1. V. M. Berezovskii, The Chemistry of Vitamins [in Russian], Moscow (1959).
2. N. D. Ierusalimskii, I. V. Konova, N. M. Neronova, et al., Vitamin Resources and Their Exploitation [in Russian], Moscow (1961), Chapter 5, p. 119.
3. L. Smith, Vitamin B12 [Russian translation], Moscow (1962),
4. V. G. Makarevich and T. N. Laznikova, Vopr. Med. Khim.,2, 91 (1957).
5. L. Ya. Areshkina and E. P. Skorobogatova, Vitamin Resources and Their Exploitation [in Russian], Moscow (1961), Chapter 5, p. 164.