Joydev K. Laha

Structure–activity relationship study of bone morphogenetic protein (BMP) signaling inhibitors

A structure-activity relationship study of dorsomorphin, a previously identified inhibitor of SMAD 1/5/8 phosphorylation by bone morphogenetic protein (BMP) type 1 receptors ALK2, 3, and 6, revealed that increased inhibitory activity could be accomplished by replacing the pendent 4-pyridine ring with 4-quinoline. The activity contributions of various nitrogen atoms in the core pyrazolo[1,5-a]pyrimidine ring were also examined by preparing and evaluating pyrrolo[1,2-a]pyrimidine and pyrazolo[1,5-a]pyridine derivatives. In addition, increased mouse liver microsome stability was achieved by replacing the ether substituent on the pendent phenyl ring with piperazine. Finally, an optimized compound 13 (LDN-193189 or DM-3189) demonstrated moderate pharmacokinetic characteristics (e.g., plasma t(1/2)=1.6h) following intraperitoneal administration in mice. These studies provide useful molecular probes for examining the in vivo pharmacology of BMP signaling inhibition.

Carboetomidate: a pyrrole analog of etomidate designed not to suppress adrenocortical function.

Background:Etomidate is a sedative hypnotic that is often used in critically ill patients because it provides superior hemodynamic stability. However, it also binds with high affinity to 11&bgr;-hydroxylase, potently suppressing the synthesis of steroids by the adrenal gland that are necessary for survival. The authors report the results of studies to define the pharmacology of (R)-ethyl 1-(1-phenylethyl)-1H-pyrrole-2-carboxylate (carboetomidate), a pyrrole analog of etomidate specifically designed not to bind with high affinity to 11&bgr;-hydroxylase. Methods:The hypnotic potency of carboetomidate was defined in tadpoles and rats using loss of righting reflex assays. Its ability to enhance wild-type &agr;1&bgr;2&ggr;2l and etomidate-insensitive mutant &agr;1&bgr;2M286W&ggr;2l human &ggr;-aminobutyric acid type A receptor activities was assessed using electrophysiologic techniques. Its potency for inhibiting in vitro cortisol synthesis was defined using a human adrenocortical cell assay. Its effects on in vivo hemodynamic and adrenocortical function were defined in rats. Results:Carboetomidate was a potent hypnotic in tadpoles and rats. It increased currents mediated by wild-type but not etomidate-insensitive mutant &ggr;-aminobutyric acid type A receptors. Carboetomidate was a three orders of magnitude less-potent inhibitor of in vitro cortisol synthesis by adrenocortical cells than was etomidate. In rats, carboetomidate caused minimal hemodynamic changes and did not suppress adrenocortical function at hypnotic doses. Conclusions:Carboetomidate is an etomidate analog that retains many beneficial properties of etomidate, but it is dramatically less potent as an inhibitor of adrenocortical steroid synthesis. Carboetomidate is a promising new sedative hypnotic for potential use in critically ill patients in whom adrenocortical suppression is undesirable.

Synthesis of carbolines by photostimulated cyclization of anilinohalopyridines.

A general synthetic route to prepare all four carboline regioisomers by photostimulated cyclization of anilinohalopyridines is described. The methodology affords various substituted carbolines in good to excellent yields. In the case of α-carbolines, the S(RN)1 methodology complements previously reported palladium-catalyzed cyclization approaches.

One-Pot Synthesis of α-Carbolines via Sequential Palladium-Catalyzed Aryl Amination and Intramolecular Arylation

A one-pot synthesis of alpha-carbolines via a palladium-catalyzed aryl amination followed by intramolecular arylation is described. 2,3-Dichloro- and 2,3-dibromopyridines have been shown to react with readily available anilines to obtain various substituted alpha-carbolines in moderate to excellent yields.

Palladium-Catalyzed Intramolecular Oxidative Coupling Involving Double C(sp2)–H Bonds for the Synthesis of Annulated Biaryl Sultams

The palladium-catalyzed intramolecular oxidative coupling described herein involves a double C(sp(2))-H bond functionalization in sulfonanilides, providing a workable access to biaryl sultams annulated into a six-membered ring that are otherwise difficult to obtain by literature methods. The other synthetic applications of this protocol including the synthesis of biaryl sultams containing a seven-membered ring and analogous sultones are also presented.

Access to Biaryl Sulfonamides by Palladium-Catalyzed Intramolecular Oxidative Coupling and Subsequent Nucleophilic Ring Opening of Heterobiaryl Sultams with Amines

The installation of sulfonamide pharmacophores on heterobiaryls has successfully been executed by a previously unknown palladium-catalyzed intramolecular oxidative coupling in N-arylsulfonyl heterocycles followed by novel ring opening of heterobiaryl sultams with amine nucleophiles. The protocol has a wide scope of substrates warranting broad applications in the synthesis of heterobiaryls containing an o-sulfonyl or carboxyl functional group.

A Tandem Approach to Functionalized Carbazoles from Indoles via Two Successive Regioselective Oxidative Heck Reactions Followed by Thermal Electrocyclization

A direct one-pot approach to the synthesis of carbazoles (mono-, di-, and trisubstituted) and α-carbolines from readily available indoles or 7-azaindoles and alkenes is described. Based on mechanistic studies, the tandem reaction follows the sequence: palladium-catalyzed regioselective C-3 alkenylation/palladium-catalyzed C-2 alkenylation/thermal electrocyclization.

