Multiwell fluorometric and colorimetric microassays for the evaluation of beta-secretase (BACE-1) inhibitors

Electrochemiluminescence and electrochemical dual-mode detection of BACE1 activity based on the assembly of peptide and luminol co-functionalized silver nanoparticles induced by cucurbit[8]uril

A novel electrochemiluminescence (ECL) and electrochemical dual-mode sensor was developed for detecting the activity of beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) and screening its inhibitor. Specifically, the adamantane (ADA)-functionalized peptide (P1), a designed substrate peptide for BACE1, was immobilized on the electrode surface via host-guest interaction between β-cyclodextrin (β-CD) and ADA. The aggregation of the peptide (P2) and luminol co-functionalized silver nanoparticles could be induced by cucurbit [8]uril (CB[8] due to the ability of CB[8] to accommodate two aromatic residues simultaneously. The obtained (CB[8]-P2-AgNPs-luminol)n aggregates with both ECL and electrochemical activity, used as the dual-mode signal probe, could be captured to the N-terminal of P1 through CB[8]. Once the substrate P1 was cleaved by BACE1, the probe-binding polypeptide fragment detached from the electrode surface, resulting in a remarkable decrease in the ECL and electrochemical signals. Taking advantage of the signal amplification function of the signal probe, the sensitive dual-mode assay for BACE1 activity can be achieved with the low detection limits of 33.11 pM for ECL and 53.19 pM for electrochemical mode. The superior analytical performance of this novel dual-mode sensor toward BACE1 activity suggested the promising application in early diagnosis of Alzheimer's disease (AD).

Neuroprotective properties of Solanum leaves in Transgenic Drosophila melanogaster model of Alzheimer's disease

INTRODUCTION

We investigated the effect of African eggplant (AE) (Solanum macrocarpon L) and Black nightshade (BN) (Solanum nigrum L) leaves; two tropical vegetables consumed by humans on behavioral, biochemical and histological indices in Drosophila melanogaster model of Alzheimer's disease (AD).

MATERIALS AND METHOD

Transgenic flies expressing human Amyloid Precursor Protein (hAPP) and β-secretase (hBACE 1) were exposed to the pulverized leaf samples (0.1 and 1.0%) in their diets for fourteen days. Thereafter, the flies were assessed for their behavioral indices and routine histology of brain cells. Furthermore, fly head homogenates were assayed for β-amyloid level, activities of acetylcholinesterase (AChE) and β-secretase (BACE-1), as well as oxidative stress markers.

RESULTS

Result showed that the significantly lower (p < 0.05) behavioral parameters (survival, locomotor performance and memory index), higher AChE and BACE-1 activities, β-amyloid, ROS and lipid peroxidation levels, as well as reduced antioxidant indices observed in the AD flies, were significantly ameliorated (p < 0.05) in AD flies treated with the leaf samples.

DISCUSSION

This study has showed that leaves of AE and BN ameliorated behavioral and biochemical indices in AD flies via neural enzyme modulatory, and antioxidant mechanisms.

CONCLUSION

Hence, this study further justifies the neuroprotective properties of both AE and BN.

Sinomenine Attenuates Trimethyltin-Induced Cognitive Decline via Targeting Hippocampal Oxidative Stress and Neuroinflammation

Sinomenine is the main bioactive ingredient of the medicinal plant Sinomenium acutum with neuroprotective potential. This study was designed to assess beneficial effect of sinomenine in alleviation of trimethyltin (TMT)-induced cognitive dysfunction. TMT was administered i.p. (8 mg/kg, once) and sinomenine was daily given p.o. 1 h after TMT for 3 weeks at doses of 25 or 100 mg/kg. Cognitive performance was assessed in various behavioral tests. In addition, oxidative stress- and inflammation-associated factors were measured and histochemical evaluation of the hippocampus was conducted. Sinomenine at a dose of 100 mg/kg significantly and partially increased discrimination index in novel object recognition (NOR), improved alternation in short-term Y maze, increased step-through latency in passive avoidance paradigm, and also reduced probe trial errors and latency in the Barnes maze task. Moreover, sinomenine somewhat prevented inappropriate hippocampal changes of malondialdehyde (MDA), reactive oxygen species (ROS), protein carbonyl, nitrite, superoxide dismutase (SOD), tumor necrosis factor α (TNFα), interleukin 6 (IL 6), acetylcholinesterase (AChE) activity, beta secretase 1 (BACE 1) activity, and mitochondrial membrane potential (MMP) with no significant effect on glutathione (GSH), catalase, glutathione reductase, glutathione peroxidase, and myeloperoxidase (MPO). In addition, lower reactivity (IRA) for glial fibrillary acidic protein (GFAP) as an index of astrocyte activity was observed and loss of CA1 pyramidal neurons was attenuated following sinomenine treatment. This study demonstrated that sinomenine could lessen TMT-induced cognitive dysfunction which is partly due to its attenuation of hippocampal oxidative stress and neuroinflammation.

