Pyruvic acid represents a key molecule in prebiotic chemistry to form metabolites and amino acids. Without liquid water on the early Earth, endogenous formation of pyruvic acid is unlikely, and an exogenous delivery constitutes an appealing alternative. However, despite the detection of more than 200 molecules in space, pyruvic acid is elusive. Here, we describe its formation by barrierless recombination of hydroxycarbonyl (HOCO⋅) and acetyl (CH₃CO⋅) radicals in ices of acetaldehyde (CH₃CHO) and carbon dioxide (CO₂) modeling interstellar conditions driven by cosmic rays. Exploiting isotopically labeled ices and photoionization reflectron time-of-flight mass spectrometry, the reaction products were selectively photoionized in the temperature-programmed desorption phase and isomers discriminated based on their ionization energies. This reveals a key reaction pathway for pyruvic acid synthesis through non-equilibrium reactions in interstellar cold molecular clouds and star-forming regions, thus offering a unique entry point to abiotic organic synthesis in deep space.

丙酮酸是益生元化学中形成代谢产物和氨基酸的关键分子。在地球早期没有液态水的情况下，丙酮酸的内源性形成是不可能的，而外源性的传递则是一种有吸引力的选择。然而，尽管在太空中检测到200多个分子，丙酮酸仍然难以捉摸。在这里，我们通过羟基的barrierless重组描述其形成（HOCO⋅）和乙酰基（CH ₃ CO⋅）乙醛（CH的冰自由基₃ CHO）和二氧化碳（CO ₂）模拟由宇宙射线驱动的星际条件。利用同位素标记的冰和光电离反射飞行时间质谱，反应产物在程序升温脱附相中被选择性电离，并根据其电离能识别异构体。这揭示了星际冷分子云和恒星形成区域中丙酮酸通过非平衡反应合成的关键反应途径，从而为深空非生物有机合成提供了独特的切入点。