Near-infrared fluorescent indolizine-dicyanomethylene-4H-pyran hybrids for viscosity imaging in living cells.

The development of near-infrared organic fluorescent dyes with tunable emission profiles is highly required in the field of biological sensing and imaging. In this paper, we designed and synthesized two organic fluorescent dyes, DCM-1 and DCM-2, through the hybridization of indolizine and dicyanomethylene-4H-pyran skeleton. These two compounds show near-infrared fluorescence with emission maximum approximately at 640 and 680 nm, respectively. Notably, both DCM-1 and DCM-2 have specific responses to viscosity without being interfered by biological relevant species. Cell experiments demonstrate that DCM-1 and DCM-2 can detect dynamic changes in viscosity within living cells, suggesting their potential applications in chemical biology research.

Design and Synthesis of 2-Phenylindolizine Acetamides: Molecular Docking, in Vitro Antimicrobial and Anticancer Activity Evaluation.

In the present work, we synthesized a small library of 2-phenylindolizine acetamide derivatives 7a-i and studied their biological activity. The synthesis was accomplished starting with easily available starting material phenacyl bromide 1 proceeding through the key intermediate 6-methyl-7-nitro-2-phenylindolizine 4. All the compounds 7a-i were characterized using spectroscopy viz., 1H-NMR, 13C NMR, FTIR, and mass spectrometry. Interestingly, 2-phenylindolizine scaffolds 7c, 7f and 7g revealed a remarkable antibacterial activity against relevant organisms S. aureus, E. coli, S. pneumoniae, P. aeruginosa. The target compounds 7e and 7h showed excellent anticancer activity against Colo-205 and MDA-MB-231 cell lines with IC50 values of 68.62, 62.91, 54.23 and 46.34 µM respectively. Additionally, all the 2-phenylindolizine acetamide derivatives 7a-i were subjected to molecular docking prediction by Autodock 4.2. Compounds 7a, 7f and 7c exhibited very good hydrogen bonding amino acid interactions Asp83 (2.23 Å), Asp83 (2.08 Å), His74 (2.05 Å), His76 (1.71 Å), Ser80 (1.05 Å) with active site of Topoisomerase-IV from S. pneumoniae (4KPE). Further, the compounds 7a-i have revealed acceptable ranges for drug-likeliness properties upon evaluation using SwissADME for ADMET and physiochemical properties.

Selective recognition of DNA parallel G-quadruplexes by 3,8a-disubstituted indolizinones.

Owing to its potential biological relevance, DNA G-quadruplex has been considered as a prospective anti-cancer target. Some known G-quadruplex-interactive N-containing compounds with low cytotoxicity have become prospective anticancer drugs. Here we reported a new type of N-containing alkaloids 3,8a-disubstituted indolizinones, and investigated their substituent effects at 3- and 8a-positions in targeting to DNA c-myc G-quadruplex. And then we used 3-naphtyl-8a-(pyridin-2-yl) substrate I8 as an example, and investigated its ability in targeting to DNA parallel G-quadruplexes in vitro.

Dithiolation indolizine exerts viability suppression effects on A549 cells via triggering intrinsic apoptotic pathways and inducing G2/M phase arrest.

Indolizine derivatives have been reported for the treatment of numerous diseases. However, few studies were carried out for non-small cell lung cancer (NSCLC). We synthesized series of indolizine compounds. The results of MTT assay showed compound 8 (C8) markedly inhibited the proliferation of A549 cells, however, C8 (15, 30 µg/mL) had little cytotoxicity in other cell lines (SH-SY5Y, HepG2, and BEAS-2B cells), Hoechst staining and JC-1 staining showed that C8 induced changes in the nucleus morphology, increased the loss in mitochondrial membrane potential in A549 cells. The results of flow cytometry manifested that cell cycle of the cells was arrested in the G2 / M phase by C8, ROS levels and the proportion of apoptosis of cells increased. We performed western blotting analysis to detect the expression levels of apoptosis and cycle-related proteins. These results validated that the apoptosis of cells was triggered by endoplasmic reticulum stress (ERS) and the PI3K/Akt-mediated mitochondrial pathway collaboratively. Besides, the utilization of PI3K/Akt inhibitors and p53 inhibitors further proves the above argument and C8-induced cycle arrest of A549 cells is majorly regulated by p53. C8 induced the accumulation of ROS contents involved in mitochondrial damage. The proliferation of A549 cells was inhibited after treatment with the compound, which induced apoptosis and cycle arrest of cells. It is suggested that C8(dithiolation indolizine) is a potential candidate compound against non-small cell lung cancer.

