Antimitotic activity of two macrocyclic bis(bibenzyls), isoplagiochins A and B from the Liverwort Plagiochila fruticosa

Two bis(bibenzyls), isoplagiochins A (1) and B (2) have been isolated by the guidance of inhibitory effect of tubulin polymerization from the liverwort Plagiochila fruticosa (Plagiochilaceae). Isoplagiochins A and B inhibited the polymerization of tubulin at IC₅₀ 50 and 25 μM, respectively. Furthermore structure–activity relationship based on their conformations was discussed. The presence of two aromatic rings which can be connected through two atoms bridge spacer of double bond may serve to maintain the backbone conformation.     

Synthesis and evaluation of diaryl sulfides and diaryl selenide compounds for antitubulin and cytotoxic activity

We have devised a procedure for the synthesis of analogs of combretastatin A-4 (CA-4) containing sulfur and selenium atoms as spacer groups between the aromatic rings. CA-4 is well known for its potent activity as an inhibitor of tubulin polymerization, and its prodrugs combretastatin A-4 phosphate (CA-4P) and combretastatin A-1 phosphate (CA-1P) are being investigated as antitumor agents that cause tumor vascular collapse in addition to their activity as cytotoxic compounds. Here we report the preparation of two sulfur analogs and one selenium analog of CA-4. All synthesized compounds, as well as several synthetic intermediates, were evaluated for inhibition of tubulin polymerization and for cytotoxic activity in human cancer cells. Compounds 3 and 4 were active at nM concentration against MCF-7 breast cancer cells. As inhibitors of tubulin polymerization, both 3 and 4 were more active than CA-4 itself. In addition, 4 was the most active of these agents against 786, HT-29 and PC-3 cancer cells. Molecular modeling binding studies are also reported for compounds 1, 3, 4 and CA-4 to tubulin within the colchicine site.     

Di-substituted pyridinyl aminohydantoins as potent and highly selective human β-secretase (BACE1) inhibitors

The identification of highly selective small molecule di-substituted pyridinyl aminohydantoins as β-secretase inhibitors is reported. The more potent and selective analogs demonstrate low nanomolar potency for the BACE1 enzyme as measured in a FRET assay, and exhibit comparable activity in a cell-based (ELISA) assay. In addition, these pyridine-aminohydantoins are highly selectivity (>500×) against the other structurally related aspartyl proteases BACE2, cathepsin D, pepsin and renin.Our design strategy followed a traditional SAR approach and was supported by molecular modeling studies based on the previously reported aminohydantoin 3a. We have taken advantage of the amino acid difference between the BACE1 and BACE2 at the S2′ pocket (BACE1 Pro₇₀ changed to BACE2 Lys₈₆) to build ligands with >500-fold selectivity against BACE2. The addition of large substituents on the targeted ligand at the vicinity of this aberration has generated a steric conflict between the ligand and these two proteins, thus impacting the ligand’s affinity and selectivity. These ligands have also shown an exceptional selectivity against cathepsin D (>5000-fold) as well as the other aspartyl proteases mentioned. One of the more potent compounds (S)-39 displayed an IC₅₀ value for BACE1 of 10 nM, and exhibited cellular activity with an EC₅₀ value of 130 nM in the ELISA assay.     

Novel BACE1 inhibitors with a non-acidic heterocycle at the P1′ position

We have reported potent peptidic and non-peptidic BACE1 inhibitors with a hydroxymethylcarbonyl (HMC) isostere as a substrate transition-state mimic. However, our potent inhibitors possess a tetrazole ring at the P₁′ position. It is desirable that central nervous system (CNS) drugs do not possess an acidic moiety. In this study, we synthesized non-acidic BACE1 inhibitors with heterocyclic derivatives at the P₁′ position. KMI-1764 (27) exhibited potent inhibitory activity (IC₅₀ = 27 nM). Interestingly, these non-acidic inhibitors tended to follow the quantitative structure–activity relationship (QSAR) equation and interacted with BACE1-Arg235 in the binding model.     

