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

作者：Illos Roni A; Clodic Gilles; Bolbach Gerard; Weis**uch Isabelle; Lahav Meir^*

来源：Origins of Life and Evolution of the Biosphere, 2010, 40(1): 51-63.

DOI：10.1007/s11084-009-9186-1

• Homochiral oligopeptides
• Desymmetrization of racemic isotactic oligopeptides
• Racemic alpha-amino acid-thioesters
• Origin of homochirality of peptides
• MALDI-TOF MS

Thioesters of alpha-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(d(10))-Leu, first activated with N,N'-carbonyldiimidazole, then initiated with ethanethiol or with DL(d(3))-LeuSEt yielded a library of peptides Lip to 30 detectable residues where those of homochiral sequence (isotactic) are the dominant diastereoisomers. At these conditions, racemic beta-sheets are formed and operate as stereoselective templates in the process of chain-elongation. Isotopic L:L(d(10))-Leu co-peptides were obtained in the polymerization of L(d(10))-Leu with L-LeuSEt. By contrast, mixtures of oligo-D-Leu and oligo-L(d(10))-Leu were obtained in the polymerization of mixtures of D-LeuSEt with activated L(d(10))-Leu. Isotactic co-peptides containing Leu and Val residues were formed in the polymerization of mixtures of activated DL(d(g))-Val with DL(d(3))-LeuSEt in water, implying that the racemic P-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.

• 出版日期2010-2