It has been suggested that the first informational macromolecules on early Earth were composed of different nucleobases and a backbone different from ribose phosphate due to the challenges of synthesizing nucleotides under plausible prebiotic conditions. The goal of this study was to elucidate chemical reaction pathways for nitrogen heterocycle adducts synthesized in Miller Urey spark discharge experiments by means of retrosynthetic analysis. Six reactions containing a nitrogen heterocycle and a synthetic precursor were heated and analyzed by electrospray ionization mass spectrometry. Two modifications were commonly observed in reactions containing a nitrogen heterocycle and glycolonitrile, which resemble parts of the backbone of peptide nucleic acids (PNA). These types of reactions may have been robust on early Earth and represent the first steps in synthesizing alternative nucleotides.