1. A. P. Orekhov, The Chemistry of the Alkaloids [in Russian], Moscow (1955), p. 819.
2. S. Yu. Yunusov, Alkaloids [in Russian], Tashkent (1981).
3. K. Mothes, J. Pharm. Pharmacol.,11, 193 (1959).
4. H. W. Liebisch, ?Cyclisierung mechanismen bei der Alkaloid-Biosynthese,? Fortschr. Chem. Forsch.,9, 534 (1968).
5. G. S. Il'in, Lecture on Published Studies for the Degree of Doctor of Biological Sciences [in Russian], Moscow (1961).