Experimental and Model Investigation of the Oscillatory Transenantiomerization of L-α-Phenylalanine

Abstract

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.

Condensation oscillations in the peptidization of phenylglycine

“…The reaction occurs in a nonmonotonic fashion and is apparently linked with the oscillatory chiral conversion of amino acids reported previously [4][5][6]. The S-and Renantiomers appear to differ somewhat in their dynamics, a phenomenon that may arise from the presence of different amounts of trace impurities in the commercial samples.…”

“…We first observed oscillatory chiral conversion in selected profens: S(+)-ibuprofen, S (+)-naproxen, S,R(±)-2-phenylpropionic acid, S(+)-flurbiprofen, R(-)-flurbiprofen, and S,R(±)-ketoprofen [1-3]. Later we described an analogous behavior in several amino acids: L-alanine, L-a-phenylalanine, and L-tyrosine [4][5][6]. We have characterized similar phenomena in selected hydroxy acids [7,8] (L-lactic acid, R-a-hydroxybutyric acid, S-a-hydroxybutyric acid, R-mandelic acid, and S-mandelic acid) as well.…”

“…We have suggested two simple models of oscillatory chiral conversion [11]. The simpler model [5,12] is based on autocatalytic dimerization. Oscillations appear in this model in both enantiomer subsystems.…”

On ups and downs by analysis of profen drugs. A mini review

“…[21], the theoretical model of two linked Templators was first coined, aiming to interpret the observed phenomenon of spontaneous oscillatory chiral conversion of the low-molecular-weight carboxylic acids. In this model, the concept of a molecular template playing the crucial role in the oscillatory process appeared, which was influenced by another model proposing similar interpretation of a different oscillatory process and originally named as the Templator model [22,23].…”

“…The model proved to be capable of reproducing the oscillatory concentration changes of the (R) and (S) antimers, and those of the enantiomeric excess [21]. Moreover, it was implemented with onedimensional [21] and two-dimensional [24] diffusion terms in order to visualize the formation and time evolution of spatial patterns that were otherwise invisible in the colorless profen solutions. Further extensions of the same model were proposed in Refs [25] and [26].…”