Prebiotic syntheses of vitamin coenzymes: II. Pantoic acid,pantothenic acid,and the composition of coenzyme A

Summary Pantoic acid can by synthesized in good prebiotic yield from isobutyraldehyde or -ketoisovaleric acid + H₂CO + HCN. Isobutyraldehyde is the Strecker precursor to valine and -ketoisovaleric acid is the valine transamination product. Mg²⁺ and Ca²⁺ as well as several transition metals are catalysts for the -ketoisovaleric acid reaction. Pantothenic acid is produced from pantoyl lactone (easily formed from pantoic acid) and the relatively high concentrations of -alanine that would be formed on drying prebiotic amino acid mixtures. There is no selectivity for this reaction over glycine, alanine, or -amino butyric acid. The components of coenzyme A are discussed in terms of ease of prebiotic formation and stability and are shown to be plausible choices, but many other compounds are possible. The -OH of pantoic acid needs to be capped to prevent decomposition of pantothenic acid. These results suggest that coenzyme A function was important in the earliest metabolic pathways and that the coenzyme A precursor contained most of the components of the present coenzyme. Offprint requests to. S.L. Miller