2-Acetamido-2,6-dideoxy+galactose (N-acetyl-r_-fucosamine, 6) is a constituent of the O-chain of the antigenic lipopolysaccharide of the Pseudomonas aeruginosal-', Fisher immunotype 2, Lanyi types 0:7ab and 011, and of the polysaccharides of certain enteric bacteria4. L-Fucosamine has been obtained by the, acidic hydrolysis of Pneumococcus Type V (ref. 5) and Type XII (ref. 6) capsular polysaccharides. In connection with work on the structure and biological activity of Pseudomonas aeruginosa antigens, certain derivatives of N-acetyl+fucosamine were needed. Four syntheses -7 I0 of this sugar or its derivatives are known, but because of low yields, none of these methods was preparatively useful. Moreover, certain dervatives required for our proposed stereocontrolled oligosaccharide synthesis were not accessible by the literature procedures. To circumvent the limitations of the published procedures, we have developed a new and straightforward synthesis of N-acetyl-L-fucosamine by azidonitration" of a glycal precursor. In the present synthesis, 3,4-di-O-acetyl-l,5-anhydro-2,6-dideoxy-L-lyxo-hex-I-enitol(3,4-di-0-acetyl-L-fucal, 1) was converted into 3,4-di-0-acetyl-2-azido-2,6dideoxy-cr-L-galactopyranosyl nitrate (2) and 3,4-di-0-acetyl-Zazido-2,6-dideoxy-L-galactose ( 3) in 95% combined yield by reaction with ceric ammonium nitrate and sodium azide. It is noteworthy that products 2 and 3 have the azido group at the 2-position in the equatorial (L-galucto) orientation, and this is to be expected" owing to the quasiaxial orientation of the 4-acetoxy group of 1. The formation of 3 possibly occurs by way of 2, as it was found that a solution of pure 2 in aqueous acetone changed into 3 on being kept.
Acetolysis of the crude azidonitration products gave 1,3,5-tri-0-acetyl-2azido-2,6-dideoxy+galactopyranose (4) as an anomeric mixture. The same anomeric mixture 4 was also obtained by the conventional acetylation of 3. The