1. V. M. Berezovskii, L. S. Tul'chinskaya, and N. A. Polyakova, Zh. Obshch. Khim.,35, 673 (1965).
2. L. S. Tul'chinskaya, T. A. Zhilina, V. D. Klebanova, et al., Zh. Obshch. Khim.,42, 1135 (1972).
3. C. F. Spencer, German (West) Patent No. 2,444,394; Chem. Abstr.,83, 58883 (1975).
4. V. M. Berezovskii, A. I. Stepanov, N. A. Polyakova, et al., Bioorg. Khim.,3, 521 (1977).
5. Sh. Otani, M. Takatsu, M. Nakano, et al., J. Antibiot.,27, 88 (1974).