Condensation of vaporous amino acids in the presence of silica. Formation of bi- and tricyclic amidines

Abstract

Amino acids (alanine, valine, norvaline, leucine, and 2-aminoisobutyric acid) were subjected to repeated (5-9 times) sublimation in the presence of silica at temperature of 220-240 degrees C. The major amino acid condensation products were diketopiperazines (DKPs) in yields of 27-89%. Mixtures of by-products have been isolated from the DKPs by means of chloroform extraction. On the basis of fast atom bombardment mass spectrometric studies of the mixtures it is proposed that under these conditions further dehydration proceeds resulting in bicyclic (BCA) and tricyclic (TCA) amidine derivatives of DKPs; the BCA formation has been confirmed by means of IR and 1H NMR spectroscopy in the case of 2-aminoisobutyric acid. During the sublimation, thermal destruction of the cyclic products was also observed accompanied by the cycle degradation and cleavage of alkyl substituents. The BCAs and TCAs are considered as possible sources of linear di- and tripeptides.

Glycine oligomerization on silica and alumina

“…They demonstrated the catalytic ability of silica and alumina surfaces to convert amino acid vapors (in vacuum and temperatures above 200~ into oligopeptides, cyclic anhydrides [12,13] and other reaction products [14]. The "vacuum environments" do not reflect the assumed prebiotic conditions and amino acid decomposition would precede their sublimation under normal air pressure.…”

Silica, Alumina, and Clay-Catalyzed Alanine Peptide Bond Formation

“…Clay minerals promote the polymerization of activated amino acid adenylates (PaechtHorowitz 1977(PaechtHorowitz , 1978Paecht-Horowitz and Eirich 1988;Paecht-Horowitz and Lahav 1977;Paecht-Horowitz et al 1970). At temperatures above the boiling point of water, polymerization of amino acids on silica or alumina was also observed without activation (Rohlfing and McAlhaney 1976;Basiuk et al 1990Basiuk et al , 1991Basiuk et al , 1992Gromovoy et al 1991;Basiuk 1992;Basiuk and Gromovoy 1994).…”

Imidazo[1,2-a]pyrazine-3,6-diones Derived from α-Amino Acids: A Theoretical Mechanistic Study of Their Formation via Pyrolysis and Silica-Catalyzed Process

“…The linkage can be formed by the condensation of the COOH group of the amino acid and the SiOH group of the surface releasing one water molecule. According to our previous results, this process is favorable under anhydrous conditions and elevated temperatures. , The ester-type linkage can be identified in IR spectra due to the ν C  O band at 1750−1760 cm -1 . ,, For several decades, it was believed to be an “activated intermediate” in the silica-catalyzed intermolecular condensation of amino acids. − ,− , On the other hand, recent quantum chemical calculations by Ugliengo's group 39 did not confirm the enhanced reactivity of this linkage. We hoped to provide an additional insight for our particular type of surface reactions.…”

“…For example, due to the abundance of metal cations (e.g., Na, Ca, Al, and Fe) in clays and seawater, the salt-induced peptide formation reaction was suggested to be the simplest and most universal mechanism to produce peptides from amino acid building blocks . Nevertheless, most studies in this area − focus on the role of catalytically active inorganic oxide surfaces. In turn, pure cation-free silica and alumina became the most commonly used models of clays and other complex minerals, where the role of surface silicon and aluminum atoms in the process of amino acids activation became another specific problem.…”