Biol. Pharm. Bull. 28(2) 344—348 (2005)

proteins in the body, resulting from the reaction of glucose with amino groups on proteins. The first stable adducts formed during glycation are Amadori compounds. The adducts undergo dehydration and oxidative fragmentations to yield heterogenous compounds collectively referred to as advanced glycation end-products (AGEs). Glycation is thought to contribute to the development of pathologies associated with diabetes, atherosclerosis, chronic renal failure, and neurodegenerative diseases because the formation of chemically stable AGEs can alter protein structure and function. Amadori compounds are considered to be key intermediates in glycation and precursors of various reactive intermediates such as dicarbonyl and lower molecular weight sugars, which are more reactive with protein than glucose. However, much of the evidence on the degradation of Amadori compounds and formation of intermediates is based on studies conducted at high temperature, high and low pH, and in nonaqueous systems. In addition, there is insufficient information on the kinetics and products of the decomposition of sugar moieties of Amadori compounds because of the lack of suitable analytical techniques. The usefulness of the stable isotope tracer technique using C labeling of substrates and NMR spectroscopy has become accepted in metabolic investigations including degradation pathways of metabolites. Owing to the high specificity of detection, the application of the tracer technique enables analysis of biofluids and reaction mixtures without resorting to extraction and chromatographic separations. Therefore the decomposition and loss of compounds under sample purification and separation procedures can be minimized. In addition, all products arising from a labeled substrate can be detected if they contain the labeled carbon and the detection sensitivity of NMR is sufficient. This technique is thus expected to provide information that is inaccessible by other methods and considered to be suitable for the investigation of complicated degradation pathways of Amadori compounds. Thus, in this study, a C-labeled model Amadori compound, [1-13C]Ne-(1-deoxy-D-fructos-1yl)hippuryl-lysine, was synthesized and degradation mixtures of the labeled compound under aerobic conditions analyzed using C-NMR spectroscopy to investigate the potential of the C-labeling and NMR approach.