Unprecedented Direct Asymmetric Total Syntheses of 5,8'-Naphthylisoquinoline Alkaloids from their Fully Substituted Precursors Employing a Novel Nickel/N,N-ligand-Catalyzed Atroposelective Cross-Coupling Reaction.

A general and concise synthetic pathway for the preparation of four different 5,8'-coupled naphthylisoquinoline alkaloids, employing a specially developed nickel/N,N-ligand-catalyzed atroposelective Negishi coupling is reported. In the first reported direct atroposelective coupling of the fully substituted precursors, the naturally occurring cross-coupled products were generally obtained directly in reasonable yields and high enantiomeric purities. For the synthesis of the cross-coupling precursors, we employed a modification of Bringmann's known approach to the dihydroisoquinoline compounds and a newly developed route for the naphthalene building blocks. For the latter 1,8-dioxynaphthalene precursors, our strategy utilized Hartwig's borylation/methylation approach and included the efficient installation of orthogonal protecting groups.

Atroposelective NiII -Catalyzed Cross-Coupling Reactions Enable a Deeper Understanding of Negishi Couplings: Isolation and Application of Solid Aryl Higher-Order Zincates.

The Negishi cross-coupling reactions involves the application of organozinc reagents and is a highly versatile reaction in synthetic organic chemistry. The transmetallation step plays a pivotal role in the mechanism of these types of cross-coupling reactions. In this study, mechanistic investigations are presented indicating that higher-order zincates are the transmetallating active species in Pd- and Ni-catalyzed Negishi cross-coupling reactions. These findings are supported by halide salt addition experiments and by obtaining a single X-ray crystal structure of the solid monoaryl higher-order zincate [1-NaphthylZnX3 ]2- Mg(THF)2 2+ . The procedure developed in this work was further applied to the synthesis of various monoaryl higher-order zincates, after which their synthetic usefulness in terms of high reactivity towards transmetallation in Negishi cross-couplings, as well as stability, was exemplified in several reactions.

A novel 4'-brominated derivative of fisetin induces cell cycle arrest and apoptosis and inhibits EGFR/ERK1/2/STAT3 pathways in non-small-cell lung cancer without any adverse effects in mice.

The therapeutic toxicity and resistance to currently available treatment options are major clinical challenges for the management of lung cancer. As a novel strategy, we synthesized analogues of a known flavonol, fisetin, which has shown anti-tumorigenic potential against cancer in cell culture with no adverse effects in animal models. We studied the synthetic analogues of fisetin for their anti-cancer potential against lung cancer cells, toxicity in mice and efficacy in a xenograft model. Brominated fisetin analogues were screened for their effects on the viability of A549 and H1299 lung cancer cells, and three analogues (3a, 3b, 3c), showed improved activity compared to fisetin. These analogues were more effective in restricting lung cancer cell proliferation, inducing G2 M phase cell cycle arrest and apoptosis. The fisetin analogues also downregulated EGFR/ERK1/2/STAT3 pathways. Fisetin analogue-induced apoptosis was accompanied by a higher Bax to Bcl-2 expression ratio. Based on the in vitro studies, the most effective fisetin analogue 3b was evaluated for in vivo toxicity, wherein it did not show any hepatotoxicity or adverse health effects in mice. Furthermore, analogue 3b showed greater antitumor efficacy (p < .001) as compared to its parent compound fisetin in a human lung cancer cell xenograft study in athymic mice. Together, our data suggest that the novel fisetin analogue 3b is more effective in restricting lung cancer cell growth, both in vitro as well as in vivo, without any apparent toxicity, supporting its further development as a novel anti-lung cancer agent.

Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones.

