Syntheses and structure-activity relationships of 5,6,7, 8-tetrahydro-5,5,8,8-tetramethyl-2-quinoxaline derivatives with retinoic acid receptor alpha agonistic activity

Investigation of selective retinoic acid receptor alpha antagonist ER-50891 and related analogs for male contraception

Retinoic acid receptor alpha (RARα) antagonist ER-50891 and 15 analogs were prepared and tested in vitro for potency and selectivity at RARα, RARβ, and RARγ using transactivation assays. Minor modifications to the parent molecule such as the introduction of a C4 tolyl group in place of the C4 phenyl group on the quinoline moiety slightly increased the RARα selectivity but larger substituents significantly decreased the potency. Replacement of the pyrrole moiety of ER-50891 with triazole, amides, or a double bond produced inactive compounds. ER-50891 was found to be stable in male mouse liver microsomes and was tested in male mice to assess its effects on spermatogenesis. Characteristic, albeit modest and transient, effects on spermatogenesis were observed.

Recent advances in the design of RAR α and RAR β agonists as orally bioavailable drugs. A review

Retinoic acid receptors (RARs) α, β, and γ are members of the nuclear receptor superfamily. Compounds which bind to and activate the RARs are termed retinoids which regulate a wide variety of biological processes such as vertebrate embryonic morphogenesis and organogenesis, cell growth arrest, differentiation, and apoptosis, as well as their disorders. Although many synthetic selective RARα, RARβ, and RARγ agonists have been designed and prepared, these have generally been lipophilic acids without good drug-like properties and with low oral bioavailability. Recently this has been changing and drug design approaches to highly potent and selective RARα and RARβ agonists with low lipophilicity that are orally bioavailable and less toxic have been developed, that have a range of potential therapeutic uses. This review covers these new advances.

Probing biological activity through structural modelling of ligand-receptor interactions of 2,4-disubstituted thiazole retinoids

Retinoids, such as all-trans-retinoic acid (ATRA), regulate cellular differentiation and signalling pathways in chordates by binding to nuclear retinoic acid receptors (RARα/β/γ). Polar interactions between receptor and ligand are important for binding and facilitating the non-polar interactions and conformational changes necessary for RAR-mediated transcriptional regulation. The constraints on activity and RAR-type specificity with respect to the structural link between the polar and non-polar functions of synthetic retinoids are poorly understood. To address this, predictions from in silico ligand-RAR docking calculations and molecular dynamics simulations for a small library of stable, synthetic retinoids (designated GZ series) containing a central thiazole linker structure and different hydrophobic region substituents, were tested using a ligand binding assay and a range of cellular biological assays. The docking analysis showed that these thiazole-containing retinoids were well suited to the binding pocket of RARα, particularly via a favorable hydrogen bonding interaction between the thiazole and Ser232 of RARα. A bulky hydrophobic region (i.e., present in compounds GZ23 and GZ25) was important for interaction with the RAR binding pockets. Ligand binding assays generally reflected the findings from in silico docking, and showed that GZ25 was a particularly strongly binding ligand for RARα/β. GZ25 also exhibited higher activity as an inducer of neuronal differentiation than ATRA and other GZ derivatives. These data demonstrate that GZ25 is a stable synthetic retinoid with improved activity which efficiently regulates neuronal differentiation and help to define the key structural requirements for retinoid activity enabling the design and development of the next generation of more active, selective synthetic retinoids as potential therapeutic regulators of neurogenesis.

Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2':6',2''-terpyridine ligand: implications for actinide(III)/lanthanide(III) partitioning

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2' : 6',2''-terpyridine (CyMe(4)-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO(2)(2+)) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. (1)H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1:1 complexes with Eu(III), Ce(III) and Yb(III), while both 1:1 and 1:2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2:2 helical complexes was formed with Cu(I), with a slight preference (1.4:1) for a single directional isomer. In contrast, a 1:1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligands.

Complete 1H and 13C NMR assignments and Z/E-stereoconfiguration determination of isomers of 1,4-diketone derivatives

Complete 1H and 13C NMR assignments and Z/E-stereoconfiguration determination for a series of new isomers of 1,4-diketone derivatives obtained via self-sorting tandem reaction were accomplished by means of one- and two-dimentional NMR experiments including 1H, 13C, gCOSY, gHSQC, gHMBC, and NOESY.

Marked improvement induced in photoaged skin of hairless mouse by ER36009, a novel RARgamma-specific retinoid, but not by ER35794, an RXR-selective agonist

BACKGROUND

Photoaging (premature skin aging) results largely from repeated exposure of the skin to ultraviolet (UV) radiation from the sun. Topical all-trans retinoic acid (RA), the only agent that has been approved for the treatment of photoaging, has been shown to reverse this process. In this study, we evaluated the pharmacologic effects of novel synthetic retinoids, ER36009 and ER35794, on murine wrinkles induced by UVB. ER36009 is a specific agonist of retinoic acid receptor (RAR)gamma, the most abundant RAR subtype in the skin, while ER35794 is a potent retinoid X receptor (RXR)-selective agonist.

