Tropolone Alkaloids Research Articles

Antitumor efficacy of 2-(6,8-dimethyl-5-nitro-4-chloroquinoline-2-yl)-5,6,7-trichloro-1,3-tropolone in lung cancer xenografts.

e15008 Background: Lung cancer is the most common cancer worldwide. The efficacy of chemotherapy for this tumor does not exceed 40%. Moreover, all cytotoxic agents cause many side effects. The search for new substances with an antitumor effect seems to be relevant. Tropolone alkaloids, which are seven-membered non-benzenoid aromatic compounds, are promising inhibitors of tumor growth. The purpose of the study was to evaluate the antitumor efficacy of 2-(6,8-dimethyl-5-nitro-4-chloroquinoline-2-yl)-5,6,7-trichloro-1,3-tropolone in subcutaneous xenografts of lung cancer A549 cells in immunodeficient Balb/c Nude mice. Methods: The study was performed on a PDX model of lung cancer created by subcutaneous injection of A549 cell suspension, 5x106 cells in 0.2 ml of a solution of serum-free nutrient medium 199 and Matrigel (1:1). Animals were equally divided into 5 groups (each n = 5). Experimental groups 1, 2, 3 and 4 received 2-(6,8-dimethyl-5-nitro-4-chloroquinoline-2-yl)-5,6,7-trichloro-1,3-tropolone at doses of 0.0055, 0.055, 0.55 and 2.75 mg/g, respectively; the control group received 1% starch gel. The dynamics of the growth of a subcutaneous xenograft was evaluated by measuring tumor nodes. The volumes of tumor nodes were calculated using the Shrek’s formula for the ellipsoid: V = a×b×c×p/6, where V is the tumor volume (mm3), and a, b, c are the maximum dimensions of the ellipsoid in three planes (mm). The data were statistically analyzed using the Exel and Medstatistic progams. Results: The dynamics of subcutaneous xenograft growth in groups 1, 2, 3 and 4 significantly differed from the control group (p = 0.023). The average tumor volumes on the 39th day after the implantation in the control group and in experimental groups 1, 2, 3 and 4 were 1159.2, 895.3, 565.8, 80.7 and 76.7 mm3, respectively. The inhibition of tumor growth (ITG) was in direct proportion to the dose of the administered substance. Lower ITG(%) (32.4, 23.2 and 10.3% in experimental groups 2, 3 and 4, respectively) was associated with lower concentrations of О154 (0.55 mg/g, 0.055 mg/g and 0.0055 mg/g, respectively). Conclusions: The study demonstrated statistically significant differences in xenograft volume indices in all experimental groups compared to the control group.

Phytochemical Profiles, Physicochemical Analysis, and Biological Activity of Three Colchicum Species

Background: Colchicum is a genus of the Colchicaceae family with various isolated compounds, especially tropolone alkaloids and flavonoids, which are used for osteoarthritis, gout, cancer, inflammatory diseases, jaundice, and sexual impotence in different societies. Objectives: The current study aimed to evaluate the phytochemical and physicochemical properties and anti-inflammatory activities of three Colchicum species. Methods: Total tropolone alkaloid, total phenolic/total tannin, and total flavonoid contents were determined using acidic potassium dichromate, Folin-Ciocalteu, and aluminum chloride methods, respectively. Moreover, the HPLC method was used for identification and quantitation purposes of tropolone alkaloids. Physicochemical properties of three Colchicum species, including macroscopic and organoleptic properties, solubility, foreign matter, ash values, and heavy metal contents, were evaluated. Besides, in vitro anti-inflammatory activities of the corms also were determined using the protein denaturation technique as a rapid screening method. Results: The highest levels of tropolone alkaloid, phenolic compounds, tannins, and flavonoids were observed in C. autumnale, C. speciosum, and C. robustum, respectively. HPLC analysis indicated the presence of colchicine, demecolcine, 2-demethyl colchicine, 3-demethyl colchicine, colchicoside, colchifoline, cornigerine, and N-deacetyl-N-formyl colchicine in these Colchicum species. The physicochemical properties of C. speciosum and C. robustum corms are appropriate compared to the standard Colchicum autumnale corm. Moreover, all Colchicum species exhibited high anti-inflammatory activities compared to standard drugs. Conclusions: This study demonstrated that the corm of the Colchicum species contained similar main compounds with different amounts, as well as appropriate physicochemical properties. Moreover, the valuable biological effects of these plants stimulate the cultivations on a large scale.

