Depending on the position of the functional groups, a distinction is made between ketononoses and aldononoses.

Aldononoses have seven chiral centers, which allows the formation of 128 stereoisomers (2⁷), which differ in the position of the hydroxyl groups or the asymmetric carbon atom. Ketononoses have six chiral centers, which gives the possibility of 64 different possible stereoisomers.

• Neuraminic acid
• Sialic acid
• Legionaminic acid
• Pseudaminic acid