Vitamin B12- Peptide Nucleic Acid Conjugates.

Abstract

Vitamin B12 (cobalamin, Cbl) is an essential nutrient for all mammals and some bacteria. From a chemical point of view, it is a highly functionalized molecule, which enables conjugation at multiple positions and attachment of various cargoes. Both mammalian and bacterial cells have developed a specific transport pathway for the uptake of vitamin B12, and as a consequence, cobalamin is an attractive candidate for the delivery of biologically relevant molecules into cells. Indeed, hybrid molecules containing vitamin B12 in their structure have found various applications in medicinal chemistry, diagnostics, and biological sciences.Herein, we describe synthetic strategies toward the synthesis of vitamin B12 conjugates with peptide nucleic acid (PNA ) oligomers. Such short-modified oligonucleotides targeted at bacterial DNA or RNA can act as antibacterial agents if efficiently taken up by bacterial cells. The uptake of such oligonucleotides is hindered by the bacterial cell envelope, but vitamin B12 was found to efficiently deliver antisense PNA into Escherichia coli and Salmonella Typhimurium cells. This paves the way to the use of vitamin B12-PNA conjugates in antibacterial and diagnostic applications.Vitamin B12-PNA conjugates can be prepared via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) that gives access to covalently linked hybrids or via connecting both building blocks by reduction-sensitive disulfide bridge. Both approaches require prior modification of vitamin B12 by incorporation of the azide moiety or via transformation of the native functional group into a moiety reactive toward thiols. Conjugation of vitamin B12 with PNA-tagged substrates efficiently furnishes designed conjugates.