Total Synthesis of the Repeating Unit of the O‐antigen from <i>Proteus mirabilis</i> OC (CCUG 10702) Serogroup O75: Stepwise and One‐Pot Approaches

Abstract Proteus mirabilis is a pathogenic Gram‐negative bacterium that causes several kinds of infections in human beings. Herein, we present the first total synthesis of the O‐antigen tetrasaccharide repeating unit of P. mirabilis OC (CCUG 10702) serogroup O75 with an aminoethyl linker appended at the reducing end. The tetrasaccharide comprising D‐glucosamine, L‐rhamnose, D‐galactose and D‐galactosamine with a key (1→4)‐α‐glycosidic linkage between D‐galactose and L‐rhamnose was assembled by three stepwise [1+1+1+1], [1+2+1] and [2+2] assembly approaches and one one‐pot [1+2+1] assembly. The respective routes provided the tetrasaccharide in yields of 23 %, 18 %, 20 %, and 26 % from suitably protected monosaccharide building blocks.