A wide range of N-(ethoxycarbonylmethyl)enaminones, prepared by the Eschenmoser sulfide contraction between N-(ethoxycarbonylmethyl)pyrrolidine-2-thione and various bromomethyl aryl and heteroaryl ketones, underwent cyclization in the presence of silica gel to give ethyl 6-(hetero)aryl-2,3-dihydro-1H-pyrrolizine-5-carboxylates within minutes upon microwave heating in xylene at 150 °C. Instead of functioning as a nucleophile, the enaminone acted as an electrophile at its carbonyl group during the cyclization. Yields of the bicyclic products were generally above 75%. The analogous microwave-assisted reaction to produce ethyl 2-aryl-5,6,7,8-tetrahydroindolizine-3-carboxylates from (E)-ethyl 2-[2-(2-oxo-2-arylethylidene)piperidin-1-yl]acetates failed in nonpolar solvents, but occurred in ethanol at lower temperature and microwave power, although requiring much longer time. A possible mechanism for the cyclization is presented, and further functionalization of the newly created pyrrole ring in the dihydropyrrolizine core is described.

Deciphering the chemical instability of sphaeropsidin A under physiological conditions - degradation studies and structural elucidation of the major metabolite.

The fungal metabolite sphaeropsidin A (SphA) has been recognised for its promising cytotoxicity, particularly towards apoptosis- and multidrug-resistant cancers. Owing to its intriguing activity, the development of SphA as a potential anticancer agent has been pursued. However, this endeavour is compromised since SphA exhibits poor physicochemical stability under physiological conditions. Herein, SphA's instability in biological media was explored utilizing LC-MS. Notably, the degradation tendency was found to be markedly enhanced in the presence of amino acids in the cell medium utilized. Furthermore, the study investigated the presence of degradation adducts, including the identification, isolation and structural elucidation of a major degradation metabolite, (4R)-4,4',4'-trimethyl-3'-oxo-4-vinyl-4',5',6',7'-tetrahydro-3'H-spiro[cyclohexane-1,1'-isobenzofuran]-2-ene-2-carboxylic acid. Considering the reduced cytotoxic potency of aged SphA solutions, as well as that of the isolated degradation metabolite, the reported antiproliferative activity has been attributed primarily to the parent compound (SphA) and not its degradation species. The fact that SphA continues to exhibit remarkable bioactivity, despite being susceptible to degradation, motivates future research efforts to address the challenges associated with this instability impediment.

The Phylum Bryozoa: From Biology to Biomedical Potential.

Less than one percent of marine natural products characterized since 1963 have been obtained from the phylum Bryozoa which, therefore, still represents a huge reservoir for the discovery of bioactive metabolites with its ~6000 described species. The current review is designed to highlight how bryozoans use sophisticated chemical defenses against their numerous predators and competitors, and which can be harbored for medicinal uses. This review collates all currently available chemoecological data about bryozoans and lists potential applications/benefits for human health. The core of the current review relates to the potential of bryozoan metabolites in human diseases with particular attention to viral, brain, and parasitic diseases. It additionally weighs the pros and cons of total syntheses of some bryozoan metabolites versus the synthesis of non-natural analogues, and explores the hopes put into the development of biotechnological approaches to provide sustainable amounts of bryozoan metabolites without harming the natural environment.

1-Aryl-3-(4-methoxybenzyl)ureas as potentially irreversible glycogen synthase kinase 3 inhibitors: Synthesis and biological evaluation.

Glycogen synthase kinase 3 (GSK-3) has become known for its multifactorial involvement in the pathogenesis of Alzheimer's disease. In this study, a benzothiazole- and benzimidazole set of 1-aryl-3-(4-methoxybenzyl)ureas were synthesised as proposed Cys199-targeted covalent inhibitors of GSK-3ß, through the incorporation of an electrophilic warhead onto their ring scaffolds. The nitrile-substituted benzimidazolylurea 2b (IC50 = 0.086 ±â€¯0.023 µM) and halomethylketone-substituted benzimidazolylurea 9b (IC50 = 0.13 ±â€¯0.060 µM) displayed high GSK-3ß inhibitory activity, in comparison to reference inhibitor AR-A014418 (1, IC50 = 0.072 ±â€¯0.043) in our assay. The results suggest further investigation of 2b and 9b as potential covalent inhibitors of GSK-3ß, since a targeted interaction might provide improved kinase-selectivity.