Anilinotriazoles as potent gamma secretase modulators

The design and synthesis of a novel series of potent gamma secretase modulators is described. Exploration of various spacer groups between the triazole ring and the aromatic appendix in 2 has led to anilinotriazole 28, which combined high in vitro and in vivo potency with an acceptable drug-like profile.     

Design,synthesis and evaluation of 2-amino-imidazol-4-one derivatives as potent β-site amyloid precursor protein cleaving enzyme 1 (BACE-1) inhibitors

Inhibition of β-site amyloid precursor protein cleaving enzyme 1 (BACE1) to prevent brain β-amyloid (Aβ) peptide’s formation is a potential effective approach to treat Alzheimer’s disease. In this report we described a structure-based optimization of a series of BACE1 inhibitors derived from an iminopyrimidinone scaffold W-41 (IC₅₀ = 7.1 μM) by Wyeth, which had good selectivity and brain permeability but low activity. The results showed that occupying the S₃ cavity of BACE1 enzyme could be an effective strategy to increase the biological activity, and five compounds exhibited stronger inhibitory activity and higher liposolubility than W-41, with L-5 was the most potent inhibitor against BACE1 (IC₅₀ = 0.12 μM, logP = 2.49).     

Discovery and initial optimization of 5,5′-disubstituted aminohydantoins as potent β-secretase (BACE1) inhibitors

8,8-Diphenyl-2,3,4,8-tetrahydroimidazo[1,5-a]pyrimidin-6-amine (1) was identified through HTS, as a weak (micromolar) inhibitor of BACE1. X-Ray crystallographic studies indicate the 2-aminoimidazole ring forms key H-bonding interactions with Asp32 and Asp228 in the catalytic site of BACE1. Lead optimization using structure-based focused libraries led to the identification of low nanomolar BACE1 inhibitors such as 20b with substituents which extend from the S₁ to the S₃ pocket.     

Synthesis and biological evaluation of quinazolinone-based hydrazones with potential use in Alzheimer’s disease

Discovering multifunctional agents for the treatment of Alzheimer’s disease (AD) is an attractive therapeutic approach. BACE1 (β-site amyloid precursor protein cleaving enzyme 1) inhibitors may play a pivotal role in treating AD. Therefore, the discovery of novel non-peptide BACE1 inhibitors with desirable blood brain barrier permeability is a favorable approach for treatment. Moreover, the antioxidant potential of a drug could serve as an added value for designing dual-acting therapeutic agents. Here, we report the design, synthesis and biological evaluation of quinazolinone-hydrazone derivatives as new multi-target candidates for the treatment of AD. The compounds were investigated for their in vitro BACE1 inhibitory potential using a FRET-based enzymatic assay and also screened for antioxidant activity using DPPH. Among them, compound 4h bearing a 2,3-dichlorophenyl moiety showed the highest activity with an IC₅₀ value of 3.7 μM against BACE1. In addition, compound 4i with a 2,4-dihydroxyphenyl scaffold demonstrated moderate BACE1 inhibitory activity (IC₅₀ = 27.6 μM) with a significant antioxidant effect (IC₅₀ = 8.4 μM). Furthermore, docking studies revealed strong interaction between compound 4h and the key residues of BACE1 active site. These results demonstrate that quinazolinone-hydrazone derivatives represent a valuable scaffold for the discovery of novel non-peptidic BACE1 inhibitors.     

