Neurosteroid analogues. 15. A comparative study of the anesthetic and GABAergic actions of alphaxalone, Δ16-alphaxalone and their corresponding 17-carbonitrile analogues.

Alphaxalone, a neuroactive steroid containing a 17ß-acetyl group, has potent anesthetic activity in humans. This pharmacological activity is attributed to this steroid's enhancement of γ-amino butyric acid-mediated chloride currents at γ-amino butyric acid type A receptors. The conversion of alphaxalone into Δ(16)-alphaxalone produces an analogue that lacks anesthetic activity in humans and that has greatly diminished receptor actions. By contrast, the corresponding 17ß-carbonitrile analogue of alphaxalone and the Δ(16)-17-carbonitrile analogue both have potent anesthetic and receptor actions. The differential effect of the Δ(16)-double bond on the actions of alphaxalone and the 17ß-carbonitrile analogue is accounted for by a differential effect on the orientation of the 17-acetyl and 17-carbonitrile substituents.