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.     

Prolonged stability by cyclization: Macrocyclic phosphino dipeptide isostere inhibitors of β-secretase (BACE1)

Cyclization of recently reported linear phosphino dipeptide isostere inhibitors of BACE1 via side chain olefin metathesis yielded macrocyclic BACE1 inhibitors. The most potent compound II-P1 (IC₅₀ of 47 nM) and the corresponding linear analog I were tested for serum stability. The approach led to three times prolonged half life serum stability of 44 min for the macrocyclic inhibitor II-P1 compared to the linear compound I.     

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.     

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.     

Synthesis,characterization, and PK/PD studies of a series of spirocyclic pyranochromene BACE1 inhibitors

The development of 1,3,4,4a,5,10a-hexahydropyrano[3,4-b]chromene analogs as BACE1 inhibitors is described. Introduction of the spirocyclic pyranochromene scaffold yielded several advantages over previous generation cores, including increased potency, reduced efflux, and reduced CYP2D6 inhibition. Compound 13 (BACE1 IC₅₀ = 110 nM) demonstrated a reduction in CSF Aβ in wild type rats after a single dose.     

Design and synthesis of novel anti-Alzheimer’s agents: Acridine-chromenone and quinoline-chromenone hybrids

A novel series of acridine-chromenone and quinoline-chromenone hybrids were designed, synthesized, and evaluated as anti-Alzheimer’s agents. All synthesized compounds were evaluated as cholinesterases (ChEs) inhibitors and among them, 7-(4-(6-chloro-2,3-dihydro-1H-cyclopenta[b]quinolin-9-ylamino)phenoxy)-4-methyl-2H-chromen-2-one (8e) exhibited the most potent anti-acetylcholinesterase (AChE) inhibitory activity (IC₅₀ = 16.17 μM) comparing with rivastigmine (IC₅₀ = 11.07 μM) as the reference drug. Also, compound 8e was assessed for its β-secretase (BACE1) inhibitory and neuroprotective activities which demonstrated satisfactory results. It should be noted that both kinetic study on the inhibition of AChE and molecular modeling revealed that compound 8e interacted simultaneously with both the catalytic active site (CAS) and peripheral anionic site (PAS) of AChE.     

Design,synthesis, and X-ray structural studies of BACE-1 inhibitors containing substituted 2-oxopiperazines as P1′-P2′ ligands

We report the design and synthesis of a series of BACE1 inhibitors incorporating mono- and bicyclic 6-substituted 2-oxopiperazines as novel P1′ and P2′ ligands and isophthalamide derivative as P2-P3 ligands. Among mono-substituted 2-oxopiperazines, inhibitor 5a with N-benzyl-2-oxopiperazine and isophthalamide showed potent BACE1 inhibitory activity (K_i = 2 nM). Inhibitor 5g, with N-benzyl-2-oxopiperazine and substituted indole-derived P2-ligand showed a reduction in potency. The X-ray crystal structure of 5g-bound BACE1 was determined and used to design a set of disubstituted 2-oxopiperazines and bicyclic derivatives that were subsequently investigated. Inhibitor 6j with an oxazolidinone derivative showed a BACE1 inhibitory activity of 23 nM and cellular EC₅₀ of 80 nM.     

Dual-target-directed 1,3-diphenylurea derivatives: BACE 1 inhibitor and metal chelator against Alzheimer’s disease

Dual-target-directed 1,3-diphenylurea derivatives were designed by hybridizing BACE 1 inhibitor 1 with metal chelator LR-90. A database consisted of 1,3-diphenylurea derivatives was built and screened by the pharmacophore model (Hypo 1) of BACE 1 inhibitor. Based on the predicted results, 11 compounds (6a–d, 9a–g) with favorable Fitvalues were selected, synthesized and evaluated for their BACE 1 inhibitory activities, which showed that the predicted results were in good agreement with the experimental values. Besides, the synthesized compounds also displayed the ability to chelate metal ions. The most effective BACE 1 inhibitor 9f (27.85 ± 2.46 μmol/L) was selected for further receptor-binding studies, the result of which indicated that an essential hydrogen bonds was formed between the urea group of 9f and the catalytic aspartate Asp228.     