Fluorescent indolizine derivative YI-13 detects amyloid-ß monomers, dimers, and plaques in the brain of 5XFAD Alzheimer transgenic mouse model.

Alzheimer disease (AD) is a neurodegenerative disorder characterized by the aberrant production and accumulation of amyloid-ß (Aß) peptides in the brain. Accumulated Aß in soluble oligomer and insoluble plaque forms are considered to be a pathological culprit and biomarker of the disorder. Here, we report a fluorescent universal Aß-indicator YI-13, 5-(4-fluorobenzoyl)-7,8-dihydropyrrolo[1,2-b]isoquinolin-9(6H)-one, which detects Aß monomers, dimers, and plaques. We synthesized a library of 26 fluorescence chemicals with the indolizine core and screen them through a series of in vitro tests utilizing Aß as a target and YI-13 was selected as the final imaging candidate. YI-13 was found to stain and visualize insoluble Aß plaques in the brain tissue, of a transgenic mouse model with five familial AD mutations (5XFAD), by a histochemical approach and to label soluble Aß oligomers within brain lysates of the mouse model under a fluorescence plate reader. Among oligomers aggregated from monomers and synthetic dimers from chemically conjugated monomers, YI-13 preferred the dimeric Aß.

Indolizine-phenothiazine hybrids as the first dual inhibitors of tubulin polymerization and farnesyltransferase with synergistic antitumor activity.

In the incessant search for innovative cancer control strategies, this study was devoted to the design, synthesis and pharmacological evaluation of dual inhibitors of farnesyltransferase and tubulin polymerization (FTI/MTIs). A series of indolizine-phenothiazine hybrids 16 (amides) and 17 (ketones) has been obtained in a 4-step procedure. The combination of the two heterocycles provided potent tubulin polymerization inhibitors with similar efficiency as the reference phenstatin and (-)-desoxypodophyllotoxin. Ketones 17 were also able to inhibit human farnesyltransferase (FTase) in vitro. Interestingly, three molecules 17c, 17d and 17f were very effective against both considered biological targets. Next, nine indolizine-phenothiazine hybrids 16c, 16f, 17a-f and 22b were evaluated for their cell growth inhibition potential on the NCI-60 cancer cell lines panel. Ketones 17a-f were the most active and displayed promising cellular activities. Not only they arrested the cell growth of almost all tested cancer cells, but they displayed cytotoxicity potential with GI50 values in the low nanomolar range. The most sensitive cell lines upon treatment with indolizine-phenothiazine hybrids were NCI-H522 (lung cancer), COLO-205 and HT29 (colon cancer), SF-539 (human glioblastoma), OVCAR-3 (ovarian cancer), A498 (renal cancer) and especially MDA-MB-435 (melanoma). Demonstrating the preclinical effectiveness of these dual inhibitors can be crucial. A single dual molecule could induce a synergy of antitumor activity, while increasing the effectiveness and reducing the toxicity of the classical combo treatments currently used in chemotherapy.

Microwave-Assisted Synthesis of Fluorescent Pyrido[2,3-b]indolizines from Alkylpyridinium Salts and Enaminones.

Pyridinium ylides are well recognized as dipoles for cycloaddition reactions. In its turn, the microwave-assisted interaction of N-(cyanomethyl)-2-alkylpyridinium salts with enaminones unexpectedly proceeds as a domino sequence of cycloisomerization and cyclocondensation reactions, instead of a 1,3-dipolar cycloaddition. The reaction takes place in the presence of sodium acetate as base and employs benign solvents. The optical properties of the resulting pyrido[2,3-b]indolizines were studied, showing green light emission with high fluorescence quantum yields.

Cytotoxic substituted indolizines as new colchicine site tubulin polymerisation inhibitors.

A potential microtubule destabilising series of new indolizine derivatives was synthesised and tested for their anticancer activity against a panel of 60 human cancer cell lines. Compounds 11a, 11b, 15a, and 15j showed a broad spectrum of growth inhibitory activity against cancer cell lines representing leukaemia, melanoma and cancer of lung, colon, central nervous system, ovary, kidney, breast, and prostate. Among them, compound 11a was distinguishable by its excellent cytostatic activity, showing GI50 values in the range of 10-100 nM on 43 cell lines. The less potent compounds 15a and 15j in terms of GI50 values showed a high cytotoxic effect against tested colon cancer, CNS cancer, renal cancer and melanoma cell lines and only on few cell lines from other types of cancer. In vitro assaying revealed tubulin polymerisation inhibition by all active compounds. Molecular docking showed good complementarity of active compounds with the colchicine binding site of tubulin.

