Quantitation of α-hydroxy acids in complex prebiotic mixtures via liquid chromatography/tandem mass spectrometry

Spark discharge experiments, like those performed by Stanley Miller in the 1950s, generate complex, analytically challenging mixtures that contain biopolymer building blocks. Recently, α-amino acids and α-hydroxy acids (AHAs) were subjected to environmental cycling to form simple depsipeptides (peptides with both amide and ester linkages). The synthesis of AHAs under possible primordial environments must be examined to better understand this chemistry.

We report a direct, quantitative method for AHAs using ultrahigh-performance liquid chromatography and triple quadrupole mass spectrometry. Hexylamine ion-pairing chromatography and selected reaction monitoring detection were combined for the rapid analysis of ten AHAs in a single run. Additionally, prebiotic simulation experiments, including the first-ever reproduction of Miller's 1958 cyanamide spark discharge experiment, were performed to evaluate AHA synthesis over a wide range of possible primitive terrestrial environments.

The quantitating transition for each of the AHAs targeted in this study produced a limit of detection in the nanomolar concentration range. For most species, a linear response over a range spanning two orders of magnitude was found. The AHAs glycolic acid, lactic acid, malic acid, and α-hydroxyglutaric acid were detected in electric discharge experiments in the low micromolar concentration range.

The results of this work suggest that the most abundant building blocks available for prebiotic depsipeptide synthesis would have been glycolic, lactic, malic, and α-hydroxyglutaric acids, and their corresponding amino acids, glycine, alanine, and aspartic and glutamic acids. Copyright © 2016 John Wiley & Sons, Ltd.