Synthesis and Base Pairing Properties of 1′,5′‐Anhydro‐L‐Hexitol Nucleic Acids (L‐HNA)

Oligonucleotides composed of 1',5'-anhydro-arabino-hexitol nucleosides belonging to the L series (L-HNA) were prepared and preliminarily studied as a novel potential base-pairing system. Synthesis of enantiopure L-hexitol nucleotide monomers equipped with a 2'-(N(6)-benzoyladenin-9-yl) or a 2'-(thymin-1-yl) moiety was carried out by a de novo approach based on a domino reaction as key step. The L oligonucleotide analogues were evaluated in duplex formation with natural complements as well as with unnatural sugar-modified oligonucleotides. In many cases stable homo- and heterochiral associations were found. Besides T(m) measurements, detection of heterochiral complexes was unambiguously confirmed by LC-MS studies. Interestingly, circular dichroism measurements of the most stable duplexes suggested that L-HNA form left-handed helices with both D and L oligonucleotides.