Asymmetric Induction by a Nitrogen ¹⁴N/¹⁵N Isotopomer in Conjunction with Asymmetric Autocatalysis

Abstract

Chirality arising from isotope substitution, especially with atoms heavier than the hydrogen isotopes, is usually not considered a source of chirality in a chemical reaction. An N 2 ,N 2 ,N 3 ,N 3‐tetramethyl‐2,3‐butanediamine containing nitrogen (14N/15N) isotope chirality was synthesized and it was revealed that this isotopically chiral diamine compound acts as a chiral initiator for asymmetric autocatalysis.

Chemical Mechanisms of Prebiotic Chirality Amplification

“…Summarizing the discussion above, we would like to point out that only the models of chirality amplification based on DNLEs, i.e., on asymmetric autocatalysis and asymmetric autoamplification/dynamic chirality control [ 33 , 34 , 42 , 47 ], stand close to the expected conditions for mimicking natural selection in chemical systems [ 55 ]. The DNLE-based models, dealing with far-from-equilibrium chemical systems, operate by analogy with competition-based biological processes (which are fundamentally irreversible) [ 48 , 55 , 56 ], while the models exploiting crystallization-assisted chiral amplification [ 53 , 54 ] or “hyperpositive” nonlinear effects [ 49 ] lack this similarity.…”

“…It is thus compatible with the hypothesis of extraterrestrial introduction of organic matter with initial small enantiomeric imbalance ( Figure 2 ). It is important to notice that the asymmetric bias could be introduced to the Soai reaction not only by nonracemic chiral product/autocatalyst but also by extraneous chiral additives, such as quartz, chiral inorganic crystals, helical silica gel, small chiral (including isotopically chiral) organic molecules [ 20 , 32 – 34 ], and the abiogenous chiral amino acids obtained from the Murchison meteorite [ 35 ], simulating the “chiral triggers” of extraterrestrial origin.…”

A Quantification of the Soai Reaction

“…The Soai reaction, that is, the addition of diisopropylzinc to prochiral pyrimidine carbaldehydes, is a long‐standing ambition of organic chemists . It achieves remarkable enantiomeric excess ( ee ) amplification because of asymmetric autocatalysis and is able to recognize a huge variety of chiral and cryptochiral additives, among them even chiral compounds because of isotopic substitution ( 1 H/ 2 H, 12 C/ 13 C, 16 O/ 17 O, or 14 N/ 15 N) . This extreme sensitivity originates from another extraordinary feature: namely, the Soai reaction is able to display spontaneous mirror‐image symmetry breaking (MISB), also known as spontaneous absolute asymmetric synthesis, by yielding enantiomerically enriched pyrimidyl alkanols even in the absence of any external chiral influence.…”

Isotope chirality in long‐armed multifunctional organosilicon (“Cephalopod”) molecules

“…Second, the organosilicon molecules shown in Figure are sophisticated models also for asymmetric autocatalysis (Soai reaction) . Presently, the Soai reaction is the only well‐documented chemical reaction which is efficient enough towards chiral induction permitting (1) observation of very small quantities of inductor molecules (including its own product), (2) detection of very faint structural asymmetry (cryptochirality), including even (3) asymmetric induction by isotope chirality . This latter feature appears to be connected with the structure of intermediates of this particular reaction.…”