Activated sialic acid derivatives for protein derivatisation and conjugation
Derivatives of PSAs are synthesized, in which a reducing and/or non-reducing end terminal sialic acid unit is transformed into a N-hydroxysuccinimide (NHS) group. The derivatives may be reacted with substrates, for instance substrates containing amine or hydrazine groups, to form non-cross-linked/crosslinked polysialylated compounds. The substrates may, for instance, be therapeutically useful drugs, peptides or proteins or drug delivery systems.
1. 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.
2. The compound according to claim 1 in which R 2 is selected from alkanediyl, arylene, alkarylene, heteroarylene, alkyl-heteroarylene any of which may be interrupted by either thioester, ester, amine or amide linkages, and in which A is NR 5 or a linker group joined to the rest of the molecule through a group NR 5 .
3. A process for forming a compound according to claim 1 , which comprises reacting PSA with a bifunctional reagent, said bifunctional reagent comprising a functionality which is an NHS ester and another functionality reactive at the 2 or 7 carbon atom of a terminal sialic acid unit, under conditions such that covalent conjugation between the reagent and the sialic acid unit occurs and the NHS group remains unchanged, said reaction optionally preceded by derivatizing the terminal sialic acid of said PSA.
4. The process according to claim 3 wherein said sialic acid unit in the PSA is derivatized to generate an amine group.
5. The process according to claim 4 wherein terminal sialic acid unit is a reducing terminal unit and where the derivatizing comprises:
a) reducing the reducing terminal sialic acid unit to form a vicinal diol group;
b) selectively oxidizing the vicinal diol group formed in step a) to form an aldehyde group;
c) converting the aldehyde of step b) to an amino group by reductive amination.
6. The process according to claim 4 wherein said PSA having a terminal sialic acid at the non-reducing terminal end is oxidized selectively in the non-reducing terminal sialic acid unit at the C-7, C-8 vicinal diol group to form an aldehyde on carbon atom 7; and converting the aldehyde group to an amino group by reductive amination.
7. The process according to claim 4 in which the NHS reagent is selected from:
bis[2-succinimidyloxycarbonyl-oxy)ethyl]sulfone (BSOCOES),
bis(sulfosuccinimidyl)suberate) (BS 3 ),
disuccinimidyl glutarate (DSG),
dithiobis (succinimidyl propionate) (DSP),
disuccinimidyl suberate (DSS),
disuccinimidyl tartrate (DST) or its sulfo analog,
3,3′-dithiobis (sulfosuccinimidyl propionate) (DTSSP), and
ethylene glycol bis(succinimidyl succinate) (EGS) or its sulfo analog.
8. The process according to claim 7 in which the reaction with the NHS reagent is carried out in aprotic solvent.
9. The process according to claim 3 in which the sialic acid unit is subjected to a preliminary step in which a thiol group is generated.
10. The process according to claim 9 in which the NHS reagent is selected from:
N-(α-maleimidoacetoxy)succinimide ester(AMAS),
N-(β-maleimidopropyloxy)succinimide ester (BMPS),
N-(ξ-maleimidocapryloxy)succinimide ester (EMCS) or its sulfo analog,
N-(γ-maleimidobutyryloxy)succinimide ester (GMBS) or its sulfo analog,
succinimidyl-4-(N-maleimidomethyl)-cyclohexane-1-carboxy-(6-amidocaproate) (LC-SMCC),
m-maleimido benzoyl-N-hydroxysuccinimide ester (MBS) or its sulfo analog,
succinimidyl-4-(N-maleimidomethyl)-cyclohexane-1-carboxyate) or its sulfo analog,
succinimidyl-4-(p-maleimido phenyl)butyrate (SMBP) or its sulfo analog,
succinimidyl-6-(β-maleimido-propionamido) hexanoate (SMPH),
N-(k-maleimidoundecanoyloxy) sulfosuccinimide-ester (sulfo-KMUS),
succinimidyl 6-[3-2(2-pyridyldithio)-propionamido]hexanoate (LC-SPDP) or its sulfo analog,
4-succinimidyloxycarbonyl-methyl-α-(2-pyridyldithio)toluene (SMPT),
N-succinimidyl-3-(2-pyridyldithio)propionate (SPDP),
N-succinimidyl [4-vinylsulfonyl)benzoate (SVSB),
succinimidyl 3-(bromoacetamido)propionate (SBAP),
N-succinimidyliodoacetate (SIA), and
N-succinimidyl(4-iodoacetyl)aminobenzoate (SIAB) or its sulfo analog.
11. A method comprising reacting a biologically useful compound having a primary amine group with the compound of claim 1 under conditions in which the active hydrogen of the amine is replaced by the acyl group remaining after the N-succinimidyloxy group is replaced.
12. The method according to claim 11 in which the biologically useful molecule is a protein or peptide of which the primary amine group is the N-terminus or is the γ-amino group of a lysine unit.
13. A method which comprising reacting a biologically useful compound having a primary amine group with the product of a process of claim 3 under conditions in which the active hydrogen of the amine is replaced by the acyl group remaining after the N-succinimidyloxy group is replaced.
14. The method according to claim 13 in which the biologically useful molecule is a protein or peptide of which the primary amine group is the N-terminus or is the γ-amino group of a lysine unit.