Photoswitchable inhibitors of human ß-glucocerebrosidase.

Light-switchable inhibitors of the enzyme ß-glucocerebrosidase (GCase) have been developed by anchoring a specific azasugar to a dihydroazulene or an azobenzene responsive moiety. Their inhibitory effect towards human GCase, before and after irradiation are reported, and the effect on thermal denaturation of recombinant GCase and cytotoxicity were studied on selected candidates.

Challenging Approach to the Development of Novel Estrogen Receptor Modulators Based on the Chemical Properties of Guaiazulene.

Tamoxifen, a therapeutic agent for breast cancer, has been associated with genetic polymorphisms in the metabolism of N,N-dialkylaminoethyl substituent, which plays an important role in the expression of selective estrogen receptor modulator (SERM) activity. To solve this problem, we developed a novel estrogen receptor (ER) modulator, Az-01, on the basis of the aromaticity, dipole moment, and isopropyl group of guaiazulene. Az-01 showed four-fold lower binding affinity for ER than E2 but had similar ER-binding affinity to that of 4-hydroxytamoxifen (4-HOtam). Unlike tamoxifen, Az-01 acted as a partial agonist with very weak estrogenic activity at high concentrations when used alone, and it showed potent anti-estrogenic activity in the presence of E2. The cell proliferation and inhibition activities of Az-01 were specific to ER-expressing MCF-7 cells, and no effect of Az-01 on other cell proliferation signals was observed. These findings are important for the development of new types of SERMs without the N,N-dialkylaminoethyl substituent as a privileged functional group for SERMs.

Synthesis of Azulene Derivatives from 2H-Cyclohepta[b]furan-2-ones as Starting Materials: Their Reactivity and Properties.

A variety of synthetic methods have been developed for azulene derivatives due to their potential applications in pharmaceuticals and organic materials. Particularly, 2H-cyclohepta[b]furan-2-one and its derivatives have been frequently used as promising precursors for the synthesis of azulenes. In this review, we describe the development of the synthesis of azulenes by the reaction of 2H-cyclohepta[b]furan-2-ones with olefins, active methylenes, enamines, and silyl enol ethers as well as their reactivity and properties.

Development of Heterocycle-Substituted and Fused Azulenes in the Last Decade (2010-2020).

Azulene derivatives with heterocyclic moieties in the molecule have been synthesized for applications in materials science by taking advantage of their unique properties. These derivatives have been prepared by various methods, involving electrophilic substitution, condensation, cyclization, and transition metal-catalyzed cross-coupling reactions. Herein, we present the development of the synthetic methods, reactivities, and physical properties for the heterocycle-substituted and heterocycle-fused azulenes reported in the last decade.

Painting argyrins blue: Negishi cross-coupling for synthesis of deep-blue tryptophan analogue ß-(1-azulenyl)-l alanine and its incorporation into argyrin C.

The argyrins are a family of non-ribosomal peptides that exhibits different biological activities through only small structural changes. Ideally, a biologically active molecule can be tracked and observed in a variety of biological and clinical settings in a non-invasive manner. As a step towards this goal, we report here a chemical synthesis of unnatural deep blue amino acid ß-(1-azulenyl)-l alanine with different fluorescence and photophysical properties, which allows a spectral separation from the native tryptophan signal. This might be especially useful for cell localization studies and visualizing the targeted proteins. In particular, the synthesis of ß-(1-azulenyl)-l alanine was achieved through a Negishi coupling which proved to be a powerful tool for the synthesis of unnatural tryptophan analogs. Upon ß-(1-azulenyl)-l alanine incorporation into argyrin C, deep blue octapeptide variant was spectrally and structurally characterized.

A Concise, Efficient and Scalable Total Synthesis of Thapsigargin and Nortrilobolide from (R)-(-)-Carvone.

A concise, efficient and scalable synthesis of thapsigargin and nortrilobolide from commercially available (R)-(-)-carvone was developed. Our synthetic strategy is inspired by nature's carbon-carbon bond formation sequence, which facilitates the construction of a highly functionalized sesquiterpene lactone skeleton in five steps via an enantioselective ketone alkylation and a diastereoselective pinacol cyclization. We envision that this strategy will permit the construction of other members of the family, structural analogs and provide a practical synthetic route to these important bioactive agents. In addition, we anticipate that the prodrug Mipsagargin, which is currently in late-stage clinical trials for the treatment of cancer, will also be accessible via this strategy. Hence, the limited availability from natural sources, coupled with an estimated demand of one metric ton per annum for the prodrug, provides a compelling mandate to develop practical total syntheses of these agents.