Design, Synthesis and in Vitro Evaluation of Tylophorine Derivatives as Possible Antitumor Agents.

Structural simplification and modification of natural products are always very important resources to antitumor drugs. By introducing various aminomethyl groups and amide groups into the phenanthrene ring of tylophorine, a novel series of tylophorine derivatives have been designed and synthesized, and their antiproliferative activities against MCF-7, A549 and HepG-2 cells have been evaluated, too. The results indicated that most of the prepared compounds exhibited good antitumor activities. Especially, one compound with an {ethyl[2-(morpholin-4-yl)ethyl]amino}methyl group at the side chain exhibited the most significant cytotoxic effects.

Alkyl Group Migration in Ni-Catalyzed Conjunctive Coupling with C(sp3) Electrophiles: Reaction Development and Application to Targets of Interest.

A catalytic conjunctive cross-coupling reaction is developed that allows the construction of chiral organoboronic esters from alkylboron ate complexes and alkyl iodide electrophiles. The process occurs most efficiently with a Ni/Pybox-comprised catalyst and with an acenapthoquinone-derived boron ligand. Because of the broad functional group tolerance of this reaction, it can be a versatile tool for organic synthesis. Applications to the construction of (R)-coniine and (-)-indolizidine 209D are described.

Discovery of fused heterocyclic carboxamide derivatives as novel α7-nAChR agonists: Synthesis, preliminary SAR and biological evaluation.

The α7 nicotinic acetylcholine receptor (α7 nAChR) has emerged as a promising therapeutic target for schizophrenia. In our previous work, a novel series of α7-nAChR agonists bearing scaffold of indolizine were discovered. To explore the effect of aromaticity on the activity and find more active agents, herein, fused heterocyclic carboxamide derivatives were designed and synthesized in this study. Based on the evaluation by two-electrode voltage clamp in Xenopus oocytes, 27 of the synthesized compounds showed obvious agonism of α7 nAChR. Particularly, compounds 10a and 10e showed significantly higher Emax than EVP-6124. The result illustrated the importance of aromaticity to the activity of agonism. Compound 10a, which showed EC50 of 1.88 µM and Emax of 72.4%, was further characterized comprehensively, including co-application with type II positive allosteric modulator PNU-120596, selectivity with other closely related ligand-gated ion channel, etc. The results showed that 10a showed moderate selectivity over other subtypes such as α4ß2 and α3ß4 nAChR. 10a evoked α7-like currents that were inhibited by MLA and enhanced in the presence of the α7 PAM PNU-120596. The analysis of binding mode and understanding of structure-activity relationship provided insights to develop more potent novel α7-nAChR agonists.

Copper-Hydride-Catalyzed Enantioselective Processes with Allenyl Boronates. Mechanistic Nuances, Scope, and Utility in Target-Oriented Synthesis.

Synthesis of complex bioactive molecules is substantially facilitated by transformations that efficiently and stereoselectively generate polyfunctional compounds. Designing such processes is hardly straightforward, however, especially when the desired route runs counter to the inherently favored reactivity profiles. Furthermore, in addition to being efficient and stereoselective, it is crucial that the products generated can be easily and stereodivergently modified. Here, we introduce a catalytic process that delivers versatile and otherwise difficult-to-access organoboron entities by combining an allenylboronate, a hydride, and an allylic phosphate. Two unique selectivity problems had to be solved: avoiding rapid side reaction of a Cu-H complex with an allylic phosphate, while promoting its addition to an allenylboronate as opposed to the commonly utilized boron-copper exchange. The utility of the approach is demonstrated by applications to concise preparation of the linear fragment of pumiliotoxin B (myotonic, cardiotonic) and enantioselective synthesis and structure confirmation of netamine C, a member of a family of anti-tumor and anti-malarial natural products. Completion of the latter routes required the following noteworthy developments: (1) a two-step all-catalytic sequence for conversion of a terminal alkene to a monosubstituted alkyne; (2) a catalytic SN2'- and enantioselective allylic substitution method involving a mild alkylzinc halide reagent; and (3) a diastereoselective [3+2]-cycloaddition to assemble the polycyclic structure of a guanidyl polycyclic natural product.

