Occurrence of 2,4-dihydroxy-3,3,4-trimethylpyroglutamic acid as an N-acyl substituent in the O-polysaccharide chain of the lipopolysaccharide of Vibrio anguillarum V-123.

A new and highly branched amino acid was found as an N-acyl substituent of the O-polysaccharide chain obtained from the lipopolysaccharide of Vibrio anguillarum V-123 (serogroup JO-2) and evidence is presented to support the structure as 2,4-dihydroxy-3,3,4-trimethylpyroglutamic acid. Acid hydrolysis of the O-polysaccharide gave the lactone of 2,4-dihydroxy-3,3,4-trimethylglutamic acid, together with 2-amino-2-deoxy-D-galacturonic acid, 2-amino-2,6-dideoxy-D-glucose (D-quinovosamine), and 4-amino-4,6-dideoxy-D-glucose (D-viosamine). Degradation of the O-polysaccharide with hydrogen fluoride yielded a fragment (H1) that was indicated by the 1H-NMR data to be 4-amino-4,6-dideoxy-D-glucose N-acetylated with 2,4-dihydroxy-3,3,4-trimethylpyroglutamic acid. The configuration of the amino acid was not determined.