Amides Are Novel Protein Modifications Formed by Physiological Sugars

Abstract

The Maillard reaction, or nonenzymatic browning, proceeds in vivo, and the resulting protein modifications (advanced glycation end products) have been associated with various pathologies. Despite intensive research only very few structures have been established in vivo. We report here for the first time N 6 -{2-[(5-amino-5-carboxypentyl)amino]-2-oxoethyl}lysine (GOLA) and N 6 -glycoloyllysine (GALA) as prototypes for novel amide protein modifications produced by reducing sugars. Their identity was confirmed by independent synthesis and coupled liquid chromatography/mass spectrometry. Model reactions with N ␣ -t-butoxycarbonyl-lysine showed that glyoxal and glycolaldehyde are immediate precursors, and reaction pathways are directly linked to N ⑀ -carboxymethyllysine via glyoxal-imine structures. GOLA, the amide cross-link, and 1,3-bis(5-amino-5-carboxypentyl)imidazolium salt (GOLD), the imidazolium cross-link, share a common intermediate. The ratio of GOLA to GOLD is greater when glyoxal levels are low at constant lysine concentrations. GOLA and GALA formation from the Amadori product of glucose and lysine depends directly upon oxidation. With the advanced glycation end product inhibitors aminoguanidine and pyridoxamine we were able to dissect oxidative fragmentation of the Amadori product as a second mechanism of GOLA formation exactly coinciding with N ⑀ -carboxymethyllysine synthesis. In contrast, the formation of GALA appears to depend solely upon glyoxal-imines. After enzymatic hydrolysis GOLA was found at 66 pmol/mg of brunescent lens protein. This suggests amide protein modifications as important markers of pathophysiological processes.

Conversion of Arginine into Ornithine by Advanced Glycation in Senescent Human Collagen and Lens Crystallins

“…The strongest argument against covalent incorporation of ornithine as an explanation for our findings is that ornithine would have to be chemically bound via an N-␣-amino group in order to leave the ␦-amino group free for derivatization into DMO and yet allow intact release upon acid hydrolysis. Whereas sugar amide bonds have been described (23), this type of linkage is yet unheard of.…”

Silica chloride catalyzed efficient route to novel 1-amidoalkyl-2-naphthylamines under sonic condition in water

“…Only silica gel could not catalyze this reaction (Table 1, entry 2). Some other catalysts such as Amberlyst-120, Dowex-50 and acidic alumina were employed and were found to catalyze this reaction with moderate yields (Table 1, entries [3][4][5]. The best result was obtained when silica chloride was used, which is evident from the yield and the reaction duration (Table 1, entry 8).…”

“…The amide group is an essential building block for numerous natural products, synthetic pharmaceuticals, and a wide variety of biologically active compounds [5]. As a consequence; the development of general methods for the synthesis of amide derivatives has been the subject of considerable synthetic efforts and still requires attention.…”

Therapeutic Modalities in Diabetic Nephropathy: Standard and Emerging Approaches

“…AGEs are excreted by the kidneys and tend to increase in the setting of renal impairment. 202 Receptors for AGE (RAGE) specifically recognize proteins that bound AGE, and enable macrophages to stimulate the removal and replacement of senescent macromolecules that have been cross-linked and denatured by long-term exposure to glucose. 203 This AGE-RAGE interaction may play a role in the pathologic process associated with the AGE accumulation.…”