Prebiotic Synthesis of Simple Sugars by an ..
Sugar-driven prebiotic synthesis of ammonia from nitrite.
The proposed occurrence of hydrogen cyanide 5 on the early Earth is supported by the propensity of this simple small molecule to form when organic matter is bombarded with excess energy,, and by its widespread presence in the solar system and beyond in comets, the atmospheres of planets and their satellites, and in the interstellar medium–. Furthermore, 5 is strongly implicated in prebiotic chemistry, mainly because of the essential role it plays in the Strecker synthesis of amino acids and the Oró synthesis of adenine. Accordingly, we wondered if the key cyanohydrin nitrile group reduction step of the Kiliani–Fischer synthesis could be effected selectively under prebiotically plausible conditions, in which case iterative homologation of formaldehyde 1 with 5 would be possible. If 5 itself could also be selectively reduced and thus converted to 1 we reasoned that it might even be possible to generate sugars starting from 5 as the sole carbon source. The finely tuned conditions of the reduction step in the conventional synthetic organic Kiliani–Fischer synthesis suggested that a prebiotic variant might not be found, but the attractiveness of the overall route, in terms of its simplicity, warranted such a search.
A prebiotic synthesis of long-chain isoprenoids ..
As a first foray into this area we chose to study the photochemistry of copper(I) cyanide complexes in aqueous solutions of hydrogen cyanide 5, because we anticipated that this would reveal the basic features of cyanometallate photoredox systems chemistry. Piecing together literature reports,, a copper(I) ↔ copper(II) photoredox cycle can be drawn (). On irradiation with ultraviolet light, tricyanocuprate(I) 8 undergoes photooxidation to tricyanocuprate(II) 9, with concomitant production of a hydrated electron. Dimerization of 9 gives the cyano-bridged binuclear complex 10, which then reductively eliminates cyanogen 11, giving dicyanocuprate(I) 12. Complexation of additional cyanide ions by 12 then regenerates 8 and completes the cycle. The cycle operates with or without hydrated electron scavengers such as nitrate, and in the absence of such scavengers it was noted that relatively large molecules could be detected by mass spectroscopy. These large molecules were tentatively suggested to be oligomers produced by base-catalysed polymerization of 5. We have repeated this experiment with no added scavengers of hydrated electrons, and examined the intermediates and products by nuclear magnetic resonance (NMR) spectroscopy. In this way we have discovered a remarkable iterative Kiliani–Fischer systems chemistry synthesis of glycolaldehyde 2 and glyceraldehyde 3 that is initiated by the reduction of 5.