Identification of an imino group indispensable for cleavage by a small ribozyme.

The hairpin ribozyme is a small, noncoding RNA (ncRNA) that catalyzes a site-specific phosphodiester bond cleavage reaction. Prior biochemical and structural analyses pinpointed the amidine moiety of base Ade38 as a key functional group in catalysis, but base changes designed to probe function resulted in localized misfolding of the active site. To define the requirements for chemical activity using a conservative modification, we synthesized and incorporated N1-deazaadenosine into the full-length ribozyme construct. This single-atom variant severely impairs activity, although the active-site fold remains intact in the accompanying crystal structures. The results demonstrate the essentiality of the imino moiety as well as the importance of its interaction with the substrate in the precatalytic and transition-state conformations. This work demonstrates the efficacy of single-atom approaches in the analysis of ncRNA structure-function relationships.

Efficient syntheses of 5'-deoxy-5'-fluoroguanosine and -inosine.

Substitution of oxygen with a weak hydrogen bond acceptor such as fluorine provides a single-atom modification that can have grave effects on the chemical and medicinal properties of nucleoside analogues. To that end, we present a simple and high-yielding method for the novel synthesis of 5'-deoxy-5'-fluoroguanosine and 5'-deoxy-5'-fluoroinosine utilizing an intramolecular electron-withdrawing approach. The properties of the resulting modified nucleosides, as well as the halogenated intermediates, are notable for their similarity to nucleoside analogues used in the treatment of cancer, as well as enzyme inhibitors designed to target parasitic protozoa.