Nuclear magnetic resonance studies of d-erythrose 4-phosphate in aqueous solution. Structures of the major contributing monomeric and dimeric forms

Abstract

N.m.r. studies show that a concentrated (∼ 1.0 M) aqueous solution of d-erythrose 4-phosphate is composed of an equilibrium mixture of the monomeric aldehyde and hydrated aldehyde forms, which interconvert rapidly, together with a major contribution from three dimeric forms. In dilute solutions (∼0.04 M), the hydrated monomer is predominant and dimeric forms are not detectable at this concentration. The chemical structures and stereochemistry of the three dimers have been elucidated by 1H- and 13C-n.m.r. spectroscopy of d-erythrose 4-phosphate and its (4,4- 2H 2) and (3,4,4′- 2H 3) derivatives, aided by the use of the model compounds, glycolaldehyde, d-glyceraldehyde, and dL-glyceraldehyde 3-phosphate, which also form dimers in concentrated aqueous solution. In some cases, the tert-butyldimethylsilyl derivatives of the model dimeric compounds were prepared and isolated. The two major dimers of d-erythrose 4-phosphate, I and II, are asymmetrically substituted 1,3-dioxane and 1,3-dioxolane structures, respectively, and dimer III is the α anomer of dimer I.