Antiretroviral (HIV-1) activity of azulene derivatives.

The antiretroviral activity of azulene derivatives was detected for the first time. A series of eighteen diversely substituted azulenes was synthesized and tested in vitro using HIV-1 based virus-like particles (VLPs) and infectious HIV-1 virus in U2OS and TZM-bl cell lines. Among the compounds tested, the 2-hydroxyazulenes demonstrated the most significant activity by inhibiting HIV-1 replication with IC50 of 2-10 and 8-20 µM for the VLPs and the infectious virus, respectively. These results indicate that azulene derivatives may be potentially useful candidates for the development of antiretroviral agents.

Chemo- and Regioselective Functionalization of Nortrilobolide: Application for Semisynthesis of the Natural Product 2-Acetoxytrilobolide.

The difference in reactivity of the hexaoxygenated natural product thapsigargin (1) and the pentaoxygenated nortrilobolide (3) was compared in order to develop a chemo- and regioselective method for the conversion of nortrilobolide (3) into the natural product 2-acetoxytrilobolide (4). For the first time, a stereoselective synthesis of 2-acetoxytrilobolide (4) is described, which involves two key reactions: the first chemical step was a one-pot substitution-oxidation reaction of an allylic ester into its corresponding α,ß-unsaturated ketone. The second process consisted of a stereoselective α'-acyloxylation of the key intermediate α,ß-unsaturated ketone to afford its corresponding acetoxyketone, which was converted into 2-acetoxytrilobolide (4) in a few steps. This innovative approach would allow the synthesis of a broad library of novel and valuable penta- and hexaoxygenated guaianolides as potential anticancer agents.

Breakdown of interference rules in azulene, a nonalternant hydrocarbon.

We have designed and synthesized five azulene derivatives containing gold-binding groups at different points of connectivity within the azulene core to probe the effects of quantum interference through single-molecule conductance measurements. We compare conducting paths through the 5-membered ring, 7-membered ring, and across the long axis of azulene. We find that changing the points of connectivity in the azulene impacts the optical properties (as determined from UV-vis absorption spectra) and the conductivity. Importantly, we show here that simple models cannot be used to predict quantum interference characteristics of nonalternant hydrocarbons. As an exemplary case, we show that azulene derivatives that are predicted to exhibit destructive interference based on widely accepted atom-counting models show a significant conductance at low biases. Although simple models to predict the low-bias conductance do not hold with all azulene derivatives, we demonstrate that the measured conductance trend for all molecules studied actually agrees with predictions based on the more complete GW calculations for model systems.

Syntheses of donor-acceptor-functionalized dihydroazulenes.

The dihydroazulene (DHA)/vinylheptafulvene (VHF) photo/thermoswitch has been of interest for use in molecular electronics and advanced materials. The switching between the two isomers has previously been found to depend strongly on the presence of donor and acceptor groups. The fine-tuning of optical and switching properties relies on ready access to new derivatives via efficient synthetic protocols. The central DHA core is conveniently prepared in a four-step synthesis starting from acetophenone and tropylium substrates. Here, the outcome of this reaction as a function of the nature of the substituent group on the phenyl unit of acetophenone is investigated in detail. A wide variety of functional groups (nitro, cyano, halo, alkyl, amido, and thioether) was tolerated, and the route provided access to a large selection of substituted DHA derivatives (position 2 of DHA). These compounds were investigated for their ability to undergo subsequent functionalization in the seven-membered ring by a regioselective bromination-elimination protocol, introducing a bromo substituent at position 7. Halo-substituted DHAs were subjected to palladium-catalyzed cyanation, Sonogashira, Cadiot-Chodkiewicz, and Suzuki couplings and for the latter reaction; optimized conditions were developed by varying the palladium catalyst. In general, our focus was on reducing the formation of fully unsaturated azulene byproducts.

Design, synthesis and biological activity of α-nitrile substituted guaiazulene-based chalcone derivatives.

