Synthesis and biological evaluation of novel technetium-99m labeled phenylbenzoxazole derivatives as potential imaging probes for β-amyloid plaques in brain

Two uncharged (99m)Tc-labeled phenylbenzoxazole derivatives were biologically evaluated as potential imaging probes for β-amyloid plaques. The (99m)Tc and corresponding rhenium complexes were synthesized by coupling monoamine-monoamide dithiol (MAMA) and bis(aminoethanethiol) (BAT) chelating ligand via a pentyloxy spacer to phenylbenzoxazole. The fluorescent rhenium complexes 6 and 9 selectively stainined the β-amyloid plaques on the sections of transgenic mouse, and showed high affinity for Aβ((1-42)) aggregates (K(i)=11.1 nM and 14.3 nM, respectively). Autoradiography in vitro indicated that [(99m)Tc]6 clearly labeled β-amyloid plaques on the sections of transgenic mouse. Biodistribution experiments in normal mice revealed that [(99m)Tc]6 displayed moderate initial brain uptake (0.81% ID/g at 2 min), and quickly washed out from the brain (0.25% ID/g at 60 min). The preliminary results indicate that the properties of [(99m)Tc]6 are promising, although additional refinements are needed to improve the ability to cross the blood-brain barrier.     

Synthesis and biological evaluation of 18F-labled 2-phenylindole derivatives as PET imaging probes for β-amyloid plaques

A novel series of fluorinated 2-phenylindole derivatives were synthesized and evaluated as β-amyloid imaging probes for PET. The in vitro inhibition assay demonstrated that their binding affinities for Aβ_1–42 aggregates ranged from 28.4 to 1097.8 nM. One ligand was labeled with ¹⁸F ([¹⁸F]1a) for its high affinity (K_i = 28.4 nM), which was also confirmed by in vitro autoradiography experiments on brain sections of transgenic mouse (C57BL6, APPswe/PSEN1, 11 months old, male). In vivo biodistribution experiments in normal mice showed that this radiotracer displayed high initial uptake (5.82 ± 0.51% ID/g at 2 min) into and moderate washout (2.77 ± 0.31% ID/g at 60 min) from the brain. [¹⁸F]1a could be developed as a promising new PET imaging probe for Aβ plaques although necessary modifications are still needed.     

Synthesis and biological evaluation of novel styryl benzimidazole derivatives as probes for imaging of neurofibrillary tangles in Alzheimer’s disease

This paper describes the synthesis and biological evaluation of styrylbenzimidazole (SBIM) derivatives as agents for imaging neurofibrillary tangles (NFT) in patients with Alzheimer’s disease (AD). SBIM derivatives were prepared with 4-iodobenzene-1,2-diamine and substituted cinnamaldehydes. In binding experiments using recombinant tau and Aβ_1–42 aggregates, SBIM-3 showed higher affinity for the tau aggregates than Aβ_1–42 aggregates (ratio of K_d values was 2.73). In in vitro autoradiography and fluorescent staining, [¹²⁵I]SBIM-3 (or SBIM-3) bound NFT in sections of AD brain tissue. In biodistribution experiments using normal mice, all [¹²⁵I]SBIM derivatives showed high initial uptake into (3.20–4.11%ID/g at 2 min after the injection) and rapid clearance from (0.12–0.33%ID/g at 60 min after the injection) the brain. In conclusion, appropriate structural modifications of SBIM derivatives could lead to more useful agents for the in vivo imaging of NFT in AD brains.     

Synthesis and characterization of magnetic β-cyclodextrin-chitosan nanoparticles as nano-adsorbents for removal of methyl blue

A novel nano-adsorbent, β-cyclodextrin-chitosan (CDC) modified Fe(3)O(4) nanoparticles (CDCM) is fabricated for removal of methyl blue (MB) from aqueous solution by grafting CDC onto the magnetite surface. The characteristics results of FTIR, SEM and XRD show that CDC is grafted onto Fe(3)O(4) nanoparticles. The grafted CDC on the Fe(3)O(4) nanoparticles contributes to an enhancement of the adsorption capacity because of the strong abilities of CDCM, which includes the multiple hydroxyl, carboxyl groups, amino groups and the formation of an inclusion complex due to the β-CD molecules through host-guest interactions, to adsorb MB. The adsorption of MB onto CDCM is found to be dependent on pH and temperature. Adsorption equilibrium is achieved in 50 min and the adsorption kinetics of MB is found to follow a pseudo-second-order kinetic model. Equilibrium data for MB adsorption are fitted well by Langmuir isotherm model. The maximum adsorption capacity for MB is estimated to be 2.78 g/g at 30°C. The CDCM was stable and easily recovered. Moreover the adsorption capacity was about 90% of the initial saturation adsorption capacity after being used four times.     

