The impact of isomers of hemiaminal-1,2,4-triazole conjugates differently substituted in the phenyl ring and their Cu2+ complexes on the catalytic activity of the antigenomic delta ribozyme

Abstract

The ability of four stable hemiaminals differently substituted in the phenyl ring and their complexes with Cu2+ ions to inhibit catalytic cleavage of the antigenomic delta ribozyme was compared. The hemiaminals were novel chiral derivatives of 1,2,4-triazole [i.e. (2,4-dinitrophenyl)(4H-1,2,4-triazol-4-ylamino) methanol (2,4-dnbald), (2-nitrophenyl)(4H-1,2,4-triazol-4-ylamino) methanol (2-nbald), (3-nitrophenyl)(4H-1,2,4-triazol-4-ylamino) methanol (3-nbald) and (4-nitrophenyl)(4H-1,2,4-triazol-4-ylamino) methanol (4-nbald)]. The complexes of nbalds with Cu2+ were characterized using UV and EPR methods and additionally, the formation of 2,4-dnbald–Cu2+ complex with CuL2 stoichiometry was confirmed by mass spectrometry.The data suggest that there are two ways in which nbalds and their Cu2+ complexes can influence catalytic cleavage of antigenomic delta ribozyme. The coordinated Cu2+ ions may play the role of new cationic ligands increasing the affinity of the complexes to the ribozyme. Such situation occurs in the case of 2- and 2,4-nbald. Their Cu2+ complexes decrease ribozyme cleavage rates twice more efficiently than uncomplexed compounds. Moreover, the Cu2+ complexes displace the catalytic divalent metal ions from their strong binding sites located in the ribozyme J4/2 region as shown by the Pb2+-induced cleavage approach. On the other hand, 3- and 4-nbald inhibit catalysis more strongly as compared to 2-nbald and 2,4-dnbald but the ribozyme cleavage rates are changed only slightly upon Cu2+ complexation. The mechanism of ribozyme inhibition by interfering with the formation of a correct ribozyme tertiary structure seems to operate in this case.