The synthesis of 3-amino-2,3,6-trideoxy-l-xylo-hexopyranose derivatives

Derivatives (the 3-acetamido-4-benzoate 12, the 3-acetamido-4-acetate 13, and the N-acetyl derivative 14) of the methyl glycoside of the title sugar were prepared in a sequence of high-yielding steps from methyl 3-azido-4,6-O-benzylidene-2,3-di-deoxy-α-d-arabino-hexopyranoside (4). N-Bromosuccinimide converted 4 into the crystalline 4-O-benzoyl-6-bromide 5, which was treated with silver fluoride to afford the 5,6-unsaturated glycoside 6. Catalytic hydrogenation of 6 led, essentially, to a 7:1 mixture of 12 and its 5-epimeric d-arabino isomer 7. Alternatively, 6 was debenzoylated to 10, and the latter treated with lithium aluminum hydride to give crystalline methyl 3-amino-2,3,6-trideoxy-α-d-threo-hex-5-enopyranoside (11). Reduction of 11 (as its salt) by hydrogen, with subsequent N-acetylation, furnished the methyl β-l-xylo-glycoside 13 almost exclusively, with net inversion at C-5. Compound 13 was readily converted into the crystalline target compound 14. When dehydrobromination by silver fluoride was attempted with the 3-acetamido analog (2) of 5, a 3,6-anhydro product (1) was obtained, instead of the expected 5,6-alkene 3.