In present study, seventeen α-nitrile substituted guaiazulene-based chalcone derivatives including twelve new were designed, synthesized, and assayed for antiviral, cytotoxicity and signal pathway activities. All derivatives showed potential antiviral activity towards influenza virus or herpes simplex virus (HSV), 7 g with the substitution of nitro group showed strong effects towards H1N1 virus at 30 µM with inhibitory rate of 66.0%, 7o with thiophene exhibited potent anti HSV-1 activities with inhibitory rate of 65.8%. Moreover, several compounds exhibited inhibitory effects on tumor cells and hypoxia-inducible factor-1 (HIF1) signaling pathways. These results showed that α-nitrile substituted guaiazulene-based chalcones offered a promising framework for the further development of new highly efficient drugs.

Golgi-modifying properties of macfarlandin E and the synthesis and evaluation of its 2,7-dioxabicyclo[3.2.1]octan-3-one core.

Golgi-modifying properties of the spongian diterpene macfarlandin E (MacE) and a synthetic analog, t-Bu-MacE, containing its 2,7-dioxabicyclo[3.2.1]octan-3-one moiety are reported. Natural product screening efforts identified MacE as inducing a novel morphological change in Golgi structure defined by ribbon fragmentation with maintenance of the resulting Golgi fragments in the pericentriolar region. t-Bu-MacE, which possesses the substituted 2,7-dioxabicyclo[3.2.1]octan-3-one but contains a tert-butyl group in place of the hydroazulene subunit of MacE, was prepared by chemical synthesis. Examination of the Golgi-modifying properties of MacE, t-Bu-MacE, and several related structures revealed that the entire oxygen-rich bridged-bicyclic fragment is required for induction of this unique Golgi organization phenotype. Further characterization of MacE-induced Golgi modification showed that protein secretion is inhibited, with no effect on the actin or microtubule cytoskeleton being observed. The conversion of t-Bu-MacE and a structurally related des-acetoxy congener to substituted pyrroles in the presence of primary amines in protic solvent at ambient temperatures suggests that covalent modification might be involved in the Golgi-altering activity of MacE.

Novel azulene derivatives for the treatment of erectile dysfunction.

Based on the dopamine D(4) receptor partial agonist FAUC 3019, a series of azulenylmethylpiperazines was synthesized and affinities for the monoaminergic GPCRs including dopamine, serotonin, histamine and α-adrenergic receptor subtypes were determined. Ligand efficacies of the most promising test compounds revealed the N,N-dimethylaminomethyl substituted azulene 11 to be the most potent D(4) partial agonist (EC(50)=0.41 nM). This candidate was investigated for its ability to promote penile erection. Applying an in vivo animal model, test compound 11 turned out to stimulate penile erection in male rats with superior potency in low concentrations when compared to apomorphine.

Synthesis and anti-influenza activity of aminoalkyl rupestonates.

A series of aminoalkyl rupestonates were designed and synthesized by reacting rupestonic acid with 1,ω-dibromoalkanes, followed by amination. All of the new compounds were bioassayed in vitro to determine their activities against influenza A (H3N2, H1N1) and B viruses. The results showed that compounds 5a-5g, which each contain a 1H-1,2,4-triazolyl moiety, were found to be the most potent set of compounds. Compound 5g was demonstrated to possess the highest inhibitory activity against influenza H3N2 and H1N1, with IC(50) values of 0.97 and 0.42 µM, respectively. Our results also indicated that compounds 2g, 3g, 4g and 5g, which contain ten-CH(2)-unit spacers between the rupestonic acid and amino functional groups, were the most potent inhibitors of influenza H1N1 among the synthesized compounds. Unfortunately, most of the synthesized compounds did not show an obvious activity against influenza B; the only exceptions were compounds 5d and 5f, which had IC(50) values of 17.3 and 3.2 µM, respectively. Compounds 4g and 5g were potent inhibitors of influenza H1N1, and they might be potentially developed as new lead anti-influenza virus compounds. Further studies of the mechanism of action are underway.

Synthesis and antigastric ulcer activity of novel 5-isoproyl-3,8-dimethylazulene derivatives.

5-Isoproyl-3,8-dimethylazulene derivatives were synthesized and evaluated for antigastric ulcer activity in vivo. Some of them possess the best activity against gastric ulcer with ulcer index values lower than the drug reference (omeprazole). The structure-activity relationship (SAR) shows that the lipophilic flat structure contributes to quite potent antigastric ulcer activity.