METHOD

After a 10-week exposure to escalating doses of UVB irradiation, the animals were treated three times per week with ER36009 (0.0001%, 0.00025%, 0.0005%), ER35794 (0.025%, 0.05%, 0.1%), RA (0.05%) or acetone (control) for 3 weeks.

RESULTS

ER36009 exerted a dose-dependent wrinkle-effacing effect, and 0.0005% ER36009-treated skin was significantly different from the control. ER36009 also significantly and dose-dependently increased both epidermal thickness and the area of the dermal repair zone defined by newly synthesized collagen. The effect of 0.0005% ER36009 on photodamaged skin was superior to that of 0.05% RA. In contrast, ER35794 was inactive in this model, though this compound exhibited lower local toxicity than other retinoids.

CONCLUSIONS

These data indicate that RARgamma, but not RXR, plays an important role in the improvement of the signs of photoaging, and so a specific RARgamma agonist might be superior to an RAR pan-agonist for clinical treatment. We conclude that ER36009 is a candidate for a potent anti-skin-aging agent.

Topical ER36009, a RARgamma-selective retinoid, decreases abdominal white adipose tissue and elicits changes in expression of genes related to adiposity and thermogenesis

Chronic topical treatment of rats with a new RARgamma-selective retinoid, ER36009, resulted in a significant reduction of epididymal white adipose tissue and a significant increase of interscapular brown adipose tissue without affecting food intake. ER36009 markedly decreased PPARgamma, 11beta-HSD1, and Bcl-2 mRNA levels, and increased Bax mRNA in white adipose tissue, while it upregulated UCP1 and UCP3 mRNAs in brown adipose tissue and UCP3 mRNA in gastrocnemial muscle. These results suggest that ER36009 has multiple effects on adipose tissue biology and the energy balance. Topically applied ER36009 may have potential for the treatment of obesity.

A modular synthesis of unsymmetrical tetraarylazadipyrromethenes

[reaction: see text] A stepwise route to unsymmetrical tetraarylazadipyrromethenes by a condensation of 2,4-diaryl-5-nitroso-pyrroles with 2,4-diarylpyrroles is described. This modular building-block approach allows for the introduction of up to four different aryl substituents on the azadipyrromethene and is tolerant of a varied substituent set. An efficient synthesis of the 2,4-diarylpyrroles building blocks from 1,3-diaryl-4-nitro-butan-1-ones by nitro hydrolysis to a keto-aldehyde and subsequent ammonia condensation reaction has been achieved. The facile conversion of 2,4-diarylpyrroles into their alpha-nitroso analogues by their reaction with sodium nitrite generated the second building block required for the synthesis.

Effect of E6060 [4-{5-[7-fluoro-4-(trifluoromethyl)benzo[b]furan-2-yl]-1H-2-pyrrolyl}benzoic acid], a novel subtype-selective retinoid, on lupus-like nephritis in female (NZBxNZW)F1 mice

Disease amelioration by retinoids in various nephritic models has been reported from either immunological or pathophysiologic viewpoints. It has also been reported that retinoids exert immunosuppressive effects in a retinoic acid receptor (RAR)-alpha-dependent manner. In particular, synthetic retinoid agonists with selectivity to RAR-alpha have been reported to have a remarkable disease-ameliorating effect in some immune disease models via their potent immunosuppressive activities; however, there has been no report in which the effect of RAR-alpha-selective agonists in the nephritic models was examined. In this report, we investigated the effect of a newly synthesized RAR-alpha-selective retinoid agonist, E6060 [4-{5-[7-fluoro-4-(trifluoromethyl)benzo[b]furan-2-yl]-1H-2-pyrrolyl}benzoic acid], on the disease progression in a murine lupus nephritis model. Female (NZBxNZW)F1 mice were prophylactically treated with E6060 from 5 months of age, and their nephritic (proteinuria, blood urea nitrogen) and immunological parameters (serum anti-DNA autoantibodies and total serum immunoglobulins) were monitored with age up to 10 months old. E6060 at 0.03 and 0.1 mg/kg (once daily, p.o.) significantly improved survival rate and prevented the development of proteinuria in (NZBxNZW)F1 mice. Anti-DNA autoantibodies and total serum IgG were also significantly reduced in the E6060-treated mice. Among IgG isotypes, IgG2a was substantially reduced by E6060 treatment, indicating reduced T helper 1 responses in E6060-treated mice. In accordance with this possibility, elevation of serum interleukin-12 (p40) in old female (NZBxNZW)F1 mice was significantly inhibited by E6060 treatment. Our data suggest that the RAR-alpha-selective retinoid E6060 is a promising candidate of new remedy for lupus nephritis in systemic lupus erythematosus patients.

