An efficient and versatile synthesis of bisPNA-peptide conjugates based on chemoselective oxime formation

Oligomers with two identical peptide nucleic acid sequences joined by a flexible hairpin linker (bisPNA) can stably bind to specific DNA sequences without altering plasmid supercoiling, thus offering a unique opportunity to attach various functional entities to high molecular weight DNA. Current synthetic approaches, however, severely limit the possibility to link peptides or other chemical moieties (i.e., sugars, oligonucleotides, etc.) to bisPNA. Here we report a novel strategy for the synthesis of bisPNA-peptide conjugates in which chemoselective ligation of bisPNA to peptides was accomplished through oxime formation between an oxy-amine-containing peptide and a bisPNA-methyl ketone (complementary modifications can also be used). The described synthesis is highly efficient, does not require a protection strategy, and is carried out under mild aqueous conditions. Through this methodology long peptide sequences in either C to N or N to C polarity can be linked to bisPNA. In addition, this protocol makes the conjugation of cysteine-containing peptides feasible and allows disulfide bond formation to be controlled. This same approach can be exploited to link oligonucleotides, sugars, or other chemical entities to bisPNA.