SYNTHESIS OF PEPTIDE NUCLEIC-ACID MONOMERS CONTAINING THE 4 NATURAL NUCLEOBASES - THYMINE, CYTOSINE, ADENINE, AND GUANINE AND THEIR OLIGOMERIZATION

The preparation of mixed-sequence PNAs (PNAs containing the four natural nucleobases; thymine, cytosine, adenine, and guanine) is described. The PNA monomers containing thymine, Cbz-protected cytosine, or adenine or benzyl-protected guanine were prepared via convergent syntheses. Subsequent to introduction of the carboxymethyl linker at N-1 of the pyrimidines or N-9 of the purines and suitable protection of exocyclic groups, the nucleobase derivatives were coupled to the Boc-protected backbone esters 10a or 10b and finally hydrolyzed affording the monomers 12a-d. The exocyclic amino groups of cytosine and adenine were protected with a benzyloxycarbonyl group. The exocyclic amino group of guanine was left unprotected whereas O-6 was protected as the benzyl ether. Two mixed-sequence 10-mers, each with five purines incorporated, and a mixed-sequence 15-mer Containing seven purines were assembled essentially following standard solid phase peptide synthesis protocols.