MS/MS Sequencing of Digitally Encoded Poly(alkoxyamine amide)s

Monodisperse sequence-coded oligo(alkoxyamine amide)s were thoroughly investigated by tandem mass spectrometry to evaluate the robustness of this analytical approach as a reliable sequencing methodology. Studied samples were synthesized by orthogonal iterative chemistry on a solid support, and the 0/1 coding system was based on the mass of two amide synthons that alternate with a nitroxide moiety. The major fragmentation pathway experienced by these co-oligomers proceeded via homolysis of all fragile C-ON bonds between a coding unit and a nitroxide moiety. The relative rate of competing C-ON bond cleavages was observed to be sequence-dependent, offering an additional means to validate the sequences reconstructed from the MS/MS fragments. The same fragmentation rules applied for all studied samples, varying in terms of chain length, charge state, encoded sequence, end-groups, and nitroxide moiety. Ion mobility separation was coupled to MS/MS to sequence some more complex co-oligomers composed of both different nitroxides and coding units.