Comparative LC-MS analysis of tropolone alkaloids from in vitro cultures and native sources of Gloriosa superba by Kendrick mass defect plots.

Gloriosa superba L. is a promising antitumoural plant species as a source of colchicinoids. Ethnobotanical applications of G. superba are associated with different plant parts such as leaves, seeds, fruits, tuber and the whole plant. A comparative phytochemical study of purified extracts from in vitro cultures and native tubers of G. superba was carried out by ultrahigh-performance liquid chromatography-high-resolution mass spectrometry (UHPLC-HR-MS) in combination with the mass defect filtering (MDF) technique. The individual compounds were tentatively annotated using database correlations, retention time (Rt), accurate m/z data obtained by electrospray ionisation (ESI) (+)-HR-MS, proposed elemental composition, ring double bond equivalent (RDBeq) values and HR-MS/MS fragmentation patterns. Moreover, the identification was based on transforming the exact mass ratio (m/z) for the protonated molecular ions [М + Н]+ of the observed metabolites in Kendrick nominal masses (NKMs) and calculation of the Kendrick mass defect (KMD), which made it possible to graphically present the ion peaks in Kendrick plots. Building Kendrick plots allows easy differentiation of small structural differences such as methylation or demethylation of compounds from the same homologous series. In this way, a wide range of tropolone alkaloids was characterised. A greater variety was observed in in vitro cultures, compared to native sources. This LC-MS analysis unambiguously demonstrated the presence of tropolone alkaloids in in vitro cultures of G. superba. This approach of LC-MS data interpretation can be used to understand complex mass spectra such as those of plant extracts.

Tropolone alkaloids from Colchicum kurdicum (Bornm.) Stef. (Colchicaceae) as the potent novel antileishmanial compounds; purification, structure elucidation, antileishmanial activities and molecular docking studies

Natural compounds played an important role for prevention and treatment of the disease as well as are the important compounds for the design of the new bioactive compounds. In this study, eight tropolone alkaloids were isolated from Colchicum kurdicum including colchicoside, 2-demethyl colchicine, 3-demethyl colchicine, demecolcine, colchifoline, N-deacetyl-N-formyl colchicine, colchicine and cornigerine by column and preparative thin layer chromatography. The chemical structures were identified by 1H NMR and 13C NMR spectroscopy. Moreover, the antileishmanial activity on Leishmania major, anti-inflammatory activity, iron chelating activity and toxicity studies including hemolytic activity, brine shrimp toxicity, cytotoxicity and acute toxicity and docking study of all isolated bioactive compounds were evaluated. As result, colchicoside and colchicine had potent leishmanicidal effects and N-deacetyl-N-formyl colchicine and cornigerine had the highest anti-inflammatory effects. All compounds had the significant iron chelating activity. According to toxicity studies, isolated compounds showed the low hemolytic activity and cytotoxicity, high LC50, LC90 and LD50. In the molecular docking study, colchicoside had the high dockscore. According to the study, with future studies all isolated compounds could be used for design the novel antileishmanial drugs.

Investigation of Mechanism Activity of Antitumor and Radiosensitizing Activity of Preparations К-26 and K-26w

Introduction. Tropolone alkaloid – colchicine, there is very interesting object for synthesis of its derivatives, with such properties as, alkylation, a low toxicity, high antineoplastic activity and especially overcoming of multidrug resistance (MDR). We had been developed the antineoplastic preparation К-26 derivative of colchicine. К-26 has shown high cytotoxic activity on 60 lines of tumoral cells of the human in vitro, at National Institute of the Cancer of the USA (NCI). Further on the basis of К-26 its water-soluble form named term К-26w has been received. The work purpose. Studying of the mechanism of action of preparations К-26 and К-26w on: alkylating ability, mitotic activity, topoisomerase II, MDR2, р53 and colony-forming cells spleen (CFCs). Materials and methods. All researches have been carrying out by a standard technique. Studying mitotic activity of preparations was carrying out on duodenum and tumor СаРа after preparation influence. On models of a tumor of the Sarcoma 180 action of preparations has been investigated: the alkylating - on synthesis DNA/RNA, nucleosoma DNA degradation, activity topoisomerase II; on an expression MDR2 and р53 genes. Studying CFCs carry out by a standard technique on outbred mice. Results. К-26, К-26w and etoposide inhibited in cells of the Sarcoma 180: synthesis DNA/RNA on 84/65%, 95/85% and 55/35%, accordingly, in relation to the control; activity topoisomerase II on 80%, 90% and 60% accordingly. By method RT-PCR it is shown, К-26, К-26w and etoposide: inhibited an expression of MDR2 gene on 83%, 91% and 62%; increase expression р53 gene to 74%, 88% and 55%, accordingly, under the relation of the control of referential gene GARDH (100%). High ability К-26 and К-26w in an induction apoptosis tumoral cells and CFCs to 12 units is shown. Conclusion. Revealed ability К-26 and К-26w to suppress synthesis DNA/RNA activity topoisomerases, to stimulate р53, and also to suppress an expression of a multidrug resistance MDR2 gene, it explains their high antineoplastic activity which is connected with mitotic activity leading to cell fission synchronization, and radiosensitization activity. Special interest represents found at К-26w and К-26 suppression MDR2 as they are aimed for treatment of such resistant tumor as a kidney cancer. Stimulation CFCs which provides formation of haemopoetic and immune cells can protect an organism from their intensive cytotoxic action.

