Methylene blue-based 7-nitro-1,2,3-benzoxadiazole NIR fluorescent probe triggered by H2S

A new Methylene blue–based 7-nitro-1,2,3-benzoxadiazole NIR fluorescent probe 3, 7-bis-dimethylamino-10-(7-nitrobenzo[c][1,2,5]oxadiazol-4-yl)-10H-phenothiazine (leuco-MB-NBD) was designed and synthesized. Leuco-MB-NBD showed high sensitivity and selectivity for H₂S as a fluorescent probe in C₂H₅OH-PBS (9:1, v/v, pH = 7.4) solution, this fluorescent assay showed a linear range of 0–50.0 μM and a LOD (limit of detection) of 0.43 μM. Moreover, the probe leuco-MB-NBD has lower toxicity at low concentrations to HCT-116 cells and can be used for cell imaging. Additionally, Leuco-MB-NBD is triggered by hydrogen sulfide to generate methylene blue, methylene blue which has potential rescuing effects on the mitochondrial activity can act as an antidote against sulfide intoxication.     

A selective and sensitive turn-on chemosensor for detection of Fe3+ in aqueous solution and its cell imaging in dorsal root ganglia neurons and MKN-45 cells

A new turn-on fluorescent chemosensor (RBTM) for Fe³⁺ was designed based on Rhodamine B and a thiocarbonylimidazole moiety. The spectroscopic probe used for characterization of the synthesized system showed 300-fold fluorescence enhancement for the detection of Fe³⁺ with a 1:1 stoichiometry in EtOH/H₂O solution (2:1, v/v, HEPES buffer, 1 mM, pH 7.30). Upon addition of Fe³⁺ in aqueous ethanol, the probe displayed a significant fluorescence enhancement and a distinct color change (colorless to pink) that can be detected by the naked eye. The binding constant between the probe and Fe³⁺ was determined to be 1.16 × 10⁴ M⁻¹ and the corresponding detection limit was calculated to be 0.256 µM. In addition, the energy gaps between the HOMO and LUMO in RBTM and RBTM-Fe³⁺ were calculated using DFT calculations to be 92.93 kcal/mol and 37.49 kcal/mol, respectively. The results indicate that binding of Fe³⁺ to RBTM lowered the HOMO–LUMO energy gap of the complex and stabilized the system. Fluorescence imaging experiments demonstrated that RBTM can be used as a fluorescent probe to detect Fe³⁺ in MKN-45 cells and dorsal root ganglia, thus revealing that RBTM could be used for biological applications.     

A new Rhodamine B-based ‘on–off’ chemical sensor with high selectivity and sensitivity toward Fe3+ and its imaging in living cells

A new fluorescent chemosensor based on a Rhodamine B and pyrrole conjugate (RBPY) has been designed and synthesized. UV–vis absorption and fluorescence spectroscopic studies show that RBPY exhibits a high selectivity and sensitivity toward Fe³⁺ among many other metal cations in a MeOH/H₂O solution (3:2, v/v, pH 7.10, HEPES buffer, 0.1 mM) by forming a 1:1 complex with Fe³⁺. Furthermore, results reveal that the formation of the RBPY–Fe³⁺ complex is fully reversible in the presence of sulfide anions and could also be used as an efficient sensor for S²⁻. Importantly, fluorescence microscopy experiments further demonstrated that RBPY can be utilized as a fluorescent probe for the detection of Fe³⁺ in human liver (L-02) cells.     

