SYNTHESIS OF O-ALPHA-D-RHAP-(1-]3)-O-ALPHA-D-RHAP-(1-]2)-O-ALPHA-D-RHAP-(1-]12)-OXYDODECANOYL-BOVINE SERUM-ALBUMIN

The title compound (19), a conjugate of a trisaccharide based upon the repeating trisaccharide of alpha-D-rhamnose, which comprises the polysaccharide portion of ''A-band'' lipopolysaccharide from a mutant (AK1401) of Pseudomonas aeruginosa, strain PAO1, with bovine serum albumin (BSA) was synthesized starting with methyl alpha-D-mannopyranoside. Suitably protected D-rhamnose derivatives, namely, ethyl 3,4-di-O-benzyl-1-thio-alpha-D-rhamnopyranoside (11) and 3-O-acetyl-2,4-di-O-benzyl-alpha-D-rhamnopyranosyl chloride (12), were used as the glycosyl acceptor and donor, respectively, in the synthesis of disaccharide 13. O-Deacetylation of 13 gave 14, a glycosyl acceptor that reacted with 12 to yield the trisaccharide 15. N-Iodosuccinimide-trifluoromethanesulfonic acid was used as an activator of the thioglycoside in the synthesis of 16 and 17 from 15. Compound 16 was converted into the hydrazide 18 by treatment with hydrazine. The conjugation was achieved by coupling of the intermediate acyl azide derivative of 18 with BSA.