1H-Tetrazole as Catalyst in Phosphomorpholidate Coupling Reactions:  Efficient Synthesis of GDP-Fucose, GDP-Mannose, and UDP-Galactose

An improved procedure is described for the efficient and high-yield (76-91%) synthesis of nucleoside diphosphate sugars from the readily available nucleoside 5'-monophosphomorpholidate and sugar 1-phosphate in the presence of 1H-tetrazole. Comparative kinetic investigations by means of (31)P NMR spectroscopy with different additives (1,2,4-triazole, acetic acid, N-hydroxysuccinimide, 4-(dimethylamino)pyridine hydrochloride, perchloric acid) and mass spectrometric analysis suggest that tetrazole acts as an acid and as a nucleophilic catalyst in the pyrophosphate bond formation.