Synthesis and evaluation of Al18F-NODA complex conjugated 2-(4-aminophenyl)benzothiazole as a potential tumor imaging agent

The objective of the study was to prepare and evaluate a ¹⁸F-radiolabled tracer (Al¹⁸F-5), derivated from the antitumor agent 2-(4-aminophenyl)benzothiazole, as a PET probe for tumor imaging. Al¹⁸F-5 was successfully prepared with approx. 40% radiochemical yield in aqueous phase. In in vitro cell uptake experiments and competition assay, Al¹⁸F-5 displayed good tumor-binding ability and specificity in HeLa cells (24.7 ± 0.9% ID/10⁶ cells, IC₅₀ = 63.8 ± 13.6 nM) and MCF-7 cells (6.8 ± 0.3% ID/10⁶ cells, IC₅₀ = 331.1 ± 33.7 nM). The nonradioactive compound, Al¹⁹F-5, visibly marked HeLa cells and MCF-7 cells but did not stain HEB cells in florescent staining, which further indicated the tumor-binding ability of Al¹⁸F-5. In in vivo PET imaging, HeLa and MCF-7 tumors were clearly delineated by specific accumulation of Al¹⁸F-5 in model mice. In biodistribution study, Al¹⁸F-5 exhibited good tumor uptake (4.66 ± 0.13% ID/g and 3.69 ± 0.56% ID/g, respectively), moderate tumor-to-muscle ratio (3.38 and 2.48, respectively) at 1 h post injection, which were in a good consistency with the results of PET imaging. In conclusion, Al¹⁸F-5 might be developed as a candidate PET probe for tumor imaging, though additional optimizations are still needed to improve pharmacokinetics in vivo.     

Chemical modifications by ionic liquid-inspired cations improve the activity and the stability of formate dehydrogenase in [MMIm][Me2PO4]

The formate dehydrogenase (FDH, EC: 1.2. 1.2) from Candida boidinii was found to be inactivated and unstable in the presence of high concentration (>50%) of the water soluble dimethylimidazolium dimethyl phosphate ([MMIm][Me₂PO₄]) ionic liquid. In order to circumvent this problem, the enzyme was chemically modified by cations usually present in ionic liquids: cholinium (1), hydroxyethyl-methylimidazolium (2) and hydroxypropyl-methylimidazolium (3) cations were activated with carbonyldiimidazole before being reacted with the FDH leading to a heterogeneous population of 6–7 biocatalysts. FDH modified by (1) or (3) led to 3–9 modifications while FDH modified by (2) led to 6 proteins presenting 7–12 grafted cations. Specific activity of the modified enzymes was decreased by a 2.5–3-fold factor (0.10–0.15 μmol min⁻¹ mg⁻¹) compared to the non-modified FDH (0.33 μmol min⁻¹ mg⁻¹) when assayed in carbonate buffer (pH 9.7, 25 mM). After modification, the FDH still present 0.06 μmol min⁻¹ mg⁻¹ in 70% [MMIm][Me₂PO₄] (v:v) (30–45% of their activity in aqueous buffer) while the native enzyme is inactive at this ionic liquid concentration, proving the efficiency of this strategy. The half-life of the modified enzyme is also increased by a 5-fold factor after modification by (1) (t_1/2 of 9 days) and by a 3-fold factor after modification by (2) or (3) (t_1/2 of 6 and 5 days respectively) in aqueous solution. When stored in 37.5% [MMIm][Me₂PO₄] (v:v), both modified and unmodified FDH have an increased half-life (t_1/2 of 6–9 days). This grafting strategy is found to be good methods to mimic and study the stabilizing effect of ionic liquids on enzymes.     

Substituted sulfonamide bioisosteres of 8-hydroxyquinoline as zinc-dependent antibacterial compounds

