Synthesis of Sulfur-Containing Exo-Bicyclic Dienes and Their Diels-Alder Reactions To Access Thiacycle-Fused Polycyclic Systems.

The stereocontrolled synthesis of unprecedented sulfur-containing exo-bicyclic 1,3-dienes is reported through a palladium-catalyzed reductive cyclization of sulfur-linked 2-bromoenynes. The fused bicyclic structure provides a better stability to the thiacyclic diene compared to the simple 3,4-dimethylenetetrahydrothiophene. Their reactivity toward several dienophiles has been investigated, and various original thiacycle-fused polycyclic systems have been obtained with high or total diastereoselectivity. Moreover, they are the first exo-bicyclic dienes used in Diels-Alder reactions. The relative configurations of four cycloadducts have been unambiguously assigned by X-ray crystallographic analysis. Mechanistic details of the cycloadditions have been examined by computational means.

MRT-92 inhibits Hedgehog signaling by blocking overlapping binding sites in the transmembrane domain of the Smoothened receptor.

The Smoothened (Smo) receptor, a member of class F G protein-coupled receptors, is the main transducer of the Hedgehog (Hh) signaling pathway implicated in a wide range of developmental and adult processes. Smo is the target of anticancer drugs that bind to a long and narrow cavity in the 7-transmembrane (7TM) domain. X-ray structures of human Smo (hSmo) bound to several ligands have revealed 2 types of 7TM-directed antagonists: those binding mostly to extracellular loops (site 1, e.g., LY2940680) and those penetrating deeply in the 7TM cavity (site 2, e.g., SANT-1). Here we report the development of the acylguanidine MRT-92, which displays subnanomolar antagonist activity against Smo in various Hh cell-based assays. MRT-92 inhibits rodent cerebellar granule cell proliferation induced by Hh pathway activation through pharmacologic (half maximal inhibitory concentration [IC50] = 0.4 nM) or genetic manipulation. Using [(3)H]MRT-92 (Kd = 0.3 nM for hSmo), we created a comprehensive framework for the interaction of small molecule modulators with hSmo and for understanding chemoresistance linked to hSmo mutations. Guided by molecular docking and site-directed mutagenesis data, our work convincingly confirms that MRT-92 simultaneously recognized and occupied both sites 1 and 2. Our data demonstrate the existence of a third type of Smo antagonists, those entirely filling the Smo binding cavity from the upper extracellular part to the lower cytoplasmic-proximal subpocket. Our studies should help design novel potent Smo antagonists and more effective therapeutic strategies for treating Hh-linked cancers and associated chemoresistance.

Discovery, molecular and pharmacological characterization of GSA-10, a novel small-molecule positive modulator of Smoothened.

Activation of the Smoothened (Smo) receptor mediates Hedgehog (Hh) signaling. Hh inhibitors are in clinical trials for cancer, and small-molecule Smo agonists may have therapeutic interests in regenerative medicine. Here, we have generated and validated a pharmacophoric model for Smo agonists and used this model for the virtual screening of a library of commercially available compounds. Among the 20 top-scoring ligands, we have identified and characterized a novel quinolinecarboxamide derivative, propyl 4-(1-hexyl-4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxamido) benzoate, (GSA-10), as a Smo agonist. GSA-10 fits to the agonist pharmacophoric model with two hydrogen bond acceptor groups and four hydrophobic regions. Using pharmacological, biochemical, and molecular approaches, we provide compelling evidence that GSA-10 acts at Smo to promote the differentiation of multipotent mesenchymal progenitor cells into osteoblasts. However, this molecule does not display the hallmarks of reference Smo agonists. Remarkably, GSA-10 does not recognize the classic bodipy-cyclopamine binding site. Its effect on cell differentiation is inhibited by Smo antagonists, such as MRT-83, SANT-1, LDE225, and M25 in the nanomolar range, by GDC-0449 in the micromolar range, but not by cyclopamine and CUR61414. Thus, GSA-10 allows the pharmacological characterization of a novel Smo active site, which is notably not targeted to the primary cilium and strongly potentiated by forskolin and cholera toxin. GSA-10 belongs to a new class of Smo agonists and will be helpful for dissecting Hh mechanism of action, with important implications in physiology and in therapy.

Stereoselective multicomponent assembly of enantiopure oxazolopiperidines and -azepines.

A multicomponent reaction (MCR) based on a cyclohydrocarbonylation (CHC) driven by hydroformylation was set up toward the efficient diastereoselective preparation of oxazolopiperidines (4a-e) and -azepines (7a-d). The bicyclic oxazolidines were obtained from chiral N-alkenylamino alcohols via transient cyclic iminium intermediates that underwent an intramolecular cyclization from the appendant oxygen. On the basis of a series of different experimental conditions, the diastereocontrol observed during the formation of the oxazolidines is best explained by the stereoelectronic effect induced by an A(1,3)-strain in a common cyclic iminium intermediate (A). This new sequence is suitable for diversity oriented syntheses, allowing the preparation of enantiopure (S)- and (R)-coniceine in five steps from commercially available material.

