The discovery of 4-(3-pentylamino)-2,7-dimethyl-8-(2-methyl-4-methoxyphenyl)-pyrazolo-[1 ,5-a]-pyrimidine: a corticotropin-releasing factor (hCRF1) antagonist.

Structure activity relationship studies led to the discovery of 4-(3-pentylamino)-2,7-dimethyl-8-(2-methyl-4-methoxyphenyl)-pyrazo lo-[1,5-a]-pyrimidine 11-31 (DMP904), whose pharmacological profile strongly supports the hypothesis that hCRF1 antagonists may be potent anxiolytic drugs. Compound 11-31 (hCRF1 Ki = 1.0+/-0.2 nM (n = 8)) was a potent antagonist of hCRF1-coupled adenylate cyclase activity in HEK293 cells (IC50= 10.0+/-0.01 nM versus 10 nM r/hCRF, n = 8); alpha-helical CRF(9-41) had weaker potency (IC50 = 286+/-63 nM, n = 3). Analogue 11-31 had good oral activity in the rat situational anxiety test; the minimum effective dose for 11-31 was 0.3 mg/kg (po). Maximal efficacy (approximately 57% reduction in latency time in the dark compartment) was observed at this dose. Chlordiazepoxide caused a 72% reduction in latency at 20 mg/kg (po). The literature compound 1 (CP154526-1, 30 mg/kg (po)) was inactive in this test. Compound 11-31 did not inhibit open-field locomotor activity at 10, 30, and 100 mg/kg (po) in rats. In beagle dogs, this compound (5 mg/kg, iv, po) afforded good plasma levels. The key iv pharmacokinetic parameters were t1/2, CL and Vd,ss values equal to 46.4+/-7.6 h. 0.49+/-0.08 L/kg/h and 23.0+/-4.2 L/kg, respectively. After oral dosing, the mean Cmax, Tmax t1/2 and bioavailability values were equal to 1260+/-290 nM, 0.75+/-0.25 h. 45.1+/-10.2 h and 33.1%, respectively. The overall rat behavioral profile of this compound suggests that it may be an anxiolytic drug with a low motor side effect liability.

4-(1,3-Dimethoxyprop-2-ylamino)-2,7-dimethyl-8-(2, 4-dichlorophenyl)pyrazolo[1,5-a]-1,3,5-triazine: a potent, orally bioavailable CRF(1) receptor antagonist.

Structure-activity studies in the pyrazolo[1,5-a]-1,3,5-triazine series led to the discovery that compound 11i (DMP696) is a potent hCRF(1) receptor antagonist (K(i) = 1.7 nM vs 7.5 nM for alpha-hel-CRF(9-41), hCRF(1) adenylate cyclase IC(50) = 82 nM vs 286 nM for alpha-hel-CRF(9-41)). Compound 11i has excellent oral pharmacokinetic profiles in rats and dogs (37% and 50% oral bioavailabilities, respectively). This compound displays good activity in the rat situational anxiety model (MED = 3 mg/kg (po)), whereas a literature standard 1 (CP154526-1) was inactive (MED > 30 mg/kg (po)). Analogue 11i reduced stereotypical mouth movements in rhesus monkeys by 50% at 21 mg/kg (po) using the human intruder paradigm. Overall, the profile of pyrazolotriazine 11i indicates that hCRF(1) receptor antagonists may be anxiolytic agents, which have reduced motor side effect profiles.

Thiazolo[4,5-d]pyrimidine thiones and -ones as corticotropin-releasing hormone (CRH-R1) receptor antagonists.

A series of thiazolo[4,5-d]pyrimidine thiones and -ones was prepared and discovered to have good binding affinity to the CRH-R1 receptor, thus showing promise as a new class of potential anxiolytics and/or antidepressants.

Purin-8-ones as corticotropin-releasing hormone (CRH-R1) receptor antagonists.

A series of purin-8-ones was prepared and discovered to have excellent binding affinity to the CRH-R1 receptor. Structure-activity studies focused on amine side-chain optimization, urea substitution and pyridyl isostere incorporation. Thus, the highly potent purin-8-ones show promise as a new class of potential anxiolytics and/or antidepressants.

4-Aryl-2-anilinopyrimidines as corticotropin-releasing hormone (CRH) antagonists.

A series of 4-aryl-2-(N-ethylanilino)pyrimidines has been synthesized as corticotropin-releasing hormone (CRH) inhibitors. The effect of substitution on each aromatic ring on receptor binding was investigated.

Non-peptide corticotropin-releasing hormone antagonists: syntheses and structure-activity relationships of 2-anilinopyrimidines and -triazines.