A series of substituted sulfonamide bioisosteres of 8-hydroxyquinoline were evaluated for their antibacterial activity against the common mastitis causative pathogens Streptococcus uberis, Staphylococcus aureus and Escherichia coli, both in the presence and absence of supplementary zinc. Compounds 9a-e, 10a-c, 11a-e, 12 and 13 were demonstrated to have MICs of 0.0625 µg/mL against S. uberis in the presence of 50 µM ZnSO₄. Against S. aureus compounds 9g (MIC 4 µg/mL) and 11d (MIC 8 µg/mL) showed the greatest activity, whereas all compounds were found to be inactive against E. coli (MIC > 256 µg/mL); again in the presence of 50 µM ZnSO₄. All compounds were demonstrated to be significantly less active in the absence of supplementary zinc. Compound 9g was subsequently confirmed to be bactericidal, with an MBC (≥3log₁₀ cfu/mL reduction) of 0.125 µg/mL against S. uberis in the presence of 50 µM ZnSO₄. To validate the sanitising activity of compound 9g in the presence of supplementary zinc, a quantitative suspension disinfection (sanitizer) test was performed. In this preliminary test, sanitizing activity (>5log₁₀ reduction of CFU/mL in 5 min) was observed against S. uberis for compound 9g at concentrations as low as 1 mg/mL, validating the potential of this compound to function as a topical sanitizer against the major environmental mastitis-causing microorganism S. uberis.     

Synthesis of novel chromeno-annulated cis-fused pyrano[3,4-c]benzopyran and naphtho pyran derivatives via domino aldol-type/hetero Diels–Alder reaction and their cytotoxicity evaluation

New chromeno-annulated cis-fused pyrano[3,4-c]benzopyran and naphtho pyran derivatives have been synthesized by domino aldol-type reaction/hetero Diels–Alder reaction generated from o-quinone methide in situ from 7-O-prenyl derivatives of 8-formyl-2,3-disubstituted chromenones with resorcinols/naphthols in the presence of 20 mol % ethylenediamine diacetate (EDDA), triethylamine (2 mL) as co-catalyst in CH₃CN under reflux conditions in good yields. The structures were established based on spectroscopic data, and further confirmed by X-ray diffraction analysis. The results showed that compounds 4h and 4j exhibited very potent cytotoxicity against human cervical cancer cell line (HeLa). Compound 4h displayed good inhibitory activity against both breast cancer cell lines, MDA-MB-231 and MCF-7. Further, the compound 4i exhibited good cytotoxicity against only MDA-MB-231, and compound 4j showed promising activity against human lung cancer cell line, A549 with IC₅₀ value of 2.53 ± 0.07 μM, which was comparable to the standard doxorubicin (IC₅₀ = 1.21 ± 0.1 μM).     

Three new 2-(2-phenylethyl)chromones from ‘Chong-lou’ agarwood of Aquilaria sinensis

Three new 2-(2-phenylethyl)chromones (1, 2 and 3), together with four known analogues 4~7 were isolated from ‘Chong-lou’ agarwood originating from Aquilaria sinensis for the first time. Their new structures were elucidated on the basis of spectroscopic techniques (UV, IR, MS, 1D and 2D NMR), as well as by comparison with the literature data. Compounds 6 and 7 exhibited significant cytotoxicity against human cancer cell line K562 with IC₅₀ values of 19.79 ± 0.03 and 21.39 ± 0.05 μM, respectively.     

Pt(II) complexes with (N,N′) or (C,N,E)− (E = N,S) ligands: Cytotoxic studies,effect on DNA tertiary structure and structure–activity relationships

The cytotoxic activity of two series of platinum(II) complexes containing the polyfunctional imines R¹–CHN–R² [R¹ = phenyl or ferrocenyl unit and R² = (CH₂)_n–CH₂–NMe₂ where n = 1 or 2) (1 and 2) or C₆H₄-2-SMe (3)] acting as a bidentate (N,N′) (4–7) or terdentate [C(phenyl or ferrocenyl),N,N′]^? (8–10) or [C(ferrocenyl),N,S]^? ligand (11) in front of A549 lung, MDA-MB231 breast and HCT116 colon human adenocarcinoma cell lines is reported. The results reveal that most of the platinum(II) complexes are active against the three assayed lines and compounds 6, 7 and the platinacycles 10 and 11 exhibit a remarkable antiproliferative activity, even greater than cisplatin itself, in the cisplatin resistant HCT116 human cancer cell line. Electrophoretic DNA migration studies showed that most of them modify the DNA tertiary structure in a similar way as the reference cisplatin. Solution studies of a selection of the most relevant complexes have also been performed in order to test: (a) their stability in the aqueous biological medium and/or the formation of biologically active species and (b) their proclivity to react with 9-methylguanine (9-MeG), as a model nucleobase. Computational studies at DFT level have also been performed in order to explain the different solution behaviour of the complexes and their proclivity to react with the nucleobase.     

