Abstract
Chemically modified oligonucleotides are increasingly applied in nucleic acid based therapeutics and diagnostics. LNA (locked nucleic acid) and its diastereomer alpha-L-LNA are two promising examples thereof that exhibit increased thermal and enzymatic stability. Herein, the synthesis, biophysical characterization, and molecular modeling of N2'-functionalized 2'-amino-alpha-L-LNA is described. Chemoselective N2'-functionalization of protected amino alcohol 1 followed by phosphitylation afforded a structurally varied set of target phosphoramidites, which were incorporated into oligodeoxyribonucleotides. Incorporation of pyrene-functionalized building blocks such as 2'-N-(pyren-1-yl)carbonyl-2'-amino-alpha-L-LNA (monomer X) led to extraordinary increases in thermal affinity of up to +19.5 degrees C per modification against DNA targets in particular. In contrast, incorporation of building blocks with small nonaromatic N2'-functionalities such as 2'-N-acetyl-2'-amino-alpha-L-LNA (monomer V) had detrimental effects on thermal affinity toward DNA/RNA complements with decreases of as much as -16.5 degrees C per modification. Extensive thermal DNA selectivity, favorable entropic contributions upon duplex formation, hybridization-induced bathochromic shifts of pyrene absorption maxima and increases in circular dichroism signal intensity, and molecular modeling studies suggest that pyrene-functionalized 2'-amino-alpha-L-LNA monomers W-Y having short linkers between the bicyclic skeleton and the pyrene moiety allow high-affinity hybridization with DNA complements and precise positioning of intercalators in nucleic acid duplexes. This rigorous positional control has been utilized for the development of probes for emerging therapeutic and diagnostic applications focusing on DNA targeting.