Synthesis and 5 alpha-reductase inhibitory activity of 8-substituted benzo[f]quinolinones derived from palladium mediated coupling reactions.

Benzoquinolinones have been shown to be potent, selective inhibitors of the Type I 5 alpha-reductase enzyme, which is responsible for the production of dihydrotestosterone from testosterone localized in the scalp. In an effort to identify compounds that demonstrate inhibition of both 5 alpha-reductase isozymes, we have employed 8-bromobenzoquinolinone as an advanced intermediate for participation in a variety of palladium mediated carbon-carbon bond forming reactions. By varying the 8-substituent it is possible to alter the selectivity profile of the series.

LY191704 inhibits type I steroid 5 alpha-reductase in human scalp.

Conversion of testosterone to dihydrotestosterone (DHT) has been demonstrated to be catalyzed by two isoforms of steroid 5 alpha-reductase, designated types I and II. Although several classes of steroid-based inhibitors of the type II isoform have been identified, these agents have not demonstrated highly selective pharmacological activity against human type I 5 alpha-reductase. LY191704 is representative of a series of nonsteroidal agents that have potent [apparent inhibitory constant (Ki) = 11.3 nM] inhibitory activity in human scalp skin homogenates (pH 7.5), a source of type I 5 alpha-reductase. [3H]-DHT production in the presence and absence of LY191704 is consistent with a noncompetitive mode of inhibition. In human prostatic homogenates (pH 5.5), a source of type II 5 alpha-reductase, LY191704 is virtually inactive as an inhibitor [concentration of inhibitor producing 50% inhibition of enzymatic activity (IC50) > 1,000 nM] of [3H]-DHT formation. LY191704 does not inhibit the type I or type II isoforms of rat 5 alpha-reductase, nor does the compound compete for binding to the murine androgen receptor expressed in SF9 cells using a baculo virus expression system. The benzoquinolinones, as exemplified by LY191704, possess exquisite pharmacological selectivity and provide a tool to understand the role of human type I 5 alpha-reductase in normal and pathophysiological states. These agents may also find clinical utility in treating androgen-dependent dermatological conditions.

LY191704: a selective, nonsteroidal inhibitor of human steroid 5 alpha-reductase type 1.

Androgens, in particular dihydrotestosterone (DHT), play a key role in differentiation, growth, and maintenance of the mammalian prostate. Production of DHT from testosterone is catalyzed by two distinct membrane-bound steroid 5 alpha-reductase [5 alpha-reductase; 3-oxo-5 alpha-steroid delta 4-dehydrogenase; 3-oxo-5 alpha-steroid:(acceptor) delta 4-oxidoreductase, EC 1.3.99.5] isozymes designated types 1 and 2. Benign prostatic hyperplasia (BPH), a disease that occurs almost universally in males, is characterized by obstructive and irritative urinary voiding symptoms and has been associated with an overproduction of DHT. Recently, steroidal inhibitors of 5 alpha-reductase type 2 have been used successfully for treatment of BPH. Described here is a nonsteroidal inhibitor of 5 alpha-reductase type 1, LY191704 (8-chloro-4-methyl-1,2,3,4,4a,5,6,10b-octaahydro-benzo[f]quinol in-3(2H)-one). This compound was identified based on its capacity to inhibit 5 alpha-reductase activity in a human genital skin fibroblast cell line (Hs68). Surprisingly, LY191704 is inactive when tested in freshly isolated prostate cells obtained from subjects with BPH, whereas previously described 4-azasteroids are active. LY191704 is, however, a potent inhibitor of the 5 alpha-reductase activity of BPH cells that have been maintained in culture. Analysis of human and rat 5 alpha-reductases expressed from transfected cDNAs in simian COS cells indicates that LY191704 is a specific noncompetitive inhibitor of the human 5 alpha-reductase type 1. Taken together, the results suggest that prostate cells have the capacity to express both 5 alpha-reductase isozymes and that LY191704 may be useful in treatment of human endocrine disorders associated with overproduction of DHT by 5 alpha-reductase type 1.

Synthesis and excitatory amino acid pharmacology of a series of heterocyclic-fused quinoxalinones and quinazolinones.

As part of our program aimed at the development of potent excitatory amino acid antagonists, we synthesized and evaluated a series of substituted 1,2,4-triazolo[4,3-a]quinoxalin-4(5H)-ones, 4, tetrazolo[1,5-a]quinoxalin-4(5H)-ones, 5, and pyrazolo[1,5-c]quinazolin-5(6H)-ones, 6, and an imidazo[1,2-a]quinoxalin-4(5H)-one, 7. In general, the same heterocycles which demonstrated the best affinity for the AMPA receptor also demonstrated the best affinity for the glycine site on the NMDA receptor complex. 1-Propyl-7,8-dichloro-1,2,4-triazolo[4,3-a]quinoxalin-4(5H)-one, 4d, was found to bind with the greatest affinity to the AMPA receptor with an IC50 of 0.83 microM and antagonized 40 microM AMPA-induced depolarization in the cortical slice preparation with an IC50 of 44 microM. 7,8-Dichloro-1,2,4-triazolo[4,3-a]quinoxalin-4(5H)-one, 4a, and 7,8-dichloroimidazo[1,2-a]quinoxalin-4(5H)-one, 7, possessed the best affinity for the glycine site with IC50 values of 0.63 and 1.26 microM, respectively. It is noteworthy that the SAR for the heterocyclic compounds did not directly parallel that of known quinoxalinediones (e.g. DNQX, 2, and DCQX, 15) at the AMPA receptor nor that of the kynurenic acids at the glycine site on the NMDA receptor complex.