In vivo and in vitro pharmacological studies of methoxycarbonyl-carboetomidate.

BACKGROUND:We previously developed 2 etomidate analogs that retain etomidates favorable hemodynamic properties but whose adrenocortical effects are reduced in duration or magnitude. Methoxycarbonyl (MOC)-etomidate is rapidly metabolized and ultrashort acting whereas (R)-ethyl 1-(1-phenylethyl)-1H-pyrrole-2-carboxylate (carboetomidate) does not potently inhibit 11&bgr;-hydroxylase. We hypothesized that MOC-etomidates labile ester could be incorporated into carboetomidate to produce a new agent that possesses favorable properties individually found in each agent. We describe the synthesis and pharmacology of MOC-(R)-ethyl 1-(1-phenylethyl)-1H-pyrrole-2-carboxylate (MOC-carboetomidate), a “soft” analog of carboetomidate. METHODS:MOC-carboetomidates octanol:water partition coefficient was determined chromatographically and compared with those of etomidate, carboetomidate, and MOC-etomidate. MOC-carboetomidates 50% effective concentration (EC50) and 50% effective dose for loss of righting reflexes (LORR) were measured in tadpoles and rats, respectively. Its effect on &ggr;-aminobutyric acid A (GABAA) receptor function was assessed using 2-microelectrode voltage clamp electrophysiological techniques and its metabolic stability was determined in pooled rat blood using high performance liquid chromatography. Its duration of action and effects on arterial blood pressure and adrenocortical function were assessed in rats. RESULTS:MOC-carboetomidates octanol:water partition coefficient was 3300 ± 280, whereas those for etomidate, carboetomidate, and MOC-etomidate were 800 ± 180, 15,000 ± 3700, and 190 ± 25, respectively. MOC-carboetomidates EC50 for LORR in tadpoles was 9 ± 1 &mgr;M and its EC50 for LORR in rats was 13 ± 5 mg/kg. At 13 &mgr;M, MOC-carboetomidate enhanced GABAA receptor currents by 400% ± 100%. Its metabolic half-life in pooled rat blood was 1.3 min. The slope of a plot of the duration of LORR in rats versus the logarithm of the hypnotic dose was significantly shallower for MOC-carboetomidate than for carboetomidate (4 ± 1 vs 15 ± 3, respectively; P = 0.0004123). At hypnotic doses, the effects of MOC-carboetomidate on arterial blood pressure and adrenocortical function were not significantly different from those of vehicle alone. CONCLUSIONS:MOC-carboetomidate is a GABAA receptor modulator with potent hypnotic activity that is more rapidly metabolized and cleared from the brain than carboetomidate, maintains hemodynamic stability similar to carboetomidate, and does not suppress adrenocortical function.

Synthesis of Fused Imidazoles, Pyrroles, and Indoles with a Defined Stereocenter α to Nitrogen Utilizing Mitsunobu Alkylation Followed by Palladium-Catalyzed Cyclization

Nitrogen-containing fused heterocycles comprise many compounds that demonstrate interesting biological activities. A new synthetic approach involving Mitsunobu alkylation of imidazoles, pyrroles, and indoles followed by palladium-catalyzed cyclization has been developed providing access to fused heterocycles with a defined stereochemistry α to nitrogen. While ethyl imidazole or indole carboxylates are good substrates for Mitsunobu alkylation with optically pure secondary benzylic alcohols, the corresponding pyrroles are poor substrates presumably due to the increased pK(a) of the NH. The presence of a synthetically versatile trichloroacetyl functional group on the pyrroles significantly reduces the pK(a) and thereby facilitates Mitsunobu alkylation. Subsequent cyclization of the alkylated products mediated by palladium in the presence or absence of a ligand gave fused heterocycles in good to excellent yields.

Diaminothiazoles Modify Tau Phosphorylation and Improve the Tauopathy in Mouse Models

Background: Tau is hyperphosphorylated in the tauopathies. Targeting Tau kinases CDK5 and GSK3β represents a potential therapeutic approach. Results: Inhibitors of Tau kinases are neuroprotective, decrease PHF-1 immunoreactivity, and induce recovery of memory by fear conditioning. Conclusion: Diaminothiazoles as CDK5 and GSK3β inhibitors improve the tauopathy in mouse models. Significance: Dual kinase inhibition can be critical for efficacy when treating tauopathies. Although Tau accumulation is a feature of several neurodegenerative conditions, treatment options for these conditions are nonexistent. Targeting Tau kinases represents a potential therapeutic approach. Small molecules in the diaminothiazole class are potent Tau kinase inhibitors that target CDK5 and GSK3β. Lead compounds from the series have IC50 values toward CDK5/p25 and GSK3β in the low nanomolar range and no observed toxicity in the therapeutic dose range. Neuronal protective effects and decreased PHF-1 immunoreactivity were observed in two animal models, 3×Tg-AD and CK-p25. Treatment nearly eliminated Sarkosyl-insoluble Tau with the most prominent effect on the phosphorylation at Ser-404. Treatment also induced the recovery of memory in a fear conditioning assay. Given the contribution of both CDK5/p25 and GSK3β to Tau phosphorylation, effective treatment of tauopathies may require dual kinase targeting.