Screening of our chemical library using a rat corticotropin-releasing hormone (CRH) receptor assay led to the discovery that 2-anilinopyrimidine 15-1 weakly displaced [125I]-0-Tyr-oCRH from rat frontal cortex homogenates when compared to the known peptide antagonist alpha-helical CRH(9-41) (Ki = 5700 nM vs 1 nM). Furthermore, 15-1 weakly inhibited CRH-stimulated adenylate cyclase activity in the same tissue, but it was less potent than alpha-helical CRH(9-41) (IC50 = 20 000 nM vs 250 nM). Systematic structure-activity relationship studies, using the cloned human CRH1 receptor assay, defined the pharmacophore for optimal binding to hCRH1 receptors. Several high-affinity 2-anilinopyrimidines and -triazines were discovered, some of which had superior pharmacokinetic profiles in the rat. This paper describes the structure-activity studies which improved hCRH1 receptor binding affinity and pharmacokinetic parameters in the rat. Compound 28-17 (mean hCRH1 Ki = 32 nM) had a significantly improved pharmacokinetic profile in the rat (19% oral bioavailability at 30 mg/kg) as well as in the dog (20% oral bioavailability at 5 mg/kg) relative to the early lead structures.

Corticotropin-releasing hormone receptor antagonists: framework design and synthesis guided by ligand conformational studies.

As described in the preceding paper (Arvanitis et al. J. Med. Chem. 1999, 42), anilinopyrimidines I were identified as potent antagonists of corticotropin-releasing hormone-1 receptor (CRH1-R, also referred to as corticotropin-releasing factor, CRF1-R). Our next goal was to understand the receptor-bound conformation of the antagonists and to use this information to help guide preclinical optimization of the series and to develop new leads. Since receptor structural information was not available, we assumed that these small, high-affinity antagonists would tend to bind in conformations at or energetically close to their global minima and that rigid analogues that maintained the important stereoelectronic features of the bound anilinopyrimidine would also bind tightly. Conformational preferences and barriers to rotation of the anilinopyrimidines were determined by semiempirical methods, and X-ray and variable-temperature NMR spectroscopy provided experimental results that correlated well with calculated structures. Using these data, a key dihedral angle was constrained to design fused-ring analogues, substituted N-arylpyrrolopyridines II, synthesis of which provided CRH1 receptor antagonists with potency equal to that of the initial congeneric leads (Ki = 1 nM) and which closely matched the conformation held by the original compound, as determined by crystallography. In addition to providing a useful template for further analogue synthesis, the study unequivocally determined the active conformation of the anilinopyrimidines. Theoretical and spectroscopic studies, synthesis, and receptor binding data are presented.

Synthesis, corticotropin-releasing factor receptor binding affinity, and pharmacokinetic properties of triazolo-, imidazo-, and pyrrolopyrimidines and -pyridines.

The synthesis and CRF receptor binding affinities of several new series of N-aryltriazolo- and -imidazopyrimidines and -pyridines are described. These cyclized systems were prepared from appropriately substituted diaminopyrimidines or -pyridines by nitrous acid, orthoester, or acyl halide treatment. Variations of amino (ether) pendants and aromatic substituents have defined the structure-activity relationships of these series and resulted in the identification of a variety of high-affinity agents (Ki's < 10 nM). On the basis of this property and lipophilicity differences, six of these compounds (4d,i,n,x, 8k, 9a) were initially chosen for rat pharmacokinetic (PK) studies. Good oral bioavailability, high plasma levels, and duration of four of these compounds (4d,i,n,x) prompted further PK studies in the dog following both iv and oral routes of administration. Results from this work indicated 4i,x had properties we believe necessary for a potential therapeutic agent, and 4i1 has been selected for further pharmacological studies that will be reported in due course.

Structure-activity studies on 4-substituted-2-anilinopyrimidine corticotropin releasing factor (CRF) antagonists.

Structure-activity studies around the 4-position of 2-anilinopyrimidine corticotropin releasing factor (CRF) antagonists suggest that there is a large lipophilic cavity in the rat CRF receptor, which can accommodate a wide variety of substituents at this position in contrast to the steric constraints observed for other positions on the 2-anilinopyrimidine core. The chemical syntheses and biological activities of 2-anilinopyrimidine CRF antagonists with carbon-linked substituents at the 4-position are reported. Significant improvements in rat pharmacokinetic parameters were achieved relative to those for the lead structure. While the lead compound 1 (rCRF Ki = 44 nM) afforded no detectable rat plasma levels after intraperitoneal (i.p.) or oral (p.o.) dosing, compounds 3-3 (rCRF Ki = 16 nM) and 3-4 (rCRF Ki 59 nM) gave high rat plasma levels at 30 mg/kg (i.p., p.o.) (Cmax = 1389 nM and 8581 nM (i.p.) respectively; Cmax = 113 nM and 988 nM (p.o.), respectively). Furthermore 3-3 and 3-4 had superior bioavailabilities at these doses (59 and 46% (i.p.), respectively; 2 and 10%, (p.o.), respectively).

Piperidinyltetralin sigma ligands.

Sigma receptor ligands have been proposed to be potential antipsychotic drugs based on their activity profile in animal behavioral models and their indirect modulation of dopaminergic function. Compound 15 (DuP 734) is a combined antagonist of sigma-1 and serotonin 5HT2 receptors, which has been entered into phase I clinical trials as a potential antipsychotic drug. Tetralins 1 and 2 were prepared to determine whether restriction of the conformation of 15 and its analogs may lead to differences in binding selectivity or in vivo profile. The syntheses and the structure-activity relationships of these compounds are reported herein. A reduced derivative, 14, had high affinity for sigma-1 and serotonin 5HT2 receptors as well as excellent oral activity in some animal antipsychotic models. Furthermore, compound 14 failed to cause catalepsy in the rat up to 90 mg/kg (po).