Inhibition of [3H]-MK801 binding and protection against NMDA-induced lethality in mice by a series of imipramine analogs.

A series of imipramine analogs were tested for inhibition of [3H]-MK801 binding and for their ability to protect against NMDA-induced lethality in mice. The structure-activity relationship (SAR) for the inhibition of [3H]-MK801 binding found primary amines on short linkers to be optimum. For protection against NMDA lethality, compounds containing an unsaturated link to a cyclic amine were the most potent analogs tested. Possible explanations for the lack of correlation observed are briefly discussed.

5,7-Dichlorokynurenic acid, a potent and selective competitive antagonist of the glycine site on NMDA receptors.

Fourteen substituted derivatives of kynurenic acid were compared for their ability to block ionic currents evoked by N-methyl-D-aspartate (NMDA) plus glycine, or kainate, in voltage-clamped Xenopus oocytes injected with rat brain messenger RNA. Among these analogues there was an excellent correlation between the Ki for displacing [3H]glycine binding to rat brain membranes, and the ability to inhibit ionic currents evoked by glycine/NMDA in Xenopus oocytes. In the oocyte 5,7-dichlorokynurenic acid (5,7-DCK) was a competitive blocker of the glycine recognition site on NMDA receptors, and was more potent (KB 65 nM in Schild analysis) and selective (509-fold more potent vs glycine than kainate) than the prototype glycine antagonist, 7-chlorokynurenic acid, 5,7-DCK also reduced NMDA-induced neuron injury in rat cortical cell cultures.

Stereoselectivity and mode of inhibition of phosphoinositide-coupled excitatory amino acid receptors by 2-amino-3-phosphonopropionic acid.

DL-2-Amino-3-phosphonopropionic acid, a phosphonate-substituted derivative of aspartic acid, has been shown to be an inhibitor of excitatory amino acid-stimulated phosphoinositide hydrolysis in rat brain slices. In this study, the enantiomers of 2-amino-3-phosphonopropionic acid were synthesized and used to further characterize the stereoselectivity and mechanism of interaction of this compound for inhibiting phosphoinositide-coupled (metabotropic) excitatory amino acid receptors. L-2-Amino-3-phosphonopropionic acid was 3-5 times more potent than D-2-amino-3-phosphonopropionic acid as an inhibitor of ibotenate-stimulated [3H]inositol monophosphate formation in slices of the rat hippocampus or quisqualate-stimulated [3H]inositol monophosphate formation in neonatal rat cerebral cortical slices. Carbachol-stimulated phosphoinositide hydrolysis was not inhibited by L-2-amino-3-phosphonopropionic acid, and L-2-amino-3-phosphonopropionic acid had no appreciable affinity for ionotropic excitatory amino acid receptors at concentrations required to inhibit metabotropic excitatory amino acid responses. The inhibitory effects of L-2-amino-3-phosphonopropionic acid or L-2-amino-4-phosphonobutyric acid on phosphoinositide hydrolysis were not competitive, because they could not be surmounted by increasing concentrations of ibotenate or quisqualate. L-2-Amino-3-phosphonopropionic acid inhibition also could not be prevented by washing the tissue before incubation with ibotenate. Thus, L-2-amino-3-phosphonopropionic acid is a stereoselective inhibitor of metabotropic excitatory amino acid receptors with little affinity for ionotropic receptors. However, the inhibitory effects of L-2-amino-3-phosphonopropionic acid or L-2-amino-4-phosphonobutyric acid were not readily reversed, and the site at which they act to inhibit metabotropic excitatory amino acid receptors remains to be determined.

Substituted 5-amino-4,5,6,7-tetrahydroindazoles as partial ergoline structures with dopaminergic activity.

Two series of tetrahydroindazoles were synthesized and evaluated for dopaminergic activity. A number of these partial ergoline analogues possess substituents that could mimic the C-8 substituent of the dopaminergic ergolines. Of the unsymmetrically substituted amine series 7a-k, the (monopropylamino)tetrahydroindazole 7b was most interesting as it was found to selectively activate the dopamine (DA) autoreceptor at a dose of 5 mg/kg in rats. The disubstituted amines 7g-k had significant DA postsynaptic activity as measured by increases of serum corticosterone levels in rats. The 6-substituted-5-aminotetrahydroindazoles 10a-d were found to possess only marginal dopaminergic activity.