A convenient synthesis of 4-amino-4-deoxy- l-arabinose and its reduction product, 1,4-dideoxy-1,4-imino- l-arabinitol

Abstract

Methyl β- d-xylopyranoside in a mixture of N,N-dimethylformamide and 2-methoxypropene containing a little hydrogen chloride gave preponderantly the 2,3- O-isopropylidene derivative, which was readily converted into its 4-trifluoromethanesulfonate. The facile displacement of the triflate group gave a 4-azido-4-deoxy-α- l-arabinopyranoside derivative, and this, on mild acid treatment, was hydrolyzed to the 2,3-diol, or under more vigorous conditions to 4-azido-4-deoxy- l-arabinose. Methyl 2,3-di- O-acetyl-4-azido-4-deoxy-α- l-arabinopyranoside, from the diol, appears ( 1H-n.m.r. data) to exist as an equilibrating mixture of the 4 C 1 and 1 C 4 conformers in chloroform solution. The reduction of the azido sugar by hydrogen over Pd/C in 6 m HCl yielded 4-amino-4-deoxy- l-arabinopyranose as its hydrochloride; in 0.1 m HCl, further reactions occurred to give 1,4-dideoxy-1,4-imino- l-arabinitol as the final product. The aminodeoxypentose from lipid A precursor II A, isolated from a Salmonella mutant by Raetz et al. in 1985, was shown to be identical with the synthetic aminoarabinose by t.l.c., 1H-n.m.r. spectroscopy, and g.l.c. of the acetylated reduction products.