Cleavage of the (1 goes to 3)-2-acetamido-2-deoxy-beta-D-glucopyranosyl linkage present in keratan sulfate. The A and B isoenzymes of human liver hexosaminidase (EC 3.2.1.30)

The disaccharide 2-acetamido-2-deoxy-beta-D-glucopyranosyl-(1 goes to 3)-D-[1-3H]-galactitol, prepared from keratan sulfate, was rapidly hydrolyzed by the A and B isoenzymes of normal human liver hexosaminidase (EC 3.2.1.30), and by the B isoenzyme prepared from the liver of a patient who had died of Tay-Sachs disease. The disaccharide substrate was also hydrolyzed by extracts of normal, cultured-skin fibroblasts, and fibroblasts of patients with Tay-Sachs disease, whereas it was not hydrolyzed by fibroblast extracts of patients with Sandhoff disease. Thus, effective degradation of keratan sulfate, secondary to a defect of the beta subunits present in the A and B isoenzymes of hexosaminidase, may contribute to the appearance of skeletal lesions in patients affected by Sandhoff disease.     

The dependence of the conformation of a (1→3)-β-D-glucan on chain-length in alkaline solution

(1→3)-β-D-Glucans of various degrees of polymerization were prepared by degradation of a gel-forming D-glucan with formic acid. The degraded D-glucans were separated into a water-soluble fraction (soluble D-glucan) and an insoluble fraction (insoluble D-glucan). Both D-glucans were further fractionated. The optical rotation including determination of the o.r.d. curves of the fractions and of the original gel-forming D-glucans was measured at various sodium hydroxide concentrations (0–5M). The results indicate that (1→3)-β-D-glucans of $\text{DP}$n below ca. 25 (the soluble D-glucan) took a disordered form in both neutral and alkaline solutions, whereas the D-glucans of higher $\text{DP}$n (the insoluble and the original D-glucans) took an ordered structure in dilute alkaline solution (0.1M). The proportion of ordered structure in the insoluble D-glucan increases with $\text{DP}$n to attain a maximum value at a $\text{DP}$n of around 200; this may be the lower limit of $\text{DP}$n to permit gel formation in neutral media. The formation of complexes with Congo Red in alkaline solutions by the soluble and the insoluble D-glucans supports the same conclusions.     

Dehydrative ring-closure of 3-substituted 2-quinoxalinones to give fused and nonfused pyrazoloquinoxalines

Reaction of l-ascorbic acid with o-phenylenediamine and arylhydrazines afforded 3-(1-arylhydrazono-l-threo-2,3,4-trihydroxybutyl)-2-quinoxalinones (1–6). Whereas compounds 1–6 reacted with alkali to give 1-aryl-3-(l-threo-glycerol-1-yl)-flavazoles, the corresponding acetates (7) underwent deacetylation and rearrangement to 3-[1-aryl-5-(hydroxymethyl)pyrazol-3-yl]-2-quinoxalinones (20–24). Compounds 20–24 were also prepared from 1–5 by treatment with hot hydroxylamine hydrochloride. The action of boiling acetic anhydride on 1–5 or 7 afforded colorless products identified as the pyrazole acetates (15–19), which could also be obtained by the acetylation of compounds 20–24. Deacetylation of 15 gave 20. Oxidation of 20 with potassium permanganate gave the 5-carboxylic acid 26. The i.r., n.m.r., and mass spectra of some of these compounds are discussed.     

The synthesis ofP1-[2-acetamido-2-deoxy-3-O-(β-D-glucopyranosyluronic acid)-α-D-glucopyranosyl] P2-dolichyl diphosphate (N-acetylhyalobiosyluronic dolichyl diphosphate)

Starting from 2-acetamido-4,6-di-O-acetyl-2-deoxy-3-O-(methyl 2,3,4-tri-O-acetyl-β-D-glucopyranosyluronate)-α-D-glucopyranose (20), a crystalline intermediate prepared by a conventional sequence of reactions, the total synthesis of N-acetyl-hyalobiosyluronic dolichyl diphosphate was achieved. One of the key steps involved the transformation of the disaccharide 20 into the methyloxazoline 26, which was then converted into the stable, crystalline disaccharide phosphate derivative in ～30% yield. The methyloxazoline 26 was directly prepared from the corresponding methyl α-glycoside by acetolysis. Similarly, the allyl α-glycoside was transformed into 26.