A Prebiotic Route to Lactate from Acetaldehyde, Cyanide and Carbon Dioxide

The atmospheric concentration of carbon dioxide (CO₂) has fluctuated throughout Earth's history. However, the role of CO₂ in prebiotic chemistry has been predominantly and limitedly postulated as a C1 precursor, which can be reduced to carbon monoxide or methane mimicking the Wood-Ljungdahl pathway. Herein we present neglected roles of CO₂ as an active promoter in accessing biologically important C3-builidng blocks such as lactate, via redox-economic reaction cycles starting from cyanide (C1) and acetaldehyde (C2). We verified that Lewis acidic CO₂ facilitates the formation of cyanohydrin of acetaldehyde under ambient conditions. Furthermore, selective protection of cyanohydrin to carbonate by atmospheric CO₂ led to anchimeric assisted hydrolysis of the nitrile group to generate lactate. This work supports both warm pond and hydrothermal vent hypotheses, postulating that a CO₂-rich primordial atmosphere and the acidic aqueous solution could have fostered the emergence of biologically relevant molecules and life itself.