Synthesis of novel chromenones linked to 1,2,3-triazole ring system: Investigation of biological activities against Alzheimer’s disease

In this work, novel chromenones linked to 1,2,3-triazole ring system were synthesized and evaluated for their anti-ChE activity. Among them, N-((1-(2-chlorobenzyl)-1H-1,2,3-triazol-5-yl)methyl)-8-methoxy-2-oxo-2H-chromene-3-carboxamide (6m) showed good anti-acetylcholinesterase activity (IC₅₀ = 15.42 μM). Also, compound 6m demonstrated neuroprotective effect against H₂O₂-induced cell death in PC12 neurons, however, it showed no beta-secretase (BACE1) inhibitory activity. Docking and kinetic studies separately confirmed dual binding activity of compound 6m since it targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE.     

Tasiamide F,a potent inhibitor of cathepsins D and E from a marine cyanobacterium

In search of novel protease inhibitors with therapeutic potential, our efforts exploring the marine cyanobacterium Lyngbya sp. have led to the discovery of tasiamide F (1), which is an analogue of tasiamide B (2). The structure was elucidated using a combination of NMR spectroscopy and mass spectrometry. The key structural feature in 1 is the presence of the Phe-derived statine core, which contributes to its aspartic protease inhibitory activity. The antiproteolytic activity of 1 and 2 was evaluated in vitro against cathepsins D and E, and BACE1. Tasiamide F (1) displayed IC₅₀ values of 57 nM, 23 nM, and 0.69 μM, respectively, indicating greater selectivity for cathepsins over BACE1 compared with tasiamide B (2). Molecular docking experiments were carried out for compounds 1 and 2 against cathepsins D and E to rationalize their activity towards these proteases. The dysregulated activities of cathepsins D and E have been implicated in cancer and modulation of immune responses, respectively, and these proteases represent potential therapeutic targets.     

Molecular design,synthesis and biological evaluation of cyclic imides bearing benzenesulfonamide fragment as potential COX-2 inhibitors. Part 2

A group of cyclic imides (1–10) was designed for evaluation as a selective COX-2 inhibitors and investigated in vivo for their anti-inflammatory activity. Compounds 6a, 6b, 8a, 8b, 9a, 9b, 10a and 10b were proved to be potent COX-2 inhibitors with IC₅₀ range of 0.1–4.0 μM. In vitro COX-1/COX-2 inhibition structure–activity studies identified compound 8a as a highly potent (IC₅₀ = 0.1 μM), and an extremely selective [COX-2 (SI) > 1000] comparable to celecoxib [COX-2 (SI) > 384], COX-2 inhibitor that showed superior anti-inflammatory activity (ED₅₀ = 72.4 mg/kg) relative to diclofenac (ED₅₀ = 114 mg/kg). Molecular modeling was carried out through docking the designed compounds into the COX-2 binding site to predict if these compounds have analogous binding mode to the COX-2 inhibitors. The study showed that the homosulfonamide fragment of 8a inserted deep inside the 2°-pocket of the COX-2 active site, where the SO₂NH₂ group underwent H-bonding interaction with Gln¹⁹²(2.95 Å), Phe⁵¹⁸(2.82 Å) and Arg⁵¹³(2.63 and 2.73 Å). Docking study of the synthesized compound 8a into the active site of COX-2 revealed a similar binding mode to SC-558, a selective COX-2 inhibitor.     

Design of a new fluorescent probe: Pyrrole/imidazole hairpin polyamides with pyrene conjugation at their γ-turn

Fluorophores that are conjugated with N-methylpyrrole-N-methylimidazole (Py–Im) polyamides postulates versatile applications in biological and physicochemical studies. Here, we show the design and synthesis of new types of pyrene-conjugated hairpin Py–Im polyamides (1–5). We evaluated the steady state fluorescence of the synthesized conjugates (1–5) in the presence and absence of oligodeoxynucleotides 5′-CGTATGGACTCGG-3′ (ODN 1) and 5′-CCGAGTCCATACG-3′ (ODN 2) and observed a distinct increase in emission at 386 nm with conjugates 4 and 5. Notably, conjugate 5 that contains a β-alanine linker had a stronger binding affinity (K_D = 1.73 × 10^?8 M) than that of conjugate 4 (K_D = 1.74 × 10^?6 M). Our data suggests that Py–Im polyamides containing pyrene fluorophore with a β-alanine linker at the γ-turn NH₂ position can be developed as the competent fluorescent DNA-binding probes.     

