Cytosine, synthesis from cyanoacetylene

Reports of the synthesis of cytosine from cyanoacetylene (or its hydrolysis product cyanoacetaldehyde) with cyanate, cyanogens or urea show that these substances react faster with nucleophilic compounds to give side products than to give the required main product. In addition, the formation of cytosine requires concentrations which are unrealistic in prebiotic environments. 

The synthesis of the pyrimidines involves cyanoacetylene, which is synthesised in good yield from discharge reactions of CH4 and N2. The reaction with cyanoacetylene or cyanoacetylaldehyde, in a concentrating environment, produces cytosine and uracil according to Figure 8.6. 

Some time ago, I postulated a route involving the condensation of a, / -unsaturated three-carbon compounds (e.g. acrylonitrile) with urea for the synthesis of pyrimidines. Very small yields of uracil were obtained in this manner in our laboratory. - A better C3 precursor appears to be cyanoacetylene, which, after HCN, is the major nitrogen-containing product formed from methane and nitrogen by electrical discharges. Cyanoacetylene condenses with urea or cyanate to form cytosine in 20 % yield as shown by Sanchez, et. Cytosine is readily converted into uracil by deamination. Furthermore, by... 

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