Synthesis and muscarinic activities of 1,2,4-thiadiazoles

Orthoamide und Iminiumsalze, CV. Umsetzungen von Orthoamiden der Alkincarbonsäuren mit Carbonsäureamiden

The reaction of an orthoamide derivative of phenylpropiolic acid (22a) with primary and secondary amides gives rise to the formation of a wide spectrum of reaction products. The reaction of 22a with formamide delivers a N-carbamoyl-cinnamic acid amidine, wheras the analogous reaction with methylene-diformamide leads to a ketenaminal, which is substituted in β-position by a N-formylimino group. From the orthoamide 22a and phthalimide a phthalic acid amide amidine is obtained. In contrast the reaction of diformamide with 22a affords a β-imino enamine. 2,6-Diaminopyridines can be obtained from 22a with acetamide, propionamide and butyramide in low yields. The pyridines are characterized as perchlorates. From 22a and benzamide a 4-amino-2,6-diphenylpyrimidine is obtained in low yield. In the reaction of the closely related orthoamide derivative of 4-Cl-phenylpropiolic acid 22b with benzamide are isolated as a further products two pyrimidine derivatives. A pyrimidinone and a vinylogous thiourea can be obtained from 22a and urea and thiourea, respectively.

Novel cocrystals of the potent 1,2,4-thiadiazole-based neuroprotector with carboxylic acids: virtual screening, crystal structures and solubility performance

Five new multicomponent solid forms of the biologically active 1,2,4-thiadiazole derivative (TDZH) with dicarboxylic and hydroxybenzoic acids have been discovered by combined virtual/experimental cocrystal screening.

Towards the rational design of novel drugs based on solubility, partitioning/distribution, biomimetic permeability and biological activity exemplified by 1,2,4-thiadiazole derivatives

Novel 1,2,4-thiadiazole derivatives as potent neuroprotectors were synthesized and identified. Their ability to inhibit the glutamate stimulated Ca²⁺ uptake was investigated. The solubility of thiadiazoles was measured in a buffer solution (pH 7.4) at 298 K. The distribution coefficients in 1-octanol/buffer (pH 7.4) and 1-hexane/buffer (pH 7.4) immiscible phases as model systems imitating the gastrointestinal tract epithelium and the blood-brain barrier were determined. Permeation experiments the new Permeapad™ barrier using Franz diffusion cells were conducted and the apparent permeability coefficients were obtained. The influence of the compound structure on the physicochemical properties determining the bioavailability of drug-like substances was revealed. Solubility-permeability interplay has been assessed to evaluate potential bioavailability of the compounds studied.

The impact of structural modification of 1,2,4-thiadiazole derivatives on thermodynamics of solubility and hydration processes

The influence of a structural modification on thermodynamic aspects of solubility and hydration processes of 1,2,4-thiadiazole drug-like compounds was investigated.

An Efficient One-Pot Synthesis of 5-(substituted amino)-1,2,4-thia- and -oxa-diazoles

A general protocol for the synthesis of 5-(substituted amino)-1,2,4-thiadiazoles by the cyclocondensation reaction of amidoximes with N-substituted thioureas in the presence of KF/Al2O3, and of 5-(cyclohexylamino)-1,2,4-oxadiazoles with DCC in the presence of KF/Al2O3 and thiourea, is described. The structures of the new compounds were elucidated by spectroscopic and physical data, and the crystal structure determination by X-ray diffraction of three examples.

Characterization of isomeric 1,2,4-oxadiazolyl-N-methylpyridinium salts by electrospray ionization tandem mass spectrometry

The mass spectrometry behavior of 1,2,4-oxadiazolyl-N-methylpyridinium salts has been investigated. These substances are of current interest as perspective ionic liquids, compounds used as green solvents for synthesis, and for their catalytic properties. The studies have been developed through ESI-MS/MS experiments. The obtained results demonstrate that a readily distinction between the two isomeric classes, 3- N-methylpyridinium- and 5-N-methylpyridinium-1,2,4-oxadiazoles, is possible through ESI-MS/MS experiments. A deeper investigation on the principal fragmentation pathways of characteristic ions has been also developed.

