Free radical pathways for the prebiotic formation of xanthine and isoguanine from formamide

Free radical pathways for the synthesis of xanthine and isoguanine from formamide were studied using density functional theory (B3LYP/6-311G(d,p)). The proposed mechanisms are complex and appropriate for the non-aqueous scenario of prebiotic reactions. Formation of the carbonyl bond in the nucleobases proceeds through enol-keto tautomerization since the direct formation of the CO bond is a highly endothermic step. The mechanisms show 2-amino-imidazole as a precursor for nucleobases and polyazaporphyrin. The proposed mechanisms contribute to a further understanding of the origin of biomolecules.