RETRO-ALDOL AND REDOX REACTIONS OF AMADORI COMPOUNDS - MECHANISTIC STUDIES WITH VARIOUSLY LABELED D-[C-13]GLUCOSE

Oxidation-reduction reactions necessary to justify many of the product s observed in Maillard model systems are usually attributed to molecul ar oxygen and the so-called reductons. The proline specific 1-(1'-pyrr olidinyl)-2-propanone and 1-(1'-pyrrolidinyl)-2-butanone are such comp ounds that require reduction steps to justify their formation. Experim ental evidence using glucose separately labeled at (13)C1, (13)C2, (13 )C3, (13)C4, (13)C5,,and (13)C6 indicates that 1-(1'-pyrrolidinyl)-2-p ropanone 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-ald ol reaction at C2-C3 of the 1-(prolino)-1-deoxy-4-hexosulose (an isome r of Amadori product formed by carbonyl migration) and two others by s imilar 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 target compounds. Mo del studies have indicated that reductions in Maillard systems can be effected by three pathways: through hydride transfer from formic acid; through cyclic dimerization of alpha-hydroxy carbonyl compounds follo wed by electrocyclic ring opening to produce oxidation/reduction produ cts; and by disproportionation of enediols with alpha-dicarbonyl compo unds through double proton transfer.