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 and said polysaccharides having a pendant moiety linked to the reducing terminal sialic acid unit which pendant moiety includes a functional group selected from N-maleimide, vinyl sulfone, N-iodoacetamide and orthopyridyl disulfide.
2. A compound of claim 1 wherein the pendant moiety further comprises alkylene and/or arylene and/or an oxalkylene and/or oligooxa-alkylene and/or oligopeptide.
3. A compound of claim 1 wherein the functional group is N-maleimido.
4. A compound of claim 1 wherein the polysaccharide is a polysialic acid.
5. The compound of claim 1 which has the formula
wherein:
R 1 is H or —CHOHCH 2 OH,
R 3 is —CH 2 CHR 4 R 5 or —CH(CH 2 OH)CHR 4 R 5 wherein R 4 and R 5 together represent ═N—NR 6 or R 4 is H and R 5 is —NR 6 R 7 in which R 6 is an organic group comprising the said pendant functional group and R 7 is H;
O-Gly is a glycosyl (saccharide) group;
n is 1-50; and
Ac is acetyl.
6. A compound of claim 5 in which each O-Gly is a sialic acid unit.
7. A polysialylated protein with at least one cysteine unit linked through a thioether bond to at least one reducing terminal unit of a polysialic acid.
8. A compound of claim 1 wherein polysaccharide has at least 10 saccharide units.
9. A process to prepare a polysialylated protein coupled to the reducing terminal unit of a polysaccharide which method comprises reacting the compound of claim 3 with a protein having at least one free unprotected cysteine whereby the N-maleimido group forms a thioether linkage with the thiol group of said cysteine.
10. A process to prepare a polysialylated protein which comprises reacting the compound of claim 1 with a protein having at least one-cysteine whereby the said functional group forms a thioether linkage with the thiol group of said cysteine.
11. The compound of claim 4 wherein said polysaccharide consists essentially of sialic acid units and said pendant moiety.
12. The compound of claim 8 wherein the polysaccharide has at least 50 saccharide units.
13. A compound of claim 4 wherein polysaccharide has at least 10 saccharide units.
14. A compound of claim 6 wherein polysaccharide has at least 10 saccharide units.