Linker Optimization and Therapeutic Evaluation of Phosphatidylserine-Targeting Zinc Dipicolylamine-based Drug Conjugates.

We report that compound 13, a novel phosphatidylserine-targeting zinc(II) dipicolylamine drug conjugate, readily triggers a positive feedback therapeutic loop through the in situ generation of phosphatidylserine in the tumor microenvironment. Linker modifications, pharmacokinetics profiling, in vivo antitumor studies, and micro-Western array of treated-tumor tissues were employed to show that this class of conjugates induced regeneration of apoptotic signals, which facilitated subsequent recruitment of the circulating conjugates through the zinc(II) dipicolylamine-phosphatidylserine association and resulted in compounding antitumor efficacy. Compared to the marketed compound 17, compound 13 not only induced regressions in colorectal and pancreatic tumor models, it also exhibited at least 5-fold enhancement in antitumor efficacy with only 40% of the drug employed during treatment, culminating in a >12.5-fold increase in therapeutic potential. Our study discloses a chemically distinct apoptosis-targeting theranostic, with built-in complementary functional moieties between the targeting module and the drug mechanism to expand the arsenal of antitumor therapy.

Computational, crystallographic studies, cytotoxicity and anti-tubercular activity of substituted 7-methoxy-indolizine analogues.

Indolizines are heteroaromatic compounds, and their synthetic analogues have reportedly showed promising pharmacological properties. In this study, a series of synthetic 7-methoxy-indolizine derivatives were synthesised, characterised and evaluated for in vitro whole-cell anti-tuberculosis (TB) screening against susceptible (H37Rv) and multi-drug-resistant (MDR) strains of Mycobacterium tuberculosis (MTB) using the resazurin microplate assay method. The cytotoxicity was evaluated using the MTT assay. In silico molecular-docking study was conducted for compounds 5a-j against enoyl-[acyl-carrier] protein reductase, a key enzyme of the type II fatty acid synthesis that has attracted much interest for the development of novel anti-TB compounds. Thereafter, molecular dynamic (MD) simulation was undertaken for the most active inhibitors. Compounds 5i and 5j with the methoxy functional group at the meta position of the benzoyl group, which was at the third position of the indolizine nucleus, demonstrated encouraging anti-TB activity against MDR strains of MTB at 16 µg/mL. In silico studies showed binding affinity within the range of 7.07-8.57 kcal/mol, with 5i showing the highest binding affinity. Hydrogen bonding, π-π- interactions, and electrostatic interactions were common with the active site. Most of these interactions occurred with the catalytic amino acids (Pro193, Tyr158, Phe149, and Lys165). MD simulation showed that 5j possessed the highest binding affinity toward the enzyme, according to the two calculation methods (MM/PBSA and MM/GBSA). The single-crystal X-ray studies of compounds 5c and 5d revealed that the molecular arrangements in these two structures were mostly guided by C-H···O hydrogen-bonded dimeric motifs and C-H···N hydrogen bonds, while various secondary interactions (such as π···π and C-H···F) also contributed to crystal formation. Compounds 5a, 5c, 5i, and 5j exhibited no toxicity up to 500 µg/mL. In conclusion, 5i and 5j are promising anti-TB compounds that have shown high affinity based on docking and MD simulation results.

Elucidation of Spirodactylone, a Polycyclic Alkaloid from the Sponge Dactylia sp., and Nonenzymatic Generation from the Co-metabolite Denigrin B.

Spirodactylone (1), a hexacyclic indolizidone alkaloid possessing a novel spiro ring system, was isolated from the marine sponge Dactylia sp. The structure was elucidated by extensive spectroscopic methods including application of the LR-HSQMBC NMR pulse sequence. Oxidative cyclization of denigrin B (2), an aryl-substituted 2-oxo-pyrroline derivative that was also isolated from the sponge extract, provided material identical to spirodactylone (1). This confirmed the assigned structure and provides insight into the probable biogenesis of 1.

Modular Syntheses of Phenanthroindolizidine Natural Products.

A highly concise strategy for the total synthesis of phenanthroindolizidines was developed. The one-pot iterative Suzuki-Miyaura reaction of aryl boronic acids with ortho-bromoaryl N-methyliminodiacetate (MIDA) boronate followed by a second Suzuki-Miyaura reaction with a suitable pyridyl bromide provided ortho-aza-terphenyls. Subsequent saturation of the triple bond, treatment with mesyl chloride, and reduction of the resulting dihydroindolizidinium ring afforded the hexahydroindolizines. A final vanadium-catalyzed oxidative electrocyclization provided the desired alkaloids in only three column-separation operations.

