Proline autocatalysis in the origin of biological enantioenriched chirality.

Abstract

Biological enantioenriched chirality is a phenomenon that in living organisms, amino acids and carbohydrates typically have the same absolute configuration. Perhaps one of the earliest attempts to delineate the origins of this phenomenon was a theory known as asymmetric autocatalysis, a reaction in which the structures of the chiral catalyst and the product are the same, and in which the chiral product acts as a chiral catalyst for its own production. In theory, this would mean that small asymmetries in the product will propagate rapidly. However, autocatalysis also relies on the cross-inhibition of chiral states, something that would not likely be possible on primordial Earth. But recently, theories on asymmetric autocatalysis have begun to resurface as more recent findings indicate that other mechanisms exist to stabilize the homochiral states. In this study, I propose an autocatalytic cycle, and using density functional theory, prove that (1) it is plausible on primordial Earth, and (2) it propagates arbitrary asymmetries in proline. Thus, facilitating asymmetry in proline and allowing access to a wide variety of asymmetric proline-catalyzed reactions, including those involved in the synthesis of amino acids and carbohydrates from achiral precursors.