Expanding the Rubterolone Family: Intrinsic Reactivity and Directed Diversification of PKS-derived Pyrans.

We characterized two key biosynthetic intermediates of the intriguing rubterolone family (tropolone alkaloids) that contain a highly reactive pyran moiety (in equilibrium with the hydrolyzed 1,5-dione form) and undergo spontaneous pyridine formation in the presence of primary amines. We exploited the intrinsic reactivity of the pyran moiety and isolated several new rubterolone derivatives, two of which contain a unique thiazolidine moiety. Three rubterolone derivatives were chemically modified with fluorescence and biotin tags using peptide coupling and click reaction. Overall, eight derivatives were fully characterized by HRMS/MS and 1D and 2D NMR spectroscopy and their antimicrobial, cytotoxic, anti-inflammatory and antiparasitic activities evaluated.

Chemical Constituents of the Different Parts of Colchicum micranthum and C. chalcedonicum and their Cytotoxic Activities

Colchicum species, which have been widely used as a medication for years, still remain important in treatment of Familial Mediterranean Fever, gout and Behcet's Disease. In the present work, alkaloids, phenolic compounds and cytotoxic activities from different parts of two Colchicum species, namely C. chalcedonicum and C. micranthum were investigated for the first time. From different parts of two species, alkaloids were isolated and colchicine concentrations were also determined by HPLC. The methanol extracts were investigated for their cytotoxic activity against the A549 cell line using the MTT and LDH methods. Additionally, the phenolic compounds of each extract were investigated by LC–MS/MS. Six alkaloids, namely colchicine, colchifoline, 2-demethylcolchicine, demecolcine, 4-hydroxycolchicine and N-deacetyl- N-formylcolchicine were isolated from different parts of two species. The autumn corm of C. micranthum possessed the highest amount of colchicine among all extracts. All extracts showed high cytotoxicity, while the highest toxicity was determined in the seed extract. According to the LC–MS/MS analysis, 19 phenolic compounds were shown to be present. This is the first study which highlights that the seeds of C. chalcedonicum and autumn corms of C. micranthum could be valuable for the pharmaceutical industry to obtain colchicine and other tropolone alkaloids.

Isolation, Biosynthesis and Chemical Modifications of Rubterolones A–F: Rare Tropolone Alkaloids from Actinomadura sp. 5‐2

The discovery of six new, highly substituted tropolone alkaloids, rubterolones A-F, from Actinomadura sp. 5-2, isolated from the gut of the fungus-growing termite Macrotermes natalensis is reported. Rubterolones were identified by using fungus-bacteria challenge assays and a HRMS-based dereplication strategy, and characterised by NMR and HRMS analyses and by X-ray crystallography. Feeding experiments and subsequent chemical derivatisation led to a first library of rubterolone derivatives (A-L). Genome sequencing and comparative analyses revealed their putative biosynthetic pathway, which was supported by feeding experiments. This study highlights how gut microbes can present a prolific source of secondary metabolites.

