Synthesis of nucleopeptides by employing an enzyme-labile urethane protecting group

Nucleoproteins are naturally occurring biopolymers in which the hydroxy group of a serine, a threonine, or a tyrosine moiety is linked through a phosphodiester group to the 3'- or 5'-end of a nucleic acid. For the study of the biological phenomena in which nucleoproteins are involved, for example, viral replication, nucleopeptides embodying the characteristic linkage between the peptide chain and the oligonucleotide may serve as powerful tools. However, as a result of the multifunctionality and the pronounced acid and base lability of nucleopeptides, their synthesis requires the application of a variety of orthogonally stable blocking groups, which can be removed under the mildest conditions. We have developed a new mild enzymatic deprotection method, that is, the penicillin G acylase-catalyzed hydrolysis of the N-phenylacetoxybenzyloxycarbony (PhAcOZ) group, for the synthesis of nucleopeptides. We demonstrate the wide applicability of this method by coupling the N-terminally deprotected nucleopeptides 31 a-c with PhAcOZ-protected amino acids and subsequent removal of the N-PhAcOZ group from fully protected nucleotetrapeptides 32 a,b with penicillin G acylase. The reaction conditions are very mild (pH 6.8) so that no undesired side reaction such as cleavage of the nucleotide bond or beta-elimination of the nucleotide was observed.