(Aminoalkyl)indole Isothiocyanates as Potential Electrophilic Affinity Ligands for the Brain Cannabinoid Receptor

Abstract

A series of (aminoalkyl)indole compounds, naphthalene analogs of pravadoline (1), has been shown to exhibit cannabinoid agonist activities such as antinociception in animals, inhibition of adenylate cyclase in brain membranes, and binding to the cannabinoid receptor. These pravadoline analogs were selected for the preparation of potential electrophilic affinity ligands based on the synthesis of isothiocyanate derivatives. One isothiocyanatonaphthalene derivative (8) displaced [3H]CP-55940 binding to a rat brain P2 membrane preparation with an IC50 of 690 nM, which was 10-fold less potent than the parent molecule (IC50 = 73 nM). Isothiocyanate substitution at various positions on the naphthalene moiety of the desmethyl analog 10 gave compounds that displaced [3H]CP-55940 with IC50 values between 400 and 1000 nM, compared with 46 nM for the parent compound 10. However, 6-isothiocyanato substitution on the indole ring of the desmethyl analog provided isothiocyanate 12 that displaced [3H]CP-55940 binding with an IC50 and 160 nM. After pretreatment of brain membranes with this high-affinity isothiocyanato ligand followed by washing out the ligand, the membranes were depleted of 90% of the cannabinoid receptor binding capacity. Loss of receptor binding capacity was half-maximal at 300 nM of the derivative under standard assay conditions. As a control, pretreatment with the parent compound at concentrations that were 20 times the Kd failed to alter subsequent binding activity. This study demonstrates that an isothiocyanato (aminoalkyl)-indole (12) can behave as an affinity ligand which binds irreversibly to the cannabinoid receptor in brain and which precludes subsequent binding of the cannabinoid ligand [3H]CP-55940.

Three-Dimensional Quantitative Structure−Activity Relationship Study of the Cannabimimetic (Aminoalkyl)indoles Using Comparative Molecular Field Analysis

“…18 To identify a low-energy conformation, systematic searching of the torsion angles around the C3-C(dO) and C(dO)-C1′ bonds in 15°increments was carried out while holding the torsion angles of the N1 side chain fixed as in the crystal structure. 17 The reasons for holding the torsion angles of the N1 side chain fixed are 3-fold: (1) the N1 ethylamino side chain (as in morpholinoethyl) is invariant among the AAIs in this study;…”

“…Initial structures for the AAIs were built based on the recently published X-ray crystallographic structure of (1-naphthyl)[6-isothiocyanato-1-[2-(4-morpholinyl)ethyl]-1H-indol-3-yl]methanone, the only compound in this series for which 3D structural data were available in the literature. 17 This crystal structure was modified as required to build each AAI molecule using the molecular fragments library provided within Sybyl, after which each AAI structure was energy-minimized using the Tripos force field with a distance-dependent dielectric function and a convergence criterion of 0.001 kcal/mol‚Å energy difference between successive iterations. The partial atomic charges required to calculate the electrostatic interactions were assigned based on the Gasteiger-Marsili formalism.…”

Synthesis and biological evaluation of 3-(azolylmethyl)-1H-indoles and 3-(α-azolylbenzyl)-1H-indoles as selective aromatase inhibitors

“…A Friedel Crafts procedure [41,42], using AlCl acetonitrile, and gave 3-aroyl-1-benzyl-1H-indoles 24 and 25 in excellent yields. Then the corresponding alcohols 28 and 29 were obtained by using NaBH 4 in methanol.…”

Unified Pharmacophoric Model for Cannabinoids and Aminoalkylindoles Derived from Molecular Superimposition of CB1 Cannabinoid Receptor Agonists CP55244 and WIN55212-2

“…Thus, it is highly possible that they compete for the same binding regions of the CBi cannabinoid receptor. In support of this hypothesis, binding studies (7,6) have revealed that the potent cannabinoid [ 3 H]CP55940 was displaced by WIN55212-2 and other AAIs and that, conversely, [ 3 H]WIN55212-2 was displaced by A 9 -tetrahydrocannabinol (A 9 -THC) and other cannabinoids ( Figure 1). Furthermore, irreversible covalent binding of an isothiocyanato AAI to the CBi cannabinoid receptor obstructed any subsequent interactions with the cannabinoid agonist [ 3 H]CP55940 (7).…”

“…In support of this hypothesis, binding studies (7,6) have revealed that the potent cannabinoid [ 3 H]CP55940 was displaced by WIN55212-2 and other AAIs and that, conversely, [ 3 H]WIN55212-2 was displaced by A 9 -tetrahydrocannabinol (A 9 -THC) and other cannabinoids ( Figure 1). Furthermore, irreversible covalent binding of an isothiocyanato AAI to the CBi cannabinoid receptor obstructed any subsequent interactions with the cannabinoid agonist [ 3 H]CP55940 (7). 3 Structure-activity relationship (SAR) studies of the cannabinoids (8)(9)(10)(11) and the AAIs (12)(13)(14) revealed pharmacophoric elements common to both classes of compounds (see Figure 1): (1) a lipophilic and/or sterically bulky group (i.e., the C3 side chain in the cannabinoids and the C3 aroyl group in the AAIs) that appears to be a structural prerequisite for cannabinoid activity (70); (2) a polar oxygen atom (i.e., the CI hydroxyl group of the phenolic A-ring in the cannabinoids and the C3 carbonyl oxygen in the AAIs) that may form a hydrogen bond with the receptor (75) and (3) the cyclic ring system (i.e., the cyclohexyl C-ring in the cannabinoids and the indole ring in the AAIs).…”