2,6-Diisopropylcyclohexanol

GABA(A) receptors meet all the pharmacological criteria required to be considered important general anaesthetic targets. In the following study, the modulatory effects of various commercially available and novel cyclohexanols were investigated on recombinant human γ-aminobutyric acid (GABA(A), α(1)β(2)γ(2s)) receptors expressed in Xenopus oocytes, and compared to the modulatory effects on GABA currents observed with exposures to the intravenous anaesthetic agent, propofol. Submaximal EC(20) GABA currents were typically enhanced by co-applications of 3-300 μM cyclohexanols. For instance, at 30 μM 2,6-diisopropylcyclohexanol (a novel compound) GABA responses were increased ~3-fold (although similar enhancements were achieved at 3 μM propofol). As regards rank order for modulation by the cyclohexanol analogues at 30 μM, the % enhancements for 2,6-dimethylcyclohexanol~2,6-diethylcyclohexanol~2,6-diisopropylcyclohexanol~2,6-di-sec-butylcyclohexanol ≫2,6-di-tert-butylcyclohexanol~4-tert-butylcyclohexanol>cyclohexanol~cyclopentanol~2-methylcyclohexanol. We further tested the potencies of the cyclohexanol analogues as general anaesthetics using a tadpole in vivo assay. Both 2,6-diisopropylcyclohexanol and 2,6-dimethylcyclohexanol were effective as anaesthetics with EC(50)s of 14.0 μM and 13.1 μM respectively, while other cyclohexanols with bulkier side chains were less potent. In conclusion, our data indicate that cyclohexanols are both positive modulators of GABA(A) receptors currents and anaesthetics. The positioning and size of the alkyl groups at the 2 and 6 positions on the cyclohexanol ring were critical determinants of activity.

2,6-(Me₂CH)₂C₆H₃OH (I) (100 g.) hydrogenated at 34-102 atm. over 7 g. Ni yielded mixed stereoisomeric 2,6-diisopropylcyclohexanols, b₃₀ 130.5-1.2°, n²⁰_D 1.4639; phenylurethan, m. 98-100°.I gave a phenylurethan, m. 148-50° (petr. ether).2,6-(Me₃C)₂C₆H₃OH (II) (150 g.) hydrogenated at 34-68 atm. over 7 g. Ni yielded 2 stereoisomeric 2,6-di-tert-butylcyclohexanones (III), 120 g., b₃₅ 135°, m. 35-6° (IIIa), and 30 g. b₃₀ 142-6°, m. 2-7° (IIIb).IIIa (60.6 g.) in 50 cc. Et₂O reduced with 5.18 g. LiAlH₄ in 500 cc. Et₂O gave 2 stereoisomeric 2,6-di-tert-butylcyclohexanols (IV) (in approx. equal amounts), b₃₂ 147°, m. 84-5° (isoöctane) (IVa), and b₃₂ 149-52°, m. 22-3° (IVb).IIIb (9.5 g.) reduced with 2.00 g. LiAlH₄ in 150 cc. Et₂O gave 2.7 g. (middle cut) IV.I (10 g.) and 500 cc. H₂O refluxed with stirring, treated dropwise during 0.5 hr. with 20 g. FeCl₃.6H₂O in 50 cc. H₂O, refluxed 5 hrs. with stirring, cooled, extracted with Et₂O, and the extract worked up yielded 4.0 g. 3,3',5,5'-tetraisopropyldiphenoquinone (V), purple plates, m. 196-8° (EtOH).II was converted similarly to 35% 3,3',-5,5'-tetra-tert-butyldiphenoquinone (VI), m. 245°.V (25 g.) refluxed in 500 cc. AcOH, treated with Zn dust in small portions, filtered hot, poured into 1 I. cold H₂O, and filtered yielded 19 g. [4,3,5-HO(Me₂CH)₂C₆H₂]₂, needles, m. 109-9.5° (aqueous EtOH).VI gave similarly 93% [4,3,5-HO(Me₃C)₂-C₆H₂]₂, m. 184-5°.I (89 g.) in 500 cc. EtOH treated slowly at room temperature with 248 g. 25% aqueous Me₂NH, cooled to 0°, treated dropwise during 0.5 hr. with 75 g. 37% formalin, warmed