Diphenylpropynone derivatives as probes for imaging β-amyloid plaques in Alzheimer's brains

A new series of diphenylpropynone (DPP) derivatives for use in vivo to image β-amyloid (Aβ) plaques in the brain of patients with Alzheimer’s disease (AD) were synthesized and characterized. Binding experiments in vitro revealed high affinity for Aβ (1-42) aggregates at a K_i value ranging from 6 to 326 nM. Furthermore, specific labeling of plaques was observed in sections of brain tissue from Tg2576 transgenic mice stained using one of the compounds, 1. In biodistribution experiments with normal mice, [¹²⁵I]1 displayed moderate uptake (1.55% ID/g at 2 min) and clearance from the brain with time (0.76 ID/g at 60 min). Taken together, DPP can serve as a new molecular scaffold for developing novel Aβ imaging agents by introducing appropriate substituted groups.     

Synthesis and biological evaluation of indole-chalcone derivatives as β-amyloid imaging probe

A series of chaclone derivatives containing an indole moiety were evaluated in competitive binding assays with Aβ_1-42 aggregates versus [¹²⁵I]IMPY. The affinity of these compounds ranged from 4.46 to >1008 nM, depending on the substitution on the phenyl ring. Fluorescent staining in vitro showed that one compound with a N,N-dimethylamino group intensely stained Aβ plaques within brain sections of AD transgenic mice. The radioiodinated probe [¹²⁵I]-(E)-3-(1H-indol-5-yl)-1-(4-iodophenyl)prop-2-en-1-one, [¹²⁵I]4, was prepared and autoradiography in sections of brain tissue from an animal model of AD showed that it labeled Aβ plaques specifically. However, experiments with normal mice indicated that [¹²⁵I]4 exhibited a low uptake into the brain in vivo (0.41% ID/g at 2 min). Additional chemical modifications of this indole-chalcone structure may lead to more useful imaging agents for detecting β-amyloid plaques in the brains of AD patients.     

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.     

Synthesis and characterization of 2′-azidoaminopterin as a potential photoaffinity label for folate-utilizing enzymes

A photoreactive analog of aminopterin, 2′-azidoaminopterin (VI), was synthesized and evaluated as a potential inhibitor and photoaffinity label of folate-utilizing enzymes. The compound was tightly bound to dihydrofolate reductase (DHFR) from escherichia coli (MB 1428) with K₁ equal to 3 × 10^?11M and to the enzyme from mouse (S-180) cells with K₁ approximately equal to 2 × 10^?10M. Dissociation constants measured by equilibrium dialysis using radioactive 2′-azidoaminopterin gave a value of K_D = 3.2 × 10^?9M for the bacterial enzyme. The presence of NADPH enhanced the affinity by more than an order of magnitude. Azidoaminopterin is also an inhibitor of thymidylate synthetase from Lactobacillus casei, competitive with methylene-tetrahydrofolate (K_i 7 × 10^?7M). Photolysis of the radioactive inhibitor in complex with DHFR from E. coli led to approximately 3% covalent incorporation of label into protein. The greater part of this attachment was nonspecific as shown by the lack of protection in the presence of methotrexate. Thymidylate synthetase from L. casei was not significantly inactivated upon photolysis in the presence of the inhibitor and deoxyuridylate. Model studies showed that photoreaction of the inhibitor led to covalent linkages with thiol, lysyl amino groups, and the hydroxyl groups of alcohols. Azidoaminopterin may be useful in labeling other enzymes of folate metabolism, although a minor photoproduct reacts nonspecifically with many proteins. The antifolate can be photoconjugated to polylysine as well as to proteins. The polylysine conjugates inhibit DHFR. Difference spectrum analysis of the photoproducts from the irradiation of the DHFR I complex indicates that water reacts efficiently with the enzyme-bound nitrene and must therefore have access to at least part of the bound p-aminobenzoyl group. This analysis suggests that azide analogs of protein ligands may be useful as reporter groups in probing the hydrophobicity of binding sites.     

