New furin inhibitors based on weakly basic amidinohydrazones

A novel series of amidinohydrazone-derived furin inhibitors was prepared; the most potent compounds 17 and 21 inhibit furin with K_i values of 0.46 and 0.59 μM, respectively. In contrast to inhibitor 17, which still contains a guanidino residue, compound 21 possesses only weakly basic amidinohydrazone groups.     

Design and synthesis of potent macrocyclic renin inhibitors

Two types of P1-P3-linked macrocyclic renin inhibitors containing the hydroxyethylene isostere (HE) scaffold just outside the macrocyclic ring have been synthesized. An aromatic or aliphatic substituent (P3sp) was introduced in the macrocyclic ring aiming at the S3 subpocket (S3sp) in order to optimize the potency. A 5-6-fold improvement in both the K_i and the human plasma renin activity (HPRA)IC₅₀ was observed when moving from the starting linear peptidomimetic compound 1 to the most potent macrocycle 42 (K_i = 3.3 nM and HPRA IC₅₀ = 7 nM). Truncation of the prime side of 42 led to 8-10-fold loss of inhibitory activity in macrocycle 43 (K_i = 34 nM and HPRA IC₅₀ = 56 nM). All macrocycles were epimeric mixtures in regard to the P3sp substituent and X-ray crystallographic data of the representative renin macrocycle 43 complex showed that only the S-isomer buried the substituent into the S3sp. Inhibitory selectivity over cathepsin D (Cat-D) and BACE-1 was also investigated for all the macrocycles and showed that truncation of the prime side increased selectivity of inhibition in favor of renin.     

Synthesis, biological assessment and molecular modeling of 14-aryl-10,11,12,14-tetrahydro-9H-benzo[5,6]chromeno[2,3-b]quinolin-13-amines

The synthesis and pharmacological evaluation of racemic 14-aryl-10,11,12,14-tetrahydro-9H-benzo[5,6]chromeno[2,3-b]quinolin-13-amines (19-28), prepared by Friedländer reaction of 3-amino-1-aryl-1H-benzo[f]chromene-2-carbonitriles (10-18) with suitable cycloalkanones is described. These molecules are potent, in the nanomolar range [IC₅₀ (EeAChE) = 7-101 nM], and selective inhibitors of acetylcholinesterase (AChE). The most potent inhibitor, 4-(13-amino-10,11,12,14-tetrahydro-9H-benzo[5,6]chromeno[2,3-b]quinolin-14-yl)phenol (20) [IC₅₀ (EeAChE) = 7 ± 2 nM] is four-fold more active than tacrine. Kinetic studies on compound 20 showed that this is a mixed-type inhibitor of EeAChE with a K_i of 5.00 nM. However, racemic 20 was unable to displace propidium iodide, suggesting that the inhibitor does not strongly bind to the peripheral anionic site (PAS) of AChE. Docking, molecular dynamics stimulations, and MM-GBSA calculations agree well with this behavior.     

Cholinergic and neuroprotective drugs for the treatment of Alzheimer and neuronal vascular diseases. II. Synthesis, biological assessment, and molecular modelling of new tacrine analogues from highly substituted 2-aminopyridine-3-carbonitriles

