The process in which bioorganic compounds earned their homochirality is still unclear. A symposium was organized in the title of “Homochirality of bioorganic compounds: Amino acids and peptides evolved first? Or Saccharides and RNA evolved first?” on the 41st conference of the Society for the Study of the Origin and Evolution of Life Japan. Seven presenters including the author of this paper talked on the theme from different points of view. This paper mainly describes a chemical evolutionary model of oligopeptides on the evolution and development of homochirality. Epimerization, segmentation, and stereospecific condensation of oligopeptides may explain the process of the development of homochirality. This paper also mentions the heterochiral pairing between L-amino acids and D-sugars, involving the metabolism of sugars.
Full explanation of the origin of terrestrial bioorganic homochirality (enantiomeric domination of L-form amino acids in proteins and D-form sugars in DNA/RNA) is one of the most important problems in astrobiology. One attractive hypothesis in the context of astrobiology (cosmic scenario) has been advocated that asymmetric radiations in space, such as circularly polarized photons or spin-polarized electrons, have induced asymmetric conditions on primitive interstellar media. We are executing cooperative works between three aspects of approaching methods (observations, experiments and computations) to clarify the cosmic scenario as below:
(1) Astronomical observations of circularly polarized radiation from various star-forming regions in space, using highly sensitive polarization detecting systems settled in the astronomical observatories.
(2) Simulated experiments with polarized quantum beams from high-energy particle accelerators irradiating amino acids or sugars and their precursor molecules, and following chemical and optical measurements of enantiomeric excesses.
(3) First principal simulating calculations of asymmetric optical responses and following asymmetric chemical reactions for amino acids or sugars and their precursor molecules.
The synergy effects of the approaches are expected to resolve the problems of the origin of terrestrial biological homochirality.
So-called chiral breaking problem on biological amino acids has intrigued many scientists for hundreds of years, but there has been no general consensus as yet. Racemization pressure is overwhelmingly powerful even in contemporary homochiral biological environment, not to speak of early global environment. It was essential for birth of life to escape from racemic world. Life could not say goodbye to non-life forever until a mechanism of enantioselectivity, which made exclusive choice of enantiomeric type, was established in an automated way by abiotic process. Author proposes it should be a basic principle that separates life from non-life.