Multi-target inhibitors against Alzheimer disease derived from 3-hydrazinyl 1,2,4-triazine scaffold containing pendant phenoxy methyl-1,2,3-triazole: Design,synthesis and biological evaluation

Alzheimer's disease (AD) is a complex neurological disorder with diverse underlying pathological processes. Several lines of evidence suggest that BACE1 is a key enzyme in the pathogenesis of AD and its inhibition is of particular importance in AD treatment. Ten new 3-hydrazinyl-1,2,4-triazines bearing pendant aryl phenoxy methyl-1,2,3-triazole were synthesized as multifunctional ligands against AD. We show that compounds containing Cl and NO₂ groups at the para position of the phenyl ring, namely compounds 7c (IC₅₀ = 8.55 ± 3.37 µM) and 7d (IC₅₀ = 11.42 ± 2.01 µM), possess promising BACE1 inhibitory potential. Furthermore, we assessed the neuroprotective activities of 7c and 7d derivatives in PC12 neuronal cell line, which showed moderate protection against amyloid β peptide toxicity. In addition, compound 7d demonstrated metal chelating activity and moderate antioxidant potential (IC₅₀ = 44.42 ± 7.33 µM). Molecular docking studies of these molecules revealed high-affinity binding to several amino acids of BACE1, which are essential for efficient inhibition. These results demonstrate that 1,2,4-triazine derivatives bearing an aryl phenoxy methyl-1,2,3-triazole have promising properties as therapeutic agents for AD.     

Conformational restriction approach to β-secretase (BACE1) inhibitors III: Effective investigation of the binding mode by combinational use of X-ray analysis,isothermal titration calorimetry and theoretical calculations

For further investigation of BACE1 inhibitors using conformational restriction with sp³ hybridized carbon, we applied this approach to 6-substituted aminopyrimidone derivatives 3 to improve the inhibitory activity by reducing the entropic energy loss upon binding to BACE1. Among eight stereoisomers synthesized, [trans-(1′R,2′R),6S] isomer 6 exhibited the best BACE1 inhibitory activity, which was statistically superior to that of the corresponding ethylene linker compound (R)-3. Combinational examinations of the binding mode of 6 were performed, which included isothermal titration calorimetry (ITC), X-ray crystallographic structure analysis and theoretical calculations, to clarify the effect of our conformational restriction approach. From the ITC measurement, the binding entropy of 6 was found to be ～0.5 kcal larger than that of (R)-3, which is considered to be affected by conformational restriction with a cyclopropane ring.     

Molecular similarity guided optimization of novel Nrf2 activators with 1,2,4-oxadiazole core

DDO-7204 is a novel Nrf2 activator first identified through screening of in-house database by ARE-luciferase reporter gene assay. To further optimize this kind of Nrf2 activators efficiently, the hit-based substructure search was applied to screen the Specs database virtually. DDO-7204 contains three rings of A, B, C. SAR results showed that: for ring A, the cyclane substituent is beneficial for ARE inductivity. Enhanced flexibility of linker between ring A and ring B is not preferable for the Nrf2 activity. Ring A replaced by heterocyclic aromatic is beneficial for the Nrf2 activity. The resulting compound 7 was more potent than DDO-7204. Compound 7 can induce Nrf2 translocation into nuclear not only in HCT116 cells, but also in three normal cells such as L02, NCM460 and PC12 cells. The Nrf2-regualted genes, γ-GCS, NQO1 and HO-1, were up-regulated at a concentration-dependent manner. In addition, compound 7 showed cytoprotective effects on the three normal cells against the damage of H₂O₂.     

New antifungal scaffold derived from a natural pharmacophore: Synthesis of α-methylene-γ-butyrolactone derivatives and their antifungal activity against Colletotrichum lagenarium

Thirty new and thirty-four known analogues were designed and synthesized to improve the potential use of the α-methylene-γ-butyrolactone ring, a natural pharmacophore. All structures were confirmed by ¹H and ¹³C NMR, MS, and single-crystal X-ray diffraction analyses. The results of antifungal and cytotoxic activity indicated that the synthesized analogues showed significant inhibitory activity and limited selectivity. Compound 45 exhibited the highest antifungal activity with IC₅₀ = 22.8 μM but moderate cytotoxic activity with IC₅₀ = 28.5 μM (against BGC823 cell line) and 7.7 μM (against HeLa cell line). Analysis of structure–activity relationships revealed that the incorporation of an aromatic ring into the β, γ positions of the lactone ring improved antifungal activity, and that the introduction of electron-withdrawing groups into the aromatic rings increased the activity compared with electron-donating groups. The above results identified 4-phenyl-3-phenyl-2-methylenebutyrolactone (33) as a lead scaffold for discovering and developing novel and improved crop-protection agents.     

