Retro-Aldol and Redox Reactions of Amadori Compounds: Mechanistic Studies with Variously Labeled d-[13C]Glucose

Abstract

Oxidation−reduction reactions necessary to justify many of the products observed in Maillard model systems are usually attributed to molecular oxygen and the so-called reductons. The proline specific 1-(1‘-pyrrolidinyl)-2-propanone and 1-(1‘-pyrrolidinyl)-2-butanone are such compounds that require reduction steps to justify their formation. Experimental evidence using glucose separately labeled at 13C1, 13C2, 13C3, 13C4, 13C5, and 13C6 indicates that 1-(1‘-pyrrolidinyl)-2-propanone is formed by two related pathways, initiated by a retro-aldol cleavage of proline Amadori compound at C3−C4, and 1-(1‘-pyrrolidinyl)-2-butanone is formed by three pathways, one initiated by a retro-aldol reaction at C2−C3 of the 1-(prolino)-1-deoxy-4-hexosulose (an isomer of Amadori product formed by carbonyl migration) and two others by similar retro-aldol reactions at C4−C5 from both 3-deoxyglucosone and 1-(prolino)-1,4-dideoxy-2,3-hexodiulose. All of the proposed mechanisms require reduction steps for the formation of the ta...