The synthesis, biological assessment, and molecular modelling of new tacrine analogues 11-22 is described. Compounds 11-22 have been obtained by Friedländer-type reaction of 2-aminopyridine-3-carbonitriles 1-10 with cyclohexanone or 1-benzyl-4-piperidone. The biological evaluation showed that some of these molecules were good AChE inhibitors, in the nanomolar range, and quite selective regarding the inhibition of BuChE, the most potent being 5-amino-2-(dimethylamino)-6,7,8,9-tetrahydrobenzo[1,8-b]-naphthyridine-3-carbonitrile (11) [IC₅₀ (EeAChE: 14 nM); IC₅₀ (eqBuChE: 5.2 ??M]. Kinetic studies on the easily available and potent anticholinesterasic compound 5-amino-2-(methoxy)-6,7,8,9-tetrahydrobenzo[1,8-b]-naphthyridine-3-carbonitrile (16) [IC₅₀ (EeAChE: 64 nM); IC₅₀ (eqBuChE: 9.6 ??M] showed that this compound is a mixed-type inhibitor (K_i = 69.2 nM) of EeAChE. Molecular modelling on inhibitor 16 confirms that this compound, as expected and similarly to tacrine, binds at the catalytic active site of EeAChE. The neuroprotective profile of molecules 11-22 has been investigated in SH-SY5Y neuroblastoma cells stressed with a mixture of oligomycin-A/rotenone. Compound 16 was also able to rescue by 50% cell death induced by okadaic acid in SH-SY5Y cells. From these results we conclude that the neuroprotective profile of these molecules is moderate, the most potent being compounds 12 and 17 which reduced cell death by 29%. Compound 16 does not affect ACh- nor K⁺-induced calcium signals in bovine chromaffin cells. Consequently, tacrine analogues 11-22 can be considered attractive therapeutic molecules on two key pharmacological targets playing key roles in the progression of Alzheimer, that is, cholinergic dysfunction and oxidative stress, as well as in neuronal cerebrovascular diseases.     

Synthesis, pharmacological activity and structure affinity relationships of spirocyclic σ(1) receptor ligands with a (2-fluoroethyl) residue in 3-position

In order to develop a fluorinated radiotracer for imaging of ??₁ receptors in the central nervous system a series of (2-fluoroethyl) substituted spirocyclic piperidines 3 has been prepared. In the key step of the synthesis 2-bromocinnamaldehyde acetal 5 was added to piperidones 6 with various substituents at the N-atom. Unexpectedly, this reaction led to 2-benzoxepines 8, which were contracted with acid to afford the spirocyclic 2-benzofuranacetaldehydes 9. The best yields were obtained, when the transformations up to the alcohols 10 were performed without isolation of intermediates. Generally the (2-fluoroethyl) derivatives 3 have higher ??₁ affinity and ??₁/??₂ selectivity than the corresponding (3-fluoropropyl) derivatives 2. The most promising candidate for the development as radiotracer is the (2-fluoroethyl) derivative 3a (WMS-1828, fluspidine, 1′-benzyl-3-(2-fluoroethyl)-3H-spiro[[2]benzofuran-1,4′-piperidine]), which shows subnanomolar ??₁ affinity (K_i = 0.59 nM) and excellent selectivity over the ??₂ subtype (1331-fold) as well as some other receptor systems. The novel synthetic strategy also allows the systematic pharmacological evaluation of intermediate alcohols 10. Despite their high ??₁ affinity (K_i = 6-32 nM) and selectivity the alcohols 10 are 10-30-fold less potent than the bioisosteric fluoro derivatives 3.     

Design strategies to target crystallographic waters applied to the Hsp90 molecular chaperone

A series of novel and potent small molecule Hsp90 inhibitors was optimized using X-ray crystal structures. These compounds bind in a deep pocket of the Hsp90 enzyme that is partially comprised by residues Asn51 and Ser52. Displacement of several water molecules observed crystallographically in this pocket using rule-based strategies led to significant improvements in inhibitor potency. An optimized inhibitor (compound 17) exhibited potent Hsp90 inhibition in ITC, biochemical, and cell-based assays (K_d = 1.3 nM, K_i = 15 nM, and cellular IC₅₀ = 0.5 μM).     

4- and 6-(p-Sulphamoylphenyl)androstenediones: Studies of aromatase inhibitor-based oestrone sulphatase inhibition

4-(p-Sulphamoylphenyl)androstenedione (3) and 6α-p-sulphamoylphenyl analogues 12-14 were synthesised and tested as aromatase inhibitors as well as oestrone sulphatase inhibitors in human placental microsomes. All of the p-sulphamoylphenyl compounds synthesised were powerful inhibitors of aromatase with apparent K_i values ranging between 30 and 97 nM. In addition, the aromatase inhibitory activities of 6α-p-hydroxyphenyl compounds 9-11, which may be produced from their respective sulphamoylphenyl compounds by action of oestrone sulphatase, were also high in a range of 23 and 75 nM of the K_i values. On the other hand, all of the sulphamoylphenyl compounds were poor inhibitors of oestrone sulphatase with more than about 200 μM of IC₂₅ values. Although the present findings of the oestrone sulphatase inhibition are disappointing, such attempts may be valuable to develop a new class of drugs having a dual function, aromatase inhibitor and oestrone sulphatase inhibitor, for the treatment of oestrogen-dependent breast cancer.     

