Combined ¹H, ¹³C and ¹¹B NMR and mass spectral assignments of boronate complexes of D-(+)-glucose, D-(+)-mannose, methyl-α-D-glucopyranoside, methyl-β-D-galactopyranoside and methyl-α-D-mannopyranoside

Complex formation between N-butylboronic acid and D-(+)-glucose, D-(+)-mannose, methyl-α-D-glucopyranoside, methyl-β-D- galactopyranoside and methyl α-D-mannopyranoside under neutral conditions was investigated by ¹H, ¹³C and ¹¹B NMR spectroscopy and gas chromatography-mass spectrometry (GC-MS) D-(+)-Glucose and D-(+)-mannose formed complexes where the boronates are attached to the 1,2:4,6- and 2,3:5,6-positions of the furanose forms, respectively. On the other hand, the boronic acid binds to the 4,6-positions of the two methyl derivatives of glucose and galactose. Methyl α-D-mannopyranoside binds two boronates at the 2,3:4,6-positions. ¹¹B NMR was used to show the ring size of the complexed sugars and the boronate. GC-MS confirmed the assignments.