Structural characterization and SARS-CoV-2 inhibitory activity of a sulfated polysaccharide from Caulerpa lentillifera

Caulerpa lentillifera (Bryopsidophyceae, Chlorophyta) is an edible seaweed attracting great attention for its expansion of farming scale and increasing consumption in these years. In the present study, a sulfated polysaccharide (CLSP-2) was isolated and separated from C. lentillifera, and its chemical structure was elucidated by a series of chemical and spectroscopic methods. Among these methods, mild acid hydrolysis and photocatalytic degradation were applied to release mono- and oligo-saccharide fragments which were further identified by HPLC-MSn analysis, affording the information of the sugar sequences and the sulfate substitution in CLSP-2. Results indicated that the backbone of CLSP-2 was constructed of →6)-β-Manp-(1→ with sulfated branches at C2, which were comprised of prevalent →3)-β-Galp4S-(1→, →3)-β-Galp2,4S-(1→, and minor Xyl. In addition, the virus neutralization assay revealed that CLSP-2 could effectively protect HeLa cells against SARS-CoV-2 infection with an IC50 of 48.48 μg/mL. Hence, the present study suggests CLSP-2 as a promising agent against SARS-CoV-2.