A study of protein–drug interaction based on solvent-induced protein aggregation by fluorescence correlation spectroscopy

Based on the inhibition of protein aggregation by drugs in organic solvent systems, we developed an effective method to study protein–drug interaction by fluorescence correlation spectroscopy.

Screening Platform Based on Inductively Coupled Plasma Mass Spectrometry for β-Site Amyloid Protein Cleaving Enzyme 1 (BACE1) Inhibitors

β-Site amyloid protein cleaving enzyme 1 (BACE1) is a promising therapeutic target for developing inhibitors to alleviate Alzheimer's disease (AD). Herein, we established an inductively coupled plasma mass spectrometry (ICPMS)-based inhibitor screening platform. A biotin-labeled lanthanide-coded peptide probe (LCPP; biotin-PEG₂-EVNLDAEC-DOTA-Ln) was designed to determine the activity of BACE1 and evaluate the degree of inhibition of inhibitors. The platform was first validated with two commercially available inhibitors (BSI I and BSI IV) in terms of IC₅₀ values and then applied to two newly designed inhibitors (inhibitors II and III) based on the crystal structure of BACE1 interacting with inhibitor I, and each of them contained an acylguanidine core structure. We found that their inhibition effects were improved as evaluated by the sensitive and accurate LCPP-ICPMS platform, demonstrating its ability for new drug screening.

New flavonoid - N,N-dibenzyl(N-methyl)amine hybrids: Multi-target-directed agents for Alzheimer´s disease endowed with neurogenic properties

The design of multi-target directed ligands (MTDLs) is a valid approach for obtaining effective drugs for complex pathologies. MTDLs that combine neuro-repair properties and block the first steps of neurotoxic cascades could be the so long wanted remedies to treat neurodegenerative diseases (NDs). By linking two privileged scaffolds with well-known activities in ND-targets, the flavonoid and the N,N-dibenzyl(N-methyl)amine (DBMA) fragments, new CNS-permeable flavonoid - DBMA hybrids (1-13) were obtained. They were subjected to biological evaluation in a battery of targets involved in Alzheimer's disease (AD) and other NDs, namely human cholinesterases (hAChE/hBuChE), β-secretase (hBACE-1), monoamine oxidases (hMAO-A/B), lipoxygenase-5 (hLOX-5) and sigma receptors (σ₁R/σ₂R). After a funnel-type screening, 6,7-dimethoxychromone - DBMA (6) was highlighted due to its neurogenic properties and an interesting MTD-profile in hAChE, hLOX-5, hBACE-1 and σ₁R. Molecular dynamic simulations showed the most relevant drug-protein interactions of hybrid 6, which could synergistically contribute to neuronal regeneration and block neurodegeneration.

Capillary electrophoresis integrated immobilized enzyme reactor for kinetic and inhibition assays of β-secretase as the Alzheimer's disease drug target

Capillary electrophoresis integrated immobilized enzyme reactors are becoming an increasingly popular alternative for enzyme kinetic and inhibition assays thanks to their unique set of features including cost effectiveness, repeated use of the enzyme, minuscule sample consumption, rapid analysis time and easy automation. In this work we present the development and application of a capillary electrophoresis integrated immobilized enzyme reactor based on magnetic particles for kinetic and inhibition studies of β-secretase, a key enzyme in the development of Alzheimer's disease and a promising drug target. We document the optimization of the immobilization procedure, characterization of immobilized β-secretase, optimization of a mutually compatible incubation protocol and separation method as well as the production of the capillary electrophoresis integrated immobilized enzyme reactor. The applicability of the capillary electrophoresis integrated immobilized enzyme reactor was demonstrated by kinetic assay with an unlabelled substrate and by inhibition assays using three structurally different reference inhibitors. The resulting kinetic and inhibition parameters clearly support the applicability of the herein presented method as well as document the fundamental phenomena which need to be taken in account when comparing the results to other methods.

