Vinylogous Amadori rearrangement: implications in food and biological systems.

The 4-hydroxy-alkenals are important lipid peroxidation products and are known to play a major role both in the development of degenerative diseases in biological systems and off-flavors, or rancidity in food systems. The 4-hydroxy-alkenals can also be formed in nonlipid systems from 2-deoxy-sugar moieties such as 2-deoxy-ribose. FTIR spectroscopic evidence was provided for such a transformation catalyzed by amino acids through monitoring the decrease in intensity of the aldehydic band centered at 1716 cm(-1) of the open form of 2-deoxy-ribose and increase in the intensity of the formed conjugated aldehydic band centered at 1672 cm(-1). Furthermore, 4-hydroxy-alkenals can react with nitrogen nucleophiles such as amino acids and proteins to form Schiff base adducts that are able to undergo vinylogous Amadori rearrangement (vARP) and subsequently cyclize to generate a pyrrole moiety. This cyclization is prevented in the case of secondary amino acids such as proline to form a stable vinylogous Amadori rearrangement product (vARP). Monitoring this reaction of proline with 4-hydroxy-2-nonenal (HNE) has indicated that within 15 min at 28 degrees C the 1685 cm(-1) band of HNE completely disappears and that at 50 degrees C, vARP is formed within 5 min, as indicated by the formation of a characteristic band at 1709 cm(-1).