to room temperature, stirred 1 hr., refluxed 3 hrs., poured into 2 1. cold H₂O, and filtered yielded 114 g. (crude) 4,3,5-HO(Me₂CH)₂C₆H₂CH₂NMe₂, m. 85-7°.II (103 g.) gave similarly 129 g. (crude) 4,3,5-HO(Me₃C)₂C₆H₂CH₂NMe₂, prisms, m. 92-3.5° (pert. ether).KOH (66 g.) and 206 g. II in 350 cc. EtOH treated slowly under a continuous N sweep with 106 g. BzH, stirred overnight, and filtered gave 132 g. [4,3,5-HO(Me₃C)₂C₆H₂]₂CHPh, m. 161-3°, and 23.1 g. BzONa.KOH (66 g.) in 400 cc. absolute EtOH treated with stirring with 206 g.II at room temperature, the mixture treated dropwise during 15 min. with 82.4 g. 37% formalin, cooled to 3° with stirring, filtered, the residue washed with cold absolute EtOH, the combined red filtrate and washings concentrated to 500 cc., filtered, and the combined filter cakes (124.5 g.) washed with hot H₂O containing a trace of HCl and recrystallized from EtOH gave 4,4'-methylenebis(2,6-di-tert-butylphenol) (VII), needles, m. 153-5°; the combined filtrates from the VII acidified with 90 cc. concentrated HCl, diluted with a large volume of H₂O, extracted with Et₂O, and the extract worked up yielded 64 g. 4,3,5-HO(Me₃C)₂C₆H₂CH₂OEt, viscous yellow oil, b₁₁ 162-3°, needles, m. 38-8.5° (petr. ether).II (206 g.) and 6.6 g. KOH in 400 cc. iso-PrOH treated with 41.2 g. 37% formalin, stirred 3 hrs. at 40-5°, cooled, and filtered yielded 89% VII.II (20.7 g.) added with stirring to 2.3 g. Na in 125 cc. MeOH and evaporated with stirring in vacuo, with final gentle flaming, gave the Na salt (VIII) of II, light green powder.VIII with H₂O gave II (85% recovery).VIII (0.25 mole) in 300 cc. PhMe treated at 40° with 30 g. PhNCO, stirred 2 hrs. at 50°, kept overnight, treated with 150 cc. H₂O, filtered from 18 g. solid, and the organic layer of the filtrate dried and concentrated gave an addnl. 6 g. solid; the product recrystallized gave the phenylurethan (IX) of I, needles, m. 187-8° (EtOH); the filtrates evaporated and the residue distilled yielded 15.1 g. II and left 5.7 g. VI.IX (10 g.), 8 g. NaOH, 40 cc. EtOH, and 20 cc. H₂O refluxed 5 hrs., poured into 500 cc. H₂O, extracted with Et₂O, and the extract worked up gave 3.2 g. II.I (89 g.) added at 60-5° with stirring to 11.5 g. Na dispersed in 500 cc. PhMe, refluxed 2 hrs., cooled, heated 15 hrs. at 260° in an autoclave under 28-30 atm. CO₂, cooled to 60°. vented, treated with 200 cc. H₂O, and the aqueous layer acidified with 50 cc. 12N HCl yielded 48 g. (crude) 4,3,5-HO(Me₂CH)₂C₆H₂CO₂H, needles, m. 141° (allotropic form, m. 146°).II (309 g.) refluxed with 81 g. NaOMe in 2.5 l. PhMe, the MeOH removed, the mixture cooled, heated 13 hrs. at 160°/50 atm. in an autoclave with CO₂, cooled, extracted with aqueous NaHCO₃, and the extract acidified yielded 82 g. 4,3,5-HO(Me₃C)₂C₆H₂CO₂H, m. 218-19° (C₆H₆).I (17.8 g.), 2.3 g. Na, and 150 cc. MeOH treated with stirring with 26.7 g. I and then 125 cc. CH₂:CHCN, heated 2 hrs. at 50°, cooled, poured into 500 cc. cold H₂O, extracted with Et₂O, and the extract worked up yielded 12 g. 2,6-(Me₂CH)₂C₆H₃O(CH₂)₂CN, needles, m. 94.5-96° (EtOH).VIII (from 20.7 g. II) heated with stirring with 185 g. II to 55°, treated dropwise during 1 hr. with 212 g. CH₂:CHCN, refluxed 1 hr. with stirring, treated with an addnl. 