Sugar-driven prebiotic synthesis of 3,5(6)-dimethylpyrazin-2-one: a possible nucleobase of a primitive replication process.

Reaction of glyceraldehyde with alanine amide (or ammonia) under anaerobic aqueous conditions yielded 3,5(6)-dimethylpyrazin-2-one that is considered a possible complementary residue of a primitive replicating molecule that preceded RNA. Synthesis of the dimethylpyrazin-2-one isomers under mild aqueous conditions (65 degrees C, pH 5.5) from 100 mM glyceraldehyde and alanine amide (or ammonia) was complete in about 5 days. This synthesis using 25 mM glyceraldehyde and alanine amide gave a total pyrazinone yield of 9.3% consisting of 42% of the 3,5-dimethylprazin-2-one isomer and 58% of the 3,6-dimethylpyrazin-2-one isomer. The related synthesis of the dimethylpyrazin-2-one isomers from glyceraldehyde and ammonia was about 200-fold less efficient than the alanine amide reaction. This synthetic process is considered a reasonable model of origin-of-life chemistry because it uses plausible prebiotic substrates, and resembles modern biosynthesis by employing the energized carbon groups of sugars to drive the synthesis of small organic molecules. Possible sugar-driven pathways for the prebiotic synthesis of polymerizable 2-pyrazinone monomers are discussed.