Multidisciplinary approaches for targeting the secretase protein family as a therapeutic route for Alzheimer's disease

The continual increase of the aging population worldwide renders Alzheimer's disease (AD) a global prime concern. Several attempts have been focused on understanding the intricate complexity of the disease's development along with the on- andgoing search for novel therapeutic strategies. Incapability of existing AD drugs to effectively modulate the pathogenesis or to delay the progression of the disease leads to a shift in the paradigm of AD drug discovery. Efforts aimed at identifying AD drugs have mostly focused on the development of disease-modifying agents in which effects are believed to be long lasting. Of particular note, the secretase enzymes, a group of proteases responsible for the metabolism of the β-amyloid precursor protein (βAPP) and β-amyloid (Aβ) peptides production, have been underlined for their promising therapeutic potential. This review article attempts to comprehensively cover aspects related to the identification and use of drugs targeting the secretase enzymes. Particularly, the roles of secretases in the pathogenesis of AD and their therapeutic modulation are provided herein. Moreover, an overview of the drug development process and the contribution of computational (in silico) approaches for facilitating successful drug discovery are also highlighted along with examples of relevant computational works. Promising chemical scaffolds, inhibitors, and modulators against each class of secretases are also summarized herein. Additionally, multitarget secretase modulators are also taken into consideration in light of the current growing interest in the polypharmacology of complex diseases. Finally, challenging issues and future outlook relevant to the discovery of drugs targeting secretases are also discussed.

In Silico Identification and Experimental Validation of Novel Anti-Alzheimer's Multitargeted Ligands from a Marine Source Featuring a "2-Aminoimidazole plus Aromatic Group" Scaffold

Multitargeting or polypharmacological approaches, looking for single chemical entities retaining the ability to bind two or more molecular targets, are a potentially powerful strategy to fight complex, multifactorial pathologies. Unfortunately, the search for multiligand agents is challenging because only a small subset of molecules contained in molecular databases are bioactive and even fewer are active on a preselected set of multiple targets. However, collections of natural compounds feature a significantly higher fraction of bioactive molecules than synthetic ones. In this view, we searched our library of 1175 natural compounds from marine sources for molecules including a 2-aminoimidazole+aromatic group motif, found in known compounds active on single relevant targets for Alzheimer's disease (AD). This identified two molecules, a pseudozoanthoxanthin (1) and a bromo-pyrrole alkaloid (2), which were predicted by a computational approach to possess interesting multitarget profiles on AD target proteins. Biochemical assays experimentally confirmed their biological activities. The two compounds inhibit acetylcholinesterase, butyrylcholinesterase, and β-secretase enzymes in high- to sub-micromolar range. They are also able to prevent and revert β-amyloid (Aβ) aggregation of both Aβ_1-40 and Aβ_1-42 peptides, with 1 being more active than 2. Preliminary in vivo studies suggest that compound 1 is able to restore cholinergic cortico-hippocampal functional connectivity.

New neurogenic lipoic-based hybrids as innovative Alzheimer's drugs with σ-1 agonism and β-secretase inhibition

BACKGROUND

Neurogenic agents emerge as innovative drugs for the treatment of Alzheimer's disease (AD), whose pathological complexity suggests strengthening research in the multi-target directed ligands strategy.

RESULTS

By combining the lipoic acid structure with N-benzylpiperidine or N,N-dibenzyl(N-methyl)amine fragments, new multi-target directed ligands were obtained that act at three relevant targets in AD: σ-1 receptor (σ1R), β-secretase-1 (BACE1) and acetylcholinesterase (AChE). Moreover, they show potent neurogenic properties, good antioxidant capacity and favorable CNS permeability. Molecular modeling studies on AChE, σ1R and BACE1 highlight relevant drug-protein interactions that may contribute to the development of new disease-modifying drugs.

CONCLUSION

New lipoic-based σ1 agonists endowed with neurogenic, antioxidant, cholinergic and amyloid β-peptide-reducing properties have been discovered for the potential treatment of AD.

