Compounds

The invention provides a synthetic Clostridium difficile PS-​II cell wall saccharide I, wherein R is selected from H, PO3H2 or an anionic form thereof, acetyl, and a hydroxyl protecting group; each R1-​R16 is independently selected from OH and a blocking group; each R'1 and R'2 is independently selected from H, acetyl, and an amino protecting group; and Z is selected from H, a linker and a hydroxyl protecting group. The invention also provides a process for purifying Clostridium difficile PS-​II saccharide from Clostridium difficile bacterial cells resulting in reduced contamination. Thus, hexasaccharides I (Z = CH2CH2CH2NH2; R = H, PO3H2; R1-​R16 = OH; R'1 = R'2 = COMe) were prepd. for use in prepn. of vaccines as conjugates with carrier proteins against bacteria.