Synthesis,molecular modeling studies and anticonvulsant activity of certain (1-(benzyl (aryl) amino) cyclohexyl) methyl esters

A series of (1-(benzyl (aryl) amino) cyclohexyl) methyl esters 7a-n were prepared and screened for their anticonvulsant profile. Screening of these esters 7a-n and their starting alcohols 6a and 6b revealed that compound 7k was the most potent one in the scPTZ screening test with an ED₅₀ value of 0.0056 mmol/kg being about 10- and 164-fold more potent than phenobarbital (ED₅₀ = 0.056 mmol/kg) and ethosuximide (ED₅₀ = 0.92 mmol/kg) as reference drugs, respectively. Meanwhile, in the MES test, compounds 7b and 7k at doses 0.0821 mmol/kg and 0.0334 mmol/kg, exerted 66% and 50% protection of the tested mice, respectively, compared with diphenylhydantoin, which exerted 100% protection at dose 0.16 mmol/kg. In the neurotoxicity screen test, almost all esters 7a-n did not show any minimal motor impairment at the maximum administrated dose. The anticonvulsant effectiveness of esters 7a-n was higher than their corresponding alcohols 6a and 6b. Compounds 7b and 7k exhibited pronounced anticonvulsant activity devoid of neurotoxicity in minimal motor impairment test and hepatotoxicity in the serum enzyme activity assay. 3D pharmacophore model using Discovery Studio 2.5 programs showed high fit value. The obtained experimental results of sc-PTZ activity of compounds 7a-n was consistent with the molecular modeling study.     

Synthesis and evaluation of a novel ‘off-on’ chemical sensor based on rhodamine B and the 2,5-pyrrolidinedione moiety for selective discrimination of glutathione and its bioimaging in living cells

A new “turn-on” fluorescent probe, RDMBM, based on the rhodamine B dye and the 2,5-pyrrolidinedione moiety was synthesized and characterized. Its sensing behavior toward various amino acids was evaluated via UV–vis and fluorescence spectroscopic techniques. The observed spectral changes showed that RDMBM displays high selectivity and sensitivity toward GSH in MeOH/H₂O (1:2, v/v, pH 7.40, Tris-HCl buffer, 1?mM) solution and that it undergoes 1:1 covalent binding with GSH. More importantly, the hydrogenation and ring-opening of the nitrogen atom in the spirane structure of rhodamine B derivatives were tightly bound to the induction effects of different groups. Furthermore, fluorescence imaging applications demonstrated that RDMBM can be successfully used for the detection of GSH in human breast cancer cells MCF-7.     

New coumestan and coumaronochromone derivatives from Dalbergia boehmii Taub. (Fabaceae)

Chemical investigation of leaves and heartwood of Dalbergia boehmii resulted in the isolation of two new phenolic compounds, designated dalbergestan (1) and dalbergichromone (2), along with eleven known compounds, carpachromene (3), proanthocyanidin A-2 (4); piceatannol (5); biochanin A (6); macckiain (7); homopterocarpin (8); angolensin (9); medicarpin (10); 2′,7-dihydroxy-4′,5′-dimethoxyisoflavone (11); 2′-methoxyformononetin (12); and genistein (13). The structures of the new compounds were elucidated on the basis of extensive spectroscopic analyses including, IR, UV, 1D and 2D – NMR as well as HRMS data. Some of the isolated compounds were evaluated for their in vitro insulin secretion activity on isolated mice islets, leishmanicidal activity against L. major (DESTO) promastigotes and in vitro cytotoxicity on MCF-7 cell lines. All tested compounds were inactive on glucose-stimulated insulin secretion at stimulatory glucose (20.0 mM) from MIN6 cells. Compounds 3 (IC₅₀, 70.0 μg/ml), 6 (IC₅₀, 60.3 μg/ml), 7 (IC₅₀, 86.5 μg/ml) and 13 (IC₅₀, 62.6 μg/ml) exhibited low leishmanicidal activity while compound 12 (IC₅₀, 56.8 μg/ml) displayed a moderate activity. Compounds 3 and 5 were found to be active against MCF-7 at 50 μM with IC₅₀ value 33.2 ± 3.79 μg/ml and 42.64 ± 5.05 μg/ml respectively.     