PEGylation potentiates hepatoma cell targeted liposome-mediated in vitro gene delivery via the asialoglycoprotein receptor.

Hepatocellular carcinoma is a burgeoning health issue in sub-Saharan Africa and East Asia where it is most prevalent. The search for gene medicine treatment modalities for this condition represents a novel departure from current treatment options and is gaining momentum. Here we report on nonPEGylated and on sterically stabilized PEGylated cationic liposomes decorated with D-galacto moieties linked to 24.1 Å spacers for asialoglycoprotein receptor (ASGP-R)-targeted vehiculation of pCMV-luc plasmid DNA. Cargo DNA is fully liposome associated at N/P ratio=3:1 and is partially protected from the effects of serum nucleases. Moreover, at this ratio, lipoplex dimensions (89-97 nm) are compatible with the requirements for extravasation in vivo. Ethidium displacement assays show that the reporter DNA is in a less condensed state when bound to PEGylated liposomes than with nonPEGylated liposomes. PEGylated lipoplexes were well tolerated by both HEK293 (ASGP-R-negative) and HepG2 (ASGP-R-positive) cell lines and delivered DNA to the human hepatoma cell line HepG2 by ASGP-R mediation at levels three-fold greater than nonPEGylated lipoplexes. PEGylated ASGP-R-targeted liposomes reported in this study possess the required characteristics for hepatotropic gene delivery and may be considered for further application in vivo.

Application of the Huisgen cycloaddition and 'click' reaction toward various 1,2,3-triazoles as HIV non-nucleoside reverse transcriptase inhibitors.

The development of novel anti-HIV agents remains an important medicinal chemistry challenge given that no cure for the disease is imminent, and the continued use of current NNRTIs inevitably leads to problems associated with resistance. Inspired by the pyrazole-containing NNRTI lersivirine (LSV), we embarked upon a study to establish whether 1,2,3-triazole heterocycles could be used as a new scaffold for the creation of novel NNRTIs. An especially attractive feature of triazoles used for this purpose is the versatility in accessing variously functionalised systems using either the thermally regulated Huisgen cycloaddition, or the related 'click' reaction. Employing three alternative forms of these reactions, we were able to synthesise a range of triazole compounds and evaluate their efficacy in a phenotypic HIV assay. To our astonishment, even compounds closely mimicking LSV were only moderately effective against HIV.

Novel indole sulfides as potent HIV-1 NNRTIs.

In a previous communication we described a series of indole based NNRTIs which were potent inhibitors of HIV replication, both for the wild type and K103N strains of the virus. However, the methyl ether functionality on these compounds, which was crucial for potency, was susceptible to acid promoted indole assisted SN1 substitution. This particular problem did not bode well for an orally bioavailable drug. Here we describe bioisosteric replacement of this problematic functional group, leading to a series of compounds which are potent inhibitors of HIV replication, and are acid stable.

Synthesis and in vitro growth inhibitory activity of novel silyl- and trityl-modified nucleosides.

Seventeen silyl- and trityl-modified (5'-O- and 3',5'-di-O-) nucleosides were synthesized with the aim of investigating the in vitro antiproliferative activities of these nucleoside derivatives. A subset of the compounds was evaluated at a fixed concentration of 100µM against a small panel of tumor cell lines (HL-60, K-562, Jurkat, Caco-2 and HT-29). The entire set was also tested at varying concentrations against two human glioma lines (U373 and Hs683) to obtain GI50 values, with the best results being values of ∼25µM.

Alkaloids with Activity against the Zika Virus Vector Aedes aegypti (L.)-Crinsarnine and Sarniensinol, Two New Crinine and Mesembrine Type Alkaloids Isolated from the South African Plant Nerine sarniensis.

