 Neuraminic acid may also be visualized as the product of an aldol-condensation of pyruvic acid and D-mannosamine (2-amino-2-deoxy-mannose).Neuraminic acid does not occur naturally, but many of its derivatives are found widely distributed in animal tissues and in bacteria, especially in glycoproteins and gangliosides.The "N"- or "O"-substituted derivatives of neuraminic acid are collectively known as sialic acids, the predominant form in mammalian cells being "N"-acetylneuraminic acid.