Showing papers on "Aldose published in 1994"

Enzymatic synthesis of monosaccharide fatty acid esters and their comparison with conventional products

Abstract: 5-O-Acyl-1,2-O-isopropylidene-D-xylofuranose and 6-O-acyl1,2∶3,4-di-O-isopropylidene-D-galactopyranose were enzymatically prepared from the corresponding monosaccharide acetals and commercial (crude) fatty acid mixtures. Subsequent acid-catalyzed hydrolysis of the isopropylidene group(s) gave monosaccharide esters with overall yields of 59–88%, where the monoester content was at least 80% (galactose oleate) and typically 90% for the other preparations. In contrast to sugar fatty acid esters prepared by conventional, high-temperature (trans)esterification, the enzymatically obtained monosaccharide esters contained no appreciable quantities of undersirable side products, and the only contaminants were monosaccharides and fatty acids.

Facile Chemo-Enzymatic Synthesis of Monosaccharide Fatty Acid Esters

Abstract: A range of monosaccharide fatty acid esters was prepared by enzymatic esterification of sugar acetals to provide a series of esters for detailed investigation of their surfactant properties. 6-O-acyl-D-galactopyranoses 2, 6-O-acyl-D-glucopyranoses 4 and 5-O-acyl-D-xylofuranoses 6 were prepared by Mucor miehei lipase catalysed esterification of 1,2:3,4-di-O-isopropylidene-α-D-galactopyranose 1a, 1,2-O-isopropylidene-α-D-glucofuranose 3a and 1,2-O-isopropylidene-α-D-xylofuranose 5a with decanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic acids respectively followed by cleavage of the isopropylidene group(s) of the monosaccharide acetal estes 1b-f, 3b-f and 5b-f.

Inversion of configuration around the seven-coordinated cobalt center induced by an interaction between sugars and tetrahedral oxoanions

Abstract: Carbohydrates have a widespread Occurrence in nature and are indispensable compounds to living organisms.' Naturally rare carbohydrates have also proved to be involved in many glycoproteins, glycolipids, and antibiotics and play important roles in various biological processesS2 Further, in some enzymatic reactions of carbohydrates, alkali, alkaline earth, and some of transition metal ions were suggested to act in cooperation with sugars.3 In this regard, it is very important to investigate the interactions between sugars and metal ions including the stereochemical behavior of sugars in transition metal complexes. We have studied the synthesis and characterization of nickel(I1) and cobalt(II1) complexes containing N-glycosides derived from the reaction of sugars and diamine^.^ Here, we wish to report a synthesis of novel seven-coordinated cage-type cobalt complexes containing N-glycosides from mannose-type aldoses (D-mannose or L-rhamnose (=6-deoxy-~-mannose)) and tris(Zaminoethy1)amine (tren) and an unprecedented inversion of configuration around the metal center induced by an interaction between sugars and tetrahedral oxoanions. A methanolic solution containing D-mannose (D-Man) or L-rhamnose (L-Rha) (4 equiv) and tren (1 equiv) was incubated at 60 OC for 1 h. Then, CoXz.6HzO (X = C1-, B r ) (1 equiv) was added to the solution and the mixture was refluxed for 1 h. The resultant solution was purified on a Sephadex LH-20 gel permeation column. The wine-red major band was collected and concentrated, and an addition of ethanol gave microcrystals of [Co((aldose)3-tren)]Xz.nHzO (la, aldose = D-Man, X = C1-; lb, aldose = L-Rha, X = C1-; 2a, aldose = D-Man, X = B r ; 2b, aldose = L-Rha, X = B r ) , where (aldose)3-tren is tris(N-aldosyl2-aminoeth~l)amine.~ When CoSOcnHzO was used as a metal source, similar complexes formulated as [C~((aldose)~-tren)]S04.nH20 (3a, aldose = D-Man; 3b, aldose = L-Rha) were ~ b t a i n e d . ~ The electronic absorption (AB) spectra of 1-3 in solution showed a characteristic band around 20 X lo3 cm-I, corresponding to d-d transitions of Co(I1) ions. The transmittance spectra (Nujol mull) also showed a similar absorption indicating no significant structural change around the metal on dissolution. In the circular dichroism (CD) spectra, a large Cotton effect was observed at about 20 X 103 cm-l, suggesting the coordination of sugar moieties to the cobalt ion. Further, it should be noted that the sign of the Cotton effect of 1 and 2 containing halide

Convenient Syntheses of 3-Deoxy-D-manno-2-octulosonic Acid (KDO) and 3-Deoxy-D-glycero-D-galacto-2-nonulosonic Acid (KDN) Derivatives from D-Mannose

Abstract: Horner-Wittig reactions of 4-O-benzyl-2,3:5,6-di-O-isopropylidene-D-mannose and 2,3,4,5,6,7-hexa-O-benzyl-6-D-glycero-2,3,4,5-D-galacto-heptose with methyl 2-benzyloxycarbonylamino-2-(diethoxyphosphoryl)acetate gave the corresponding α-dehydroamino acid derivatives in good yields, respectively. They were converted to methyl 3-deoxy-4,5:7,8-di-O-isopropylidene-α-D-manno-2-octulopyranosonate and methyl (methyl 3-deoxy-D-glycero-β-D-galacto-2-nonulopyranosid)onate via methyl α-oxoalkanoate derivatives.

Asymmetric reduction of α-keto acetals with potassium 9-O-(1,2-isopropylidene-5-deoxy-D-xylofuranosyl)-9-boratabicyclo[3.3.1]nonane. Enantioselective synthesis of α-hydroxy acetals with high optical purities

Abstract: Asymmetric reduction of α-keto acetals with a chiral borohydride, potassiun 9-O-(1,2-isopropylidene-5-deoxy-α- D -xylofuranosyl)-9-boratabicyclo[3.3.1]nonane in THF at −78 °C provided the corresponding α-hydroxy acetals with 87 – 99 % ee.