Two new Amaryllidaceae alkaloids, belonging to the mesembrine- and crinine-types, named crinsarnine (1) and sarniensinol (2), were isolated from the dried bulbs of Nerine sarniensis together with bowdensine (3), sarniensine (4), hippadine (5) and 1-O-acetyl-lycorine (6). Crinsarnine (1) and sarniensinol (2) were characterized using spectroscopic and chiroptical methods as (1S,2S,4aR,10bS)-2,7-dimethoxy-1,2,3,4,4a,6-hexahydro-5,11b-ethano[1,3]dioxolo-[4,5-j]phenanthridin-1-yl acetate and (6-(3aR,4Z,6S,7aS)-6-methoxy-1-methyl-2,3,3a,6,7,7a-hexa-hydro-1H-indol-3a-yl)benzo[d][1,3]dioxol-5-yl)methanol, respectively. Furthermore, the complete spectroscopic characterization of bowdensine (3) is reported for the first time. Compounds 1-6 were evaluated against the Orlando reference strain of Aedes aegypti. None of compounds showed mortality against 1st instar Ae. aegypti larvae at the concentrations tested. In adult topical bioassays, only 1 displayed adulticidal activity with an LD50 = 2.29 ± 0.049 µg/mosquito. As regards the structure-activity relationship, the pretazettine and crinine scaffold in 2 and 4 and in 1 and 3 respectively, proved to be important for their activity, while the pyrrole[de]phenanthridine scaffold present in 5 and 6 was important for their reactivity. Among the pretazettine group compounds, opening of the B ring or the presence of a B ring lactone as well as the trans-stereochemistry of the A/B ring junction, appears to be important for activity, while in crinine-type alkaloids, the substituent at C-2 seems to play a role in their activity.

Toward a Cancer Drug of Fungal Origin.

Although fungi produce highly structurally diverse metabolites, many of which have served as excellent sources of pharmaceuticals, no fungi-derived agent has been approved as a cancer drug so far. This is despite a tremendous amount of research being aimed at the identification of fungal metabolites with promising anticancer activities. This review discusses the results of clinical testing of fungal metabolites and their synthetic derivatives, with the goal to evaluate how far we are from an approved cancer drug of fungal origin. Also, because in vivo studies in animal models are predictive of the efficacy and toxicity of a given compound in a clinical situation, literature describing animal cancer testing of compounds of fungal origin is reviewed as well. Agents showing the potential to advance to clinical trials are also identified. Finally, the technological challenges involved in the exploitation of fungal biodiversity and procurement of sufficient quantities of clinical candidates are discussed, and potential solutions that could be pursued by researchers are highlighted.

In vitro antiplasmodial activity of triazole-linked chloroquinoline derivatives synthesized from 7-chloro-N-(prop-2-yn-1-yl)quinolin-4-amine.

The synthesis and in vitro evaluation of novel triazole-linked chloroquinoline derivatives as potential antiplasmodial agents against Plasmodium falciparum is reported. The 15 synthesized target compounds were obtained by means of a copper(I)-mediated click reaction between a variety of 1,2- and 1,3-azidoamines and 7-chloro-N-(prop-2-yn-1-yl)quinolin-4-amine in moderate to good yields (53-85%). The compounds were screened for antiplasmodial activity against NF54 chloroquine-sensitive and Dd2 chloroquine-resistant strains, alongside chloroquine and artesunate as reference compounds. Six of the test compounds revealed a 3-5 fold increase in antiplasmodial activity against chloroquine-resistant strain Dd2 compared to chloroquine. Among the six compounds with good antiplasmodial activity, a reduced cross-resistance relative to artesunate (>3 fold in comparison to chloroquine) was observed, mainly in derivatives that incorporated chloroquine-resistance reversing pharmacophores. A general trend for reduced chloroquine cross-resistance was also detected among 12 out of the 15 compounds tested.

