Synthesis and evaluation of the structural elements in alkylated tetrahydroisoquinolines for binding to CNS receptors

Design and discovery of a high affinity, selective and β-arrestin biased 5-HT7 Receptor Agonist

Compound 1c, 5-chloro-2-(2-(3,4-dihydroisoquinolin-2(1H)-yl)ethyl)-2,3-dihydro-1H-inden-1-one was previously reported from our laboratory showing high affinity binding to the 5-HT₇ receptor (Ki = 0.5 nM). However, compound 1c racemizes readily upon enantiomeric separation. To prevent racemization, we have redesigned and synthesized methyl and carboxyethyl analogs, compounds 2 and 3 respectively, whose binding affinities were similar to those of compound 1c. Compounds 2 and 3 cannot undergo racemization since tautomerism was no longer possible and thus, compound 2 was selected for enantiomeric separation and further evaluation. Upon enantiomeric separation, the levorotatory enantiomer, (-)2 or 2a demonstrated a higher affinity (Ki = 1.2 nM) than the (+)2 or 2b enantiomer (Ki = 93 nM) and a β-arrestin biased functional selectivity for the 5-HT₇ receptor. Although 2a showed about 8 times less activity than 5-HT in the Gs pathway, it showed over 31 times higher activity than 5-HT in the β-arrestin pathway. This constitutes a significant β-arrestin pathway preference and shows 2a to be more potent and more efficacious than the recently published β-arrestin biased 3-(4-chlorophenyl)-1,4,5,6,7,8-hexahydropyrazolo[3,4-d]azepine, the N-debenzylated analog of JNJ18038683 (Compound 7).

New dual 5-HT1A and 5-HT7 receptor ligands derived from SYA16263

We have previously reported that dual 5-HT_1A and 5-HT₇ receptor ligands might find utility as treatment options for various CNS related conditions including cognitive and anxiolytic impairments. We have also more recently reported that SYA16263 has antipsychotic-like properties with an absence of catalepsy in animal models ascribed to its ability to recruit β-arrestin to the D₂ receptor. However, SYA16263 also binds with very high affinity to 5-HT_1AR (Ki = 1.1 nM) and a moderate affinity at 5-HT₇R (Ki = 90 nM). Thus, it was of interest to exploit its pharmacophore elements in designing new dual receptor ligands. Using SYA16263 as the lead molecule, we have conducted a limited structure-affinity relationship (SAFIR) study by modifying various structural elements in the arylalkyl moiety, resulting in the identification of a new dual 5-HT_1AR and 5-HT₇R ligand, 6-chloro-2-methyl-2-(3-(4-(pyridin-2-yl)piperazin-1-yl)propyl)-2,3-dihydro-1H-inden-1-one (21), which unlike SYA16263, has a sub-nanomolar (5-HT_1AR, Ki = 0.74 nM) and a low nanomolar (5-HT₇R, Ki = 8.4 nM) affinity for these receptors. Interestingly, 21 is a full agonist at 5-HT_1AR and antagonist at the 5-HT₇R, functional characteristics which point to its potential as an antidepressant agent.

A study of the structure-affinity relationship in SYA16263; is a D2 receptor interaction essential for inhibition of apormorphine-induced climbing behavior in mice?

Dopamine (DA) and serotonin (5-HT) receptors are prime targets for the development of antipsychotics. The specific role of each receptor subtype to the pharmacological effects of antipsychotic drugs remains unclear. Understanding the relationship between antipsychotic drugs and their binding affinities at DA and 5-HT receptor subtypes is very important for antipsychotic drug discovery and could lead to new drugs with enhanced efficacies. We have previously disclosed SYA16263 (5) as an interesting compound with moderate radioligand binding affinity at the D₂ & D₃ receptors (Ki = 124 nM & 86 nM respectively) and high binding affinities towards D₄ and 5-HT_1A receptors (Ki = 3.5 nM & 1.1 nM respectively). Furthermore, we have demonstrated SYA16263 (5) is functionally selective and produces antipsychotic-like behavior but without inducing catalepsy in rats. Based on its pharmacological profile, we selected SYA16263 (5) to study its structure-affinity relationship with a view to obtaining new analogs that display receptor subtype selectivity. In this study, we present the synthesis of structurally modified SYA16263 (5) analogs and their receptor binding affinities at the DA and 5-HT receptor subtypes associated with antipsychotic action. Furthermore, we have identified compound 21 with no significant binding affinity at the D₂ receptor subtype but with moderate binding affinity at the D₃ and D₄ receptors subtypes. However, because 21 is able to demonstrate antipsychotic-like activity in a preliminary test, using the reversal of apomorphine-induced climbing behavior experiment in mice with SYA16263 and haloperidol as positive controls, we question the essential need of the D₂ receptor subtype in reversing apomorphine-induced climbing behavior.

