A compound of formula: wherein X represents a core structure; S 1,S 2,S 3 represents independently of each other a spacer group; L represents a ligand-reactive group; A represents an affinity group; Z represents aryl or heteroaryl; R' represents H or C( 1 - 6)-alkyl and R" represents C( 1 - 6)-alkyl; characterized in that A is selected from -N 3 and -CCH; X represents a group of formula (I-I) wherein the dotted lines represent the linkage of W 1, W 2, W 3 to groups S 1, S 2, S 3, and s represents an integer from 1 to 12, preferably 4 W 1 represents -NH-, W 2 represents -CONH-, W 3 represents -NHCO-; L represents hydroxysuccinimide ester of formula S 1 represents C alkylene; S 2 represents C( 1 - 24)alkylene; S 3 represents C alkylene; • wherein said alkylene being a straight-chain or branched, • wherein said alkylene being substituted or unsubstituted, • wherein one or more, preferably non-adjacent, -CH 2 - groups of said alkylene may independently from each other be replaced by one or more bridging groups Y and/or unsubstituted or substituted cycloalkyl, unsubstituted or substituted heterocycloalkyl, unsubstituted or substituted aryl, unsubstituted or substituted heteroaryl; with the proviso that heteroatoms, such as O and N, are not directly linked to each other, and wherein Y represents a group -CH -, -O-, -CO-, -CH 2 -, -SO-, -CH 2 -, -SO 2 -, -CH 2 (SO 2)-·, -COO-, -OCO-, -S-CO-,-CO-S-, -SOO-, -OSO-, -SOS-, -O-CO-O-, -OCH 2 -, -CH 2 O-,-NR 1 -, -NR 1 -CO-, -CO-NR 1 -, -NR 1 -CO-O-, -O-CO-NR 1 -, -NR 1 -CO-NR 1 -, -CH=CH-, -C=C-, -CH=CH-COO-, -OCO-CH=CH-,-CH=N-, -C(CH 3)=N-, -N=N-; R 1 represents independent from each other H or C( 1 - 6)alkyl; Z represents an aryl group selected from unsubstituted phenyl, naphthyl, and anthracenyl or a heteroaryl group selected from unsubstituted pyridyl, furyl, imidazolyl, benzimidazolyl, pyrimidinyl, thienyl, quinolinyl, indolyl, and thiazolyl. X represents a core structure; S 1,S 2,S 3 represents independently of each other a spacer group; L represents a ligand-reactive group; A represents an affinity group; Z represents aryl or heteroaryl; R' represents H or C( 1 - 6)-alkyl and R" represents C( 1 - 6)-alkyl; characterized in that A is selected from -N 3 and -CCH; X represents a group of formula (I-I) wherein the dotted lines represent the linkage of W 1, W 2, W 3 to groups S 1, S 2, S 3, and s represents an integer from 1 to 12, preferably 4 W 1 represents -NH-, W 2 represents -CONH-, W 3 represents -NHCO-; s represents an integer from 1 to 12, preferably 4 W 1 represents -NH-, W 2 represents -CONH-, W 3 represents -NHCO-; L represents hydroxysuccinimide ester of formula S 1 represents C alkylene; S 2 represents C( 1 - 24)alkylene; S 3 represents C alkylene; • wherein said alkylene being a straight-chain or branched, • wherein said alkylene being substituted or unsubstituted, • wherein one or more, preferably non-adjacent, -CH 2 - groups of said alkylene may independently from each other be replaced by one or more bridging groups Y and/or unsubstituted or substituted cycloalkyl, unsubstituted or substituted heterocycloalkyl, unsubstituted or substituted aryl, unsubstituted or substituted heteroaryl; with the proviso that heteroatoms, such as O and N, are not directly linked to each other, and wherein Y represents a group -CH -, -O-, -CO-, -CH 2 -, -SO-, -CH 2 -, -SO 2 -, -CH 2 (SO 2)-·, -COO-, -OCO-, -S-CO-,-CO-S-, -SOO-, -OSO-, -SOS-, -O-CO-O-, -OCH 2 -, -CH 2 O-,-NR 1 -, -NR 1 -CO-, -CO-NR 1 -, -NR 1 -CO-O-, -O-CO-NR 1 -, -NR 1 -CO-NR 1 -, -CH=CH-, -C=C-, -CH=CH-COO-, -OCO-CH=CH-,-CH=N-, -C(CH 3)=N-, -N=N-; R 1 represents independent from each other H or C( 1 - 6)alkyl; • wherein said alkylene being a straight-chain or branched, • wherein said alkylene being substituted or unsubstituted, • wherein one or more, preferably non-adjacent, -CH 2 - groups of said alkylene may independently from each other be replaced by one or more bridging groups Y and/or unsubstituted or substituted cycloalkyl, unsubstituted or substituted heterocycloalkyl, unsubstituted or substituted aryl, unsubstituted or substituted heteroaryl; with the proviso that heteroatoms, such as O and N, are not directly linked to each other, and wherein Y represents a group -CH -, -O-, -CO-, -CH 2 -, -SO-, -CH 2 -, -SO 2 -, -CH 2 (SO 2)-·, -COO-, -OCO-, -S-CO-,-CO-S-, -SOO-, -OSO-, -SOS-, -O-CO-O-, -OCH 2 -, -CH 2 O-,-NR 1 -, -NR 1 -CO-, -CO-NR 1 -, -NR 1 -CO-O-, -O-CO-NR 1 -, -NR 1 -CO-NR 1 -, -CH=CH-, -C=C-, -CH=CH-COO-, -OCO-CH=CH-,-CH=N-, -C(CH 3)=N-, -N=N-; R 1 represents independent from each other H or C( 1 - 6)alkyl; Y represents a group -CH -, -O-, -CO-, -CH 2 -, -SO-, -CH 2 -, -SO 2 -, -CH 2 (SO 2)-·, -COO-, -OCO-, -S-CO-,-CO-S-, -SOO-, -OSO-, -SOS-, -O-CO-O-, -OCH 2 -, -CH 2 O-,-NR 1 -, -NR 1 -CO-, -CO-NR 1 -, -NR 1 -CO-O-, -O-CO-NR 1 -, -NR 1 -CO-NR 1 -, -CH=CH-, -C=C-, -CH=CH-COO-, -OCO-CH=CH-,-CH=N-, -C(CH 3)=N-, -N=N-; R 1 represents independent from each other H or C( 1 - 6)alkyl; Z represents an aryl group selected from unsubstituted phenyl, naphthyl, and anthracenyl or a heteroaryl group selected from unsubstituted pyridyl, furyl, imidazolyl, benzimidazolyl, pyrimidinyl, thienyl, quinolinyl, indolyl, and thiazolyl.