Synthesis of N-functionalized 2,2′-dipyridylamine ligands, complexation to ruthenium (II) and anchoring of complexes to papain from papaya latex

2,2′-Dipyridylamine (dpa) derivatives carrying a thiol-targeted maleimide group located at the end of an alkyl substituent on the central amine were synthesized. Reaction with the organometallic precursors [(η6-arene)RuCl2]2 (arene = benzene or p-cymene) yielded the half-sandwich cationic complexes [(η6-arene)Ru(dpa)Cl]+ where the dipyridylamine derivatives were coordinated as bidentate N,N donor ligands. Enzymatic studies showed that these derivatives were able to inactivate the cysteine endoproteinase papain by S-alkylation of the cysteine active site.