The Origins of Homochirality Examined by Using Asymmetric Autocatalysis

Abstract

Pyrimidyl alkanol was found to act as an asymmetric autocatalyst in the enantioselective addition of diisopropylzinc to pyrimidine-5-carbaldehyde. Asymmetric autocatalysis of 2-alkynylpyrimidyl alkanol with an extremely low enantiomeric excess (ca. 0.00005% ee) exhibits enormous asymmetric amplification to afford the same compound with >99.5% ee. This asymmetric autocatalysis with amplification of ee has been employed to examine the validity of proposed theories of the origins of homochirality. Circularly polarized light, quartz, sodium chlorate, cinnabar, chiral organic crystals and spontaneous absolute asymmetric synthesis were considered as possible candidates for the origin of chirality; each could act as a chiral source in asymmetric autocatalysis. Asymmetric autocatalysis can discriminate the isotope chirality arising from the small difference between carbon (carbon-13/carbon-12) and hydrogen (D/H) isotopes. Cryptochiral compounds were also discriminated by asymmetric autocatalysis.

Natural Abundance Isotopic Chirality in the Reagents of the Soai Reaction

“…This, obviously, is due to the asymmetric natural abundance of the isotopes of H and C. However, even so, the percentages of expected enantiomeric excesses are much higher than the experimentally documented sensitivity threshold of the Soai reaction [16][17][18][19][20][37][38][39]41,42].…”

“…It has also been proved experimentally that such inductor molecules may include enantiomers of simple chiral organic compounds with chirality due only to stable isotopic substitution [32][33][34][35][36][37][38][39]. The sensitivity towards any chiral additive, or even a very small excess of the product results in the capacity of this reaction to produce very high enantiomeric excess from infinitesimally low one.…”

Stochastic and empirical models of the absolute asymmetric synthesis by the Soai-autocatalysis

“…Such reaction, called absolute asymmetric synthesis (AAS), would be the dream of all preparative organic chemists or of chemical industry managers [24]. At present, only one sufficiently documented example of AAS is known: the Soai reaction [25][26][27][28][29][30][31][32][33].…”

Chirality Synchronization of Hydrogen‐Bonded Complexes of Achiral N‐Heterocycles

“…This mesophase was proposed to result from the helical packingo fh ydrogenbonded triazine aggregates,p roviding long-range chirality synchronization. [3] Nowadays,t he focus has shifted to the spontaneous emergence of homogeneous chirality in ordered assemblies formed in supramolecular systems [4][5][6][7] by bulk crystallization (e.g., Viedma ripening) [8] and the self-assembly of achiral molecules at interfaces [9] and in helical aggregates. [2] Enantioselective synthesis,c atalysis,a nd autocatalysis have successfully been developed in recent decades for the synthesis of enantiopure molecules from achiral (prochiral) precursors.…”

“…[2] Enantioselective synthesis,c atalysis,a nd autocatalysis have successfully been developed in recent decades for the synthesis of enantiopure molecules from achiral (prochiral) precursors. [3] Nowadays,t he focus has shifted to the spontaneous emergence of homogeneous chirality in ordered assemblies formed in supramolecular systems [4][5][6][7] by bulk crystallization (e.g., Viedma ripening) [8] and the self-assembly of achiral molecules at interfaces [9] and in helical aggregates. [10][11][12][13] However,s urprisingly,s pontaneous symmetry breaking was recently also observed in liquid crystalline phases, [14,15] ranging from lamellar phases [16] to cubic, [17,18] columnar, [14,15,19] and nematic phases, [20] and even in isotropic liquids of achiral compounds.…”