2,5-Anhydrides of Sugars and Related Compounds

Stereospecific synthesis of (+)-oxybiotin from D-xylose

A new 14-step synthesis of (+)-oxybiotin, an oxygen analogue of (+)-biotin, was achieved starting from D-xylose by use of selected 2,5-anhydro sugar derivatives as key intermediates.

Synthesis of L-arabinitol and xylitol monomers for the preparation of polyamides. Preparation of an L-arabinitol-based polyamide

Dihydrochlorides of 1,5-diamino-1,5-dideoxy-2,3,4-tri-O-methyl-L-arabinitol (and xylitol) and pentachlorophenyl esters of 2,3,4-tri-O-methyl-L-arabinaric (and xylaric) acids have been prepared as suitable bifunctional monomers for linear polycondensations. A new aregic AABB-type L-arabinitol-based polyamide is also described from the corresponding monomers. It was crystalline with T(m) 250 degrees C, optically active, and soluble in the usual organic solvents, including chloroform, and in water. Its M(w) obtained by GPC was 27,500 with a polydispersity of 1.4.

An easy stereospecific synthesis of 1-amino-2,5-anhydro-1-deoxy-D-mannitol and arylamino derivatives

1-Amino-2,5-anhydro-1-deoxy-D-mannitol and a series of arylamino derivatives were prepared by nitrous acid deamination of 2-amino-2-deoxy-D-glucose and subsequent reductive amination of the resulting 2,5-anhydro-D-mannose. Some of these compounds showed an enhanced affinity for the hexose transporter of Trypanosoma brucei as compared to D-fructose.

Molecular weight manipulation of chitosan. I: Kinetics of depolymerization by nitrous acid

The kinetics of the depolymerization of chitosan in dilute aqueous HCl solutions by nitrous acid were studied. The rate of depolymerization is independent of the molecular weight of chitosan, first order with respect to the concentrations of both nitrous acid and glucosamine moieties, not catalysed by either hydrogen or chloride ions, and Arrhenius temperature dependent. Chitosan exhibits significantly decreased reactivity as the degree of deacetylation of the polymer increases. These results are consistent with a depolymerization reaction mechanism in which the rate-limiting step is nitrosation of the unprotonated amine by nitrous acidium ion.

A facile formation of 2,5-anhydro sugars by ring contraction in methyl hexopyranoside 2-triflates under conditions of nucleophilic displacement

Reaction of methyl 3,4-O-isopropylidene-2-O-(trifluoromethylsulfonyl)-alpha-L-fucopyr anoside and its beta anomer with a variety of nucleophilic reagents under mild conditions led to displacement of the triflic ester group, with migration of the ring-oxygen atom to C-2 and entry of the nucleophile at C-1, to give good yields of 2,5-anhydro sugar derivatives. Reagents employed were hydrogen fluoride-triethylamine complex, methanol in the presence of sodium hydrogencarbonate, sodium benzoate, sodium azide, potassium thiocyanate, and sodium borohydride. The same type of substitutive ring-contraction also occurred in methyl 4-O-benzyl-3-O-(4-methoxybenzyl)-2-O-(trifluoromethylsulfonyl)-alp ha-L- fucopyranoside and methyl 4,6-dideoxy-3-O-(4-methoxybenzyl)-2-O-(trifluoromethylsulfonyl)-al pha-L-xylo- hexopyranoside. The reaction is discussed in light of a literature survey of the chemical behavior of hexopyranoside 2-sulfonates in general, and 2-triflates in particular. Direct SN2 displacements, eliminations, and such different kinds of rearrangement as have previously been observed with structural analogs were not encountered in the present study. However, there is some precedent, in hexopyranoside 2-triflates, for the facile rearrangement that the four representatives here investigated have been found to undergo. The synthesis of these triflates from L-fucose is described.

Detection of neutral and aminosugars from glycoproteins and polysaccharides as their alditol acetates

A new method for the preparation and separation of alditol acetates from neutral sugars has been applied to aminosugars. Reduced aminosugars were rapidly acetylated using 1-methylimidazole as the catalyst without removal of borate formed during reduction. The alditol acetates were separated by glass capillary gas chromatography on Silar 10C. The alditol acetates of aminosugars had retention times much longer than those of neutral sugars. However, the alditol acetates of the deamination products of aminosugars had shorter retention times and were resolved from those of neutral sugars. This method was used for the simultaneous detection of neutral and aminosugars in acid hydrolysates of chitin and the glycoproteins, ovalbumin and peroxidase.

A specific method for D-galactose quantitative determination: a modification of the D-galactose oxidase assay

After treatment with D-galactose oxidase to form an aldehyde group, D-galactose or 2-acetamido-2-deoxy-D-galactose reacted with indole-hydrochloric acid to give a colored compound having a spectrum very similar to that of D-galacturonic acid, but with a maximum at 500 nm and a shoulder at 480 nm. The reaction is linear between 16.6 and 83 nmol of sugar per mL of final solution. 2-Amino-2-deoxy-D-galactose gave no reaction, even when 5 mumol were used, and 2-deoxy-D-lyxo-hexose did not interfere either.