Synthesis of peptido RNAs from unprotected peptides and oligoribonucleotides via coupling in aqueous solution

Abstract

Peptido RNAs are hybrid molecules with a phosphoramidate link between the N‐terminus of a peptide and the 5'‐phosphate of an oligoribonucleotide. Such species are formed in spontaneous co‐oligomerizations of amino acids and ribonucleotides in aqueous condensation buffer. To shed light on the properties of these fascinating molecules, a synthetic method for their preparation in monodisperse form is needed. Herein, we report how peptido RNAs can be prepared via solution‐phase coupling of unprotected peptides and oligoribonucleotides in aqueous solution. The preferred protocol uses pre‐activation of the 5'‐phosphate of the RNA as an imidazolide at pH 6.5, followed by precipitation and coupling to the peptide at pH 8 with an organocatalyst. The procedure gave peptido RNAs from water‐soluble peptides and synthetic oligoribonucleotides in up to 68 % yield. The method is convenient and inexpensive and can produce NMR quantities, opening the door to the systematic exploration of the chemistry of peptido RNAs.