threonyl-L-alanine 2,2,2-trichloroethyl ester (21) was made by coupling the respective disaccharide and tripeptide blocks.The disaccharide block was generated by coupling tetra-O-benzoyl-α-D-galactopyranosyl bromide to allyl 2,4,6-tri-O-benzyl-α-D-galactopyranoside and converting the product into O-(2,3,4,6-tetra-O-benzoyl-β-D-galactopyranosyl)-(1->3)-2,4,6-tri-O-benzyl-α-D-galactopyranosyl chloride (6) via the 1-propenyl glycoside and the free (1-OH) sugar.Alternatively, the 1-propenyl intermediate was obtained directly by using 1-propenyl 2,4,6-tri-O-benzyl-α-D-galactopyranoside (10) as the acceptor in the initial coupling reaction.An efficient 3-step synthesis of 10 was accomplished by the dibutyltin oxide-assisted, selective crotylation of allyl α-D-galactopyranoside at O-3, followed by benzylation and treatment of the product with potassium tert-butoxide.The N-benzyloxycarbonyl (Z) and N-tert-butoxycarbonyl (Boc) 2,2,2-trichloroethyl esters of Thr-Ala and Ala-Thr-Ala were formed by sequential coupling.The silver triflate-promoted glycosylation of the Z-protected dipeptide and tripeptide by 2,3,4,6-tetra-O-benzyl-α-D-galactopyranosyl chloride, and of the tripeptide by 6, proceeded with excellent α-stereoselectivity.From the disaccharide tripeptide 21, the carboxyl-deprotected and fully deproptected derivatives were prepared.
- Anisuzzaman, Abul Kashem M.,Anderson, Laurens,Navia, Juan L.
-
p. 265 - 278
(2007/10/02)
-
- The assembly of oligosaccharides from "standardized intermediates": beta-(1----3)-linked oligomers of D-galactose.
-
Several 2-O-benzoyl-4,6-di-O-benzyl-3-O-R-alpha-D-galactopyranosyl chlorides, designed as general precursors of beta-linked, interior D-galactopyranosyl residues in oligosaccharides, were tested in a sequential synthesis of the galactotriose beta-D-Galp-(1----3)-beta-D-Galp-(1----3)-D-Gal (19). The chlorides having R = tetrahydro-2-pyranyl and tert-butyldimethylsilyl gave excellent results, whereas those having R = 3-benzoylpropionyl and chloroacetyl were unsatisfactory. An activated disaccharide block (17), having R = 2,3-di-O-benzoyl-4,6-di-O-benzyl-beta-D-galactopyranosyl, was also prepared and tested as a glycosyl donor. The coupling of 17 to 1-propenyl 2-O-benzoyl-4,6-di-O-benzyl-alpha-D-galactopyranoside (14), in the molar ratio 1.13:1, gave 64% of a trisaccharide derivative (18) that could be converted into 19. This latter synthesis of 19 is efficient because all three galactose units are derived from 14 or its immediate precursor.
- Chowdhary,Navia,Anderson
-
p. 173 - 185
(2007/10/02)
-
