Fascioquinols A-F: bioactive meroterpenes from a deep-water southern Australian marine sponge, Fasciospongia sp.

Chemical investigation of a southern Australian deep-water marine sponge, Fasciospongia sp., returned the new meroterpene sulfate fascioquinol A (1) together with a series of acid mediated hydrolysis/cyclization products, fascioquinols B (2), C (3) and D (4), and strongylophorine-22 (5). Additional co-metabolites include the new meroterpenes fascioquinol E (6) and fascioquinol F (8), together with the known sponge metabolite geranylgeranyl 1,4-hydroquinone (7). Structures were assigned to 1-8 on the basis of detailed spectroscopic analysis, chemical interconversion, mechanistic and biosynthetic considerations, and literature comparisons. The known 1,4-hydroquinone 7 was identified as the dominant cytotoxic principle in the Fasciospongia sp. extract, with selective inhibitory activity against gastric adenocarcinoma (AGS, IC₅₀ 8 μM) and neuroblastoma (SH-SY5Y, IC₅₀ 4 μM) cell lines. By contrast, while the fascioquinols displayed little or no inhibitory activity towards human cell lines, 1 and 2 displayed promising Gram-positive selective antibacterial activity towards Staphylococcus aureus (IC₅₀ 0.9-2.5 μM) and Bacillus subtilis (IC₅₀ 0.3-7.0 μM).     

Synthesis and biological evaluation of analogs of altohyrtin C (spongistatin 2)

Several structural analogs that contain only part of the altohyrtin structure have been prepared and compared with synthetic altohyrtin C (2) for in vitro cytotoxicity against human colon (HCT116) and ovarian (A2780) cell lines. Whereas altohyrtin C was found to be exceedingly potent against these lines (IC₅₀=0.0003 μM), analogs 3-5 were >27,000-fold less potent (IC₅₀>8 μM). Analogs 6 and 7 also demonstrated weak cytotoxicity with IC₅₀ values for the HCT116 and A2780 cells of 4.8 μM and 2.4 μM, respectively, for 6.     

Isolation, structure elucidation and bioactivity of schischkiniin, a unique indole alkaloid from the seeds of Centaurea schischkinii

Reversed-phase HPLC analysis of the methanol extract of the seeds of Centaurea schischkinii afforded a novel indole alkaloid, named schischkiniin (1), together with four lignans, arctiin (2), matairesinoside (3), matairesinol (4), and arctigenin (5), and three flavonoids, astragalin (6), afzelin (7) and apigenin (8). While the structure of schiskiniin (1) was established unequivocally by UV, HRFABMS and a series of 1D and 2D NMR analyses, all known compounds were readily identified by comparison of their spectroscopic data with literature data. The free radical scavenging properties of these compounds were assessed using the DPPH assay, and their general toxicity and cytotoxicity were evaluated, respectively, by brine shrimp lethality and MTT cytotoxicity assays with CaCo-2 colon cancer cell lines. Arctigenin (5) exhibited promising in vitro anticancer activity (IC₅₀=7 μM) while with schischkiniin (1) the activity was of moderate level (IC₅₀=76 μM).     

The synthesis, structural characterization and in vitro anti-cancer activity of novel N-(3-ferrocenyl-2-naphthoyl) dipeptide ethyl esters and novel N-(6-ferrocenyl-2-naphthoyl) dipeptide ethyl esters