Efficient Transamidation of Primary Carboxamides by in Situ Activation with N,N-Dialkylformamide Dimethyl Acetals

Two protocols for the transamidation of primary amides with primary and secondary amines, forming secondary and tertiary amides, respectively, are described. Both processes employ N,N-dialkylformamide dimethyl acetals for primary amide activation, producing N'-acyl-N,N-dialkylformamidines as intermediates, as widely documented in the literature. Although the latter intermediates react irreversibly with amines by amidinyl transfer, we show that in the presence of certain Lewis acid additives efficient acyl transfer occurs, providing new and useful methods for amide exchange. In one protocol for transamidation, the N'-acyl-N,N-dialkylformamidine intermediates are purified by flash-column chromatography and the purified intermediates are then treated with an amine (typically, 2.5 equiv) in the presence of scandium triflate (10 mol %) in ether to form in high yields the products of transamidation. In a second procedure, N'-acyl-N,N-dialkylformamidines are generated in situ and, without isolation, are subjected to transamidation in the presence of zirconium chloride (0.5 equiv) and an amine (typically 2 equiv). A variety of different primary amides and amines are found to undergo efficient transamidation using the methods described.

Advances in the synthesis and recent therapeutic applications of 1,2,4-thiadiazole heterocycles

Chemical properties of 1,2,4-thiadiazole have been reviewed in the last few years. However, the usefulness of 1,2,4-thiadiazole as a privileged system in medicinal chemistry has prompted the advances on the therapeutic potential of this system. This review provides a brief summary of the medicinal chemistry of 1,2,4-thiadiazole system and highlights some examples of 1,2,4-thiadiazole-containing drug substances in the current literature. A survey of representative literature procedures for the preparation of 1,2,4-thiadiazole is presented in sections by generalized synthetic methods.

Synthesis of 3-Substituted Bicyclic Imidazo[1,2-d][1,2,4]thiadiazoles and Tricyclic Benzo[4,5]imidazo[1,2-d][1,2,4]thiadiazoles

A versatile synthetic route to potentially useful fused-ring [1,2,4]thiadiazole scaffolds (e.g., 7a and 10b) via exchange reactions of the precursor [1,2,4]thiadiazol-3-(2H)one derivatives (e.g., 6 and 9) with appropriately substituted nitriles (e.g., cyanogen bromide or p-toluenesulfonyl cyanide) under mild conditions is described. For example, the tricyclic 3-bromo [1,2,4]THD derivative (7a) underwent S(N)Ar substitution with a variety of nucleophiles, which included amines, malonate esters and alcohols. Likewise, the bicyclic 3-p-tosyl [1,2,4]THD (10b) was employed as a template in reaction with diamines, and the resulting substituted diamines (e.g., 12a or 12e) were further selectively derivatized at the N1 and/or N2 positions in a linear fashion. The X-ray crystal structure of the 3-methyl bicyclic [1,2,4]THD (21) was obtained, and selective methylation at the N1 position via a protection-alkylation-deprotection protocol, as illustrated in Scheme 6, was confirmed. Alternatively, a short convergent synthesis of N1-functionalized derivatives from the reaction of 10b with appropriately substituted secondary amines was also developed. Hence, these synthetic strategies were advantageously exploited to provide access to a variety of diversely derivatized 3-substituted fused-ring [1,2,4]thiadiazole derivatives.

Inhibitory Activity ofDrynariae rhizomaExtracts on Cathepsin Having Bone Resorption Activity

Effects of traditional Korean (Hanbang) medicine, Drynariae rhizoma (DR), on the protease activity of bone loss-initiation in rats and mice were investigated. Ethanol extracts-DR (EE-DR) and water extracts-DR (WE-DR) were identified as potent inhibitor of cathepsins K and L. The original WE-DR inhibits cathepsins K and L with IC50 values of 3.7 microg/ml and 4.5 microg/ml, respectively. EE-DR was more potent than that of WE-DR, because the inhibitions of cathepsin K and L increased to 0.5 microg/ml and 0.8 microg/ml, respectively. The EE-DR was proved to be the most potent. EE-DR was found to be a potent inhibitor of cathepsins K with a Ki value of 5.0 microg/ml for cathepsin K. The activity was increased by 10-fold when the assay is performed in the presence of glutathione at pH 7.0, which favors the formation of a GSH thiolate anion. Thus, it is suggested that this increase in potency is probably due to an enhanced chemical reactivity of the extract mixtures toward the thiolate of the active site of the enzyme. WE-DR exhibited time-dependet inhibition which allowed us to determine the association and dissociation rate constants with cathepsin K. Finally, EE-DR inhibits bone resorption in an in vitro assay involving mouse osteoclasts and bovine bone with an IC50 value of 70 microg/ml. WE-DR represents a new herbal formulation inhibiting cathepsin K and L activity and proteolysis of bone collagen. These results strongly suggest that DR is effective for preventing the development of bone loss induced by cathepsin K. This result also suggested that the DR is effective for bone resorptive action in bone cells.

