Neurosteroid Analogues. 10. The Effect of Methyl Group Substitution at the C-6 and C-7 Positions on the GABA Modulatory and Anesthetic Actions of (3α,5α)- and (3α,5β)-3-Hydroxypregnan-20-one

Abstract

The planar 5alpha-reduced steroid (3alpha,5alpha)-3-hydroxypregnan-20-one and the nonplanar 5beta-reduced steroid (3alpha,5beta)-3-hydroxypregnan-20-one act at GABA(A) receptors to induce general anesthesia. The structural features of the binding sites for these anesthetic steroids on GABA(A) receptors have not been determined. To determine how structural modifications at the steroid C-6 and C-7 positions effect the actions of these anesthetic steroids, an axial or equatorial methyl group was introduced at these positions. The analogues were evaluated (1) in [(35)S]-tert-butylbicyclophosphorothionate binding experiments, (2) in electrophysiological experiments using rat alpha(1)beta(2)gamma(2L) GABA(A) receptors expressed in Xenopus laevis oocytes, and (3) as tadpole anesthetics. The effects of methyl group substitution in the 5alpha- and 5beta-reduced series of compounds were strikingly similar. In both series, a 6beta-Me group gave compounds with actions similar to or greater than those of the parent steroids. A 6alpha-, 7beta- or 7alpha-Me substituent resulted in reduced potency for inhibition of radioligand binding, GABA(A) receptor modulation and tadpole anesthesia. Because of the similar effects of methyl group substitution in the two series of compounds and previous results from other studies showing that structural modifications in the steroid D ring/side chain region produce similar effects regardless of the stereochemistry of the A,B-ring fusion, we propose that either the 3alpha-hydroxyl groups of planar and nonplanar anesthetic steroids hydrogen bond to different amino acids on GABA(A) receptors or that this critical hydrogen bonding group interacts with membrane lipids instead of the receptor.

GABA released from cultured cortical neurons influences the modulation of t-[35S]butylbicyclophosphorothionate binding at the GABAA receptor

“…This receptor also has recognition sites for GABA antagonists (for review, see Kalueff, 2007), such as bicuculline, PTX, neurotoxic pesticides or TBPS, which can be displaced by the positive drugs mentioned above (Hawkinson et al, 1998;Zeng et al, 2005). (Squires et al, 1983;Supavilai and Karobath, 1984;Ghiani et al, 1996).…”

Mechanisms of neurosteroid interactions with GABAA receptors

“…These include: 1) the flexibility of the hydroxyethyl chain; 2) the location of the first sixmembered ring in a forbidden region of space (i.e., space already occupied by the receptor amino acids); and 3) the loss of a favorable hydrophobic contact normally present for the steroid B-ring in its interactions with GABA A receptors. The last possible explanation was suggested by other studies that explored the effect of methyl group substitution at C6 and C7 of the steroid B-ring (Zeng et al, 2005). A second conclusion from the benz[f]indene structure-activity study involved antagonism results obtained with 17PA.…”

Thermally stable and highly active cobalt precatalysts for vinyl-polyethylenes with narrow polydispersities: integrating fused-ring and imino-carbon protection into ligand design

“…Synthesis of 9-oxo-5,6,7,8,9-pentahydrocyclohepta[b] pyridine-2-carbonitrile ethylene ketal (3). 17 A mixture of 2 (8.0 g, 43 mmol), ethylene glycol (5.3 g, 2.0 equiv), p-TsOH (0.8 g, 10 % w/w) and toluene (300 mL) was stirred and heated to reflux for 8 h with azeotropic removal of water using a Dean-Stark apparatus and reflux condenser. On cooling to room temperature the solvent was removed and the residue purified by silica gel chromatography affording 3 …”

“…17 The ketal 4 (7.4 g, 24 mmol) was treated with p-TsOH (1.1 g, 15 % w/w) in mixture of acetone (75 mL) and water (75 mL) in a 250 mL flask. The mixture was stirred and heated to reflux for 6 h. On cooling to room temperature, the solvent was removed under reduced pressure and the aqueous layer extracted three times with dichloromethane.…”