The present invention relates to a method for treating Streptococcus pneumoniae pneumoniae) serotype 4 capsular polysaccharide, and a complex thereof. A pharmaceutical composition comprising said complex and said complex is useful for the prevention and / or treatment of a disease associated with Streptococcus pneumoniae, more specifically a disease associated with Streptococcus pneumoniae serotype 4. In addition, the synthetic saccharide of general formula (I) is useful as a marker for immunological assays for the detection of antibodies against Streptococcus pneumoniae bacteria.