Versatile near-infrared fluorescent probe for in vivo detection of Aβ oligomers

Amyloid-β oligomers (AβOs) enrichment in brain is highly related to Alzheimer’s pathogenesis, but tracing them in the brain by imaging technique is still a great challenge due to their heterogeneity and metastability. Herein, a new near-infrared (NIR) fluorescent probe, namely, PTO-41, was designed and synthesized to specifically target AβOs. PTO-41 possesses excellent functional properties including optimal fluorescent properties (emission maxima at 680 nm upon interacting with AβOs), high affinity (K_d = 349 nM), low cell toxicity, desirable lipophilicity (log P = 2.24), and fast wash out from the brain (brain_{2 min}/brain_{60 min} = 5.0). Furthermore, PTO-41 exhibits a high sensitivity toward AβOs in vitro phantom imaging experiments. More importantly, PTO-41 shows great capacity to differentiate between 4-month-old APP/PS1 model mice from age-matched control mice using in vivo imaging. In summary, PTO-41 almost meets all the requirements as a versatile NIR fluorescent probe for the detection of AβOs both in vitro and in vivo.     

No carrier added synthesis of O-(2'-[18F]fluoroethyl)-L-tyrosine via a novel type of chiral enantiomerically pure precursor, NiII complex of a (S)-tyrosine Schiff base

O-(2′-[¹⁸F]fluoroethyl)-l-tyrosine ([¹⁸F]FET) has gained much attention as a promising amino acid radiotracer for tumor imaging with positron emission tomography (PET) due to favorable imaging characteristics and relatively long half-life of ¹⁸F (110 min) allowing remote-site application. Here we present a novel type of chiral enantiomerically pure labeling precursor for [¹⁸F]FET, based on NiII complex of a Schiff’s base of (S)-[N-2-(N′-benzylprolyl)amino]benzophenone (BPB) with alkylated (S)-tyrosine, Ni-(S)-BPB-(S)-Tyr-OCH2CH2X (X = OTs (3a), OMs (3b) and OTf (3c)). A series of compounds 3a–c was synthesized in three steps from commercially available reagents. Non-radioactive FET as a reference was prepared from 3a in a form of (S)-isomer and (R,S) racemic mixture. Radiosynthesis comprised two steps: (1) n.c.a. nucleophilic fluorination of 3a–c (4.5–5.0 mg) in the presence of either Kryptofix 2.2.2.or tetrabutylammonium carbonate (TBAC) in MeCN at 80 °C for 5 min, followed by (2) removal of protective groups by treating with 0.5 M HCl (120 °C, 5 min). The major advantages of this procedure are retention of enantiomeric purity during the ¹⁸F-introduction step and easy simultaneous deprotection of amino and carboxy moieties in 3a–c. Radiochemically pure [¹⁸F]FET was isolated by semi-preparative HPLC (C18 μ-Bondapak, Waters) eluent aq 0.01 M CH₃COONH₄, pH 4/C₂H₅OH 90/10 (v/v). Overall synthesis time operated by Anatech RB 86 laboratory robot was 55 min. In a series of compounds 3a–c, tosyl derivative 3a provided highest radiochemical yield (40–45%, corrected for radioactive decay). Enantiomeric purity was 94–95% and 96–97%, correspondingly, for Kryptofix and TBAC assisted fluorinations. The suggested procedure involved minimal number of synthesis steps and suits perfectly for automation in the modern synthesis modules for PET radiopharmaceuticals. Preliminary biodistribution study in experimental model of turpentine-induced aseptic abscess and Glioma35 rat’s tumor (homografts) in Wistar rats has demonstrated the enhanced uptake of radiotracer in the tumor area with minimal accumulation in the inflamed tissues.     

