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  • progesterone
  • Chemical structures of (a) progesterone, (b) 19‐norprogesterone, (c) testosterone (R=H) and ethisterone (R=C豈CH), (d) norethindrone (R=CH 3 ) and norgestrel (R=C 2 H 5 ), (e) oestradiol (R=H) and 17α‐ethynyloestradiol (R=C°CH), (f) norethynodrel and (g) drospirenone. (els.net)