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.