NMR Spectroscopy of Ribose–Borate Complexes Revisited

Ribose–borate complexes play an important role in prebiotic chemistry, yet detailed, systematic structural characterization by NMR spectroscopy particularly of the 2:1 complexes has remained limited. The most widely cited study dates to 1988 by Chapelle and Verchere relying on 80 and 90 MHz magnets. Herein, we present updated structural characterization of ribose–borate complexes using one- and two-dimensional 1H and 13C NMR spectroscopy (performed with a 600 MHz instrument), including assignment of proton and carbon resonances via 1H–1H COSY and 1H–13C HSQC experiments. These assignments were corroborated and supported by density functional theory predictions of NMR chemical shifts. It is demonstrated that the homogeneous 2:1 complexes exist as diastereomeric pairs arising from R and S configurations at the spiro-boron center. In addition, 13C NMR spectroscopy suggests the presence of other heterogeneous 2:1 complexes that have not previously been reported or discussed. These results provide a more comprehensive reference for ribose–borate speciation, supporting future studies particularly in prebiotic chemistry.