Polysialic acid derivatives
A polysialic acid compound is reacted with a hetero-bifunctional reagent to introduce a pendant functional group for site-specific conjugation to sulfhydryl groups, for instance side chains of cysteine units in drugs, drug delivery systems, proteins or peptides. The functional group is, for instance, an N-maleimide group.
1. A compound comprising a polysaccharide having at least two sialic acid units linked 2.8 and/or 2.9 to one another, and having reducing and non-reducing terminal units, said polysaccharide having a pendant moiety X—R—Y, wherein the pendant moiety is covalently linked to the reducing terminal sialic acid unit through Y;
in which:
X is a N-maleimido, N-iodoacetamido, S-vinylsulphonyl or S-orthopyridyldisulphide group, R is alkene-diyl, arylene or aralkylene alkarylene, alkylene-oxaalkylene, or alkylene-oiigooxa-alkylene or alkyl-oligopeptidyl-alkyl group; and Y is a hydrazide, amine or N-hydroxysuccinimide group.
2. The polysaccharide of claim 1 , wherein R is C 1-6 alkanediyl, C 2-3 -alkyl-oxa-C 2-3 -alkylene, C 2-3 alkyl-oligo(oxa-C 2-3 alkylene), or C 2-6 alkylene phenyl.
3. The polysaccharide of claim 1 , wherein X is N-maleimido or orthopyridyldisulphide.
4. The polysaccharide of claim 1 , wherein Y is a hydrazide or a hydroxyl succinimide.
5. The compound of claim 1 , wherein the polysaccharide is colominic acid.
6. The compound of claim 1 , wherein the polysaccharide comprises glycosyl units other than sialic acid units.
7. The compound of claim 1 , wherein the polysaccharide is a B polysaccharide.
8. The compound of claim 1 , wherein the polysaccharide comprises at least 2, at least 5, at least 10, or at least 50 sialic acid units.
9. A polysaccharide protein conjugate comprising the polysaccharide of claim 1 linked through a thioether bond to the side chain of a cysteine unit of the protein.
10. The polysaccharide protein conjugate of claim 9 , wherein the polysaccharide is linked through a moiety joined at one or both terminal units of the polysaccharide.
11. The polysaccharide protein conjugate of claim 9 , wherein the protein contains a single cysteine.
12. The polysaccharide protein conjugate of claim 9 , wherein the polysaccharide is a B polysaccharide.
13. The polysaccharide protein conjugate of claim 9 , wherein the polysaccharide is linked through an N-succinimidyl group with the thioester linked at the α-carbon atom.
14. The polysaccharide protein conjugate of claim 9 , wherein the moiety comprises a secondary amine, a hydrazine, or an amide bond.