In earlier studies, we showed that certain low-molecular-weight carboxylic acids (profens, amino acids, hydroxy acids) can undergo spontaneous in vitro chiral conversion accompanied by condensation to from oligomers, and we proposed two simple models to describe these processes. Here, we present the results of investigations using non-chiral high-performance liquid chromatography with diode array detector (HPLC-DAD) and mass spectrometry (MS) on the dynamics of peptidization of S-, R-, and rac-phenylglycine dissolved in 70% aqueous ethanol and stored for times up to one year. The experimental results demonstrate that peptidization of phenylglycine can occur in an oscillatory fashion. We also describe, and carry out simulations with, three models that capture key aspects of the oscillatory condensation and chiral conversion processes.

Abstract:In an earlier study, we obtained experimental evidence of the oscillatory transenantiomerization of selected profen drugs (e.g., S-(+)-ibuprofen, S-(+)-naproxen, and S-(+) and R-(−)-flurbiprofen) dissolved in aqueous, aqueous-organic, and purely organic liquid media. This process was apparently catalyzed by basic or amphiprotic environments and involved ketoenol tautomerism, and the self-organization of molecules in the solution via association of the carboxylic functional group of profens through hydrogen bonding to form mixed H-bonded associates with the remaining constituents of the solution. A model of the oscillatory transenantiomerization of profens was also developed by adapting an earlier oscillatory model, the Templator. Our new model comprises two linked Templators. The essence of the Templator model adapted to the oscillatory transenantiomerization of profens is the assumption that the H-bonded profen homodimer acts as a template, able to generate new dimers having the same steric configuration as their respective monomeric units.As profens belong to the class of 2-arylpropionic acids (2-APAs), we concluded that the phenomenon of oscillatory transenantiomerization may occur in other 2-APAs as well, among them those amino acids whose molecular structure can formally be derived from propionic acid. Thus, in this study, we Address correspondence to Teresa Kowalska, Institute of Chemistry, University of Silesia, 9 Szkolna Street, 40-006 Katowice, Poland. E-mail: kowalska@us.edu.pl Oscillatory Transenantiomerization of L--Phenylalanine 1987focus our attention on L--phenylalanine (LPA; one of the nine amino acids essential for humans). Using thin layer chromatography (TLC) and polarimetry, we demonstrate the ability of LPA to undergo oscillatory transenantiomerization analogous to that observed with profens. The selforganization of molecules in a 70% ethanol solution of LPA is confirmed with photographs taken in UV light ( = 254 nm). Finally, we propose a skeleton molecular mechanism for the transenantiomerization of LPA and simulate the oscillatory interconversion of its L and D forms with two linked Templators.

In earlier studies, we have collected experimental evidence (mostly from thin‐layer chromatography and polarimetry) on the spontaneous oscillatory in vitro chiral conversion of simple carboxylic acids dissolved in 70% aqueous ethanol. To elucidate this phenomenon, we developed a simple theoretical model of two linked Templators. Recently, we have obtained additional experimental evidence of the spontaneous condensation of chiral carboxylic acids, based on the biuret test (amino acids), high performance liquid chromatography, and 13C NMR spectroscopy (profens and hydroxy acids). We briefly describe our experimental results in the context of the existing literature and outline an improved theoretical model for these phenomena. Our system resembles in some respects the reported oscillatory condensation of organic silanols. Here, the key reaction is the formation of carboxylic acid‐derived enols. Finally, we discuss the importance of the oscillatory chiral conversion of simple carboxylic acids for biochemistry, pharmacology, and related life sciences. Copyright © 2010 John Wiley & Sons, Ltd.

In this report we provide thin-layer chromatographic evidence that phenylglycine dissolved in 70% aqueous ethanol and kept at ambient temperature (22°C) undergoes spontaneous peptization, as additionally confirmed by use of the biuret test. It was also shown that an important precondition for instantaneous peptization of phenylglycine is the simultaneous presence of the R and S antimers in solution, and the most spectacular peptization effect is obtained with racemic R,S-phenylglycine. An assumption is made that polycondensation of phenylglycine results from its ability to undergo spontaneous oscillatory chiral conversion and can be regarded as a step following enolization, and competitive with chiral conversion.

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