^ abSyhora K, Mazáč R (1964). "Steroid derivatives. XXXI. A novel synthesis of 16-methylene-17α-acyloxy-20-ketopregnane derivatives". Collection of Czechoslovak Chemical Communications. 29 (10): 2351–2359. doi:10.1135/cccc19642351. ISSN0010-0765.
^ abStĕrba R (1976). "[A Czechoslovak injection-contraceptive agent administered once a month]". Zentralblatt Fur Gynakologie (in German). 98 (3): 158–160. PMID970015.