Patent ID: 8217154

Claim:
A compound which is a polysialic acid (PSA) substrate molecule having at least one of its terminal units derived from a sialic acid unit in which an ester of N-hydroxysuccinimide (NHS) is linked to the unit at either the 2 or 7-carbon of the sialic acid unit, via a linker, said compound having the general formula I, II or III in which R 1 is H or sulfonyl; R 2 is a linking group; A is NR 5 , NR 5 NR 6 , O or S wherein R 5 and R 6 are independently selected from H, C 1-4 alkyl and aryl; SylO is a sialyl group; n is 1-100; R 3 is hydrogen; and R 4 is hydrogen.