Dual Role of Hydrophobic Racemic Thioesters of α-Amino Acids in the Generation of Isotactic Peptides and Co-peptides in Water; Implications for the Origin of Homochirality

Details Dual Role of Hydrophobic Racemic Thioesters of α-Amino Acids in the Generation of Isotactic Peptides and Co-peptides in Water; Implications for the Origin of Homochirality Dual Role of Hydrophobic Racemic Thioesters of α-Amino Acids in the Generation of Isotactic Peptides and Co-peptides in Water; Implications for the Origin of Homochirality

Feb 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010oleb...40...51i&link_type=abstract

Origins of Life and Evolution of Biospheres, Volume 40, Issue 1, pp.51-63

Physics

Homochiral Oligopeptides, Desymmetrization Of Racemic Isotactic Oligopeptides, Racemic Α-Amino Acid-Thioesters, Origin Of Homochirality Of Peptides, Maldi-Tof Ms

Scientific paper

Thioesters of α-amino acids are considered as plausible monomers for the generation of the primeval peptides. DL-Leucine-thioethyl esters (LeuSEt), where the L-enantiomer was tagged with deuterium atoms, undergo polycondensation in water or in bicarbonate or imidazole buffer solutions to yield mainly heterochiral (atactic) peptides and diketopiperazine, as analyzed by MALDI-TOF and ESI mass-spectrometry. In variance, when polymerization of DL(d10) -Leu, first activated with N,N'-carbonyldiimidazole, then initiated with ethanethiol or with DL(d3) -LeuSEt yielded a library of peptides up to 30 detectable residues where those of homochiral sequence (isotactic) are the dominant diastereoisomers. At these conditions, racemic β-sheets are formed and operate as stereoselective templates in the process of chain-elongation. Isotopic L: L(d10)-Leu co-peptides were obtained in the polymerization of L(d10)-Leu with L-LeuSEt. By contrast, mixtures of oligo- D-Leu and oligo- L(d10)-Leu were obtained in the polymerization of mixtures of D-LeuSEt with activated L(d10)-Leu. Isotactic co-peptides containing Leu and Val residues were formed in the polymerization of mixtures of activated DL(d8)-Val with DL(d3) -LeuSEt in water, implying that the racemic β-sheets exert regio-enantio-selection but not chemo-selection. A reaction pathway is suggested, where LeuSEt operates both as initiator of the reaction as well as a multimer.

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