1. South African Patent No. 6805872 (1969); Chem. Abstr.,72, 12719 (1970).
2. U.S. Patent No. 3509167 (1970); Ref. Zh. Khim., No. 4N463 (1971).
3. West German Patent No. 1177645 (1965)
4. Pharm. Ind. (Quelendorf),26, 728 (1965).
5. N. O. Saldabol, S. A. Giller, L. N. Alekseeva, et al., Khim. Farm. Zh., No. 2, 27 (1967).