1. Patent application 2061754, Fed. Rep. Germany (1970).
2. Patent application 63-215695, Japan (1988). Chem. Abstr.,110, No. 956335.
3. USA Pat. 3197469 (1965).
4. Fed. Rep. Germany Pat. 527177 (1969).
5. R. Brattsend, A. Thalen, A. Roempke, et al., J. Steroid Biochem.,16, 779–786 (1982).