Azoles as Auxiliaries and Intermediates in Prebiotic Nucleoside Synthesis.

4,5-Dicyanoimidazole and 2-aminothiazole are azoles that have previously been implicated in prebiotic nucleotide synthesis. The former compound is a byproduct of adenine synthesis, and the latter compound has been shown to be capable of separating C and C sugars via crystallization as their aminals. We now report that the elusive intermediate cyanoacetylene can be captured by 4,5-dicyanoimidazole and accumulated as the crystalline compound cyanovinyl-4,5-dicyanoimidazole, thus providing a solution to the problem of concentration of atmospherically formed cyanoacetylene. Importantly, this intermediate is a competent cyanoacetylene surrogate, reacting with aminooxazoline in formamide to give anhydrocytidine ─ an intermediate in the divergent synthesis of purine and pyrimidine nucleotides. We also report a prebiotically plausible synthesis of 2-aminothiazole and examine the mechanism of its formation. The utilization of each of these azoles enhances the prebiotic synthesis of ribonucleotides, while their syntheses comport with the cyanosulfidic scenario we have previously described.