Title: ORO J, et al. Synthesis of purines under possible primitive earth conditions. I. Adenine from hydrogen cyanide. Arch Biochem Biophys. 1961 Aug;94:217-27.
Title: Griffiths AJF, et al. An Introduction to Genetic Analysis. 7th edition. New York: W. H. Freeman; 2000. Structure of DNA.
Title: Reader V. The assay of vitamin B(4). Biochem J. 1930;24(6):1827-31.