Stealth lipoplex decorated with triazole-tethered galactosyl moieties: a strong hepatotropic gene vector.

Mono-antennary galacto derivatives of cholesterol are being actively developed to direct lipoplexes to the asialoglycoprotein receptor (ASGP-R) on hepatocytes. Here we report on a novel ASGP-R ligand cholest-5-en-3-yl [1-(ß-D-galactopyranosyl)-1H-1,2,3-triazol-4-yl]methylcarbamate (4), assembled by a copper(I)-catalyzed azide-alkyne cycloaddition (click chemistry), and compare it with cholest-5-en-3-yl-ß-D-galactopyranoside (2) and cholest-5-en-3-yl [1-(ß-D-galactopyranosyl-1'-oxy)phen-4-yl]carbamate (3), in liposome formulations with or without 5 mol% distearoylphosphatidylethanolamine poly(ethylene glycol)2000, intended for DNA delivery to ASGP-R-positive hepatocyte-derived HepG2 cells and the ASGP-R-negative embryo kidney cell line HEK293. Transfection levels attained with lipoplex 4 were 100 and 300% greater than those for lipoplexes 2 and 3 respectively in HepG2 cells, while competition assays reduced transfection levels by up to 98%. Transfection activities achieved in HEK293 cells were up to three orders of magnitude lower. Therefore, 4 is representative of a new class of promising hepatotropic ligands for gene delivery.

Covalent-Allosteric Kinase Inhibitors.

Targeting and stabilizing distinct kinase conformations is an instrumental strategy for dissecting conformation-dependent signaling of protein kinases. Herein the structure-based design, synthesis, and evaluation of pleckstrin homology (PH) domain-dependent covalent-allosteric inhibitors (CAIs) of the kinase Akt is reported. These inhibitors bind covalently to a distinct cysteine of the kinase and thereby stabilize the inactive kinase conformation. These modulators exhibit high potency and selectivity, and represent an innovative approach for chemical biology and medicinal chemistry research.

Novel indole based NNRTIs with improved potency against wild type and resistant HIV.

The human immunodeficiency virus (HIV) pandemic remains a significant problem, especially in developing nations where the social and economic impacts are severe. Until a cure or vaccine for the disease is found, a constant supply of new compounds to fill the drug development pipeline is a requirement, given the tendency for the virus to rapidly develop resistance to current therapies. Here we disclose our efforts to improve upon the efficacy of cyclopropyl-indole derivatives developed as NNRTIs in our laboratories. To this end, modifications to the functionality occupying the small Val179 pocket have resulted in nearly two orders of magnitude increase in potency.

Synthesis of novel triazole-linked mefloquine derivatives: biological evaluation against Plasmodium falciparum.

Using 2,8-bis(trifluoromethyl)quinoline, the pharmacophore of mefloquine, as scaffold, eleven novel triazole-linked compounds have been synthesised by the application of CuAAC chemistry. The in vitro biological activity of the compounds on the Plasmodium falciparum chloroquine-sensitive strain NF54 was then determined. The compounds all showed IC50s in the lower µM range with (1R,3S,5R)-N-{[1-(2,8-bis(trifluoromethyl)quinoline-4-yl)-1H-1,2,3-triazol-4-yl]methyl}adamantan-2-amine (29) exhibiting the best activity of 1.00 µM.

C1,C2-ether derivatives of the Amaryllidaceae alkaloid lycorine: retention of activity of highly lipophilic analogues against cancer cells.

As a continuation of the studies aimed at the development of new anticancer agents derived from the Amaryllidaceae alkaloid lycorine, 35 C1,C2-ether analogues of this natural product were synthesized. The compounds were evaluated for antiproliferative activities in vitro in a panel of tumor cell lines with varied levels of apoptosis resistance. A strong correlation between the compound lipophilicity and anticancer activity was observed, indicating that cell permeability properties must be an important determinant in the design of lycorine-based anticancer agents. A theoretical docking model, consistent with the experimental observations, is presented.