Enzyme-like Acceleration for the Hydrolysis of a DNA Model Promoted by a Dinuclear Zn(Ⅱ) Catalyst in Dilute Aqueous Ethanol

摘要

Molecules containing phosphate diester moieties (RO)PO_2~- (OR') serve important biological functions because of their inherent stability toward hydrolytic and nucleophilic cleavage, making this functional group ideal for the preservation of genetic information in RNA and DNA. Several enzymes that cleave RNA and DNA contain metal ions such as Zn~(2+), and considerable research has been directed at understanding the mechanisms of hydrolysis and alcoholysis of RNA, DNA, and their model systems,as well as toward designing M~(2+)-containing catalysts for facilitating their cleavage.rnWe recently showed that the cleavages of the RNA and DNA models 1 and 2 promoted by the Zn(Ⅱ)_2 complex 3 in methanol and ethanol are accelerated by 10~(12) times or more relative to the background methanolysis reactions. In water, complex 3b is no more active than the mono-Zn(Ⅱ) complex of 1,5,9-triazacyclododecane toward the cleavage of phosphate diesters, and we surmised that the acceleration of catalysis in methanol is attributable to a medium effect of reduced dielectric constant and polarity. The catalyzed cleavages in methanol, although fast, are transesterifications and not hydrolytic reactions. In the case of the RNA models, the first formed product arises from intramolecular ring closure as it does in water, but in the DNA model cases the OAr leaving group is replaced by OR (Scheme 1).