Amadori, products ring form

Qualitative and quantitative assessments of equilibrium mixtures of Amadori rearrangement products were performed employing C-NMR spectrometry [64]. Substituents at C-6, C-4 and C-6 showed considerable influence on the equilibrium the 4,6-0-benzylidene derivative, for example, was found to be in the open-chain form only, because ring closure of 0-5 with the carbonyl function was energetically and sterically hindered. The conformation of compounds substituted at C-6 depended on the electron-withdrawing effect of the substituent. The lower the electron density at position C-5, the lower is the tendency of ring closure, so that the equilibrium is found on the side of the open-chain form. 

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