3-Heteroaryl-2-pyridones: benzodiazepine site ligands with functional delectivity for alpha 2/alpha 3-subtypes of human GABA(A) receptor-ion channels

A novel series of 3-heteroaryl-5,6-bis(aryl)-1-methyl-2-pyridones were developed with high affinity for the benzodiazepine (BZ) binding site of human gamma-aminobutyric acid (GABA(A)) receptor ion channels, low binding selectivity for alpha 2- and/or alpha 3- over alpha 1-containing GABA(A) receptor subtypes and high binding selectivity over alpha 5 subtypes. High affinity appeared to be associated with a coplanar conformation of the pyridone and sulfur-containing 3-heteroaryl rings resulting from an attractive S.O intramolecular interaction. Functional selectivity (i.e., selective efficacy) for alpha 2 and/or alpha 3 GABA(A) receptor subtypes over alpha1 was observed in several of these compounds in electrophysiological assays. Furthermore, an alpha 3 subtype selective inverse agonist was proconvulsant and anxiogenic in rodents while an alpha 2/alpha 3 subtype selective partial agonist was anticonvulsant and anxiolytic, supporting the hypothesis that subtype selective BZ site agonists may provide new anxiolytic therapies.

2-(anilinomethyl)imidazolines as alpha1A adrenergic receptor agonists: 2'-heteroaryl and 2'-oxime ether series

A series of 2'-heteroaryl and 2'-oxime anilinomethylimidazolines was prepared and evaluated in in vitro functional assays for cloned human alpha1A, alpha1B, and alpha1D receptor subtypes. Potent and selective alpha1A agonists have been identified in these series.

Novel, nonpeptidic cyanamides as potent and reversible inhibitors of human cathepsins K and L

Compounds containing a 1-cyanopyrrolidinyl ring were identified as potent and reversible inhibitors of cathepsins K and L. The original lead compound 1 inhibits cathepsins K and L with IC(50) values of 0. 37 and 0.45 M, respectively. Modification of compound 1 by replacement of the quinoline moiety led to the synthesis of N-(1-cyano-3-pyrrolidinyl)benzenesulfonamide (2). Compound 2 was found to be a potent inhibitor of cathepsins K and L with a K(i) value of 50 nM for cathepsin K. Replacement of the 1-cyanopyrrolidine of compound 2 by a 1-cyanoazetidine increased the potency of the inhibitor by 10-fold. This increase in potency is probably due to an enhanced chemical reactivity of the compound toward the thiolate of the active site of the enzyme. This is demonstrated when the assay is performed in the presence of glutathione at pH 7.0 which favors the formation of a GSH thiolate anion. Under these assay conditions, there is a loss of potency in the 1-cyanoazetidine series due to the formation of an inactive complex between the GSH thiolate and the 1-cyanoazetidine inhibitors. 1-Cyanopyrrolidinyl inhibitors exhibited time-dependent inhibition which allowed us to determine the association and dissociation rate constants with human cathepsin K. The kinetic data obtained showed that the increase of potency observed between different 1-cyanopyrrolidinyl inhibitors is due to an increase of k(on) values and that the association of the compound with the enzyme fits an apparent one-step mechanism. (13)C NMR experiments performed with the enzyme papain showed that compound 2 forms a covalent isothiourea ester adduct with the enzyme. As predicted by the kinetic analysis, the addition of the irreversible inhibitor E64 to the enzyme-cyanopyrrolidinyl complex totally abolished the signal of the isothiourea bond as observed by (13)C NMR, thereby demonstrating that the formation of the covalent bond with the active site cysteine residue is reversible. Finally, compound 2 inhibits bone resorption in an in vitro assay involving rabbit osteoclasts and bovine bone with an IC(50) value of 0.7 M. 1-Cyanopyrrolidine represents a new class of nonpeptidic compounds that inhibit cathepsin K and L activity and proteolysis of bone collagen.

Muscarinic agonists as analgesics. Antinociceptive activity versus M1 activity: SAR of alkylthio-TZTP's and related 1,2,5-thiadiazole analogs

Alkylthio-TZTPs (3-(3-alkylthio-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-met hylpyridines) and corresponding azabicyclic analogs were tested for m1 efficacy in cloned human m1 receptors and for antinociceptive activity in the mouse grid shock assay. The m1 (%PI) SAR were distinctly different from the analgesia and the salivation SAR, suggesting that analgesia is mediated by neither m1 nor M3 muscarinic receptors.