Quantum-chemical, NMR, FT IR, and ESI MS studies of complexes of colchicine with Zn(II)

Colchicine is a tropolone alkaloid from Colchicinum autumnale. It shows antifibrotic, antimitotic, and anti-inflammatory activities, and is used to treat gout and Mediterranean fever. In this work, complexes of colchicine with zinc(II) nitrate were synthesized and investigated using DFT, 1H and 13C NMR, FT IR, and ESI MS. The counterpoise-corrected and uncorrected interaction energies of these complexes were calculated. We also calculated their 1H, 13C NMR, and IR spectra and compared them with the corresponding experimentally obtained data. According to the ESI MS mass spectra, colchicine forms stable complexes with zinc(II) nitrate that have various stoichiometries: 2:1, 1:1:1, and 2:1:1 with respect to colchichine, Zn(II), and nitrate ion. All of the complexes were investigated using the quantum theory of atoms in molecules (QTAIM). The calculated and the measured spectra showed differences before and after the complexation process. Calculated electron densities and bond critical points indicated the presence of bonds between the ligands and the central cation in the investigated complexes that satisfied the quantum theory of atoms in molecules.Graphical DFT, NMR, FT IR, ESI MS, QTAIM and puckering studies of complexes of colchicine with Zn(II).

Non-enzymatic pyridine ring formation in the biosynthesis of the rubrolone tropolone alkaloids.

The pyridine ring is a potent pharmacophore in alkaloid natural products. Nonetheless, its biosynthetic pathways are poorly understood. Rubrolones A and B are tropolone alkaloid natural products possessing a unique tetra-substituted pyridine moiety. Here, we report the gene cluster and propose a biosynthetic pathway for rubrolones, identifying a key intermediate that accumulates upon inactivation of sugar biosynthetic genes. Critically, this intermediate was converted to the aglycones of rubrolones by non-enzymatic condensation and cyclization with either ammonia or anthranilic acid to generate the respective pyridine rings. We propose that this non-enzymatic reaction occurs via hydrolysis of the key intermediate, which possesses a 1,5-dione moiety as an amine acceptor capable of cyclization. This study suggests that 1,5-dione moieties may represent a general strategy for pyridine ring biosynthesis, and more broadly highlights the utility of non-enzymatic diversification for exploring and expanding natural product chemical space.

Repeated exposure to chlorpyrifos leads to prolonged impairments of axonal transport in the living rodent brain

The toxicity of the class of chemicals known as the organophosphates (OP) is most commonly attributed to the inhibition of the enzyme acetylcholinesterase. However, there is significant evidence that this mechanism may not account for all of the deleterious neurologic and neurobehavioral symptoms of OP exposure, especially those associated with levels that produce no overt signs of acute toxicity. In the study described here we evaluated the effects of the commonly used OP-pesticide, chlorpyrifos (CPF) on axonal transport in the brains of living rats using manganese (Mn2+)-enhanced magnetic resonance imaging (MEMRI) of the optic nerve (ON) projections from the retina to the superior colliculus (SC). T1-weighted MEMRI scans were evaluated at 6 and 24h after intravitreal injection of Mn2+. As a positive control for axonal transport deficits, initial studies were conducted with the tropolone alkaloid colchicine administered by intravitreal injection. In subsequent studies both single and repeated exposures to CPF were evaluated for effects on axonal transport using MEMRI. As expected, intravitreal injection of colchicine (2.5μg) produced a robust decrease in transport of Mn2+ along the optic nerve (ON) and to the superior colliculus (SC) (as indicated by the reduced MEMRI contrast). A single subcutaneous (s.c.) injection of CPF (18.0mg/kg) was not associated with significant alterations in the transport of Mn2+. Conversely, 14-days of repeated s.c. exposure to CPF (18.0mg/kg/day) was associated with decreased transport of Mn2+ along the ONs and to the SC, an effect that was also present after a 30-day (CPF-free) washout period. These results indicate that repeated exposures to a commonly used pesticide, CPF can result in persistent alterations in axonal transport in the living mammalian brain. Given the fundamental importance of axonal transport to neuronal function, these observations may (at least in part) explain some of the long term neurological deficits that have been observed in humans who have been repeatedly exposed to doses of OPs not associated with acute toxicity.

1037 Cytostatic agents, radiosesitizers and immunomodulators derived from tropolone alkaloids

1037 Cytostatic agents, radiosesitizers and immunomodulators derived from tropolone alkaloids

CYTOTOXICITY OF COLCHICINE DERIVATIVES IN PRIMARY CULTURES OF HUMAN HEPATOCYTES

Colchicine has been used to treat gout for centuries. However, owing to its toxicity it displays a variety of side effects. The replacement of colchicine by less toxic but still active derivatives would solve this drawback. The aim of this study was to examine the cytotoxicity of 17 colchicine derivatives. Primary cultures of human hepatocytes were the model of choice. Prior to testing, we measured the biochemical parameters of liver donors and the toxicological response of the hepatocytes cultures. For toxicity testing, cells were treated for 24 h with tested compounds in concentrations 1-100 microM. We monitored lactate dehydrogenase (LDH) leakage into the medium, mitochondrial activity (MTT test) and secretion of albumin. Our data show that LDH and MTT were less sensitive parameters compared to albumin secretion for monitoring the toxicity of colchicine derivatives. Compounds with lower antimitotic activity displayed lowered toxicity. Since human hepatocytes in culture are quiescent cells, they are not as susceptible to tropolone alkaloids as proliferating cells. Screening for colchicine derivatives with lowered cytotoxicity revealed that 10-O-demethylated compounds might be the substances of choice.