N-(3-ferrocenyl-2-naphthoyl) dipeptide esters (5-7) and N-(6-ferrocenyl-2-naphthoyl) dipeptide esters (8-10) were prepared by coupling either 3-ferrocenylnaphthalene-2-carboxylic acid 2 or 6-ferrocenylnaphthalene-2-carboxylic acid 4 to the dipeptide ethyl esters GlyAla(OEt) (5, 8), AlaGly(OEt) (6, 9), and AlaAla(OEt) (7, 10) using the standard N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC), 1-hydroxybenzotriazole (HOBt) protocol. All the compounds were fully characterized using a combination of ¹H NMR, ¹³C NMR, DEPT-135 and ¹H-¹³C COSY (HMQC) spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and cyclic voltammetry (CV). In vitro, the cytotoxic effects of compounds 5-10 show improvements over the corresponding N-(ferrocenyl)benzoyl derivatives, with IC₅₀ values against the H1299 lung cancer cells ranging from 1.2 μM to 8.0 μM. N-(6-ferrocenyl-2-naphthoyl)-glycine-l-alanine ethyl ester 8 was found to be the most active derivative of the naphthoyl series so far, displaying an IC₅₀ value of 1.3 ± 0.1 μM. This value is slightly lower than that found for the clinically employed anti-cancer drug cisplatin (IC₅₀ = 1.5 ± 0.1 μM against H1299).     

Malbrancheamide, a new calmodulin inhibitor from the fungus Malbranchea aurantiaca

Bioassay-directed fractionation of an ethyl acetate extract (mycelia and broth) of the fungus Malbranchea aurantiaca led to the isolation of the novel phytotoxic alkaloid (5aS,12aS,13aS)-8,9-dichloro-12,12-dimethyl-2,3,11,12,12a,13-hexahydro-1H,6H-5a,13a (epiminomethano)indolizino[7,6b]carbazol-14-one (1) of the brevianamide series. The phytotoxin was given the trivial name of malbrancheamide (1). The structure of 1 was unequivocally established by UV, NMR, MS and X-ray studies. The absolute configuration was established by X-ray analysis according to the method of Flack. According to the conformational studies using molecular mechanics analyses, 1 exists in one preferred conformation, which was optimized by DFT calculations. Compound 1 caused moderate inhibition of radicle growth of Amaranthus hypochondriacus (IC₅₀=0.37 μM) and inhibited the activation of the calmodulin-dependent enzyme PDE1 (IC₅₀=3.65±0.74 μM). This effect was comparable to that of chlorpromazine (IC₅₀=2.75±0.87 μM) a well characterized CaM antagonist. The inhibition mechanism of 1 was competitive with respect to CaM according to a kinetic analysis.     

Synthesis and cytotoxicity studies of new dimethylamino-functionalised and heteroaryl-substituted titanocene anti-cancer drugs

From the carbolithiation of N,N-dimethylamino fulvene (3a) and different ortho-lithiated heterocycles (furan, thiophene and N-methylpyrrole), the corresponding lithium cyclopentadienide intermediate (4a-c) was formed. These three lithiated intermediates underwent a transmetallation reaction with TiCl₄ resulting in dimethylamino-functionalised titanocenes 5a-c. When these titanocenes were tested against LLC-PK cells, the IC₅₀ values obtained were of 240, and 28 μM for titanocenes 5a and 5b, respectively. The most cytotoxic titanocene 5c with an IC₅₀ value of 5.5 μM is found to be almost as cytotoxic as cis-platin, which showed an IC₅₀ value of 3.3 μM, when tested on the LLC-PK cell line, and titanocene 5c is approximately 400 times better than titanocene dichloride itself.     

Lissoclibadins 1-3, three new polysulfur alkaloids, from the ascidian Lissoclinum cf. badium

Three new polysulfur alkaloids, lissoclibadins 1 (1)-3 (3), were isolated from the ascidian Lissoclinum sp. (cf. L. badium Monniot, F. and Monniot, C., 1996). The structures of 1-3 were assigned on the basis of their spectral data, and the computational modeling study was utilized for 1. Compound 1 had a trimeric structure of three identical aromatic anime moieties connected through two sulfide and a disulfide bonds. Compounds 2 and 3 were dimeric structures of the same unit as that of 1 connected through a sulfide and disulfide bonds (2) and two sulfide bonds (3). Compounds 1 and 2 inhibited the growth of the marine bacterium Ruegeria atlantica (15.2 mm at 20 μg/disk and 12.2 mm at 5 μg/disk, respectively) and 2 showed antifungal activity to Mucor hiemalis (13.8 mm at 50 μg/disk). Compounds 1-3 were cytotoxic against HL-60 (IC₅₀=0.37, 0.21, and 5.5 μM, respectively).     

