1. “Drug Discovery”, Advances in Chemistry Series 108;Kupchan,1971
2. J.A. Hogg in ref. 1, p. 14.
3. L.H. Conover in ref. 1, p. 33.
4. Drug design and development. A realistic appraisal
5. G. de Stevens in “Symposium Papers of the 11th IUPAC Symposium on Chemistry of Natural Products, 1978”, Vol.4, Bulgaria Academy of Sciences, Bulgaria 1978, p.407.