Fellutamide B is a potent inhibitor of the Mycobacterium tuberculosis proteasome

Via high-throughput screening of a natural compound library, we have identified a lipopeptide aldehyde, fellutamide B (1), as the most potent inhibitor of the Mycobacterium tuberculosis (Mtb) proteasome tested to date. Kinetic studies reveal that 1 inhibits both Mtb and human proteasomes in a time-dependent manner under steady-state condition. Remarkably, 1 inhibits the Mtb proteasome in a single-step binding mechanism with K_i = 6.8 nM, whereas it inhibits the human proteasome β5 active site following a two-step mechanism with K_i = 11.5 nM and  = 0.93 nM. Co-crystallization of 1 bound to the Mtb proteasome revealed a structural basis for the tight binding of 1 to the active sites of the Mtb proteasome. The hemiacetal group of 1 in the Mtb proteasome takes the (R)-configuration, whereas in the yeast proteasome it takes the (S)-configuration, indicating that the pre-chiral CHO group of 1 binds to the active site Thr1 in a different orientation. Re-examination of the structure of the yeast proteasome in complex with 1 showed significant conformational changes at the substrate-binding cleft along the active site. These structural differences are consistent with the different kinetic mechanisms of 1 against Mtb and human proteasomes.     

2-Arylimidazo[2,1-b]benzothiazoles: a new family of amyloid binding agents with potential for PET and SPECT imaging of Alzheimer's brain

We designed and synthesized a small series of 2-aryl-imidazo[2,1-b]benzothiazole, representing a combination of motifs from the two most potent amyloid imaging agents, PIB and IMPY. The binding affinity of the new compounds ranged from 6 to 133 nM. Among the best compounds, 3b (K_i = 6 nM) can be labeled with ¹¹CH₃ for PET imaging whereas 3j (K_i = 10.9 nM) can be labeled with ¹²³I for SPECT imaging.     

Molecular hybridization of 4-azahexacyclo[5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecane-3-ol with sigma (σ) receptor ligands modulates off-target activity and subtype selectivity

A series of N-substituted 4-azahexacyclo[5.4.1.0^2,6.0^3,10.0^5,9.0^8,11]dodecan-3-ols incorporating the respective arylalkyl subunits from several known sigma (σ) receptor ligands were synthesized and evaluated for their affinity against σ receptors and dopamine receptors. The hybrid trishomocubane-derived ligands (4-6) showed good selectivity for σ₁ and σ₂ receptors over multiple dopamine receptors. The molecular hybrid obtained from haloperidol and 4-azahexacyclo[5.4.1.0^2,6.0^3,10.0^5,9.0^8,11]dodecan-3-ol (4, σ₁K_i = 27 nM, σ₂K_i = 55 nM) showed reduced affinity for D₁-D₅ dopamine receptors when compared to haloperidol itself. The compound with the greatest σ₁ affinity in the series, benzamide 4 (σ₁K_i = 7.6 nM, σ₂K_i = 225 nM) showed a complete reversal of the subtype selectivity displayed by the highly σ₂ selective parent benzamide, RHM-2 (3, σ₁K_i = 10412 nM, σ₂K_i = 13.3 nM).     

New substrate analogue furin inhibitors derived from 4-amidinobenzylamide

A series of new peptidomimetic furin inhibitors was synthesized, which was derived from our previously described lead structure phenylacetyl-Arg-Val-Arg-4-amidinobenzylamide (1). Substitution of Val by other amino acid residues revealed several highly potent furin inhibitors with K_i values of less than 2 nM, containing guanidinoalanine, Ile, Phe or Tyr in the P3 position. The replacement of the P2 Arg by Lys was also well accepted, whereas the incorporation of d-amino acids at various positions resulted in poor inhibitors. The use of the 4-amidinobenzylamide group provides convenient synthetic access to stable proprotein convertase inhibitors and derivatives as biochemical tools and for further studies in cell culture.     

