L-Fucose (CAS No. 2438-80-4) is a natural sugar commonly derived from brown algae and human breast milk, and it is also present in certain human organs, including the skin and nervous system. Naturally, fucose is predominantly found in the L-configuration and exists in seaweed as polysaccharides such as fucoidan. On the other hand, D-configuration fucose is a rare sugar and is found in certain glycoglycerides.