Prebiotic syntheses

The spontaneous, prebiotic formation of purines from hydrogen cyanide or formamide is a fascinating subject. Adenine is formally the pentamer of hydrogen cyanide. 

There is good reason to assume that formaldehyde, being formed photo-chemicaUy from carbon dioxide and water vapour, or by electrical discharge from methane and water vapour, was ubiquitous on the newly formed Earth. Hydrogen cyanide results likewise from electrical discharge of nitrogen/ methane mixtures. 

In their experiments, Joan Oro andlater Leslie E. Orgel and Alan W Schwartz [499] could detect purines as oligomerisation products of hydrogen cyanide or hydrogen cyanide/formaldehyde mixtiu-es. Furthermore, formaldehyde accelerates the oligomerisation of hydrogen cyanide. 

Most recently, Greg Springsteen proposed a pathway for the formation of adenine from formamide. [500] 

Hydrogen cyanide is produced industrially by thermolysis of formamide, or from methane and ammonia on platinum-rhodium catalysts (following a process developed by Leonid Andrussow (1896-1988) in 1927 at BASF in Ludwigs-hafen) (Fig. 5.196). 

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Palchetti I, Mascini M (2005) Electrochemical Adsorption Technique for Immobilization of Single-Stranded Oligonucleotides onto Carbon Screen-Printed Electrodes. 261 27-43 Pascal R, Boiteau L, Commeyras A (2005) From the Prebiotic Synthesis of a-Amino Acids Towards a Primitive Translation Apparatus for the Synthesis of Peptides. 259 69-122 Paulo A, see Santos I (2005) 252 45-84 Perez EM, see Leigh DA (2006) 265 185-208 Perret F, see Coleman AW (2007) 277 31-88 Perron H, see Coleman AW (2007) 277 31-88 Pianowski Z, see Winssinger N (2007) 278 311-342 Piestert F, see Gansauer A (2007) 279 25-52... 

Saladino R, Crestini C, Costanzo G, DiMauro E (2005) On the Prebiotic Synthesis of Nucle-obases, Nucleotides, Oligonucleotides, Pre-RNA and Pre-DNA Molecules. 259 29-68 Santos I, Paulo A, Correia JDG (2005) Rhenium and Technetium Complexes Anchored by Phosphines and Scorpionates for Radiopharmaceutical Applications. 252 45-84 Santos M, see Szathmdry E (2005) 259 167-211... 

Several institutes throughout the world immediately began to carry out experiments on prebiotic chemistry. At this point, we need to realize that the prebiotic synthesis of protein building blocks is only a first step towards solving the biogenesis problem. Put simply, it is a method for making bricks which will later be used in building a multi-storey office block ... 

Among the various theories and hypotheses concerning the prebiotic synthesis of biomolecules, processes occurring at the surfaces of minerals are becoming much more popular. The minerals can serve three different functions ... 

Carbohydrates are still difficult to deal with in prebiotic chemistry although the first laboratory syntheses of carbohydrates were described more than 150 years ago, their prebiotic synthesis is still unclear. 

Thus, the estimates for the rates of the prebiotic synthesis of biomolecules also need a drastic downward correction the hypothetical primeval soup then becomes much thinner ... 

This reaction looks simple, but an enzyme-free prebiotic synthesis, in particular involving pyrimidine bases, is still very difficult. It is possible that completely new synthetic strategies will need to be devised. 

Keefe et al. (1995) from Stanley Miller s laboratory reported a possible prebiotic synthesis of pantetheine, the part of the CoA molecule without its ADP moiety. They were able to synthesize the CoA precursor from P-alanine, pantoyllactone and cysteamine. This condensation requires concentration of the reaction mixture the warm lagoon theory is required here in order to achieve prebiotic conditions ... 

The pH of the oceans forming the primordial soup is important in controlling the charged nature, or otherwise, of the amino and carboxylic acid species and hence their chemistry. Generating reaction schemes for the prebiotic synthesis of molecules requiring basic conditions will not be relevant if the oceans are acidic. Consider dissolving CO2 into water, simply written as ... 

Moderately simple syntheses have been performed for the purines cytosine and uracil but nothing seems to work as a prebiotic synthesis of the pyrimidines. Then adding the sugar ribose to the base makes them nucleosides and one phosphoric acid residue makes it a nucleotide, or specifically a mononucleotide a rare but curiously important sequence of events in present-day life but perhaps not for prebiotic chemistry and early life forms. 

Strecker synthesis The prebiotic synthesis of amino acids. 