New synthetic route to substituted dihydroazulene photoswitches.

A new procedure for functionalization of the dihydroazulene photoswitch on its seven-membered ring was developed, which has allowed isolation of the first dihydroazulene with a phenyl substituent at position 5 from a mixture of regioisomers. Light-induced ring-opening to the corresponding vinylheptafulvene and the thermal back-reaction was studied in detail.

Antitumor Effects and Tumor-specificity of Guaiazulene-3-Carboxylate Derivatives Against Oral Squamous Cell Carcinoma In Vitro.

AIM: The aim of this study was to investigate the antitumor potential of guaiazulene-3-carboxylate derivatives against oral malignant cells. MATERIALS AND METHODS: Twelve guaiazulene-3-carboxylate derivatives were synthesized by introduction of either with alkyl group [1-5], alkoxy group [6, 7], hydroxyl group [8, 9] or primary amine [10-12] at the end of sidechains. Tumor-specificity (TS) was calculated by the ratio of mean 50% cytotoxic concentration (CC50) against 3 human oral mesenchymal cell lines to that against 4 human oral squamous cell carcinoma (OSCC) cell lines. Potency-selectivity expression (PSE) was calculated by dividing TS value by CC50value against OSCC cell lines. Cell cycle analysis was performed by cell sorter. RESULTS: [6, 7] showed the highest TS and PSE values, and induced the accumulation of both subG1 and G2/M cell populations in HSC-2 OSCC cells. Quantitative structure-activity relationship analysis demonstrated that their tumor-specificity was correlated with chemical descriptors that explain the 3D shape, electric state and ionization potential. CONCLUSION: Alkoxyl guaiazulene-3-carboxylates [6, 7] can be potential candidates of lead compound for developing novel anticancer drugs.

Synthesis of a tetraazulene porphodimethene analogue.

Substituted calix[4]azulenes were prepared by reacting 6-alkylazulenes with paraformaldehyde in the presence of florisil. Hydride abstraction of a calix[4]azulene with Ph(3)CPF(6) afforded a tetraazulene analogue of the porphodimethenes.

Diverse compounds from pleuromutilin lead to a thioredoxin inhibitor and inducer of ferroptosis.

The chemical diversification of natural products provides a robust and general method for the creation of stereochemically rich and structurally diverse small molecules. The resulting compounds have physicochemical traits different from those in most screening collections, and as such are an excellent source for biological discovery. Herein, we subject the diterpene natural product pleuromutilin to reaction sequences focused on creating ring system diversity in few synthetic steps. This effort resulted in a collection of compounds with previously unreported ring systems, providing a novel set of structurally diverse and highly complex compounds suitable for screening in a variety of different settings. Biological evaluation identified the novel compound ferroptocide, a small molecule that rapidly and robustly induces ferroptotic death of cancer cells. Target identification efforts and CRISPR knockout studies reveal that ferroptocide is an inhibitor of thioredoxin, a key component of the antioxidant system in the cell. Ferroptocide positively modulates the immune system in a murine model of breast cancer and will be a useful tool to study the utility of pro-ferroptotic agents for treatment of cancer.

A new efficient route to 2-substituted azulenes based on sulfonyl group directed lithiation.

Directed lithiation of p-tolyl 1-azulenyl sulfone (1) at the 2-position of the azulenyl group was achieved by using lithium 2,2,6,6-tetramethylpiperidide (LTMP). The azulenyllithium thus generated could be efficiently trapped with various electrophiles to form 2-substituted derivatives 2 in moderate to good yields. p-Tolyl 2-trimethylsilyl-1-azulenyl sulfone (2a) was transformed into cyclic sulfone derivative 3a through the directed lithiation in the p-tolyl group and subsequent intramolecular ring closure at the 8-position. 2-(Phenylsulfanyl)-1-azulenyl p-tolyl sulfone (2b) suffered from desulfonylation to form 2-phenylsulfanylazulene (4). The Suzuki coupling reaction of 2-iodo-1-azulenyl p-tolyl sulfone (2d) with arylboronic acids followed by desulfonylation efficiently gave 2-arylazulenes 10.