N-acetylneuraminic acid, also known as sialic acid (SA), bird's nest acid, is a naturally occurring amino sugar, which was originally isolated from bovine submandibular adenomucin, hence the name sialic acid. Sialic acid is a nine-carbon monosaccharide derivative containing an amino group, and is a general term for all N- or O-derivatives of neuraminic acid or keto-deoxynonyluronic acid (KDN).