Conception and Synthesis of Sequence-Coded Morpholinos

Solid-phase morpholino chemistry was explored as a new route to synthesize abiological sequence-defined oligomers. Two comonomers, 0 and 1 containing (i) a chlorophosphoramidate reactive function, (ii) a trityl-protected morpholine, and (iii) a coding substituent (H or CH₃ for 0 and 1, respectively) on the morpholine ring were first synthesized and characterized. This binary alphabet was afterwards tested for the synthesis of digitally-encoded oligomers with different lengths and sequences. The oligomers were prepared on a modified polystyrene resin, cleaved, and characterized by liquid chromatography mass spectrometry. When using a repetitive cycle containing only morpholino coupling and trityl deprotection steps, the formed oligomers were not uniform. Thus, an additional capping step was added. In these conditions, uniform coded sequences were prepared in most cases. Furthermore, the oligomers were analyzed by tandem mass spectrometry. In the studied collision-induced dissociation conditions, the repeat units of the oligomers undergo two main-chain fragmentations and full sequence coverage was observed for all studied sequences. Therefore, the binary messages stored in the oligomers could be decoded and retrieved in all cases.