Synthesis and DNA-binding properties of apoptosis-inducing cytotoxic half-sandwich rhodium(III) complexes with methyl-substituted polypyridyl ligands

Half-sandwich organorhodium(III) complexes of the type [(η⁵-C₅Me₅)RhCl(pp)] (CF₃SO₃) containing polypyridyl ligands (pp) represent a promising class of cytostatic agents. Replacement of the polypyridyl ligands of complexes 1 (pp = phen) and 6 (pp = dppz) by methyl-substituted derivatives in 2-5 (pp = 4-Mephen, 5-Mephen, 4,7-Me₂phen, 5,6-Me₂phen) and 7 (pp = Me₂dppz) leads to a significant improvement in their antiproliferative activity towards human MCF-7 and HT-29 cancer cells. For instance, the IC₅₀ value towards HT-29 cells decreases from 4.3 ± 0.2 μM for 6 to 0.98 ± 0.49 μM for complex 7. In contrast, no activity (IC₅₀ > 100 μM) was observed for the HOOC and n-BuNHCO substituted dppz complexes 8 and 9. UV/vis, CD and NMR spectra for mixtures of complexes 7-9 with CT DNA were in accordance with intercalation of the substituted dppz ligands between the base pairs of the double helix and direct evidence for this binding mode was also provided by a 2D NOESY study for complex 7 with the hexanucleotide d(5′-CGTCGG-3′). Each of the methyl-substituted phen complexes 2-5 is significantly more active towards immortalized HEK-293 cells (IC₅₀ values 0.40 ± 0.02 to 0.94 ± 0.02 μM) than towards the cancer cells. Flow cytometric measurements of DNA fragmentation in BJAB cells following an incubation period of 72 h with 1, 5 and 6 indicate that the complexes induce specific apoptotic cell death in the non-adherent lymphoma cells.     

Organometallic SERMs (selective estrogen receptor modulators): Cobaltifens, the (cyclobutadiene)cobalt analogues of hydroxytamoxifen

The McMurry coupling of (tetraphenylcyclobutadiene)cobalt(cyclopentadienyl) ketones, (C₄Ph₄)Co[C₅H₄C(O)R], where R = Me, 3a, or Et, 3b, with a range of substituted benzophenones furnished a series of cobaltifens, organometallic analogues of tamoxifen whereby a phenyl ring has been replaced by an organo-cobalt sandwich moiety. These systems of the general formula (η⁴-C₄Ph₄)Co[η⁵-C₅H₄C(R)C(Ar)Ar′], where R = Me or Et, and Ar = Ar′ = p-C₆H₄X where X is OH, 2a and 2b, OMe, 2c and 2d, OBn, 2e and 2f, or O(CH₂)₂NMe₂, 12a and 12b, and where Ar = C₆H₄OH and Ar′ = C₆H₄O(CH₂)₂NMe₂, 2g and 2h, have been characterised by NMR spectroscopy and/or X-ray crystallography. The effect of 2a and 2b, 2g and 2h, and 12a and 12b on the growth of MCF-7 (hormone-dependent) and MDA-MB-231 (hormone-independent breast cancer cells) was studied. The dihydroxycobaltifens 2a and 2b exhibit a strong estrogenic effect on MCF-7 cells while the aminoalkyl-hydroxycobaltifens, 2g and 2h, were found to be only slightly cytotoxic on MDA-MB-231 cells (IC₅₀ = 27.5 and 17 μM); surprisingly, however, the bis-(dimethylaminoethoxy)cobaltifens, 12a and 12b were shown to be highly cytotoxic towards both cell lines (IC₅₀ = 3.8 and 2.5 μM).     

