2-Benzazepine Nitrones Protect Dopaminergic Neurons against 6-Hydroxydopamine-Induced Oxidative Toxicity

Synthesis and Biological Evaluation of Dantrolene-Like Hydrazide and Hydrazone Analogues as Multitarget Agents for Neurodegenerative Diseases

Dantrolene, a drug used for the management of malignant hyperthermia, had been recently evaluated for prospective repurposing as multitarget agent for neurodegenerative syndromes, including Alzheimer's disease (AD). Herein, twenty-one dantrolene-like hydrazide and hydrazone analogues were synthesized with the aim of exploring structure-activity relationships (SARs) for the inhibition of human monoamine oxidases (MAOs) and acetylcholinesterase (AChE), two well-established target enzymes for anti-AD drugs. With few exceptions, the newly synthesized compounds exhibited selectivity toward MAO B over either MAO A or AChE, with the secondary aldimine 9 and phenylhydrazone 20 attaining IC50 values of 0.68 and 0.81 μM, respectively. While no general SAR trend was observed with lipophilicity descriptors, a molecular simplification strategy allowed the main pharmacophore features to be identified, which are responsible for the inhibitory activity toward MAO B. Finally, further in vitro investigations revealed cell protection from oxidative insult and activation of carnitine/acylcarnitine carrier as concomitant biological activities responsible for neuroprotection by hits 9 and 20 and other promising compounds in the examined series.

Away from Flatness: Unprecedented Nitrogen-Bridged Cyclopenta[a]indene Derivatives as Novel Anti-Alzheimer Multitarget Agents

Nature-inspired, bridged polycyclic molecules share low similarity with currently available drugs, containing preferentially planar and/or achiral moieties. This "Escape from Flatland" scenario, aimed at exploring pharmacological properties of atypical molecular scaffolds, finds interest in synthetic routes leading to tridimensional-shaped molecules. Herein we report on the synthesis of N-bridged cyclopenta[a]indene derivatives, achieved through microwave-assisted thermal rearrangement of allene 3-benzazecines with high diastereoselectivity. The biological evaluation disclosed selective inhibition of human acetylcholinesterase or butyrylcholinesterase, depending on the substitution around the molecular core, which was rationalized by means of docking simulations. The most potent BChE inhibitor 31 was effective in neuroprotection from glutamatergic excitotoxicity and displayed low intrinsic cytotoxicity and good brain penetration. Overall, compound 31 and its close congeners 34 and 35 acted as multitarget agents addressing different biological events involved in neurodegeneration, particularly in the progression of Alzheimer's disease.

Investigating 1,2,3,4,5,6-hexahydroazepino[4,3-b]indole as scaffold of butyrylcholinesterase-selective inhibitors with additional neuroprotective activities for Alzheimer's disease

Due to the role of butyrylcholinesterase (BChE) in acetylcholine hydrolysis in the late stages of the Alzheimer's disease (AD), inhibitors of butyrylcholinesterase (BChE) have been recently envisaged, besides acetylcholinesterase (AChE) inhibitors, as candidates for treating mild-to-moderate AD. Herein, synthesis and AChE/BChE inhibition activity of some twenty derivatives of 1,2,3,4,5,6-hexahydroazepino[4,3-b]indole (HHAI) is reported. Most of the newly synthesized HHAI derivatives achieved the inhibition of both ChE isoforms with IC₅₀s in the micromolar range, with a structure-dependent selectivity toward BChE. Apparently, molecular volume and lipophilicity do increase selectivity toward BChE, and indeed the N²-(4-phenylbutyl) HHAI derivative 15d, which behaves as a mixed-type inhibitor, resulted the most potent (IC₅₀ 0.17 μM) and selective (>100-fold) inhibitor toward either horse serum and human BChE. Moreover, 15d inhibited in vitro self-induced aggregation of neurotoxic amyloid-β (Aβ) peptide and displayed neuroprotective effects in neuroblastoma SH-SY5Y cell line, significantly recovering (P < 0.001) cell viability when impaired by Aβ_1-42 and hydrogen peroxide insults. Overall, this study highlighted HHAI as useful and versatile scaffold for developing new small molecules targeting some enzymes and biochemical pathways involved in the pathogenesis of AD.

Insights into Structure-Activity Relationships of 3-Arylhydrazonoindolin-2-One Derivatives for Their Multitarget Activity on β-Amyloid Aggregation and Neurotoxicity

Despite the controversial outcomes of clinical trials executed so far, the prevention of β-amyloid (Aβ) deposition and neurotoxicity by small molecule inhibitors of Aβ aggregation remains a target intensively pursued in the search of effective drugs for treating Alzheimer’s disease (AD) and related neurodegeneration syndromes. As a continuation of previous studies, a series of new 3-(2-arylhydrazono)indolin-2-one derivatives was synthesized and assayed, investigating the effects of substitutions on both the indole core and arylhydrazone moiety. Compared with the reference compound 1, we disclosed equipotent derivatives bearing alkyl substituents at the indole nitrogen, and fairly tolerated bioisosteric replacements at the arylhydrazone moiety. For most of the investigated compounds, the inhibition of Aβ₄₀ aggregation (expressed as pIC₅₀) was found to be correlated with lipophilicity, as assessed by a reversed-phase HPLC method, through a bilinear relationship. The N¹-cyclopropyl derivative 28 was tested in cell-based assays of Aβ₄₂ oligomer toxicity and oxidative stress induced by hydrogen peroxide, showing significant cytoprotective effects. This study confirmed the versatility of isatin in preparing multitarget small molecules affecting different biochemical pathways involved in AD.

