17 beta-Nitro-5 alpha-androstan-3 alpha-ol and its 3 beta-methyl derivative: Neurosteroid analogs with potent anticonvulsant and anxiolytic activities

Many 17-substituted androstan-3 alpha-ol analogs act as positive allosteric modulators of GABA(A) receptors and exert anticonvulsant and anxiolytic-like activity actions in animal models. The endogenous neurosteroid allopregnanolone (17 beta-acetyl; 1) is among the most potent of these. Here we demonstrate that 3 alpha-hydroxy-17 beta-nitro-5 alpha-androstane (2b) and its 3 beta-methyl analog (3 alpha-hydroxy-3 beta-methyl-17 beta-nitro-5 alpha-androstane; 2c) modulate GABA(A) receptors as assessed by [(35)S]t-butylbicyclo-phosphorothionate and [(3)H] flunitrazepam binding with potencies equivalent to or greater than 1. These compounds also had potencies equivalent to or greater than 1 in the pentylenetetrazol and 6 Hz seizure models in the mouse. Furthermore, 2b exhibited anxiolytic-like activity in the elevated zero maze. The 3 beta-hydroxy, 3 alpha-desmethyl analog (2a) was devoid of activity on GABA(A) receptors in vitro but had moderate activity in the seizure models, possibly as a result of epimerization in vivo at the 3-position. This conclusion was supported by the lack of in vivo activity of the 3 beta-hydroxy, 3 alpha-methyl analog (2d), which is not expected to undergo epimerization. We conclude that nitro can serve as a bioisostere for acetyl at the 17 beta-position of 5 alpha-androstan-3 alpha-ol, such that the nitro analog fully retains the bioactivity of the endogenous neurosteroid at GABA(A) receptors. (C) 2009 Elsevier B.V. All rights reserved.