Design, Synthesis, and Evaluation of Donepezil-Like Compounds as AChE and BACE-1 Inhibitors

An ecofriendly synthetic pathway for the synthesis of donepezil precursors is described. Alternative energy sources were used for the total synthesis in order to improve yields, regioselectively, and rate of each synthetic step and to reduce the coproduction of waste at the same time. For all products, characterized by an improved structural rigidity respect to donepezil, the inhibitor activity on AChE, the selectivity vs BuChE, the side-activity on BACE-1, and the effect on SHSY-5Y neuroblastoma cells viability were tested. Two potential new lead compounds for a dual therapeutic strategy against Alzheimer's disease were envisaged.

8-Tetrahydropyran-2-yl chromans: highly selective beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibitors

A series of 2,3,4,4a,10,10a-hexahydropyrano[3,2-b]chromene analogs was developed that demonstrated high selectivity (>2000-fold) for BACE1 vs Cathepsin D (CatD). Three different Asp-binding moieties were examined: spirocyclic acyl guanidines, aminooxazolines, and aminothiazolines in order to modulate potency, selectivity, efflux, and permeability. Guided by structure based design, changes to P2' and P3 moieties were explored. A conformationally restricted P2' methyl group provided inhibitors with excellent cell potency (37-137 nM) and selectivity (435 to >2000-fold) for BACE1 vs CatD. These efforts lead to compound 59, which demonstrated a 69% reduction in rat CSF Aβ1-40 at 60 mg/kg (PO).

Reprint of: Liquid chromatographic enzymatic studies with on-line Beta-secretase immobilized enzyme reactor and 4-(4-dimethylaminophenylazo) benzoic acid/5-[(2-aminoethyl) amino] naphthalene-1-sulfonic acid peptide as fluorogenic substrate

High throughput screening (HTS) techniques are required for the fast hit inhibitors selection in the early discovery process. However, in Beta-secretase (BACE1) inhibitors screening campaign, the most frequently used methoxycoumarin based peptide substrate (M-2420) is not widely applicable when aromatic or heterocycle compounds of natural source show auto-fluorescence interferences. Here, in order to overcome these drawbacks, we propose the use of a highly selective 4-(4-dimethylaminophenylazo)benzoic acid/5-[(2-aminoethyl)amino]naphthalene-1-sulfonic acid (DABCYL/1,5-EDANS) based peptide substrate (Substrate IV), whose cleavage product is devoid of spectroscopic interference. HrBACE1-IMER was prepared and characterized in terms of units of immobilised hrBACE1. BACE1 catalyzed Substrate IV cleavage was on-line kinetically characterized in terms of KM and vmax, in a classical Michaelis and Menten study. The on-line kinetic constants were found consistent with those obtained with the in solution fluorescence resonance energy transfer (FRET) standard method. In order to further validate the use of Substrate IV for inhibition studies, the inhibitory potency of the well-known BACE1 peptide InhibitorIV (IC₅₀: 0.19 ± 0.02 μM) and of the natural compound Uleine (IC₅₀: 0.57 ± 0.05) were determined in the optimized on-line hrBACE1-IMER. The IC₅₀ values on the hrBACE1-IMER system were found in agreement with that obtained by the conventional methods confirming the applicability of Substrate IV for on-line BACE1 kinetic and inhibition studies.

From the dual function lead AP2238 to AP2469, a multi-target-directed ligand for the treatment of Alzheimer's disease

The development of drugs with different pharmacological properties appears to be an innovative therapeutic approach for Alzheimer's disease. In this article, we describe a simple structural modification of AP2238, a first dual function lead, in particular the introduction of the catechol moiety performed in order to search for multi-target ligands. The new compound AP2469 retains anti-acetylcholinesterase (AChE) and beta-site amyloid precursor protein cleaving enzyme (BACE)1 activities compared to the reference, and is also able to inhibit Aβ₄₂ self-aggregation, Aβ₄₂ oligomer-binding to cell membrane and subsequently reactive oxygen species formation in both neuronal and microglial cells. The ability of AP2469 to interfere with Aβ₄₂ oligomer-binding to neuron and microglial cell membrane gives this molecule both neuroprotective and anti-inflammatory properties. These findings, together with its strong chain-breaking antioxidant performance, make AP2469 a potential drug able to modify the course of the disease.