Several factors indicate that the amino acids detected in all of these carbonaceous chondrites are indigenous and that they must have originated abiotically. First, the presence of protein and non-protein amino acids, with approximately equal quantities of D and L enantiomers points to a nonbiological origin and precludes terrestrial contamination. In addition, the non-extractable fraction of the Murchison is significantly heavier in 13C than terrestrial samples. Finally, the relative abundances of some compounds detected resemble those of products formed in prebiotic synthesis experiments. The aliphatic hydrocarbons are randomly distributed in chain length, and the C2, C3, and C4 amino acids have the highest concentrations (i.e., the most easily synthesized amino acids with the least number of possible structures are most abundant) [4]. 

Pascal R, Boiteau L, Commeyras A (2005) From the Prebiotic Synthesis of a-Amino Acids Towards a Primitive Translation Apparatus for the Synthesis of Peptides. 259 69-122 Paulo A, see Santos I (2005) 252 45-84... 

The prebiotic synthesis of pyrimidines is based on cyanoacetylene, which is obtained in good yields by sparking mixtures of methane and nitrogen and by the... 

It should be kept in mind that these prebiotic syntheses concern only the bases, and not the mononucleotides of the nucleic acids. The mononucleotide consists of three moieties attached to each other - the base, the phosphate, and the sugar - and we do not yet know how this prebiotic synthesis may have taken place. 

Figure 3.5 The prebiotic synthesis of pyrimidines of nucleic acids. (From Miller, 1998.)...

Enzymes and nucleic acids are not simply polymers, they are copolymers. This seems to be a trivial observation, and partly is however it bears significance to an often forgotten point, that the study of the prebiotic synthesis of polypeptides and nucleic acids - and their properties - cannot ignore the general rules of copolymerization. 

Chemical activation is indeed the weak point of the prebiotic chemistry of polycondensation. In principle, this should be a prebiotic activation, namely a kind of spontaneous reaction under prebiotic conditions. Several more or less friendly activation methods have been used in the field, and most of them cannot, reasonably, be called prebiotic. On the other hand, the chemist must start working with some tool at hand. Let us now take a few examples from the literature on the prebiotic synthesis of biopolymers. 

In particular, the aminoacyl phosphate derivatives of 5 -AMP could condense to a polypeptide containing up to 56 residues. This is certainly a very elegant and impressive reaction, hut its relevance from the point of view of prebiotic chemistry is doubtful since, as already mentioned, it is not obvious whether and to what extent this reaction can be extended to co-oligopeptides. Also, of course, AMP cannot be considered (thus far) a prebiotic molecule. Here again we encounter the old problem of the RNA world, the fact that the prebiotic synthesis of mononucleotides is not understood. There is no doubt that if a robust and credible prebiotic route... 

There is another general lesson that we can learn from these experiments. If our proteins are the product of contingency, most probably the pathway to their prebiotic synthesis cannot be reproduced in the laboratory. This is indeed the bottle neck in the bottom-up approach to the origin of life. 

We have learned previously that the synthesis of exactly our proteins on Earth is doomed by conhngency - we cannot hope to hnd out the exact condihons that deternuned the hnal sequence of a given protein or a nucleic acid from our Earth. Once this biher assertion is accepted, we should at least attempt experiments that show that the prebiotic synthesis of some specihc sequence in many identical copies is possible. Also, it is perhaps surprising that there has been so little reported in the... 

More convincing evidence has been obtained for the synthesis of simpler compounds, such as straight-chain fatty acids. This observation is important because, as we have already seen in the chapter on self-organization and self-reproduction, these compounds form stable vesicles. Prebiotic synthesis of these compounds was reported for example by Nooner et al. (1976). More recently monocarboxylic acids have been observed from a spark discharge synthesis (Yuen et al, 1981) and from a Fischer-Tropf type of reaction (McCollom et al, 1999 Rushdi and Simoneit,... 

I believe that the bottom-up approach to the origin of life will enjoy a considerable boost, when conditions are found for the prebiotic synthesis of many identical copies of long (>30) co-oligopeptide or co-oligonucleotide sequences. This would at least show that the prebiotic synthesis of enzymes and/or RNA is in principle possible. This remains the main problem with the prebiotic RNA world. 

Bujdak, J., Eder, A., Yongyai, Y., Faybikova, K., and Rode, B. M. (1995). Peptide chain elongation a possible role of montmorillonite in prebiotic synthesis of protein precursors. Orig. Life Evol. Biosph., 5,431 1. 

Studies in prebiotic synthesis. IV, The conversion of 4-aminoimidazole-5-carbonitrile derivatives to purines. J. Mol. Biol, 38, 121-8. 

FIGURE 26-36 Possible prebiotic synthesis of adenine from ammonium cyanide. Adenine is derived from five molecules of cyanide, denoted by shading. 

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