Pyridinyl aminohydantoins as small molecule BACE1 inhibitors

A novel class of pyridinyl aminohydantoins was designed and prepared as highly potent BACE1 inhibitors. Compound (S)-4g showed excellent potency with IC₅₀ of 20 nM for BACE1. X-ray crystallography indicated that the interaction between pyridine nitrogen and the tryptophan Trp76 was a key feature in the S2′ region of the enzyme that contributed to increased potency.     

Acylated iridoid glycosides and acylated rhamnopyranoses from Gmelina arborea flowers

Nine acylated iridoid glycosides (1–9), five acylated rhamnopyranoses (10–14) and verbascoside (15) were isolated from Gmelina arborea flowers, including 5 new compounds (1, 2, and 10–12). The cytoprotective activity of 11 selected compounds (1–8, 10, 11, and 15) against CCl₄-induced cytotoxicity on liver was determined. Compounds 1, 2, 4, 7, 8 and 15 displayed hepatoprotective activity. 6-O-α-l-(2″, 3″-di-O-trans-p-hydroxycinnamoyl)rhamnopyranosylcatalpol (2) exhibited the most potent cytoprotective effect with an EC₅₀ value of 42.5 μM (SI = 19.3) compared with biphenyldimethylesterate (DDB, EC₅₀ = 277.3 μM, SI = 9.8) and bicylo-ethanol (EC₅₀ = 279.2 μM, SI = 12.2). Among the acylated iridoid glycosides, the compounds (2 and 8) containing phenolic hydroxy groups were more active than were those lacking them.     

Biotransformation of isoimperatorin and imperatorin by Glomerella cingulata and β-secretase inhibitory activity

Biotransformation studies conducted on the furanocoumarins isoimperatorin (1) and imperatorin (3) have revealed that 1 was metabolized by Glomerella cingulata to give the corresponding reduced acid, 6,7-furano-5-prenyloxy hydrocoumaric acid (2), and 3 was transformed by G. cingulata to give the dealkylated metabolite, xanthotoxol (4) in high yields (83% and 81%), respectively. The structures of the new compound 2 have been established on the basis of spectral data. The metabolites 2 and 4 were tested for the β-secretase (BACE1) inhibitory activity in vitro, and metabolite 2 slightly inhibited the β-secretase activity with an IC₅₀ value of 185.6 ± 6.8 μM. The metabolite 4 was less potent activity than compounds 1–3. In addition, methyl ester (2Me), methyl ether (2a) and methyl ester and ether (2aMe) of 2 were synthesized, and investigated for the ability to inhibit β-secretase. Compound 2aMe exhibited the best β-secretase inhibitory activity at the IC₅₀ value 16.2 ± 1.2 μM and found to be the 2aMe showed competitive mode of inhibition against β-secretase with K_i value 11.3 ± 2.8 μM.     

Design,synthesis and evaluation of 6-(4-((substituted-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)phenanthridine analogues as antimycobacterial agents

Focus in this Letter is made to design and synthesize a series of nineteen new 6-(4-((substituted-1H-1,2,3-triazol-4-yl)methyl)piperazin-1-yl)phenanthridine analogues employing click chemistry and evaluated for their anti-tubercular activity against Mycobacterium tuberculosis H₃₇Rv. Among the tested compounds, 7f and 7j exhibited good activity (MIC = 3.125 μg/mL), while 8a displayed excellent activity (MIC = 1.56 μg/mL) against the growth of M. tuberculosis H₃₇Rv. In addition, 7f, 7j and 8a compounds were subjected to cytotoxic studies against mouse macrophage (RAW264.7) cell lines and the selectivity index values are >15 indicating suitability of compounds for further drug development.     

