Sialic acids as such, sialic acid derivatives, analogues, glycosides and sialooligosaccharides have been subject of many synthetic investigations. These studies were aimed at a further exploration of the properties of sialic acids, the preparation of substrates and inhibitors for sialidases, sialyltransferases or for sialic acid converting enzymes, and to make compounds accessable for analytical purposes or for studies related to metabohsm or biological functions of sialic acids.