99mTc- and Re-labeled 6-dialkylamino-2-naphthylethylidene derivatives as imaging probes for β-amyloid plaques

Based on the conjugate strategy, two neutral ^99mTc labeled 2-(1-(6-(dialkylamino)naphthalen-2-yl)ethylidene)malononitrile (DDNP) and 1-(6-(dialkylamino)naphthalen-2-yl)ethanone (ENE) derivatives, and their corresponding rhenium complexes were synthesized. In vitro fluorescent staining indicated that the corresponding rhenium derivatives selectively stained the β-amyloid (Aβ) plaques in the brain sections of AD model mice with low background. Compared with FDDNP and FENE, the affinities of the corresponding rhenium derivatives to Aβ aggregates decreased about 10-14-fold. In vivo biodistribution experiments in normal mice showed that ^99mTc-MAMA-ENE displayed medium initial brain uptake (0.65 %ID/g at 2 min) with a reasonable washout from the brain (0.19 %ID/g at 2 h) while ^99mTc-MAMA-DDNP showed a low brain uptake (0.28 %ID/g at 2 min). Further optimize these ^99mTc-labeled tracers in order to improve their binding affinities to Aβ plaques and diffusion through the blood brain barrier may generate useful imaging agents for SPECT.     

Novel anilinophthalimide derivatives as potential probes for β-amyloid plaque in the brain

A group of novel 4,5-dianilinophthalimide derivatives has been synthesized in this study for potential use as β-amyloid (Aβ) plaque probes. Staining of hippocampus tissue sections from Alzheimer’s disease (AD) brain with the representative compound 9 indicated selective labeling of it to Aβ plaques. The binding affinity of radioiodinated [¹²⁵I]9 for AD brain homogenates was 0.21 nM (K_d), and of other derivatives ranged from 0.9 to 19.7 nM, except for N-methyl-4,5-dianilinophthalimide (K_i > 1000 nM). [¹²⁵I]9 possessed the optimal lipophilicity with Log P value of 2.16, and its in vivo biodistribution in normal mice exhibited excellent initial brain uptake (5.16% ID/g at 2 min after injection) and a fast washout rate (0.56% ID/g at 60 min). The encouraging results suggest that this novel derivative of [¹²³I]9 may have potential as an in vivo SPECT probe for detecting amyloid plaques in the brain.     

Synthesis and evaluation of 18F-labeled mitiglinide derivatives as positron emission tomography tracers for β-cell imaging

Measuring changes in β-cell mass in vivo during progression of diabetes mellitus is important for understanding the pathogenesis, facilitating early diagnosis, and developing novel therapeutics for this disease. However, a non-invasive method has not been developed. A novel series of mitiglinide derivatives (o-FMIT, m-FMIT and p-FMIT; FMITs) were synthesized and their binding affinity for the sulfonylurea receptor 1 (SUR1) of pancreatic islets were evaluated by inhibition studies. (+)-(S)-o-FMIT had the highest affinity of our synthesized FMITs (IC₅₀ = 1.8 μM). (+)-(S)-o-[¹⁸F]FMIT was obtained with radiochemical yield of 18% by radiofluorination of racemic precursor 7, hydrolysis, and optical resolution with chiral HPLC; its radiochemical purity was >99%. In biodistribution experiments using normal mice, (+)-(S)-o-[¹⁸F]FMIT showed 1.94 ± 0.42% ID/g of pancreatic uptake at 5 min p.i., and decreases in radioactivity in the liver (located close to the pancreas) was relatively rapid. Ex vivo autoradiography experiments using pancreatic sections confirmed accumulation of (+)-(S)-o-[¹⁸F]FMIT in pancreatic β-cells. These results suggest that (+)-(S)-o-[¹⁸F]FMIT meets the basic requirements for an radiotracer, and could be a candidate positron emission tomography tracer for in vivo imaging of pancreatic β-cells.     

