DNA or RNA oligonucleotide 2'-hydrazides for chemoselective click-type ligation with carbonyl compounds

Aqueous Activation of RNA 2'-OH for Conjugation with Amines and Thiols

Strategies for covalent modification of RNA are important for enabling biological studies of the biopolymer and for enhancing properties of therapeutic RNAs. While a number of electrophiles have been observed to react with RNA, few methods exist for reaction with nucleophiles. Here, we describe new reagents that enable efficient conjugation of amines and other nucleophiles to unmodified RNA postsynthetically via transient activation of 2'-OH groups. Reaction of single-stranded RNA in aqueous solution with phenolic imidazolecarbamates at room temperature results in stoichiometric and superstoichiometric yields of imidazolecarbonyl group adducts, and control experiments with DNA confirm the site of reaction in RNA as 2'-OH. Subsequent incubation of imidazolecarbonyl-activated RNAs with primary or selected secondary amines results in rapid, high-yield conversion to carbamate conjugates. The activation and subsequent nucleophile reaction can be carried out either stepwise or in a one-pot reaction. Thiols and phenol species react to yield (thio)carbonate adducts, and amino acid sidechains also react, suggesting possible future utility for protein conjugates and analysis of protein-RNA interactions. The activation method is found to be selective to unpaired regions of RNA, and can be directed to a specific location in a strand by use of a loop-inducing helper DNA. The results establish novel and efficient reagents and methods for modifying RNA postsynthetically with nucleophiles.

Chemistry of Peptide-Oligonucleotide Conjugates: A Review

Peptide-oligonucleotide conjugates (POCs) represent one of the increasingly successful albeit costly approaches to increasing the cellular uptake, tissue delivery, bioavailability, and, thus, overall efficiency of therapeutic nucleic acids, such as, antisense oligonucleotides and small interfering RNAs. This review puts the subject of chemical synthesis of POCs into the wider context of therapeutic oligonucleotides and the problem of nucleic acid drug delivery, cell-penetrating peptide structural types, the mechanisms of their intracellular transport, and the ways of application, which include the formation of non-covalent complexes with oligonucleotides (peptide additives) or covalent conjugation. The main strategies for the synthesis of POCs are viewed in detail, which are conceptually divided into (a) the stepwise solid-phase synthesis approach and (b) post-synthetic conjugation either in solution or on the solid phase, especially by means of various click chemistries. The relative advantages and disadvantages of both strategies are discussed and compared.