The instant disclosure provides O-acetylated high molecular weight polygalacturonic acids or pharmaceutically acceptable salts thereof, having at least one of: (a) a molecular weight greater than 1 x 106 Da； (b) a degree of mefhylation less than about 10% per mole； and (c) an intervening rhamnose content ranging from about 2% to about 15% per mole, useful as a synthetic immunogenic Vi antigen. The instant disclosure further provides methods of preparing an O-acetylated high molecular weight polygalacturonic acid or pharmaceutically acceptable salt thereof of, pharmaceutical compositions and/or vaccine compositions comprising the same, and methods of immunization using any of the foregoing.
