A method of preparing a compound of formula (III):
(M)
x
-(S)
y
-(M′)
z
(III)
wherein x is from 1 to 6, y is from 1 to 12, z is from 0 to 10, each M and each M′ is independently a mycolic acid residue including a β-hydroxy acid moiety and each S is a monosaccharide unit; the method comprising reacting one or more mycolic acids with one or more saccharide units wherein the hydroxyl group of each β-hydroxy acid moiety is protected prior to reaction with the one or more saccharide units.