Identification and mechanism of action of the acylguanidine MRT-83, a novel potent Smoothened antagonist.

There is a clear need to develop novel pharmacological tools to improve our understanding of Smoothened (Smo) function in normal and pathological states. Here, we report the discovery, the mechanism of action, and the in vivo activity of N-(2-methyl-5-(3-(3,4,5-trimethoxybenzoyl)guanidino)phenyl)biphenyl-4-carboxamide (MRT-83), a novel potent antagonist of Smo that belongs to the acylguanidine family of molecules. MRT-83 fits to a proposed pharmacophoric model for Smo antagonists with three hydrogen bond acceptor groups and three hydrophobic regions. MRT-83 blocks Hedgehog (Hh) signaling in various assays with an IC50 in the nanomolar range, showing greater potency than the reference Smo antagonist cyclopamine. MRT-83 inhibits Bodipy-cyclopamine binding to human and mouse Smo but does not modify Wnt signaling in human embryonic kidney 293 transiently transfected with a Tcf/Lef-dependent Firefly luciferase reporter together with a Renilla reniformis luciferase control reporter. MRT-83 abrogates the agonist-induced trafficking of endogenous mouse or human Smo to the primary cilium of C3H10T1/2 or NT2 cells that derive from a pluripotent testicular carcinoma. Stereotaxic injection into the lateral ventricle of adult mice of MRT-83 but not of a structurally related compound inactive at Smo abolished up-regulation of Patched transcription induced by Sonic Hedgehog in the neighboring subventricular zone. These data demonstrate that MRT-83 efficiently antagonizes Hh signaling in vivo. All together, these molecular, functional and biochemical studies provide evidence that MRT-83 interacts with Smo. Thus, this novel Smo antagonist will be useful for manipulating Hh signaling and may help develop new therapies against Hh-pathway related diseases.

Virtual screening-based discovery and mechanistic characterization of the acylthiourea MRT-10 family as smoothened antagonists.

The seven-transmembrane receptor Smoothened (Smo) is the major component involved in signal transduction of the Hedgehog (Hh) morphogens. Smo inhibitors represent a promising alternative for the treatment of several types of cancers linked to abnormal Hh signaling. Here, on the basis of experimental data, we generated and validated a pharmacophoric model for Smo inhibitors constituted by three hydrogen bond acceptor groups and three hydrophobic regions. We used this model for the virtual screening of a library of commercially available compounds. Visual and structural criteria allowed the selection of 20 top scoring ligands, and an acylthiourea, N-(3-benzamidophenylcarbamothioyl)-3,4,5-trimethoxybenzamide (MRT-10), was identified and characterized as a Smo antagonist. The corresponding acylurea, N-(3-benzamidophenylcarbamoyl)-3,4,5-trimethoxybenzamide (MRT-14), was synthesized and shown to display, in various Hh assays, an inhibitory potency comparable to or greater than that of reference Smo antagonists cyclopamine and N-((3S,5S)-1-(benzo[d][1,3]dioxol-5-ylmethyl)-5-(piperazine-1-carbonyl)pyrrolidin-3-yl)-N-(3-methoxybenzyl)-3,3-dimethylbutanamide (Cur61414). Focused virtual screening of the same library further identified five additional related antagonists. MRT-10 and MRT-14 constitute the first members of novel families of Smo antagonists. The described virtual screening approach is aimed at identifying novel modulators of Smo and of other G-protein coupled receptors.

A general approach to aza-heterocycles by means of domino sequences driven by hydroformylation.

The development of hydroformylative domino reactions of easily accessible vinyl acetamides is described. Extremely regioselective hydroformylation of terminal double bounds provides a transient N-acyliminium that can be trapped by various nucleophiles to give several aza-heterocylic scaffolds in a diastereoselective manner.

Application of Rhodium-Catalyzed Cyclohydrocarbonylation to the Syntheses of Enantiopure Homokainoids.

Kainic acid, rigidified (S)-glutamic acid, is a well-known kainite receptor agonist for the excitatory transmission in the central nerve system. Our interest in highly selective kainite ligands, prompted us to design a series of new kainic homologues, "homokainoids", i.e., conformationally rigidified (S)-glutamic acids. For the syntheses of enantiopure novel homokainoids (pipecolinoglutamic acids), we successfully applied cyclohydrocarbonylation (CHC) reaction that has been developed in these laboratories. Efficient total syntheses of enantiopure novel homokainoids from (R)-serine feature the highly diastereoselective conjugate addition and the regioselective CHC process in the key steps.

A new method for the synthesis of chiral beta-branched alpha-amino acids.

A new method for the synthesis of chiral beta-branched alpha-amino acids based on a copper-mediated directed allylic substitution reaction with Grignard reagents is reported. This is the first case in which a delta-stereogenic center is controlling the diastereoselectivity of an o-DPPB-directed allylic substitution. Depending on the alkene geometry of the starting material either diastereomer, anti or syn, is accessible with good levels of acyclic stereocontrol.

Potentiation of apple procyanidin-triggered apoptosis by the polyamine oxidase inactivator MDL 72527 in human colon cancer-derived metastatic cells.