1,2,5-Thiadiazole analogues of aceclidine as potent m1 muscarinic agonists

The acetyl group of the muscarinic agonist aceclidine 4 was replaced by various 1,2,5-thiadiazoles to provide a new series of potent m1 muscarinic agonists 17 and 18. Optimal m1 muscarinic agonist potency was achieved when the 1,2,5-thiadiazole substituent was either a butyloxy, 17d, or butylthio, 18d, group. Although 1,2,5-oxadiazole 37 and pyrazine 39 are iso-pi-electronic with 1,2,5-thiadiazole 17d, both analogues were substantially less active than 17d. Compounds with high muscarinic affinity and/or m1 muscarinic agonist efficacy were also obtained when the 3-oxyquinuclidine moiety of 17d or 18c was replaced by ethanolamines, hydroxypyrrolidines, hydroxyazetidine, hydroxyisotropanes, or hydroxyazanorbornanes. The structure-activity data support the participation of the oxygen or sulfur atom in the substituent on the 1,2,5-thiadiazole in the activation of the m1 receptor. Several of these new 1,2,5-thiadiazoles have m1 agonist efficacy, potency, and selectivity comparable to those of xanomeline 2 in the muscarinic tests investigated.

Synthesis, ligand binding, and quantitative structure-activity relationship study of 3 beta-(4'-substituted phenyl)-2 beta-heterocyclic tropanes: evidence for an electrostatic interaction at the 2 beta-position

A set of 3 beta-(4'-substituted phenyl)-2 beta-heterocyclic tropanes was designed, synthesized, and characterized. We discovered that these compounds can function as bioisosteric replacements for the corresponding WIN 35,065-2 analogs which possess a 2 beta-carbomethoxy group. Several of the compounds showed high affinity and selectivity for the dopamine transporter (DAT) relative to the serotonin and norepinephrine transporters. From the structure-activity relationship study, the 3 beta-(4'-chlorophenyl)-2 beta-(3'-phenylisoxazol-5-yl)tropane (5d) emerged as the most potent and selective compound. The binding data for 2 beta-heterocyclic tropanes were found to show a high correlation with molecular electrostatic potential (MEP) minima near one of the heteroatoms in the 2 beta-substituents. In contrast, low correlations were found for other MEP minima near the 2 beta-substituent as well as for calculated log P or substituent volume. These quantitative structure-activity relationship studies are consistent with an electrostatic contribution to the binding potency of these WIN 35,065-2 analogs at the DAT.

Stereoisomerism and muscarinic receptor agonists: synthesis and effects of the stereoisomers of 3-[5-(3-amino-1,2,4-oxadiazol)yl]-1- azabicyclo[2.2.1]heptane

The preparation and the biological activities of the four stereoisomers of 3-[5-(3-amino-1,2,4-oxadiazol)yl]-1-azabicyclo[2.2.1]heptane are described. The most potent stereoisomer, 3a, has the 3R,4R configuration, and in vitro activities in (pD2(% efficacy): ileum 8.8 (87%), hippocampus 9.8 (116%) and ganglion 10.2 (36%)). 3b (3S,4S) was weaker (ileum 8.1 (121%), hippocampus 8.5 (107%), ganglion 9.0 (63%)). The other two stereoisomers, 4a (3S,4R; ileum 7.1 (108%), hippocampus 8.2 (116%), ganglion 7.3 (31%)) and 4b (3R,4S; ileum 7.0 (100%), hippocampus 7.0 (120%), ganglion 7.2 (67%)) are of comparable activity, with an analogous profile to that of the more potent stereoisomers. Thus, compounds 3a and 4a, possessing the 4R stereochemistry, showed selectivity for the hippocampus over the ileum. Compound 3a was, however, more potent in the ganglion than in the hippocampus. All four stereoisomers were full agonists in the hippocampus, indicating M1 activity; however, they were partial agonists in the depolarisation of the rat superior cervical ganglion, another M1-mediated response. This may be due to M2-mediated hyperpolarization. With 3a (0.01 mg/kg i.p.), expression of c-fos mRNA was observed in the hypothalamus and in brain areas involved in sensory processing; these effects were totally blocked by pretreatment with 2 mg/kg scopolamine. In particular, activation of the superior colliculus is consistent with potent M2 activity.