Synthesis and molecular modeling of 1H-pyrrolopyrimidine-2,4-dione derivatives as ligands for the α1-adrenoceptors

Three different series of 1H-pyrrolopyrimidine-2,4-dione derivatives were designed and synthesized as ligands for the α(1)-adrenergic receptors (α(1)-ARs). A microwave-assisted protocol was developed in order to improve purity and yields of some final products. The majority of the synthesized compounds, tested in binding assays, displayed α(1)-AR affinities in the nanomolar range. Highest affinity values were found in derivatives 10b and 10c (K(i)=1.4 nM for both) whereas compound 10e was endowed with the best profile in term of α(1)-AR affinity (K(i)=2.71 nM) coupled with high selectivity towards 5-HT(1A) receptors (K(i) >10,000). Molecular docking studies were performed on human α(1)-ARs and human 5-HT(1A) receptors in order to rationalize the observed experimental affinity and selectivity; these computational studies helped to clarify molecular requirements for the design of high-selective α(1)-adrenergic ligands.     

Synthesis and evaluation of pyridylbenzofuran, pyridylbenzothiazole and pyridylbenzoxazole derivatives as ¹⁸F-PET imaging agents for β-amyloid plaques

The synthesis and SAR of new β-amyloid binding agents are reported. Evaluation of important properties for achieving good signal-to-background ratio is described. Compounds 27, 33, and 36 displayed desirable lipophilic and pharmacokinetic properties. Compound 27 was further evaluated with autoradiographic studies in vitro on human brain tissue and in vivo in Tg2576 mice. Compound 27 showed an increased signal-to-background ratio compared to flutemetamol 4, indicating its suitability as PET ligand for β-amyloid deposits in AD patients. The preparation of the corresponding (18)F-labeled PET radioligand of compound 27 is presented.     

Synthesis and structure–activity relationships evaluation of benzothiazinone derivatives as potential anti-tubercular agents

N-Alkyl and heterocycle substituted 1,3-benzothiazin-4-one (BTZ) derivatives were synthesized. The anti-mycobacterial activities of these compounds were evaluated by determination of minimal inhibitory concentration (MIC) for Mycobacterium tuberculosis H37Ra and M. tuberculosis H37Rv. It was found that an extended or branched alkyl chain analog could enhance the potency, and activities of N-alkyl substituted BTZs were not affected by either nitro or trifluoromethyl at 6-position. Trifluoromethyl plays an important role in maintaining anti-tubercular activity in the piperazine or piperidine analogs. Compound 8o, which contains an azaspirodithiolane group, showed a MIC of 0.0001 μM against M. tuberculosis H37Rv, 20-fold more potent than BTZ043 racemate. These results suggested that the volume and lipophilicity of the substituents were important in maintaining activity. In addition, compound 8o was nontoxic to Vero cells and orally bioavailable in a preliminary pharmacokinetics study.     

Synthesis,biological evaluation and molecular dynamic simulations of novel Benzofuran-tetrazole derivatives as potential agents against Alzheimer’s disease

A series of novel Benzofuran-tetrazole derivatives were successfully synthesised by integrating multicomponent Ugi-azide reaction with the molecular hybridization approach. Interestingly, a number of synthesized derivatives (5c, 5d, 5i, 5l, 5q and 5s) exhibited significant reduction of aggregation of “human” amyloid beta peptide, expressing on transgenic Caenorhabditis elegans (C. elegans) strain CL4176. Further, in silico docking results have evidenced the exquisite interaction of active compounds with the help of TcAChE–E2020 complex. These findings underscore the potential of these hybrids as lead molecules against Alzheimers’s disease.     

