Reagent for the formation of succinimidyl active esters, used for attaching Ru complexes to 5'-amino modified oligonuleotides for use in time-resolved fluorescence techniques: Helv. Chim. Acta, 71, 2085 (1988). In situ formation of succinimidyl active esters can be used in peptide coupling in aqueous solutions: Tetrahedron Lett., 30, 1927 (1989).