The oestrogens (US spelling: estrogens) are female sex hormones produced in the ovaries, and also in the placenta during pregnancy. They are responsible for the female sex characteristics, and together with progesterone control the menstrual cycle. Oestrogens were first isolated from the urine of pregnant women, in which levels increase some 50-fold during the pregnancy. In horses, levels rise by as much as 500 times during pregancy. Oestrogens occur both in free form, and as glucuronides

Progestogen Drugs

Quantities of progesterone (Figure 5.128) for drug use are readily available by semi-synthesis using the Marker degradation (see page 264). However, progesterone is poorly absorbed, and it is not suitable for oral use, being rapidly metabolized in the liver. Many semi-synthetic analogues have been produced, and it was thus appreciated that the a,p-unsaturated ketone system in ring A was essential for activity. The side-chain function at C-17 could be modified, and ethisterone (17a-ethynyltestosterone) (Figure 5.129), developed as a potential androgen, was found to be active orally as a progestational agent. This incorporates an ethynyl side-chain at C-17, a feature of several semi-synthetic steroidal hormones used as drugs. This group, referred to as 'ethinyl' in drug molecules, is introduced by nucleophilic

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