Cytotoxic terpenoids from the stem bark of Taxus wallichiana

Chemical study of the stem bark of Taxus wallichiana Zucc. afforded the isolation of two new cyclopenta[b]naphthalene terpenoids, wallichianones A (1) and B (2) and 13 taxane diterpenoids, baccatin III (3), 10-deacetylbaccatin III (4), baccatin IV (5), 1-dehydroxybaccatin IV (6), 1-deoxybaccatin VI (7), taxol (8), 10-deacetyltaxol (9), 7-epi-10-deacetyltaxol (10), taxol-7-xyloside (11), 7-xylosyl-10-deacetyltaxol C (12), cephalomannine (13), 10-deacetylcaphalomannine (14), and 7-epi-10-deacetylcephalomannine (15). Their structures were identified by comprehensive analyses of the spectroscopic methods, including NMR and mass spectra. The absolute configurations of 1 and 2 were clarified by time-dependent density functional theory (TD-DFT) electronic circular dichroism (ECD) spectroscopic analyses. Compounds 3 and 7–15 showed cytotoxicity against all five human cancer cell lines, including lung (SK-LU-1), liver (HepG2), breast (MCF7), skin (SK-Mel-2), and prostate (LNCaP), with IC₅₀ values ranging from 1.4 ± 0.2 to 88.1 ± 5.8 μM. Compounds 9–11, 14, and 15 were additionally cytotoxic against human embryonic kidney (HEK-293A) cell line (IC₅₀ = 14.5 ± 1.0–48.4 ± 1.0 μM), however, 13 was noncytotoxic toward this cell line. The positive control, ellipticine showed cytotoxicity against all the cell lines, with IC₅₀ values in a range of 1.5 ± 0.1–2.0 ± 0.3 μM. Preliminary analysis of the structural and cytotoxicity relationship of compounds 3–15 suggested that the phenylalanine substituent at C-13 may contribute an important role for the cytotoxicity of the taxane diterpenoids.     

Synthesis and structure–activity relationships of N-aryl(indol-3-yl)glyoxamides as antitumor agents

The synthesis and study of the structure–activity relationships of cytotoxic compounds based on N-pyridinyl or N-aryl-2-(1-benzylindol-3-yl)glyoxamide skeleton, represented by the lead structures D-24241 and D-24851, are described. The presence of N-(pyridin-4-yl) moiety was crucial for activity and 2-[1-(4-chloro-3-nitrobenzyl)-1H-indol-3-yl]-2-oxo-N-(pyridin-4-yl)acetamide (55), the most potent derivative, showed IC₅₀ = 39 nM, 51 nM and 11 nM against HeLa/KB (human cervix carcinoma), L1210 (murine leukemia) and SKOV3 (human ovarian carcinoma) cell lines proliferation assay, respectively, as active as the lead compounds.     

Transformation and expression of a staphylococcal plasmid in Escherichia coli

Abstract A multiple antibiotic-resistant Staphylococcus aureus , was found to possess three plasmid bands in agarose gel electrophoresis. A plasmid of approximately 4.3 kb (pMC790/2) was found to code for ampicillin and tetracycline resistance and to have one Eco RI site when transformed into S. aureus RN 4220. pMC790/2 in unmodified form was transformed into a recA⁻ E. coli at a frequency of 1.2×10⁴ transformants/μg of plasmid DNA. Plasmid (pMC790/2) replicated, maintained itself stably and expressed far better in the E. coli host than in S. aureus .     

