Scheme 1.

Proposed early reactions of R5P (1) with amines stemming from the acyclic form in equilibrium with the furanose. A traditional series of Maillard reactions (path A) leads through an Amadori product (2) to an α-dicarbonyl product (3), while an isomerization series (path B) leading to ribulose 5-phosphate (4) may be encouraged by a general base catalysis (i.e., removal of the C-2 hydrogen) of the amine.