Synthesis of molecularly encoded oligomers using a chemoselective "AB + CD" iterative approach

Abstract

A library of eight sequence-defined model oligomers, whose sequence is based on a (0,1) binary code, is prepared through chemoselective repeating cycles of amidification and copper-assisted alkyne-azide cycloaddition reactions from a non-modified Wang resin. This library is constructed from two AB (A = acid, B = alkyne) building blocks, i.e., 4-pentynoic acid and 2-methyl-4-pentynoic acid acting, respectively, as non-coding (0) and coding (1) monomer, and 1-amino-11-azido-3,6,9-trioxaundecane as complementary CD (C = amine, D = azide) spacer building block. In particular, encoded triads are synthesized by consecutive covalent attachment of five building blocks (i.e., three coding/non-coding monomers and two spacers). In this communication, optimal protocols for the synthesis of the targeted oligomers are reported along with their full characterization by (1) H NMR, MALDI-TOF mass spectrometry, and size-exclusion chromatography. It is found that all possible encoded triads (i.e., eight possibilities) could be synthesized using this approach. Indeed, monodisperse sequence-defined oligomers are prepared and characterized in all cases.

Keywords: amidification; copper-assisted alkyne-azide cycloaddition; sequence-controlled oligomers.