Liquid chromatographic enzymatic studies with on-line Beta-secretase immobilized enzyme reactor and 4-(4-dimethylaminophenylazo) benzoic acid/5-[(2-aminoethyl) amino] naphthalene-1-sulfonic acid peptide as fluorogenic substrate

High throughput screening (HTS) techniques are required for the fast hit inhibitors selection in the early discovery process. However, in Beta-secretase (BACE1) inhibitors screening campaign, the most frequently used methoxycoumarin based peptide substrate (M-2420) is not widely applicable when aromatic or heterocycle compounds of natural source show auto-fluorescence interferences. Here, in order to overcome these drawbacks, we propose the use of a highly selective 4-(4-dimethylaminophenylazo)benzoic acid/5-[(2-aminoethyl)amino]naphthalene-1-sulfonic acid (DABCYL/1,5-EDANS) based peptide substrate (Substrate IV), whose cleavage product is devoid of spectroscopic interference. HrBACE1-IMER was prepared and characterized in terms of units of immobilised hrBACE1. BACE1 catalyzed Substrate IV cleavage was on-line kinetically characterized in terms of KM and vmax, in a classical Michaelis and Menten study. The on-line kinetic constants were found consistent with those obtained with the in solution fluorescence resonance energy transfer (FRET) standard method. In order to further validate the use of Substrate IV for inhibition studies, the inhibitory potency of the well-known BACE1 peptide InhibitorIV (IC50: 0.19±0.02μM) and of the natural compound Uleine (IC50: 0.57±0.05) were determined in the optimized on-line hrBACE1-IMER. The IC50 values on the hrBACE1-IMER system were found in agreement with that obtained by the conventional methods confirming the applicability of Substrate IV for on-line BACE1 kinetic and inhibition studies.

From single target to multitarget/network therapeutics in Alzheimer's therapy

Brain network dysfunction in Alzheimer’s disease (AD) involves many proteins (enzymes), processes and pathways, which overlap and influence one another in AD pathogenesis. This complexity challenges the dominant paradigm in drug discovery or a single-target drug for a single mechanism. Although this paradigm has achieved considerable success in some particular diseases, it has failed to provide effective approaches to AD therapy. Network medicines may offer alternative hope for effective treatment of AD and other complex diseases. In contrast to the single-target drug approach, network medicines employ a holistic approach to restore network dysfunction by simultaneously targeting key components in disease networks. In this paper, we explore several drugs either in the clinic or under development for AD therapy in term of their design strategies, diverse mechanisms of action and disease-modifying potential. These drugs act as multi-target ligands and may serve as leads for further development as network medicines.

Recent advances in the multitarget-directed ligands approach for the treatment of Alzheimer's disease

With 27 million cases worldwide documented in 2006, Alzheimer's disease (AD) constitutes an overwhelming health, social, economic, and political problem to nations. Unless a new medicine capable to delay disease progression is found, the number of cases will reach 107 million in 2050. So far, the therapeutic paradigm one-compound-one-target has failed. This could be due to the multiple pathogenic mechanisms involved in AD including amyloid β (Aβ) aggregation to form plaques, τ hyperphosphorylation to disrupt microtubule to form neurofibrillary tangles, calcium imbalance, enhanced oxidative stress, impaired mitochondrial function, apoptotic neuronal death, and deterioration of synaptic transmission, particularly at cholinergic neurons. Approximately 100 compounds are presently been investigated directed to single targets, namely inhibitors of β and γ secretase, vaccines or antibodies that clear Aβ, metal chelators to inhibit Aβ aggregation, blockers of glycogen synthase kinase 3β, enhancers of mitochondrial function, antioxidants, modulators of calcium-permeable channels such as voltage-dependent calcium channels, N-methyl-D-aspartate receptors for glutamate, or enhancers of cholinergic neurotransmission such as inhibitors of acetylcholinesterase or butyrylcholinesterase. In view of this complex pathogenic mechanisms, and the successful treatment of chronic diseases such as HIV or cancer, with multiple drugs having complementary mechanisms of action, the concern is growing that AD could better be treated with a single compound targeting two or more of the pathogenic mechanisms leading to neuronal death. This review summarizes the current therapeutic strategies based on the paradigm one-compound-various targets to treat AD. A treatment that delays disease onset and/or progression by 5 years could halve the number of people requiring institutionalization and/or dying from AD. 

