Interstellar Formation of Lactaldehyde, A Key Intermediate in the Methylglyoxal Pathway

Aldehydes are ubiquitous in star-forming regions and carbonaceous chondrites, serving as essential intermediates in metabolic pathways and molecular mass growth processes to vital biomolecules necessary for the origins of life.

However, their interstellar formation mechanisms have remained largely elusive. Here, we unveil the formation of lactaldehyde (CH₃CH(OH)CHO) by barrierless recombination of formyl (HĊO) and 1-hydroxyethyl (CH₃ĊHOH) radicals in interstellar ice analogs composed of carbon monoxide (CO) and ethanol (CH₃CH₂OH). Lactaldehyde and its isomers 3-hydroxypropanal (HOCH₂CH2CHO), ethyl formate (CH₃CH₂OCHO), and 1,3-propenediol (HOCH₂CHCHOH) are identified in the gas phase utilizing isomer-selective photoionization reflectron time-of-flight mass spectrometry and isotopic substitution studies.

These findings reveal fundamental formation pathways for complex, biologically relevant aldehydes through non-equilibrium reactions in interstellar environments. Once synthesized, lactaldehyde can act as a key precursor to critical biomolecules such as sugars, sugar acids, and amino acids in deep space.

In contemporary biochemistry, seven is a key intermediate in the methylglyoxal pathway (purple arrows) and a precursor to the formation of critical biorelevant molecules including pyruvic acid (5), methylglyoxal (8), and lactic acid (11), linking to the tricarboxylic acid (TCA) cycle. Lactaldehyde (7) is prepared in interstellar ice analogs composed of carbon monoxide and ethanol (15) through energetic processing by galactic cosmic ray proxies. This process involves carbon–carbon bond coupling via radical–radical recombination of the formyl (HĊO, 16) with the 1-hydroxyethyl (CH₃ĊHOH, 17) radical. Lactaldehyde (7) serves as a precursor to sugar-related molecules such as glycolaldehyde (2) and lactic acid (11) thus contributing to the synthesis of sugars and sugar acids, respectively. — Nature Communications via PubMed

Interstellar formation of lactaldehyde, a key intermediate in the methylglyoxal pathway, Nature Communications via PubMed (open access)

Astrobiology, Astrochemistry