Anticholinesterase Efficiency of Some Tropolone Alkaloids and Their Lumiderivatives

Anticholinesterase Efficiency of Some Tropolone Alkaloids and Their Lumiderivatives

New homoaporphine base from Merendera robusta

The alkaloid composition of the bulb casing of Merendera robusta Bge. (Liliaceae) was investigated. The tropolone alkaloid colchicine was identified. A new homoaporphine base for which the structure methylmerenderine hydroxide was established by spectral and chemical methods was isolated.

Seasonal and spatial variations of alkaloids in Merendera montana in relation to chemical defense and phenology.

Merendera montana (Liliaceae) is an endemic plant broadly, but exclusively, occurring in the Iberian Peninsula where it is one of the most abundant species in rangelands grazed by sheep and on the routes used by migrating sheep herds. In spite of showing a peculiar phenology adapted to Mediterranean regions (leaves remain green from fall to spring and are absent in summer), this species has also successfully colonized high altitude environments (up to 2300 m), and abundant populations can be found in montane and subalpine pasturcs. Chemical analysis has shown a high forage quality as well as the presence of tropolone alkaloids (similar to other species of the genus Merendera), mainly colchicine, 3-demethylcolchicine, and colchicoside. In general terms, the alkaloid content was significantly lower in the subterranean corms than in the leaves. No remarkable seasonal variations in total alkaloids was found, although an increase of colchicoside in the corms and a decrease of colchicine was noted in summer. Both chemical deterrents and phenology could be the cause of the widespread ecological adaptation of Merendera montana. The alkaloid content would prevent intake by wild herbivores during winter, while the absence of aerial organs in summer, coinciding exactly with the highest domestic herbivore pressure, would permit this species to colonize rich soil habitats where there is low plant competition.

X-Ray structural investigation of the alkaloid speciosine

The molecular and crystalline structures of a tropolone alkaloid of the colchicine series — speciosine — have been determined by x-ray structural analysis. It has been established that the presence of an orthohydroxyphenyl group does not lead to appreciable changes of the colchicine skeleton in the speciosine molecule. In the crystals, the speciosine molecules are linked into zigzag chains through O6−H…O1 intermolecular H-bonds.

N-oxides of homoaporphine alkaloids from Merendera raddeana

The alkaloid complex of the leaves, stems, seeds, and seed pods ofMerendera raddeana Rgl. (familyLiliaceae) has been investigated. A number of known tropolone alkaloids and their photochemical isomers have been isolated together with the homoaporphine bases merenderine, kreysiginine, and O-methyl-kreysiginine and their N-oxides, which have not been described in the literature. One of them (merenderine N-oxide) has been characterized by its physical constants and has been investigated by IR, PMR, and mass-spectral methods. By a study of the PMR spectrum of the fraction of neutral alkaloids from the leaves of the plant it has been established that it consists mainly of a mixture of equal amounts of colchicine and cornigerine.

2,10-Didemethylcolchicine ? A new alkaloid from Merendera robusta

The alkaloid complex ofMerendera robusta Bge. (familyLiliaceae) growing in the Tashkent province of the Uzbek SSR has been investigated. The main alkaloids of this plant are colchicine and colchamine. Eleven tropolone alkaloids and their photochemical isomers have been isolated and identified. A new alkaloid of phenolic nature has been isolated for which the structure of 2,10-didemethylcolchicine has been established.

Photochemical isomers of tropolone alkaloids

This review, which covers the literature up to 1989, generalizes advances in the field of the study of the photochemical isomers of colchicine and tropolone alkaloids related to it. Information is given on their natural sources, methods of isolation, structure, and configuration, and photochemical and thermal interconversions. Characteristics distinguishing them from the topolone alkaloids in their UV, IR, mass, and2H and13C NMR spectra of the photochemical isomers are pointed out.