Homochirality asymmetric autocatalysis

We describe highly enantioselective asymmetric autocatalysis with amplification of chirality and asymmetric autocatalysis initiated by chiral triggers. Asymmetric autocatalysis correlates between the origin of chirality and the homochirality of organic compounds. We also describe spontaneous absolute asymmetric synthesis in combination with asymmetric autocatalysis. 

Keywords Asymmetric autocatalysis Amplification of chirality Pyrimidyl alkanol Automultiplication Origin of homochirality... 

Experimental Approaches to the Understanding of the Origins of Biological Homochirality Using Asymmetric Autocatalysis... 

Soai K, Sato I, Shibata T (2004) Asymmetric autocatalysis and the origin of homochirality of biomolecules. In Malhotra SV (ed) Methodologies in asymmetric catalysis. J Am Chem Soc, Washington, DC, p 85... 

Thus, the origin of homochirality of biomolecules might have involved the inherently achiral nucleotide base cytosine. In conjunction with the subsequent amplification of chirality by asymmetric autocatalysis, spontaneously formed chiral crystals of achiral cytosine acted as an origin of homochirality in biomolecules. The structure of cytosine indicates that the Nl-atom may be prochiral (marked by an asterisk in Fig. 3.5). In contrast, uracil and adenosine do not have asymmetric atoms. It remains unknown whether the distantly related structure of guanine can... 

Blackmond, Donna G. Asymmetric Autocatalysis and its Implications for the Origin of Homochirality. Proceedings of the National Academy of Sciences 101 (2004) 5,732-36. This review describes the kinetics of autocatalysis and possible mechanisms for spontaneous resolution of mixtures having a miniscule excess of one enantiomer. 

Blackmond DG Asymmetric autocatalysis and its implications for the origin of homochirality. Proc Natl Acad Sci USA 2004, 101(l6) 5732-5736. 

Asymmetric autocatalysis with amplification of chirality is a very efficient method of asymmetric catalysis. One of the implications is that the existence of a chemical reaction has been shown in which very slight bias of chirality can be amplified significantly to reach almost enantiopure. The reaction has been employed for the study on the origins of homochirality and on the chiral discrimination. We describe how we find the reaction and the recent aspects of asymmetric autocatalysis. 

Enantioenriched organic compounds such as leucine [34] and hexahelicene [35] with only ca. 2% ee have been induced by the irradiation with CPL. These low enantiomeric enrichments have not been correlated with the homochirality of organic compounds. We performed the direct irradiation of CPL to the asymmetric autocatalyst 1. R)- and (5)-pyrimidyl alkanols 1 exhibit positive and negative Cotton effects in circular dichroism (CD) spectra at 313 nm, respectively [36]. Therefore, the direct irradiation of rac-alkanol 1 by CPL would induce the asymmetric photodegradation of pyrimidyl alkanol 1. Indeed, direct irradiation of rac- by 1-CPL and the subsequent asymmetric autocatalysis produce highly enantioenriched (5)-alkanol 1 with >99.5% ee (Scheme 9). On the other hand, irradiation with r-CPL instead of /-CPL formed (/ )- with >99.5% ee. This process provides direct correlation of the handedness of CPL with that of the organic compound. 

Kawasaki T, Suzuki K, Hakoda Y, Soai K (2008) Achiral nucleobase cytosine acts as an origin of homochirality of biomolecules in conjunction with asymmetric autocatalysis. Angew Chem IntEd 47 496 99. doi 10.1002/anie.200703634... 

Another attempt to explain the homochirality of biomolecules is based on autocatalysis. The great advantage of asymmetric catalysis is that the catalyst and the chiral product are identical and thus do not need to be separated (Buschmann et al., 2000). The racemic mixture must have been affected by a weak perturbation in order that autocatalysis, which acts as an amplifier of enantioselectivity, could have led to only one of the two enantiomeric forms. This perturbation could have been due to the slight energy difference of the enantiomers referred to above, or to statistical fluctuations. 

---