Synthesis and evaluation of ethyleneoxylated and allyloxylated chalcone derivatives for imaging of amyloid β plaques by SPECT

We report radioiodinated chalcone derivatives as new SPECT imaging probes for amyloid β (Aβ) plaques. The monoethyleneoxy derivative 2 and allyloxy derivative 8 showed a high affinity for Aβ(1–42) aggregates with K_i values of 24 and 4.5 nM, respectively. Fluorescent imaging demonstrated that 2 and 8 clearly stained thioflavin-S positive Aβ plaques in the brain sections of Tg2576 transgenic mice. In vitro autoradiography revealed that [¹²⁵I]2 displayed no clear accumulation toward Aβ plaques in the brain sections of Tg2576 mice, whereas the accumulation pattern of [¹²⁵I]8 matched with the presence of Aβ plaques both in the brain sections of Tg2576 mice and an AD patient. In biodistribution studies using normal mice, [¹²⁵I]2 showed preferable in vivo pharmacokinetics (4.82%ID/g at 2 min and 0.45%ID/g at 60 min), while [¹²⁵I]8 showed only a modest brain uptake (1.62%ID/g at 2 min) with slow clearance (0.56%ID/g at 60 min). [¹²⁵I]8 showed prospective binding properties for Aβ plaques, although further structural modifications are needed to improve the blood brain barrier permeability and washout from brain.     

Synthesis of oxadiazole-coupled-thiadiazole derivatives as a potent β-glucuronidase inhibitors and their molecular docking study

A new series of oxadiazole with thiadiazole moiety (6–27) were synthesized, characterized by different spectroscopic techniques and evaluated for β-glucuronidase inhibitory potential. Sixteen analogs such as 6, 7, 8, 9, 10, 12, 13, 14, 17, 18, 20, 23, 24, 25, 26 and 27 showed IC₅₀ values in the range of 0.96 ± 0.01 to 46.46 ± 1.10 μM, and hence were found to have excellent inhibitory potential in comparison to standard d-saccharic acid 1,4-lactone (IC₅₀ = 48.4 ± 1.25 μM). Two analogs such as 16 and 19 showed moderate inhibitory potential while analogs 11, 15, 21 and 22 were found inactive. Our study identifies new series of potent β-glucuronidase inhibitors for further investigation. Structure activity relationships were established for all compounds which showed that the activity is varied due to different substituents on benzene ring. The interaction of the compounds with enzyme active site were confirmed with the help of docking studies, which reveals that the electron withdrawing group and hydroxy group make the molecules more favorable for enzyme inhibition.     

Synthesis of N₄'-[¹⁸F]fluoroalkylated ciprofloxacin as a potential bacterial infection imaging agent for PET study

Syntheses and evaluation of fluoroalkylated ciprofloxacin analogues are described. Among these analogues, N?'-3-fluoropropylciprofloxacin (16) showed the most efficient antibacterial activity against E. coli strains (DH5α and TOP10) and a high binding affinity for DNA gyrase of bacteria. To develop bacteria-specific infection imaging agents for positron emission tomography (PET), no-carrier-added N?-3-[1?F]fluoropropylciprofloxacin ([1?F]16) was prepared in two steps from N?-3-methanesufonyloxypropylciprofloxacin, resulting in a 40% radiochemical yield (decay corrected for 100 min) via the tert-alcohol media radiofluorination protocol with high radiochemical purity (> 99%) as well as high specific activity (149 ± 75 GBq/μmol). The agent was stable (> 90%), as shown by an in vitro human serum stability assay. A bacterial uptake and blocking study of [1?F]16 using authentic compound 16 in TOP10 cells demonstrated its high specific bacterial uptake. The results suggest that this radiotracer holds promise as a useful bacterial infection radiopharmaceutical for PET imaging.     

Synthesis of fluorescent nucleoside analogs as probes for 2′-deoxyribonucleoside kinases

We are reporting on the synthesis of fluorescent nucleoside analogs with modified sugar moieties (e.g., sugars other than ribose and 2′-deoxyribose). Four novel derivatives of the fluorescent thymidine analog 6-methyl-3-(β-D-2′-deoxyribofuranosyl) furano-[2,3-d]pyrimidin-2-one were synthesized via Sonogashira reaction and subsequent copper-catalyzed cycloaddition. These compounds represent promising tools for studying nucleoside metabolism inside living cells, as well as for screening directed evolution libraries of 2′-deoxyribonucleoside kinases with new and improved activity for the corresponding nucleoside analogs.