Delivery of Proapoptotic Agents in Glioma Cell Lines by TSPO Ligand-Dextran Nanogels

Translocator protein 18-kDa (TSPO) is a versatile mitochondrial target for molecular imaging and therapy. Moreover, selective TSPO ligands have been widely investigated for diagnostic purposes and explored to target drug delivery systems directed to cancer cells overexpressing TSPO. Indeed, poly(d,l-lactic-co-glycolic acid (PLGA) polymers and nanocarriers decorated with TSPO ligands are capable of transporting TSPO ligands inside cancer cells, inducing survival inhibition in cancer cells and producing mitochondrial morphology modification. The aim of this work was to prepare nanogels (NGs) made with TSPO ligand dextran conjugates (TSPO-Dex) that are useful as potential delivery systems of two TSPO ligands as apoptotic agents. Synthesis and complete characterization of TSPO–dextran conjugates, an average molecular weights analysis, TSPO ligand release profiles, thermal behaviour and swelling studies were achieved. NG preparation, characterization and in vitro biological studies were also performed. The release of TSPO ligands released from dextran conjugates at 37 °C occurred in human serum at a faster rate than that detected in phosphate buffer. Cytotoxicity studies demonstrated that NGs produced from TSPO ligand–dextran conjugates induce survival inhibition in rat C6 glioma cell lines. Cellular uptake was also proven by fluorescence microscopy.

A greener and efficient access to substituted four- and six-membered sulfur-bearing heterocycles

The regioselective functionalization of four- and six-membered cyclic sulfones was investigated using a lithiation/functionalization strategy.

Synthesis of novel tetrahydrobenzazepine derivatives and their cytoprotective effect on human lymphocytes

Cytoprotective compounds such as amifostine play an important role in chemo- and radiotherapy due to their ability to reduce the side effects of these treatments. Our work was initiated with the intention to design, synthesise and test a new class of heterocyclic compounds that would have an antioxidative profile with the potential to be further developed as cytoprotective agents. The design was based on the privileged tetrahydrobenzazepine scaffold found in many natural products with a wide range of biological properties. This structure was further functionalised with moieties known to possess antioxidative features such as tertiary amine and styrene double bond. A series of eight tetrahydrobenzazepine derivatives of isoquinoline, 3,4-dihydro-β-carboline and pyridine were synthesised employing the Heck reaction as a key transformation. Some of the prepared compounds were tested for their in vitro effects on chromosome aberrations in peripheral human lymphocytes using the cytochalasin-B blocked micronucleus (MN) assay. Three tetrahydrobenzoazepine derivatives showed significant cytoprotective properties, comparable or even better to those of the radioprotective agent amifostine.

The novel tetramethylpyrazine bis-nitrone (TN-2) protects against MPTP/MPP+-induced neurotoxicity via inhibition of mitochondrial-dependent apoptosis

Mitochondrial-dependent apoptosis plays an important role in the degeneration of dopaminergic neurons in Parkinson's disease (PD). Methyl-4-phenyl-1,2,3,6-tetra- hydropyridine (MPTP), the most widely used neurotoxin to simulate PD, is converted to 1-methyl-4-phenylpyridinium (MPP(+)) in vivo. MPP(+) induces excessive intracellular reactive oxygen species (ROS), leading to mitochondrial-dependent apoptosis via sequentially opening mitochondria permeability transition pore (mPTP) to release cytochrome c from mitochondria into cytoplasm and activate pro-apoptotic caspase proteins. We have previously synthesized 2,5-[[(1,1-dimethylethyl)oxidoimino]methyl]-3,6-trimethylpyrazine (TN-2), a novel derivative of the Chinese herb medicine tetramethylpyrazine (TMP). TN-2 is armed with two powerful free radical-scavenging nitrone moieties. TN-2 significantly reversed the loss of dopaminergic neurons in the substantia nigra and the decrease in dopamine level in the striatum induced by MPTP in mice. TN-2 ameliorated the MPTP-induced decrease of brain superoxide dismutase activity and glutathione concentration and increase of brain malondialdehyde. In addition, TN-2 inhibited MPP(+)-induced neuronal damage/apoptosis in primary cerebellum granular neurons (CGNs) and SH-SY5Y cells. TN-2 decreased excessive intracellular ROS, prevented the loss of mitochondrial membrane potential, blocked the release of mitochondrial cytochrome c and inhibited the activation of caspase-3 and caspase-9. Moreover, TN-2 treatment increased the mRNA expression of mitochondrial biogenesis factors peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1 (PGC- 1α and β) and mitochondrial transcription factor A (Tfam) in SH-SY5Y cells and CGNs. These results suggest that TN-2 protects dopaminergic neurons against MPTP/MPP(+)-induced neurotoxicity via the inhibition of mitochondrial-dependent apoptosis and possibly via the activation of mitochondrial biogenesis, indicating that TN-2 is a potential new treatment for PD.