Identification of a new biaryl scaffold generating potent renin inhibitors

The discovery and SAR of a series of potent renin inhibitors possessing a novel biaryl scaffold are described herein. Molecular modeling revealed that the cyclopropylamide spacer present in 1 can be replaced by a simple, substituted aromatic ring such as a toluene in 2. The resulting compounds exhibit subnanomolar renin IC₅₀ and good oral bioavailability in rats.     

Design and synthesis of indole, 2,3-dihydro-indole,and 3,4-dihydro-2H-quinoline-1-carbothioic acid amide derivatives as novel HCV inhibitors

An efficient synthetic methodology to provide indole, 2,3-dihydro-indole, and 3,4-dihydro-2H-quinoline-1-carbothioic acid amide derivatives is described. These conformationally restricted heterobicyclic scaffolds were evaluated as a novel class of HCV inhibitors. Introduction of an acyl group at the NH₂ of the thiourea moiety has been found to enhance inhibitory activity. The chain length and the position of the alkyl group on the indoline aromatic ring markedly influenced anti-HCV activity. The indoline scaffold was more potent than the corresponding indole and tetrahydroquinoline scaffolds and analogue 31 displayed excellent activity (EC₅₀ = 510 nM) against HCV without significant cytotoxicity (CC₅₀ >50 μM).     

Synthesis and activity evaluation of benzoylurea derivatives as potential antiproliferative agents

3-Haloacylamino benzoylureas (3-HBUs) consist of a new family of tubulin ligands that kill cancer cells through mitotic arrest. In exploring the structure–activity relationship (SAR), 17 analogues defined through variations of formylurea at the 1-position of the aromatic ring were synthesized. SAR analysis revealed that (i) the p–π conjugation between the aromatic ring and formylurea was essential; (ii) suitable aryl substitutions at the N′-end increased anticancer activity with a mechanism different from that of parent compounds; and (iii) introduction of pyridyl at the N′-end provided an opportunity of making soluble salts to improve bioavailability. Among the analogues, 16c bearing 3,4,5-trimethoxyphenyl and 16g bearing 2-pyridyl at the N′-end showed an enhanced activity and were active in hepatoma cells that were resistant to tubulin ligands including the parent compounds. Furthermore, 16c and 16g killed cancer cells with a mechanism independent of mitotic arrest, indicating a change of action mode.     

Thioether-bridged arylalkyl-linked N-phenylpyrazole derivatives: Design,synthesis, insecticidal activities,structure-activity relationship and molecular-modeling studies

Owing to thioether diverse physicochemical properties by non-covalent interactions with bio-macromolecules, thioether derivatives containing heterocyclic moiety are known for their interesting insecticidal bioactivities and attracting considerable attention as neuroactive insecticides. Here we synthesis a series of novel thioether bridged N-phenylpyrazole derivatives incorporating various (hetero)aromatic substituents into 4-position of the pyrazole ring. Structure-activity relationship (SAR) studies resulted in compounds 6d and 7d with the most potent insecticidal activity among the series containing various substituted benzene substituents (LC₅₀?=?13.70–25.47?μg/g). Further optimization to increase the lipophilicity and charge density of aromatic substituents of compounds 6d and 7d resulted in compounds 12d, 14d and 16d with sulfur-containing heterocycle substituents possessing good insecticidal activity against Musca domestica L. among the series (LC₅₀?=?0.67–1.30?μg/g). The thioether bridge N-phenylpyrazole derivatives, which exhibit different length of the spacer arm introduced between N-phenylpyrazole moiety and the (hetero)aromatic substituents, were also prepared and evaluated. By contrast, the insecticidal activities of compounds containing the short thioether bridge, 1,2-bis((hetero)aromatic thio) ethane, are higher than that containing the long thioether bridge, 1,3-bis((hetero)aromatic thio) propane. The results of molecular docking and pharmacophore analyses indicated A299, T303, and L306 of a subunit were essential to form non-covalent interactions contacts with the ligands. Specially, the sulfur-containing heterocycle substituent derivatives 12d and 14d as the sterically favored areas could form the important hydrophobic interactions with the deeper residue P295.     