Enantioseparation of 5-chloro-2-{2-[3,4-dihydroisoquinoline-2(1H)-yl]ethyl}-2-methyl-2,3-dihydro-1H-inden-1-one (SYA 40247), a high-affinity 5-HT7 receptor ligand, by HPLC-PDA using amylose tris-(3, 5- dimethylphenylcarbamate) as a chiral stationary phase

In previous structure-activity relationship studies to identify new and selective 5-HT₇ receptor (5-HT₇ R) ligands, we identified the chiral compound, 5-chloro-2-{2-[3,4-dihydroisoquinoline-2(1H)-yl]ethyl}-2-methyl-2,3-dihydro-1H-inden-1-one (SYA 40247), with high-affinity binding to the 5-HT₇ R. Thus, it was of interest to separate the enantiomers in order to evaluate their affinity at the 5-HT₇ R. To achieve this separation, a normal-phase analytical method using HPLC-PDA and a 4.6 × 250 mm Chiralpak AD-H column was developed. Optimized isocratic conditions of 1.00 mL/min 95:5:0.1 v/v/v hexane-ethanol-diethylamine and a 254 nm analysis wavelength yielded a 6.07 min baseline separation. The method was scaled up to a 10 × 250 mm Chiralpak AD-H column, allowing 3 mg of racemate to be separated with a single injection, and 6 mg for an overlapping double injection in the same run. The separated enantiomers were reinjected into the analytical HPLC system, peak identities confirmed by retention time and PDA UV spectra, and the enantiomeric purities determined to be 100% for peak 1 and 100% for peak 2. A Jasco P-1020 polarimeter was used to determine the specific rotation [α] of the enantiomers of peaks 1 and 2, which were -86.2 and +93.3 (deg mL)/(g dm) respectively. No racemization was observed, and the enantiomeric purity remained at 100% for each peak.

New analogs of SYA013 as sigma-2 ligands with anticancer activity

Our previous study has revealed 4-(4-(4-chlorophenyl)-1,4-diazepan-1-yl)-1-(4-fluorophenyl)butan-1-one·2HCl (SYA013) 1 as a sigma ligand with moderate selectivity for the sigma-2 receptor. Given the overexpression of sigma receptors in solid tumors and reports of sigma ligands with anticancer activities, we selected 1 for evaluation in several solid tumor cell lines. In addition, we have synthesized new analogs of 1 and now report that several of them bind preferentially at the sigma-2 receptor and have shown inhibition of several cancer cell lines including MDA-MB-231, MDA-MB-486, A549, PC-3, MIA PaCa-2 and Panc-1 cells. In particular, compounds 1 and 12 have demonstrated sub-micromolar activity against the Panc-1 cell line. It has also been observed that several of these compounds demonstrate selective toxicity toward cancer cells, when compared to normal cells.

Photoinduced Intramolecular Bifurcate Hydrogen Bond: Unusual Mutual Influence of the Components

A series of 7-hydroxy-2-methylidene-2,3-dihydro-1H-inden-1-ones with 2-pyrrolyl (3), 4-dimethylaminophenyl (4), 4-nitrophenyl (5), and carboxyl group (6) as substituents at the exocyclic double bond was synthesized in the form of the E-isomers (4-6) or predominantly as the Z-isomer (3) which in solution is converted to the E-isomer. The synthesized compounds and their model analogues were studied by NMR spectroscopy, X-ray analysis, and MP2 theoretical calculations. The E-isomers having intramolecular O-H···O═C hydrogen bond are converted by UV irradiation to the Z-isomers having bifurcated O-H···O···H-X hydrogen bond. Unexpected shortening (and, thus, strengthening) of the O-H···O═C component of the bifurcated hydrogen bond upon the formation of the C═O···H-X hydrogen bond was found experimentally, proved theoretically (MP2), and explained by a roundabout interaction of the H-donor (HX) and H-acceptor (C═O) via the system of conjugated bonds.