1. A. Burger, in Burger’s Medicinal Chemistry, ed. M.E. Wolff, 4th edn., Part 1, Wiley-Interscience, New York (1980) p. 1.
2. R. Duschinsky, E. Pleven and C. Heidelberger, J. Am. Chem. Soc. 79 (1957) 4559.
3. C. Heidelberger, Prog. Nucleic Acid Res. Mol. Biol. 4 (1965) 1.
4. C. Heidelberger, P. V. Danenberg and R. G. Moran, Adv. Enzymol. 54 (1983) 57.
5. D. V. Santi, J. Med. Chem. 23 (1980) 103.