Synthesis of a new Riboflavin-Nucleotide and its Insertion into G-quadruplex forming ODNs with anti-HIV Activity

In the last years, G-rich oligonucleotides (GROs) able to form G-quadruplexes, have attracted considerable interest in biological and therapeutic fields. G-quadruplex are among the most studied DNA structures because they are thought to be involved in important biological processes such as the modulation of gene expression; in addition they present a large variety of biological properties ranging from anticancer to antiviral activities. In all cases, the G-quadruplex formation is a crucial prerequisite for the biological effects. Recently, we reported the synthesis and full characterization of a mini-library of G quadruplex ODNs carrying aryl groups at the 5’-end through a phosphodiester bond and endowed with prominent anti-HIV activity. In this frame, we report here, the synthesis of new Riboflavin-Nucleoside (RF, Vitamin B) building block in which the ribityl chain is rigidified by 2',4' benzylidene group, the 5'-OH function is protected with DMT group and the 3’ position is functionalized with phosphoramidite. The new Riboflavin building block is incorporated into different ODN sequences able to form Gquadruplex structures using the well known phosphoramidite chemistry. This research project has been encouraged by recent studies on the use of RF as useful tool for both in vivo and in vitro studies: the Riboflavin is internalized through RF transporters and is one of the most efficient natural photosensitizers. Several modified ODN sequences have been synthesized with a solid phase synthetic approach in good yields; their biophysical and biological characterization has been carried out in order to evaluate the effect of RF-nucleotide insertion into G-quadruplex arrangements and their anti-HIV activity.