Capping of oligonucleotides with “clickable” m3G-CAPs

Abstract

The RNA components of small nuclear ribonucleoproteins (U snRNPs) possess a characteristic 5′-terminal 2,2,7-trimethyl-guanosine CAP structure (m₃G-CAP). This cap is an important component of the nuclear localization signal of U snRNPs. Here we report synthesis of four m₃G-CAP constructs and the effective attachment of these onto oligonucleotides (ONs) using Cu(I) [3 + 2] cycloaddition (“click chemistry”). The four constructs (1–4, Fig. 1) are equipped with a handle that in principle allows for universal conjugation to any cargo and differ in their complexity starting from m₃GpppA_(linker) to m₃GpppA_(OMe)U_(OMe)A_(linker) that resembles the native m₃G-CAP followed by the 2′-O-methylated sequence AUA. The four m₃G-CAP containing constructs are equipped with an azide linker and by taking advantage of initial attachment of a novel activated triple bond donor p-aminomethyltoluic acid (PATA) to ONs on solid support we were able to synthesize novel bioconjugates equipped with different constructs carrying the m₃G-CAP Nuclear Localisation Signal (NLS) for the investigation of nuclear delivery.