Towards the PET radiotracer for p75 neurotrophin receptor: [11C]LM11A-24 shows biological activity in vitro,but unfavorable ex vivo and in vivo profile

Mature neurotrophins as well as their pro forms are critically involved in the regulation of neuronal functions. They are signaling through three distinct types of receptors: tropomyosin receptor kinase family (TrkA/B/C), p75 neurotrophin receptor (p75^NTR) and sortilin. Aberrant expression of p75^NTR in the CNS is implicated in a variety of neurodegenerative diseases, including Alzheimer’s disease. The goal of this work was to evaluate one of the very few reported p75^NTR small molecule ligands as a lead compound for development of novel PET radiotracers for in vivo p75^NTR imaging. Here we report that previously described ligand LM11A-24 shows significant inhibition of carbachol-induced persistent firing (PF) of entorhinal cortex (EC) pyramidal neurons in wild-type mice via selective interaction with p75^NTR. Based on this electrophysiological assay, the compound has very high potency with an EC₅₀ <10 nM. We optimized the radiosynthesis of [¹¹C]LM11A-24 as the first attempt to develop PET radioligand for in vivo imaging of p75^NTR. Despite some weak interaction with CNS tissues, the radiolabeled compound showed unfavorable in vivo profile presumably due to high hydrophilicity.     

Synthesis and evaluation of phosphopeptides containing iminodiacetate groups as binding ligands of the Src SH2 domain

Phosphopeptide pTyr-Glu-Glu-Ile (pYEEI) has been introduced as an optimal Src SH2 domain ligand. Peptides, Ac-K(IDA)pYEEIEK(IDA) (1), Ac-KpYEEIEK (2), Ac-K(IDA)pYEEIEK (3), and Ac-KpYEEIEK(IDA) (4), containing 0–2 iminodiacetate (IDA) groups at the N- and C-terminal lysine residues were synthesized and evaluated as the Src SH2 domain binding ligands. Fluorescence polarization assays showed that peptide 1 had a higher binding affinity (K_d = 0.6 μM) to the Src SH2 domain when compared with Ac-pYEEI (K_d = 1.7 μM), an optimal Src SH2 domain ligand, and peptides 2–4 (K_d = 2.9–52.7 μM). The binding affinity of peptide 1 to the SH2 domain was reduced by more than 2-fold (K_d = 1.6 μM) upon addition of Ni²⁺ (300 μM), possibly due to modest structural effect of Ni²⁺ on the protein as shown by circular dichroism experimental results. The binding affinity of 1 was restored in the presence of EDTA (300 μM) (K_d = 0.79 μM). These studies suggest that peptides containing IDA groups may be used for designing novel SH2 domain binding ligands.     

Synthesis and biological evaluation of thioadatanserin and its dialkylated products as partial 5-HTR1A agonists and 5-HTR2A antagonists for potential use in depression and anxiety disorders

Thionation of adatanserin hydrochloride (2) with Lawesson's reagent in toluene/triethylamine afforded novel compound, (3r,5r,7r)-N-(2-(4-(pyrimidin-2-yl)piperazin-1-yl)ethyl)adamantane-1-carbothioamide (thioadatanserin, 3) in 84–90% isolated yield. Thioadatanserin underwent a tandem double alkylation with methyl iodide and benzyl bromide in NaH/THF to produce novel dialkylated products 6 and 7 respectively. The single X-ray crystal structure of 7 was determined to be 1-(2-((E- ((3r,5r,7r)-adamantan-1-yl)benzylthio)methylene)amino)ethyl)-1-benzyl-4- (pyrimidin-2-yl)piperazin-1-ium bromide showing that the piperazine ring adopts a chair-like configuration that is not co-planar with the pyrimidine ring. Thioadatanserin emerged as a dual potent partial agonist with activity against 5-HTR_1A (EC₅₀ 6.7 nM) and antagonist activity against 5-HTR_2A (IC₅₀ 62.3 nM) and was selective over 5-HTR_2C receptor (IC₅₀ > 3333 nM) in the PathHunter® β-arrestin assays.