DuP 734 [1-(cyclopropylmethyl)-4-(2'(4''-fluorophenyl)-2'-oxoethyl)- piperidine HBr], a sigma and 5-hydroxytryptamine2 receptor antagonist: receptor-binding, electrophysiological and neuropharmacological profiles.

It has been suggested that sigma receptor antagonists may be useful as antipsychotic drugs and that 5-hydroxytryptamine (5-HT2) receptor antagonists produce improvements of the negative symptoms of schizophrenia. [1-(Cyclopropylmethyl)-4-(2'-(4''-fluorophenyl)-2'- oxoethyl)-piperidine HBr] (DuP 734) is a novel compound with high affinity for the sigma (Ki = 10 nM) and 5-HT2 (Ki = 15 nM) receptors, but low affinity for dopamine receptors (Ki > 1000 nM) as well as 33 other receptors, ion channels and second messenger systems in vitro. DuP 734 did not inhibit the synaptosomal uptake of dopamine, 5-HT or norepinephrine. Oral administration of DuP 734 potently blocked 5-hydroxy-L-trytophan (5-HTP)-induced head twitch in the rat (ED50 = 6.5 mumol/kg), indicating 5-HT2 antagonist activity. Extracellular single-unit recording studies demonstrated that DuP 734 antagonized the effect of the selective sigma ligand (+)-3-(3-hydroxyphenyl-N-(1-propyl) piperidine [(+)-3-PPP] on dopamine neuronal activity in the substantia nigra of the rat with an ED90 of 3.6 mumol/kg i.v. The sigma receptor agonists (+)-SKF 10,047 and phencyclidine both elicited rotational behavior in rats with unilateral lesion of the substantia nigra. The rotational behavior induced by either (+)-SKF 10,047 or phencyclidine was dose-dependently antagonized by DuP 734 with oral ED50 of 8.7 and 19.6 mumol/kg, respectively. The 5-HT2 receptor antagonist ICI 169,369, even at high doses (up to 33 mumol/kg, s.c.), did not antagonize the rotational behavior induced by (+)-SKF 10,047.(ABSTRACT TRUNCATED AT 250 WORDS)

Novel piperidine sigma receptor ligands as potential antipsychotic drugs.

sigma receptor ligands represent a new class of potential antipsychotic drugs. This paper presents the structure-activity relationships leading to novel disubstituted piperidine sigma ligands, which have little or no affinity for dopamine D2 receptors. Selectivity for sigma sites over dopamine D2 or serotonin 5-HT2 receptors appears to be governed by the chemical nature of the piperidine nitrogen substituent, its distance from the basic nitrogen, and its orientation relative to the other piperidine substituent. Several of these compounds have good oral potency in some animal models used to evaluate potential antipsychotic drugs. The N-cyclopropylmethyl ketones and ethers (e.g. 6i (DuP 734), 6q, 18a, and 18n) have the best in vivo potency. Compounds 6i (DuP 734) and 6q did not cause catalepsy in the rat, even at very high doses. On the basis of the pharmacology profiles of these sigma ligands, we propose these compounds may be effective antipsychotic drugs, which do not induce extrapyramidal side effects or tardive dyskinesia.

Kinetic analysis of the inhibition of sulfate transport in human red blood cells by isothiocyanates.

A kinetic analysis of anion self-exchange in human red blood cells, in the presence of an irreversible inhibitor, is presented and applied to the study of the inactivation of sulfate transport by three isothiocyanates: 3-isothiocyano-1,5-naphthalenedisulfonic acid, disodium salt (INDS), 1-isothiocyano-4-naphthalene sulfonic acid, sodium salt, monohydrate (INS), and 1-isothiocyano-4-benzenesulfonic acid, sodium salt, monohydrate (IBS). The time dependence of the inhibition of sulfate transport by the isothiocyanates used could be described by a single exponential and could be shown to contain a reversible and an irreversible component. In each case a portion of sulfate efflux was found to be resistant to inactivation. The residual portion of the sulfate efflux varied with inhibitor: 4% for INS, 16% for INDS, and 34% for IBS. INS showed the largest reversible inhibitory effect (12% of the flux remaining at 0.2 mM inhibitor concentration), while INDS showed the weakest effect (92% of the flux remaining at 0.3 mM inhibitor concentration). IBS had the highest rate of inactivation while INDS had the lowest. The kinetic analysis further suggests that all three isothiocyanates bind reversibly to an inhibitory site on the membrane before they bind covalently, and therefore irreversibly, to the same site on the membrane. The equilibrium constant for the dissociation of the reversibly-bound complex, Ki, and the rate of irreversible inactivation after all membrane sites are reversibly bound, kmax, have been computed for all three inhibitors: INDS (Ki = 420 micron, kmax = 5.04 hr-1), INS (Ki = 148 micron, kmax = 6.48 hr-1), and IBS (Ki = 208 micron, k(max) = 8.11 hr-1).