Photocytotoxic and anaerobic DNA cleavage activity of binuclear 3,3′-dithiodipropionic acid cobalt(II) complexes having phenanthroline bases

Dicobalt(II) complexes [{(B)Co^II}₂(μ-dtdp)₂] (1–3) of 3,3′-dithiodipropionic acid (dtdp) and phenanthroline bases (B), viz. 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3), have been prepared, characterized and their photo-induced anaerobic DNA cleavage activity studied. The elemental analysis and mass spectral data suggest binuclear formulation of the complexes. The redox inactive complexes have magnetically non-interacting dicobalt(II) core showing magnetic moment of ∼3.9 μ_B per cobalt(II) center. The complexes show good binding propensity to calf thymus DNA giving K_b values within 4.3 × 10⁵–4.0 × 10⁶ M⁻¹. Thermal melting and viscosity data predict DNA groove binding and/or partial intercalative nature of the complexes. The complexes show significant anaerobic DNA cleavage activity in green light under argon atmosphere possibly involving radical species generated from the disulfide moiety in a type-I pathway. The DNA cleavage reaction under aerobic medium in green light is found to involve hydroxyl radical species. The dppz complex 3 exhibits significant photocytotoxicity in HeLa cervical cancer cells with an IC₅₀ value of 2.3 μM in UV-A light of 365 nm, while it is essentially non-toxic in dark giving an IC₅₀ value of >200 μM. A significant reduction of the dark toxicity of the organic dppz base (IC₅₀ = 8.3 μM in dark) is observed on binding to the cobalt(II) center while essentially retaining its photocytotoxicity in UV-A light (IC₅₀ = 0.4 μM).     

Cytotoxic half-sandwich rhodium(III) complexes: Polypyridyl ligand influence on their DNA binding properties and cellular uptake

The DNA binding of polypyridyl (pp) (η⁵-C₅Me₅)Rh^III complexes of the types [(η⁵-C₅Me₅)RhCl(pp)](CF₃SO₃) (2-6) (pp = bpy, phen, dpq, dppz, dppn), [(η⁵-C₅Me₅)Rh{(Me₂N)₂CS}(pp)](CF₃SO₃)₂ (7-9) (pp = dpq, dppz, dppn) and [(η⁵-C₅Me₅)Rh(L)(pp)](CF₃SO₃) (10) (L = C₆H₅S⁻) and (11) (L = C₁₀H₇S⁻) has been studied by UV/Vis spectroscopy, circular dichroismus and viscosity measurements. Complexes 3-11 are cytotoxic towards the human MCF-7 breast and HT-29 colon cancer cell lines and exhibit IC₅₀ values in the range 0.56-10.7 μM. Stable intercalative binding into CT-DNA is indicated for the dpq and dppz complexes by large increases ΔT_m of 6-12 °C in the DNA thermal denaturation temperature for r = [complex]/[DNA] = 0.1 and by induced CD bands and large viscosity increases. In contrast, significant DNA lengthening is not observed after incubation of the biopolymer with the dppn complexes 2 and 9 at molar ratios of r < 0.08. Pronounced hypochromic shifts for the π-π^∗ transitions of the dppn ligands in the range 320-425 nm indicate the possible presence of surface stacking. The in vitro cytotoxicities of the chloro complexes 4-6 and the (Me₂N)₂CS complexes 7-9 are dependent on the size of the polypyridyl ligand with IC₅₀ values decreasing in the order dpq > dppz > dppn. For instance, IC₅₀ values of 5.3, 1.5 and 0.91 μM were determined for 7-9 against MCF-7 cells. Rapid Cl⁻/H₂O exchange leads the formation of aqua dications for 4-6, whose levels of cellular uptake and cytotoxicities are similar to those established for 7-9. Intramolecular interactions between the aromatic thiolate and dppz ligands of 10 and 11 prevent significant DNA intercalation. X-ray structural determinations have been performed for 2-7 and 11.     