Synthesis and structure–activity relationships of N-aryl-piperidine derivatives as potent (partial) agonists for human histamine H3 receptor

4-((1H-Imidazol-4-yl)methyl)-1-aryl-piperazine and piperidine derivatives were designed and synthesized as candidate human histamine type 3 agonists. The piperazine derivatives were found to have low (or no) affinity for human histamine H3 receptor, whereas the piperidine derivatives showed moderate to high affinity, and their agonistic activity was greatly influenced by substituents on the aromatic ring. Among the piperidine-containing compounds, 17d and 17h were potent human histamine H3 receptor agonists with high selectivity over the closely related human H4 receptor. Our results indicate that appropriate conformational restriction, that is, by the piperidine spacer moiety, favors specific binding to the human histamine H3 receptor.     

The development of a structurally distinct series of BACE1 inhibitors via the (Z)-fluoro-olefin amide bioisosteric replacement

The (Z)-fluoro-olefin amide bioisosteric replacement is an effective tool for addressing various shortcomings of the parent amide. In an effort to fine tune ADME properties of BACE1 preclinical candidate AM-6494, a series of structurally distinct (Z)-fluoro-olefin containing analogs was developed that culminated in compound 15. Herein, we detail design considerations, synthetic challenges, structure activity relationship (SAR) studies, and in vivo properties of an advanced compound in this novel series of BACE1 inhibitors.     

Antioxidant and antiproliferative activities of hydroxyl-substituted Schiff bases

Eight hydroxyl-substituted Schiff bases with the different number and position of hydroxyl group on the two asymmetric aromatic rings (A and B rings) were prepared by the reaction between the corresponding aromatic aldehyde and aniline. Their antioxidant effects against the stable galvinoxyl radical (GO) in ethyl acetate and methanol, and 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH)-induced DNA strand breakage, and their antiproliferative effects on human hepatoma HepG2 cells, were investigated. Structure–activity relationship analysis demonstrates that o-dihydroxyl groups on the aromatic A ring and 4-hydroxyl group attached to the aromatic B ring contribute critically to the antioxidant and antiproliferative activities.     

Farnesyltransferase inhibitors: CAAX mimetics based on different biaryl scaffolds

Mimetics of the C-terminal CAAX tetrapeptide of Ras protein were designed as farnesyltransferase (FTase) inhibitors (FTIs) by replacing AA with o-aryl or o-heteroaryl substituted p-hydroxy- or p-aminobenzoic acid, while maintaining the replacement of C with 1,4-benzodioxan-2-ylmethyl or 2-amino-4-thiazolylacetyl residue as in previous CAAX mimetics. Both FTase inhibition and antiproliferative effect were showed by two thiazole derivatives, namely those with 1-naphthyl (10 and 10a) or 3-furanyl (15 and 15a) in the central spacer, and by the benzodioxane derivative with 2-thienyl (6 and 6a) in the same position. Accumulation of unprenylated RAS was demonstrated in cells incubated with 15a. Consistently with FTIs literature, such results delineate the biaryl scaffold not only as a spacer but also as a sensible area of these mimetic molecules, where modifications at the branching aromatic ring are not indifferent and should be matter of further investigation.