Synthesis and SAR of novel quinazolines as potent and brain-penetrant c-jun N-terminal kinase (JNK) inhibitors

Quinazoline 3 was discovered as a novel c-jun N-terminal kinase (JNK) inhibitor with good brain penetration and pharmacokinetic (PK) properties. A number of analogs which were potent both in the biochemical and cellular assays were discovered. Quinazoline 13a was found to be a potent JNK3 inhibitor (IC₅₀ = 40 nM), with >500-fold selectivity over p38, and had good PK and brain penetration properties. With these properties, 13a is considered a potential candidate for in vivo evaluation.     

Synthesis and evaluation of β-carboline derivatives as potential monoamine oxidase inhibitors

Previous studies have shown that harmine is a reversible inhibitor of human monoamine oxidase A (MAO-A). Moreover, the crystal structure of human MAO-A in complex with harmine has been recently solved. This crystal structure shows that close to the methoxy group of the harmine moiety, a lipophilic pocket is left vacant within the binding site of human MAO-A. Our objective was to optimize the ??-carboline series against human MAO-A in order to explore this pocket. Therefore, a series of ??-carboline derivatives has been synthesized. The compounds were evaluated for their human monoamine oxidase A and B inhibitory potency and their K_i values were estimated. The results show that O-alkylated compounds with lipophilic groups like cyclohexyl, phenyl and aliphatic chains increase the inhibition of MAO-A compared to harmine. Compound 3e, with the trifluorobutyloxy group, was the most active of this series, with a K_i against MAO-A of 3.6 nM. Molecular docking studies show that the trifluorobutyloxy chain occupies the hydrophobic pocket vacant with harmine. The O-alkylated compounds are less active on MAO-B than on MAO-A. However, several compounds show a better inhibition on MAO-B compared to harmine. Compound 3f, with the cyclohexylmethoxy chain, displayed the best inhibitory activity against MAO-B with a K_i value of 221.6 nM. This cyclohexyl bearing analogue is also a potent MAO-A inhibitor with a K_i value of 4.3 nM. Molecular docking studies show that the cyclohexyl chain also occupies a hydrophobic pocket but in different ways in MAO-A or MAO-B.     

3-[(Imidazolidin-2-yl)imino]indazole ligands with selectivity for the α(2)-adrenoceptor compared to the imidazoline I(1) receptor

A series of 3-[(4,5-dihydroimidazolidin-2-yl)imino]indazoles has been synthesized as positional analogues of marsanidine, a highly selective ??₂-adrenoceptor ligand. Parent compound 4a and its 4-chloro (4c) and 4-methyl (4d) derivatives display ??₂-adrenoceptor affinity at nanomolar concentrations (K_i = 39.4, 15.9 and 22.6 nM, respectively) and relatively high ??₂/I₁ selectivity ratios of 82, 115 and 690, respectively. Evidence was obtained that these compounds act as partial agonists at ??_2A-adrenoceptors. Compound 4d with intrinsic activity comparable with that of marsanidine, but lower than that of clonidine, elicited pronounced cardiovascular effects in anesthetized rats at doses as low as 0.01 mg/kg iv     

Discovery of β-aminoacyl containing thiazolidine derivatives as potent and selective dipeptidyl peptidase IV inhibitors

A series of β-aminoacyl containing thiazolidine derivatives was synthesized and evaluated for their ability to inhibit DPP-IV. Several thiazolidine derivatives with an acid moiety were found to be potent DPP-IV inhibitors. Among them, compound 2da is the most active in this series with an IC₅₀ value of 1 nM, and it showed excellent selectivity over DPP-IV related enzymes including DPP-2, DPP-8, and DPP-9. Compound 2da is chemically and metabolically stable, and showed no CYP inhibition, hERG binding or cytotoxicity. Compound 2db, an ester prodrug of 2da, showed good in vivo DPP-IV inhibition after oral administration in rat and dog models.     