Counter Anion Effect on the Photophysical Properties of Emissive Indolizine-Cyanine Dyes in Solution and Solid State.

Near-infrared emissive materials with tunable Stokes shifts and solid-state emissions are needed for several active research areas and applications. To aid in addressing this need, a series of indolizine-cyanine compounds varying only the anions based on size, dipole, and hydrophilicity were prepared. The effect of the non-covalently bound anions on the absorption and emission properties of identical π-system indolizine-cyanine compounds were measured in solution and as thin films. Interestingly, the anion choice has a significant influence on the Stokes shift and molar absorptivities of the dyes in solution. In the solid-state, the anion choice was found to have an effect on the formation of aggregate states with higher energy absorptions than the parent monomer compound. The dyes were found to be emissive in the NIR region, with emissions peaking at near 900 nm for specific solvent and anion selections.

Functionalized spirooxindole-indolizine hybrids: Stereoselective green synthesis and evaluation of anti-inflammatory effect involving TNF-α and nitrite inhibition.

Stereoselective synthesis of a small library of novel spiroheterocyclic hybrids including indolizine, oxindole, and substituted piperidine units has been accomplished in [bmim]Br using a [3 + 2] cycloaddition strategy in good yield and were tested for their anti-inflammatory activities. The effects of compounds (4a-o) against inflammation were studied using carrageenan-induced hind paw oedema, croton oil-induced ear oedema, and cotton pellet-induced granuloma models. Among the heterocyclic hybrids, compounds 4d, 4g, and 4o showed significant anti-inflammatory activities against acute and chronic inflammatory models. These compounds also showed significant inhibition of PGE2, TNF-α, and nitrite levels in carrageenan-induced hind paw oedema. Thus it is evident from our study that these novel spiroheterocyclic hybrids 4d, 4g, and 4o displayed significant anti-inflammatory effects that involve the reduction of PGE2, TNF-α, and nitrite levels.

Spiropyrrolidine/spiroindolizino[6,7-b]indole heterocyclic hybrids: Stereoselective synthesis, cholinesterase inhibitory activity and their molecular docking study.

A regio and stereo- selective synthesis of hitherto unexplored hybrid heterocyclic system comprising spiropyrrolidine, indolizino[6,7-b]indole units in good to excellent yields, has been developed via three component 1,3-dipolar cycloaddition and concomitant trifluoroacetic acid catalyzed Pictet-Spengler cyclization with paraformaldehyde. The newly synthesized compounds were evaluated for their in vitro acetylcholinesterase (AChE) and butylcholinesterase (BChE) enzyme inhibitory activities. Most of the synthesized compounds showed good inhibitory activity, among them, compounds 4d and 4g displayed highest potency against AChE (IC50 1.88 and 1.98 µM), and BChE (IC50 18.32 and 10.21 µM) enzyme, respectively than the standard drug, galanthamine. Molecular modeling simulation was investigated for the most active compounds 4d and 4g on AChE and BChE enzymes to disclose the binding and orientation of these molecules into active site of respective receptors.

Synthesis, cytotoxicity and structure-activity relationship of indolizinoquinolinedione derivatives as DNA topoisomerase IB catalytic inhibitors.

Our previous studies reveal that indolizinoquinolinedione scaffold is a base to develop novel DNA topoisomerase IB (TOP1) catalytic inhibitors. In this work, twenty-three novel indolizinoquinolinedione derivatives were synthesized. TOP1-mediated relaxation, nicking and unwinding assays revealed that three fluorinated derivatives 26, 28 and 29, and one N,N-trans derivative 46 act as TOP1 catalytic inhibitors with higher TOP1 inhibition (++++) than camptothecin (+++) and without TOP1-mediated unwinding effect. MTT assay against five human cancer cell lines indicated that the highest cytotoxicity is 20 for CCRF-CEM cells, 25 for A549 and DU-145 cells, 26 for HCT116 cells, and 33 for Huh7 cells with GI50 values at nanomolar range. The drug-resistant cell assay indicated that compound 26 may mainly act to TOP1 in cells and are less of Pgp substrates. Flow cytometric analysis showed that compounds 26, 28 and 29 can obviously induce apoptosis of HCT116 cells. Moreover, the structure-activity relationship (SAR) of indolizinoquinolinedione derivatives was analyzed.