Measurement of cellular beta-site of APP cleaving enzyme 1 activity and its modulation in neuronal assay systems

Amyloid-beta peptide (Abeta), a putatively causative agent of Alzheimer's disease (AD), is proteolytically derived from beta-amyloid precursor protein (APP). Here we describe cellular assays to detect the activity of the key protease beta-site of APP cleaving enzyme 1 (BACE1) based on an artificial reporter construct containing the BACE1 cleavage site of APP. These methods allow identification of inhibitors and indirect modulators of BACE1. In primary neuronal cultures transfected with human APP constructs (huAPP), Abeta production was modified by BACE1 inhibitors similarly to the production of endogenous murine Abeta in wild-type cells and to that of different transgenic neurons. To further improve the assay, we substituted the extracellular domain of APP by secreted alkaline phosphatase (SEAP). SEAP was easily quantified in the cell culture supernatants after cleavage of SEAP-APP by BACE1 or alpha-secretases. To render the assay specific for BACE1, the alpha-secretase cleavage site of SEAP-APP was eliminated either by site-directed mutagenesis or by substituting the transmembrane part of APP by the membrane domain of the erythropoietin receptor (EpoR). The pharmacology of these constructs was characterized in detail in HEK293 cells (human embryonic kidney cell line), and the SEAP-APP-EpoR construct was also introduced into primary murine neurons and there allowed specific measurement of BACE1 activity.

Development and characterization of beta-secretase monolithic micro-immobilized enzyme reactor for on-line high-performance liquid chromatography studies

beta-Site APP cleavage enzyme 1 (BACE-1) is a transmembrane aspartyl protease that cleaves the amyloid-beta precursor protein (APP), which is abundant in neurons. BACE-1 is required for the generation of amyloid-beta (Abeta) peptides implicated in the pathogenesis of Alzheimer's disease (AD). It is widely believed that halting the production of Abeta peptide, by inhibition of BACE-1, is an attractive therapeutic modality for the treatment of Alzheimer's disease. BACE-1 has never been immobilized before. In the present study, for the first time, human recombinant beta-secretase micro-immobilised enzyme reactor (hrBACE-1-micro-IMER) was prepared by using an in situ immobilisation procedure on an ethylendiamine monolithic convective interaction media (EDA-CIM) disk. The activity and kinetic parameters of the hrBACE-1-micro-IMER were investigated by insertion in a HPLC system with fluorescent and mass detection. The micro-IMER was characterized in terms of units of immobilised hrBACE-1 and best mobile phase conditions for activity, by using as substrate casein-FITC and JMV2236, a peptide mimicking the Swedish-mutated APP (amyloid precursor protein) sequence. The characterization of the hrBACE-1-micro-IMER in terms of number of enzymatic active units after covalent linking to the solid matrix was performed by using the JMV2236 peptide as substrate in a HPLC-MS system. JMV2236 was injected into the hrBACE-1-micro-IMER and enzymatically cleaved; the product of the enzymatic cleavage and the remaining non-cleaved substrate were collected on a C18 column trap and switched to the LC-electrospray ionization MS system for kinetic constants determination. Inhibition studies were carried out. The effect of donepezil and pepstatin A, as BACE-1 inhibitors, was evaluated by simultaneous injection of the compounds with the peptidic substrate. The relative IC(50) values were found in agreement with that derived by the conventional fluorescence method, confirming the applicability of this new IMER for on-line inhibition studies. The main advantages of the hrBACE-1-micro-IMER approach over the conventional methods were found to be the increased enzyme efficiency, stability and the decreased time of analysis.

Multi-target-directed coumarin derivatives: hAChE and BACE1 inhibitors as potential anti-Alzheimer compounds

The complex etiology of Alzheimer's disease (AD) prompts scientists to develop multifunctional compounds to combat causes and symptoms of such neurodegeneration. To this aim we designed, synthesized, and tested a series of compounds by introducing halophenylalkylamidic functions on the scaffold of AP2238, which is a dual binding site acetylcholinesterase inhibitor. The inhibitory activity was successfully extended to the beta-site amyloid precursor protein cleavage enzyme, leading to the discovery of a potent inhibitor of this enzyme (3) and affording multifunctional compounds (2, 6, 8) for the treatment of AD.