Synthesis and biological evaluation of imidazo[1,2-[Formula: see text]]pyridazines as inhibitors of TNF-[Formula: see text] production.

Tumor necrosis factor-alpha (TNF-[Formula: see text] is an important pro-inflammatory cytokine responsible for a diverse range of inflammatory diseases including rheumatoid arthritis. In the present manuscript, our medicinal chemistry efforts on the design, synthesis and TNF-[Formula: see text] evaluation of a series of 3, 6-disubstituted imidazo[1,2-b]pyridazine is described. The best compounds were 3-pyridyl and (4-(methylsulfonyl)phenyl) analogs 8q and 8w, showing inhibition of TNF-[Formula: see text] production with IC[Formula: see text]values of 0.9 and 0.4 [Formula: see text]M, respectively. The identified leads have potential for further development for treatment of inflammatory diseases.

Lead optimization of isocytosine-derived xanthine oxidase inhibitors.

We report our attempts at improving the oral efficacy of low-nanomolar inhibitors of xanthine oxidase from isocytosine series through chemical modifications. Our lead compound had earlier shown good in vivo efficacy when administered intraperitoneally but not orally. Several modifications are reported here which achieved more than twofold improvement in exposure. A compound with significant improvement in oral efficacy was also obtained.

Isocytosine-based inhibitors of xanthine oxidase: design, synthesis, SAR, PK and in vivo efficacy in rat model of hyperuricemia.

Structure-activity relationship studies were carried out for lead generation following structure-guided design approach from an isocytosine scaffold identified earlier for xanthine oxidase inhibition. A 470-fold improvement in in vitro IC(50) was obtained in the process. Five most potent compounds with nanomolar IC(50) values were selected for pharmacokinetics and in vivo experiments. The best compound showed good in vivo activity when administered intraperitoneally but was not active by oral route. The results suggest that improvement in oral exposure could improve the in vivo efficacy of this series.

Identification of novel isocytosine derivatives as xanthine oxidase inhibitors from a set of virtual screening hits.

In recent years, xanthine oxidase has emerged as an important target not only for gout but also for cardiovascular and metabolic disorders involving hyperuricemia. Contrary to popular belief, recent clinical trials with uricosurics have demonstrated that enhanced excretion of uric acid is, by itself, not adequate to treat hyperuricemia; simultaneous inhibition of production of uric acid by inhibition of xanthine oxidase is also important. Virtual screening of in-house synthetic library followed by in vitro and in vivo testing led to the identification of a novel scaffold for xanthine oxidase inhibition. In vitro activity results corroborated the results from molecular docking studies of the virtual screening hits. The isocytosine scaffold maintains key hydrogen bonding and pi-stacking interactions in the deep end of the xanthine-binding pocket, which anchors it in an appropriate pose to inhibit binding of xanthine and shows promise for further lead optimization using structure-based drug design approach.

Discovery of tetrahydrocarbazoles as dual pERK and pRb inhibitors.

The extracellular signal-regulated kinase (ERK) is one of the most important molecular targets for cancer that controls diverse cellular processes such as proliferation, survival, differentiation and motility. Similarly, the Rb (retinoblastoma protein) is a tumor suppressor protein and its function is to prevent excessive cell growth by inhibiting cell cycle progression. When the cell is ready to divide, pRb is phosphorylated, becomes inactive and allows cell cycle progression. Herein, we discovered a new series of tetrahydrocarbazoles as dual inhibitors of pERK and pRb phosphorylation. The in-house small molecule library was screened for inhibition of pERK and pRb phosphorylation, which led to the discovery of tetrahydrocarbazole series of compounds as potential leads. N-(3-methylcyclopentyl)-6-nitro-2,3,4,4a,9,9a-hexahydro-1H-carbazol-2-amine (1) is the dual inhibitor lead identified through screening, displaying inhibition of pERK and pRb phosphorylation with IC50 values of 5.5 and 4.8 µM, respectively. A short structure-activity relationship (SAR) study has been performed, which identified another dual inhibitor 9-methyl-N-(4-methylbenzyl)-2,3,4,4a,9,9a-hexahydro-1H-carbazol-2-amine (16) with IC50 values 4.4 and 3.5 µM for inhibition of pERK and pRb phosphorylation, respectively. This compound has a potential for further lead optimization to discover promising molecularly-targeted anticancer agents.

The extraordinary reactions of phenyldimethylsilyllithium with N,N-disubstituted amides.

