Molecular Evolution of N-Containing Cyclic Compounds in the Parent Body of the Murchison Meteorite

Primitive meteorites contain various classes of organic compounds. Because the molecular distribution in these meteorites is not fully clarified, we do not yet understand the comprehensive formation mechanism(s) of extraterrestrial organic compounds. In this study, diverse and abundant alkylated homologues of N-containing cyclic compounds were identified in the methanol extract of the Murchison meteorite by electrospray ionization using high-performance liquid chromatography/ultrahigh-resolution mass spectrometry. More than 600 positive ions were assigned to C_nH_mN⁺ and C_nH_mN₂ ⁺, in which saturated and unsaturated alkylated pyridines and alkylimidazoles are predominant. Both can be synthesized from aldehydes and ammonia through aldol condensation and imine formation under an alkaline environment. Further redox reactions could have proceeded to make these molecules evolve to various CHN compounds, including alkylpiperidines and pyridine carboxylic acids. This study indicates that aldol condensation and formose reaction with ammonia are an important mechanism for the molecular evolution of N-containing compounds in the asteroid.