Synthesis of Amino Sugars via Isoxazolines: D-Allosamine
17 September 2002 (online)
The 4,5-dihydroisoxazole 4, obtained by joining (S)-1,2-O-isopropylidene-3 -butene-1,2-diol (2) and 5,5-dimethyl-2-nitromethyl-1,3-dioxane (3), is hydroxylated via its 4-carbanion with high trans-selectivity. The product, the 3,5-disubstituted (4S,5S)-4-hydroxy-4,5-dihydroisoxazole 5, is reduced with lithium aluminium hydride to give the doubly protected 2-amino-2-deoxy-5,6-O-isopropylidene-D-allose 2,2-dimethylpropane-1,3-diyl acetal (6) exclusively. On acid-catalyzed hydrolysis in a two-phase system D-allosamine hydrochloride 1 · HCl is obtained, which is converted to its N-acetyl derivative 7, concluding a 5 step synthesis of 7 in 31% overall yield.