Phenylimino-2H-chromen-3-carboxamide derivatives as novel small molecule inhibitors of β-secretase (BACE1)

The inhibition of β secretase (BACE1) is potentially important approach to treatment of Alzheimer disease (AD). A novel series of 4-bromophenyl piperazine derivatives coupled to the phenylimino-2H-chromen-3-carboxamide scaffold were investigated as BACE1 inhibitors in this study. Docking study suggested that the phenyl-imino group of the scaffold establishes favorable π–π stacking interaction with side chain of Phe108 of flap pocket. Some of the docking proposed derivatives were synthesized and evaluated for BACE1 inhibitory activity using a FRET-based assay. High BACE1 inhibitory activities were observed from derivatives containing fused heteroaromtic groups attached through the aliphatic linkage to the N4-piperazine moiety, which may be attributed to the engagement of effective interactions with S1–S′1 sub-pocket residues. Of the most potent compounds, 9e displayed an IC₅₀ value for BACE1 of 98 nM. Some of these derivatives demonstrated good inhibitory activity on Aβ production in N2a-APPswe cells at 5 and 10 μM. These compounds might be considered as promising BACE1 inhibitory agents that could lower Aβ production in AD.     

β-Secretase (BACE1)-inhibiting C-methylrotenoids from Abronia nana suspension cultures

Suspension cultures of Abronia nana were established to produce C-methylisoflavones. A new C-methylrotenoid, named abronione A (2), was isolated along with three known rotenoids, boeravinone D (1), boeravinone A methyl ether (3), and mirabijalone D (4). The IC₅₀ values of compounds 1, 2, and 4 on β-secretase (BACE1) were 4.77, 62.21, and 4.24 μM, respectively, whereas 3 was inactive. At concentrations up to 1.0 mM, the compounds did not inhibit other proteases such as trypsin, chymotrypsin, and elastase, indicating that they were specific inhibitors of β-secretase. Compounds 1 and 4 were non-competitive inhibitors based on the Dixon plot and with K_i values of 5.01 and 4.28 μM, respectively. At 50 μM, compound 4 inhibited Aβ_1–42 production by 43.7% in APP_SW-N2a cells.     

Design,synthesis and biological evaluation of 3-benzyloxy-linked pyrimidinylphenylamine derivatives as potent HIV-1 NNRTIs

A novel series of 3-benzyloxy-linked pyrimidinylphenylamine derivatives (8a–8s) was designed, synthesized and evaluated for their in vitro anti-HIV activity in MT-4 cell cultures. Most of the compounds inhibited wild-type (wt) HIV-1 replication in the lower micromolar concentration range (EC₅₀ = 0.05–35 μM) with high selectivity index (SI) values (ranged from 10 to >4870). In particular, 8h and 8g displayed excellent antiretroviral activity against wt HIV-1 with low cytotoxicity (EC₅₀ = 0.07 μM, CC₅₀ >347 μM, SI >4870; EC₅₀ = 0.05 μM, CC₅₀ = 42 μM, SI = 777, respectively), comparable to that of the marked drug nevirapine (EC₅₀ = 0.113 μM, CC₅₀ >15 μM, SI >133). In order to confirm the binding target, 8h was selected to perform the anti-HIV-1 RT assay. Additionally, preliminary structure activity relationship (SAR) analysis and molecular docking studies of newly synthesized compounds were also discussed, as well as the predicted physicochemical properties.     

Analogs of zanamivir with modified C4-substituents as the inhibitors against the group-1 neuraminidases of influenza viruses

Unlike the group-2 neuraminidase, the group-1 neuraminidase of influenza virus possesses a flexible loop (the 150-loop) and a cavity (the 150-cavity) adjacent to the active site, and renders a conformational change from the ‘open’ form to the ‘closed’ form on binding with substrate (sialo-glycoprotein) or inhibitor (e.g., zanamivir). Zanamivir derivative 8a having an extended (piperazinocarbonyl)propyl substituent at the internal N-position of the guanidino group is designed as a possible inhibitor on the basis of computer docking to the open form of N1 subtype neuraminidase. Indeed, compound 8a exhibits strong neuraminidase inhibition and good anti-influenza activity against H1N1 virus with IC₅₀ = 2.15 μM and EC₅₀ = 0.77 μM, respectively. This study may provide a clue to future design of better group-1 neuraminidase inhibitors.