212 g. CH₂:CHCN, refluxed 6 hrs., cooled, poured into 1 l. cold H₂O, filtered to remove 130 g. amorphous. noncrystallizable solid, and the organic laver of the filtrate worked up gave 35 g. 4,3,5-HO(Me₃C)₂C₆H₂(CH₂)₂CN (X), m. 111-13° (petr. ether).X (3.0 g.), 4.6 g. NaOH, 25cc. EtOH, and 6 cc. H₂O refluxed overnight, poured into 100 cc. cold H₂O, acidified with HCl, and filtered gave 3 g. 4,3,5-HO(Me₃C)₂C₆H₂(CH₂)₂CO₂H (XI), needles, m. 172-3° (aqueous EtOH).Br (64 g.) added with stirring to 22.3 g. 4,2,6-Me(Me₃C)₂C₆H₂OH in 300 cc. Me₃COH at 25° (temperature rise to 67°), cooled, stirred 1 hr., cooled to 20°, filtered, and the residue washed with 10% aqueous Na₂S₂O₃ and H₂O and dried yielded 21.5 g. 4,3,5-HO(Me₃C)₂C₆H₂CHO (XII). m. 189°.XII (15.1 g.), 20 g. CH₂(CO₂H)₂, 55 cc. pyridine, and 2 cc. piperidine heated 1.5 hrs. on the steam bath, cooled, poured with rapid stirring into 30 cc. 12N HCl and 50 g. crushed ice, stirred 1 hr., and filtered yielded 9.5 g. 4,3,5-HO(Me₃C)₂C₆H₂CH:CHCO₂H (XIII), m. 218° (C₆H₆-isoöctane).XIII (5 g.) in 150 cc. 1% aqueous NaOH heated to 90°, treated at 90° with 15 g. Raney Ni-Al alloy in small portions with stirring, stirred 1 hr. at 90°, treated with an addnl. 5 g. alloy and 25 cc. 1% aqueous NaOH, filtered hot, the filtrate poured into dilute HCl, and the precipitate filtered off gave 3.5 g. XI.2,6-Iso-Pr(Me₃C)C₆H₃OH (XIV)Na salt (0.26 mole) and 20 g. XIV treated at 40° during 1 hr. dropwise with 100 cc. CH₂:CHCN, stirred 5 hrs., poured into 250 cc. H₂O, extracted with Et₂O, and the extract worked up gave 16.9 g. unchanged XIV and 1.7 g. 2,6-iso-Pr(Me₃C)C₆H₃O(CH₂)₂CN, b_0.3 111-15°, m. 59-60.5°.I (17.5 g.) in 30 cc. dioxane added dropwise during 0.5 hr. with stirring to 2.3 g. Na dispersed in 300 cc. dry dioxane under N at 60°, heated with stirring 20 min. to 100°, cooled to 58°, treated with 14 g. BzCl during 5 min., kept overnight, filtered, the filtrate evaporated in vacuo, the residue dissolved in Et₂O, and the solution washed with aqueous NaOH, dried, and evaporated gave 18.4 g. benzoate of I, m. 70-2° (aqueous EtOH).VIII (0.25 mole) and 300 cc. dry dioxane treated rapidly with stirring at 60° with 33 g. BzCl in 25 cc. dioxane, cooled with stirring to 25°, poured into cold H₂O, extracted with Et₂O, and the extract worked up gave 18.7 g. 4,2,6-Bz(Me₃C)₂C₆H₂OH (XIVa), m. 124-6° (ligroine).A similar run in which the mixture was poured into cold H₂O as soon as the temperature had dropped to 70° gave 20 g. 2,6,4-(Me₃C)₂(BzOCPh: )C₆H₂: O (XV), yellow needles, m. 164-6° (isoöctane).XV (10 g.) in 50 cc. EtOAc added to 0.25 g. prereduced PtO₂ in 15 cc. EtOAc, hydrogenated 2.5 hrs. at 29°/1 atm., filtered, evaporated, and the residue dissolved in Et₂O, washed with 5% aqueous NaOH, and evaporated gave 4.5 g. 4,3,5-HO(Me₃C)₂C₆H₂CHPhOBz (XVI), m. 147-50° (petr. ether); the aqueous alk. wash acidified gave 1.0 g. BzOH; the filtrate from the XVI evaporated and the residual yellow oil chromatographed on Al₂O₃ gave 2.0 g. 4,2,6-PhCH₂(Me₃C)₂C₆H₂OH, m. 59-60.5°.XVI (3.0 g.) and 3 g. 85% KOH in 40 cc. EtOH and 20 cc. H₂O refluxed 0.5 hr., poured into cold H₂O, saturated with CO₂, and filtered gave 2.22 g. XIVa; the filtrate acidified and evaporated yielded 80% BzOH.