Trishomocubane as a scaffold for the development of selective dopamine transporter (DAT) ligands

In our continued exploration of trishomocubane derivatives with central nervous system (CNS) activity, N-arylalkyl-8-aminopentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecanes (10-13) displaying affinity for the sigma (σ) receptor were also found, in several cases, to interact with the dopamine transporter (DAT). Compound 12 was identified as the first trishomocubane-derived high affinity DAT ligand (K_i = 1.2 nM), with greater than 8300-fold selectivity over the monoamine transporters NET and SERT, and only low to moderate affinity for σ₁ and σ₂ receptors.     

Synthesis and evaluation of novel N-fluoropyridyl derivatives of tropane as potential PET imaging agents for the dopamine transporter

A series of novel N-fluoropyridyl-containing tropane derivatives were synthesized and their binding affinities for the dopamine transporter (DAT), serotonin transporter (SERT) and norepinephrine (NET) were determined via competitive radioligand binding assays. Among these derivatives, compound 6d showed the highest binding affinity to DAT (K_i = 4.1 nM), and selectivity for DAT over SERT (5-fold) and NET (16-fold). Compound 6d was radiolabeled with Fluorine-18 in two steps. Regional brain distribution and ex vivo autoradiography studies of [¹⁸F]6d demonstrated that the ligand was selectively localized in the striatum region, where DAT binding sites are highly expressed. [¹⁸F]6d may be useful as a potential radioligand for imaging DATs with PET.     

New aromatic substituted pyrazoles as selective inhibitors of human adipocyte fatty acid-binding protein

a-FABP is indespensible in inflammation and may serve as a new potential drug target for inflammation related diseases. We have successfully designed and synthesized a series of aromatic substituted pyrazoles as new human a-FABP inhibitors. The compounds strongly bound to the hydrophobic binding pocket of a-FABP, while showed significantly lower binding affinities to the closely related homologue protein h-FABP. The most potent and selective compound 5g bound to a-FABP with an apparent K_i value below 1.0 nM, while did not inhibit h-FABP at 50 μM and thus represents one of the most potent and selective a-FABP inhibitors to date. The strong binding capacity of these inhibitors was further validated by their effective blockade of inflammatory responses as determined by the production of pro-inflammatory cytokines upon LPS stimulation. Compound 5g may serve as a lead compound for developing new effective therapeutic agent for prevention and treatment of atherosclerosis, type 2 diabetes and other inflammatory and metabolic related diseases.     

α-Glucosidase inhibition and antihyperglycemic activity of prenylated xanthones from Garcinia mangostana

An ethanol extract of the fruit case of Garcinia mangostan, whose most abundant chemical species are xanthones, showed potent α-glucosidase inhibitory activity (IC₅₀ = 3.2 μg/ml). A series of isolated xanthones (1-16) demonstrated modest to high inhibition of α-glucosidase with IC₅₀ values of 1.5-63.5 μM. In particular, one hitherto unknown xanthone 16 has a very rare 2-oxoethyl group on C-8. Kinetic enzymatic assays with a p-nitrophenyl glucopyranoside indicated that one of them, compound (9) exhibited the highest activity (K_i = 1.4 μM) and mixed inhibition. Using, a physiologically relevant substrate, maltose, as substrate, many compounds (6, 9, 14, and 15) also showed potent inhibition which ranged between 17.5 and 53.5 μM and thus compared favorably with deoxynojirimycin (IC₅₀ = 68.8 μM). Finally, the actual pharmacological potential of the ethanol extract was demonstrated by showing that it could elicit reduction of postprandial blood glucose levels. Furthermore, the most active α-glucosidase inhibitors (6, 9, and 14) were proven to be present in high quantities in the native seedcase by a HPLC chromatogram.     

Design of potent and selective GPR119 agonists for type II diabetes

Screening of the Merck sample collection identified compound 1 as a weakly potent GPR119 agonist (hEC₅₀ = 3600 nM). Dual termini optimization of 1 led to compound 36 having improved potency, selectivity, and formulation profile, however, modest physical properties (PP) hindered its utility. Design of a new core containing a cyclopropyl restriction yielded further PP improvements and when combined with the termini SAR optimizations yielded a potent and highly selective agonist suitable for further preclinical development (58).