1. W. Nagata, C. Tamm and T. Reichstein, Helv. Chim. Acta, 40, 41 (1957).
2. V.A. Maslennikova, F.S. Khristulus and K.N. Abubakirov, Chem. Abstr., 53, 16204 (1959).
3. F. Kaiser, E. Haack, M. Gube, U. Dölberg and H. Spingler, Naturwissenschaften, 46, 670 (1959).
4. Z. Kowalewski, H. Jäger, O. Schindler and T. Reichstein, Helv. Chim. Acta, 43, 957 (1960).
5. S. Bauer, S. Orszagh and O. Bauerova, J. Mokry, L. Masler, D. Sikl and J. Tomko, Planta Med., 8, 145 (1960).