Apple procyanidins have chemopreventive properties in a model of colon cancer, they affect intracellular signalling pathways, and trigger apoptosis in a human adenocarcinoma-derived metastatic cell line (SW620). In the present study we investigated relationships between procyanidin-induced alterations in polyamine metabolism and apoptotic effects. Apple procyanidins diminish the activities of ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase, key enzymes of polyamine biosynthesis, and they induce spermidine/spermine N(1)-acetyltransferase, which initiates retroconversion of poly-amines. As a consequence of the enzymatic changes polyamine concentrations are diminished, and N(1)-acetyl-polyamines accumulate in SW620 cells. In contrast with expectations MDL 72527, an inactivator of polyamine oxidase (PAO), improved the anti-proliferative effect of procyanidins, and caused an increase of the proportion of apoptotic cells, although it prevented the formation of hydrogen peroxide and 3-acetamidopropanal, the cytotoxic products of PAO-catalysed degradation of N(1)-acetylspermidine and N1-acetylspermine. Addition of 500 microM N1-acetylspermidine to the culture medium in the presence of procyanidins mimicked the effect of MDL 72527. Therefore we presume that the enhanced procyanidin-triggered apoptosis by MDL 72527 is mediated by the accumulation of N(1)-acetyl-polyamines. The observation that apple procyanidins enhance polyamine catabolism and reduce polyamine biosynthesis activity similar to known inducers of SSAT, without sharing their toxicity, and the potentiation of these effects by low concentrations of MDL 72527 suggests apple procyanidins for chemopreventive and therapeutic interventions.

Microwaves make hydroformylation a rapid and easy process.

[reaction: see text] Hydroformylation of alkenes can be carried out in a few minutes under microwave activation at a relatively low pressure (40 psi) using commercially available catalysts and ligands. The 80 mL vial of a Discover microwave oven was connected to a cylinder of CO and H2, and after filling the reactor at 40 psi, a mixture of an alkene, the Wilkinson catalyst, and XANTPHOS was submitted to microwave irradiation giving, after 4 min, high conversion into the corresponding aldehyde without formation of the isomerized alkene.

Acylthiourea, acylurea, and acylguanidine derivatives with potent hedgehog inhibiting activity.

The Smoothened (Smo) receptor is the major transducer of the Hedgehog (Hh) signaling pathway. On the basis of the structure of the acylthiourea Smo antagonist (MRT-10), a number of different series of analogous compounds were prepared by ligand-based structural optimization. The acylthioureas, originally identified as actives, were converted into the corresponding acylureas or acylguanidines. In each series, similar structural trends delivered potent compounds with IC(50) values in the nanomolar range with respect to the inhibition of the Hh signaling pathway in various cell-based assays and of BODIPY-cyclopamine binding to human Smo. The similarity of their biological activities, in spite of discrete structural differences, may reveal the existence of hydrogen-bonding interactions between the ligands and the receptor pocket. Biological potency of compounds 61, 72, and 86 (MRT-83) were comparable to those of the clinical candidate GDC-0449. These findings suggest that these original molecules will help delineate Smo and Hh functions and can be developed as potential anticancer agents.

Rhodium-catalyzed cyclohydrocarbonylation approach to the syntheses of enantiopure homokainoids.

Homologues of kainic acid, a naturally occurring potent glutamate receptor agonist, were designed based on a rigidified pipecolinoglutamic acid structure and can be regarded as homokainoids for their potential activities in the central nervous system. These novel homokainoids in an enantiomerically pure form were synthesized from enantiopure (R)- and (S)-Garner's aldehyde, featuring (i) the highly diastereoselective addition of alkenylcuprates to the acrylate intermediates and (ii) the Rh-catalyzed cyclohydrocarbonylation of homoallylic amine intermediates to construct the functionalized piperidine moiety in the key steps. For the introduction of a substituent at the 4- or 5-position of pipecolinoglutamic acid, a few different strategies were used, which successfully led to the formation of enantiopure homokainoids.

Identification and characterization of Hedgehog modulator properties after functional coupling of Smoothened to G15.

The seven-transmembrane receptor Smoothened (Smo) transduces the signal initiated by Hedgehog (Hh) morphogen binding to the receptor Patched (Ptc). We have reinvestigated the pharmacological properties of reference molecules acting on the Hh pathway using various Hh responses and a novel functional assay based on the coexpression of Smo with the alpha subunit of the G15 protein in HEK293 cells. The measurement of inositol phosphate (IP) accumulation shows that Smo has constitutive activity, a response blocked by Ptc which indicates a functional Hh receptor complex. Interestingly, the antagonists cyclopamine, Cur61414, and SANT-1 display inverse agonist properties and the agonist SAG has no effect at the Smo-induced IP response, but converts Ptc-mediated inactive forms of Smo into active ones. An oncogenic Smo mutant does not mediate an increase in IP response, presumably reflecting its inability to reach the cell membrane. These studies identify novel properties of molecules displaying potential interest in the treatment of various cancers and brain diseases, and demonstrate that Smo is capable of signaling through G15.