Selective retinoids and rexinoids in cancer therapy and chemoprevention

Natural and synthetic retinoids are effective inhibitors of tumor cell growth in vitro and in vivo. However, the toxicity of natural derivatives of vitamin A limits their therapeutic use. Recently, synthetic compounds selective for the different retinoid receptor isotypes have been generated that circumvent pan-retinoid toxicity. The tumor-suppressive activity of selective retinoid and/or rexinoid ligands has been established preclinically, and emerging clinical trials are supportive of the chemotherapeutic and chemopreventive potential of these compounds in multiple oncology indications, with reduced toxicity. Moreover, the combination of retinoids and/or rexinoids with chemotherapeutic agents for the synergistic modulation of specific pathways could also be of benefit in cancer therapy.

A library construction of 2,5-disubstituted pyrrole compounds by using solid/solution-phase syntheses

Using solid- and solution-phase synthesis, a library of 2,5-disubstituted pyrrole compounds was constructed. This is the first report that Stetter reaction was applied to the solid-phase synthesis for C-C bond formation. Some of 2,5-disubstituted pyrrole compounds showed the inhibitory activity of LPS-induced mouse B-lymphocyte proliferation.

Heterocycle-containing retinoids. Discovery of a novel isoxazole arotinoid possessing potent apoptotic activity in multidrug and drug-induced apoptosis-resistant cells

In a search for retinoic acid (RA) receptor ligands endowed with potent apoptotic activity, a series of novel arotinoids were prepared. Because the stereochemistry of the C9-alkenyl portion of natural 9-cis-RA and the olefinic moiety of the previously synthesized isoxazole retinoid 4 seems to have particular importance for their apoptotic activity, novel retinoid analogues with a restricted or, vice versa, a larger flexibility in this region were designed and prepared. The new compounds were evaluated in vitro for their ability to activate natural retinoid receptors and for their differentiation-inducing activity. Cytotoxic and apoptotic activities were, in addition, evaluated. In general, these analogues showed low cytotoxicity, with the restricted structures being slightly more active than the more flexible ones. As an exception, however, the isoxazole retinoid 15b proved to be particularly able to induce apoptosis at concentrations <5 microM, showing a higher activity than the classical retinoids such as all-trans-RA, 13-cis-RA, and 9-cis-RA and the previously described synthetic retinoid 4. 15b also exhibited a good affinity for the retinoid receptors. Interestingly, another important property of 15b was its ability to induce apoptosis in the HL60R multidrug-resistant (MDR) cell line, at the same concentration as is effective in HL60. Therefore, 15b represents a new retinoid possessing high apoptotic activity in an MDR cell line. The ability of 15b to act on K562 and HL60R cells suggests that this compound may have important implications in the treatment of different leukemias, and its structure could offer an interesting model for the design of new compounds endowed with apoptotic activity on MDR- and retinoid-resistant malignancies.

Syntheses and evaluation of quinoline derivatives as novel retinoic acid receptor α antagonists

In the course of studies on novel retinoids, we have designed and synthesized a series of quinoline derivatives. One of them, 4-[5-[8-(1-methylethyl)-4-phenyl-2-quinolinyl]-1H-2-pyrrolyl]benzoic acid (12f) shows potent RARalpha-selective antagonistic activity.

Discovery of novel and potent retinoic acid receptor alpha agonists: syntheses and evaluation of benzofuranyl-pyrrole and benzothiophenyl-pyrrole derivatives

In the course of our studies on retinoic acid receptor (RAR) agonists, we have designed and synthesized a series of benzofuran and benzothiophene derivatives. Some of these compounds (1a,b,e,f,j) markedly inhibited LPS-induced B-lymphocyte proliferation and exerted RARalpha selectivity. One of them, 4-[5-(4,7-dimethylbenzofuran-2-yl)pyrrol-2-yl]benzoic acid (1b), when orally administered significantly inhibited mouse antibody production and delayed type hypersensitivity (DTH) responses from a dose of 0.1 mg/kg.

Novel retinoic acid receptor alpha agonists: syntheses and evaluation of pyrazole derivatives

We have designed and synthesized a series of pyrazole derivatives as candidate retinoic acid receptor (RAR) agonists. One of them, 4-[5-(1, 5-diisopropyl-1H-3-pyrazolyl)-1H-2-pyrrolyl]benzoic acid (11b), which possesses a 2,5-disubstituted pyrrole moiety, showed selective transactivation activity for the RAR alpha receptor, and had highly potent cell-differentiating activity on HL-60 cells.

Syntheses and evaluation of naphthalenyl- and chromenyl-pyrrolyl-benzoic acids as potent and selective retinoic acid receptor alpha agonists

Synthesis and structure activity relationships (SAR) of RAR alpha-selective agonists are discussed. 4-[5-(5,8-Dimethyl-2H-3-chromenyl)-1H-2-pyrrolyl]benzoic acid (12a), which possesses a flat structural moiety and an oxygen atom at the hydrophobic part, showed highly selective transactivation activity at the RAR alpha receptor.