Still Elusive – Pd(II)‐Mediated Base Pairing by an Acetophenone Oxime Palladacycle within 15N‐Labelled Double‐Helical Oligonucleotides

Abstract

AbstractBoth α and β anomers of an acetophenone C‐nucleoside were synthesized and incorporated in the middle of short oligodeoxynucleotides. The ketone oligonucleotides were converted to 15N‐labelled oxime oligonucleotides by treatment with 15N‐hydroxylamine and, finally, cyclopalladated by treatment with lithium tetrachloropalladate. Comparison of the UV melting profiles of duplexes bearing the β anomer of either the palladacyclic or the metal‐free oxime C‐nucleoside suggested formation of a stable Pd(II)‐mediated base pair, especially with adenine or thymine as the base pairing partner. Melting profiles of the corresponding duplexes bearing the α anomer were much more convoluted, precluding meaningful comparison. 15N NMR spectra were obtained for the β anomeric oxime oligonucleotide as well as its palladacyclic derivative but the signals unfortunately diminished below detection limit when the latter was hybridized with a complementary strand placing a 15N3‐labelled thymine opposite to the palladacyclic residue.