NONENZYMATIC MODIFICATIONS OF AMINO-SUGARS INVITRO

Browning reactions of amino sugars were observed in a variety of sterile pH buffers at 25-37 °C. These reactions were signaled by an increase in absorbance at 273 nm, followed by an increase in absorbance at 320-360 nm. The reactions were maximal at pH 7.0 in phosphate buffer. Acidic solutions (pH < 2.2) of 50 mmd-glucosamine hydrochloride gave only a negligible reaction and 2-acetamido-2-deoxy-d-glucose was unreactive. Half of the d-glucosamine in a 100 mm solution in sterile 0.2 m sodium phosphate buffer, pH 7.4, at 37 °C decomposed or was transformed in 27 h. A comparison of reactivity in generating A273 and A340 chromophores showed d-mannosamine > d-galactosamine > d-glucosamine. Permanganate oxidation of incubated glucosamine solutions afforded a compound which chromatographed like 2,5-pyrazinedicarboxylic acid and gave the same ultraviolet absorption spectrum. This, together with fractionation and thin-layer chromatography of the products of glucosamine incubation, suggests that 2,5-bis(tetrahydroxybutyl)pyrazine is formed as one of the products of autocondensation of d-glucosamine in accord with the report of Candiano et al. (1988, Carbohydr. Res. 184, 67-75) on products formed in glucosamine-lysine incubation mixtures. Formation of products absorbing at 325-360 nm was inhibited by the chelator diethylenetriaminepentaacetic acid. This suggests that the later reactions may be mediated by a metal-stimulated free radical mechanism. After 4 days incubation high molecular weight products with absorbance maxima at 273 nm and 325-360 nm were detected. Some of these were retained by dialysis membranes of molecular weight cut-off > 3500 and > 12,000. © 1991.