A method for preparing an antibody conjugated to a payload comprising the step of: a) performing a Michael addition reaction with the maleimide entity in the molecule of formula: and an antibody molecule comprising at least one thiol group wherein: n is 0 or 1; m is 0 or 1; q is 0 or an integer in the range 1 to 12, for example 1 to 6, such as 2 or 3; Q is a bond or a residue from a conjugation component; X is C 0-18 alkyleneC 6-36 Aryl, wherein the aryl has 0, 1, 2, 3 or 4 substituent independently selected from the group comprising halogen, hydroxyl, C 1-6 alkyl, C 1-6 alkoxy, -COOR 3, - COR 3, -CN, -CF 3, -NO 2, -SO 2, -SO 3, -NR 4 R 5, -PO 4, and -(OCH 2 CH 2) q -OR 3; Y is C Z is a saturated or unsaturated branched or unbranched C 1-30 alkylene chain, wherein one or more carbons (such as 1, 2, 3, 4, 5, 6, 7 or 8) are optionally independently replaced by -O-, N and the chain is optionally bears one or more (such as 1, 2, 3 or 4) C substituents; R 1 is H, a solid surface or a payload molecule; R 3 is H or C 1-6 alkyl; R 4 is H or C 1-6 alkyl; R 5 is H or C 1-6 alkyl; b) wherein R 1 is a payload molecule or a solid surface hydrolysing the resultant thio-succinimide entity formed by the reaction of compound of formula and the antibody, or c) wherein R 1 is H performing a conjugation with a payload, a conjugation component or solid surface, followed by hydrolysing the thio-succinimide entity formed by the reaction of compound of formula and the antibody. a) performing a Michael addition reaction with the maleimide entity in the molecule of formula: and an antibody molecule comprising at least one thiol group wherein: n is 0 or 1; m is 0 or 1; q is 0 or an integer in the range 1 to 12, for example 1 to 6, such as 2 or 3; Q is a bond or a residue from a conjugation component; X is C 0-18 alkyleneC 6-36 Aryl, wherein the aryl has 0, 1, 2, 3 or 4 substituent independently selected from the group comprising halogen, hydroxyl, C 1-6 alkyl, C 1-6 alkoxy, -COOR 3, - COR 3, -CN, -CF 3, -NO 2, -SO 2, -SO 3, -NR 4 R 5, -PO 4, and -(OCH 2 CH 2) q -OR 3; Y is C Z is a saturated or unsaturated branched or unbranched C 1-30 alkylene chain, wherein one or more carbons (such as 1, 2, 3, 4, 5, 6, 7 or 8) are optionally independently replaced by -O-, N and the chain is optionally bears one or more (such as 1, 2, 3 or 4) C substituents; R 1 is H, a solid surface or a payload molecule; R 3 is H or C 1-6 alkyl; R 4 is H or C 1-6 alkyl; R 5 is H or C 1-6 alkyl; n is 0 or 1; m is 0 or 1; q is 0 or an integer in the range 1 to 12, for example 1 to 6, such as 2 or 3; Q is a bond or a residue from a conjugation component; X is C 0-18 alkyleneC 6-36 Aryl, wherein the aryl has 0, 1, 2, 3 or 4 substituent independently selected from the group comprising halogen, hydroxyl, C 1-6 alkyl, C 1-6 alkoxy, -COOR 3, - COR 3, -CN, -CF 3, -NO 2, -SO 2, -SO 3, -NR 4 R 5, -PO 4, and -(OCH 2 CH 2) q -OR 3; Y is C Z is a saturated or unsaturated branched or unbranched C 1-30 alkylene chain, wherein one or more carbons (such as 1, 2, 3, 4, 5, 6, 7 or 8) are optionally independently replaced by -O-, N and the chain is optionally bears one or more (such as 1, 2, 3 or 4) C substituents; R 1 is H, a solid surface or a payload molecule; R 3 is H or C 1-6 alkyl; R 4 is H or C 1-6 alkyl; R 5 is H or C 1-6 alkyl; b) wherein R 1 is a payload molecule or a solid surface hydrolysing the resultant thio-succinimide entity formed by the reaction of compound of formula and the antibody, or c) wherein R 1 is H performing a conjugation with a payload, a conjugation component or solid surface, followed by hydrolysing the thio-succinimide entity formed by the reaction of compound of formula and the antibody.