Two-dimensional 1H-, 13C-, and 31P-nuclear magnetic resonance and molecular-mechanics investigation of D-fructose 2,6-bisphosphate.

Two-dimensional nuclear magnetic resonance studies have been carried out to assign unequivocally all the proton, carbon, and phosphorus resonances of D-fructofuranose 2,6-bisphosphate (1) and to verify its structure using a 400-MHz spectrometer. Several unexpected chemical-shift values and coupling constants were obtained. Molecular mechanics calculations (Sybyl) carried out to minimize the conformational energy of 1 yield phi C-1,P-2 = + 84, phi C-3,P-2 = - 155, and phi C-5,P-6 = + 175. Thus the unusual near-gauche orientations of C-1 and C-3 to P-2 in 1 can explain their small vicinal coupling constants (3JC-1,P-2 = 1.2, and 3JC-3,P-2 = 3.8 Hz), in contrast to the expected larger value seen for 3JC-5,P-6 namely, 6.9 Hz. Treatment of a sample of this compound with sodium borohydride did not affect its nuclear magnetic resonance spectrum, substantiating that O-2 is phosphorylated. Oxidation with sodium periodate yielded an intermediate which decomposed by a beta-elimination mechanism involving the 6-phosphate group. These data establish unequivocally the 1H, 13C, and 31P assignments and explain the observed anomalous shifts. Moreover they indicate that the activator of fructose 6-phosphate 1-kinase is the beta anomer of the 4T3 conformer of D-fructose 2,6-bisphosphate.