Phenyldimethylsilyllithium reacts with N,N-dimethylamides in a variety of ways, depending upon the stoichiometry, the temperature and, most subtly, on the structure of the amide, with quite small-seeming changes in structure leading to profound changes in the nature of the products. When equimolar amounts of the silyllithium reagent and N,N-dimethylamides 6 are combined in THF at -78 degrees C, and the mixture quenched at -78 degrees C, the product is the corresponding acylsilane . If the same mixture is warmed to -20 degrees C before quenching, the product is a cis enediamine 11. The enediamines are easily isomerised from cis to trans, easily oxidised to dienediamines , and, with more difficulty, hydrolysed to alpha-aminoketones 13. If two equivalents of the silyllithium reagent are used, the product is an alpha-silylamine 20. The mechanism of formation of the enediamines appears to be by way of a Brook rearrangement of the tetrahedral intermediate 17 followed by loss of a silanoxide ion to give a carbene or carbene-like species. The 'carbene' combines with the Brook-rearranging nucleophile to give an intermediate 28, which loses another silanoxide ion to give the enediamine. The same carbene can be attacked by a second equivalent of the silyllithium reagent to give the alpha-silylamine 20. Other nucleophiles, like alkyllithiums, phenyllithium, and tributylstannyllithium also trap the carbene to give products 48-52. The intermediate anions in these reactions, when benzylic, can be further trapped with alkylating agents to give the products 33, 34 and 53-55. In special cases, the anion formed by attack on the carbene can be trapped by intramolecular reactions displacing internal leaving groups, as in the formation of the enamine 37 and the cyclopentane 41, or attacking a carbonyl group, as in the formation of the indanone 61, or attacking a double or triple bond, as in the formation of the cyclopentanes 71 and 75. In another special case, the carbene reacts with vinyllithium to give an allyllithium intermediate 56, which selectively attacks another molecule of carbene to give eventually the gamma-aminoketone 58. Small changes in the structure of the amide lead to a variety of other pathways each of which is discussed in the text. Notably, each member of the homologous series of amides Ph(CH2)nCONMe2 gives rise to a substantially different product: when n= 0, the reaction is normal, and the yield of the alph]-silylamine 20e is high; when n=1, proton transfer in the intermediate anion 64 and displacement of the phenyl group leads to the silaindane 66; when n=2, fragmentation of the intermediate anion 80, and capture of the carbene by benzyllithium leads to the 1,4-diphenylbut-2-ylamine 83; and when n=3, proton transfer in the intermediate anion 67 and displacement of the phenyl group leads to the silacyclopentane 69.

Estrogenic diazenes: heterocyclic non-steroidal estrogens of unusual structure with selectivity for estrogen receptor subtypes.

Estrogens regulate many biological functions, often acting in a tissue-selective manner. Their tissue-selective action is believed to involve differential estrogen action through the two estrogen receptor (ER) subtypes, ERalpha and ERbeta, as well as differential interaction of the ligand-receptor complexes with promoters and coregulator proteins. In the latter case, selectivity is based on the induction of specific conformations of the ligand-ER complex, conformations that are influenced by the structure of the ligand. Estrogen pharmaceuticals having an ideal balance of tissue-selective activity are being sought for menopausal hormone replacement, breast cancer prevention and therapy, and other actions. To expand on the structural diversity of ER ligands that might show such tissue selectivity, we have prepared a series of diazenes (pyrazines, pyrimidines, and pyridazines) substituted with two to four aryl groups and various short-chain aliphatic substituents. All of the pyrazine and pyrimidines bind to ER, some with high affinity and with a considerable degree of preferential binding to either ERalpha or ERbeta. One pyrimidine and one pyrazine have ERalpha affinity preferences as high as 23 and 9, respectively, and one pyrimidine has an ERbeta affinity preference of 8. The pyridazines, by contrast, are quite polar and have only very low binding affinity for the ER. In cell-based transcription assays, several of the pyrimidines and a pyrazine were found to be considerably more agonistic on ERalpha than on ERbeta. Because these triaryl diazenes have the largest volumes among the ER ligands so far investigated, their high affinity demonstrates the flexibility of the ligand binding pocket of the ERs and its tolerance for large substituents. Thus, these novel heterocyclic ligands expand the repertoire of chemical structures that bind to the estrogen receptor, and they could prove to be useful in elucidating the biological behavior of the two ER subtypes and in forming the basis for new estrogen pharmaceuticals having desirable tissue selectivity.