Cs is not clearly defined as a gene in the provided references. However, "CS" may refer to chondroitin sulfate, a glycosaminoglycan. Chondroitin sulfate is one of the major and widespread glycosaminoglycans, playing a vital role in various normal physiological and pathological processes, showing biological activities like anti-oxidation, anti-atherosclerosis, anti-thrombosis, and having insignificant immunogenicity [2].

The synthesis of chondroitin sulfate-E (CS-E) oligosaccharides was developed using a postglycosylation-transformation strategy, which provided flexibility for group transformation and derivatization, facilitating the examination of the structure-activity relationship (SAR) of CS-E molecules [1]. Additionally, there has been progress in the chemical, enzymatic and chemoenzymatic synthesis of CS and its derivatives, aiming to obtain CS with well-controlled chain lengths for reliable drug development [2].

In conclusion, chondroitin sulfate (CS) is important in various physiological and pathological processes. The research on its synthesis and structure-activity relationship helps in understanding its biological functions and provides a basis for drug development related to the associated physiological and pathological conditions.