Synthesis of Some Pyridoxine and Pyridoxal Halophosphonates

A new series of pyridoxine and pyridoxal chloro and fluorophosphonates have been synthesized. Partially protected pyridoxine 1, 2 or pyridoxal 4 reacted with methyl phosphonic dichloride in the presence of triethylamine at -10 °C. Thus, the following chlorophosphonate derivatives were obtained: 3,4\u27-0-isopropylidenepyridoxine-5\u27-0- methylchlorophosphonate (5), 4\u27,5\u27-0-isobutylidenepyridoxine-3-0- methylchlorophosphonate (6), and monoethylacetalpyridoxal-3-0- methylchlorophosphonate (7). Similarly, from adequate starting compounds 1,3 and unprotected pyridoxal (PL) in the reaction with methyl phosphonic difluoride and triethylamine, near O"C, the corresponding 3-0 or 5\u27-0-methylfluorophosphonateswere obtained; 3,4\u27-0 isopropylidenepyridoxine-5\u27-0-methylfluorophosphonate(8), 4-metoxymethylpyridoxine- 5\u27-0-methylfluorophosphonate (9) and pyridoxal- 5\u27-0-methylfluorophosphonate (10)