Synthesis, X-ray crystal structure and cytotoxicity of a new tetranuclear ruthenium arene complex

The tetranuclear ruthenium arene compound [(cym)₄Ru₄(2)Cl₆]Cl₂ (3) (cym = η⁶-p-cymene, 2 = 1,2-bis(di-N-methylimidazol-2-ylphosphino)ethane) was prepared and characterised by one- and two-dimensional NMR techniques. Its cytotoxicity against four different cell lines was determined and, with an approximate IC₅₀ of >100 μM 3 can be regarded as non-toxic. Its partition coefficient in n-octanol/water (log D_7.4) was also determined. The structures of complex 3 as well as of the related compound [(cym)₂Ru₂(4)Cl₂]Cl₂ (5) (4 = 1,2-bis(di-N-methylimidazol-2-ylphosphino)ethane dioxide) were determined by single crystal structure analysis. Upon oxidation in protic solvents, ligand 2 shows P-C bond cleavage reactions to yield P,P′-bis(N-methylimidazol-2-yl)ethylene diphosphinic acid (6).     

Polyketides from the mangrove-derived endophytic fungus Acremonium strictum

Five new polyketide derivatives, 6′-hydroxypestalotiopsone C (1), acropyrone (2), bicytosporone D (3), waol acid (4), and pestalotiopene C (5), together with seven known metabolites (6–12), were obtained from extracts of the endophytic fungus Acremonium strictum, isolated from the mangrove tree Rhizophora apiculata. The structures of the isolated compounds were elucidated on the basis of comprehensive NMR and MS analysis. Compounds 6, 7, and 9 showed moderate cytotoxic activity against human cisplatin-sensitive (IC₅₀ values 27.1, 76.2, and 8.3 μM, respectively) and resistant A2780 cell lines (IC₅₀ values 12.6, 30.1, and 19.0 μM, respectively), whereas only 9 exhibited antibacterial activity against Staphylococcus aureus (MIC value 14.3 μM).     

Bistabercarpamines A and B,first vobasinyl-chippiine-type bisindole alkaloid from Tabernaemontana corymbosa

Two novel dimeric monoterpene indole alkaloids, bistabercarpamines A (1) and B (2) possessing unprecedented bis-vobasinyl-chippiine-type skeleton, were isolated from the leaves of Tabernaemontana corymbosa. The structures were elucidated on the basis of spectroscopic data, and the absolute configurations of these isolates were determined by CD excition chirality method. Bistabercarpamine A (1) exhibited moderate cell growth inhibitory activity against HepG-2 cells with IC₅₀ of 38.14 ± 1.1 μM.     

Proteasome-inhibitory and cytotoxic constituents of Garcinia lateriflora: absolute configuration of caged xanthones

A new biflavonoid (1), a new xanthone enantiomer (2), five new caged xanthones (3-7), and several known compounds were isolated from the stem bark of Garcinia lateriflora, collected in Indonesia. The structures of the new compounds were determined by analysis of spectroscopic data, and the absolute configuration of the caged xanthones was shown for the first time at carbons 5, 7, 8, 8a, 10a, and 27, by analysis of COSY and NOESY NMR and ECD spectra. The biflavonoids exhibited proteasome-inhibitory activity, and the known compound, morelloflavone (8) was found to have the greatest potency (IC₅₀=1.3 μM). The caged xanthones were cytotoxic toward HT-29 cells, with the known compound, morellic acid (10) being the most active (ED₅₀=0.36 μM). However, when tested in an in vivo hollow fiber assay, it was inactive at the highest dose tested (20 mg/kg).     

Dinuclear copper(II) perchlorate complexes with 6-(benzylamino)purine derivatives: Synthesis,X-ray structure,magnetism and antiradical activity

The reactions of Cu(ClO₄)₂·6H₂O with 6-(benzylamino)purine derivatives in a stoichiometric 1:2 metal-to-ligand ratio led to the formation of penta-coordinated dinuclear complexes of the formula [Cu₂(μ-L^1–8)₄(ClO₄)₂](ClO₄)₂·nsolv, where L¹ = 6-(2-fluorobenzylamino)purine (complex 1), L² = 6-(3-fluorobenzylamino)purine (2), L³ = 6-(4-fluorobenzylamino)purine (3), L⁴ = 6-(2-chlorobenzylamino)purine (4), L⁵ = 6-(3-chlorobenzylamino)purine (5), L⁶ = 6-(4-chlorobenzylamino)purine (6), L⁷ = 6-(3-methoxybenzylamino)purine (7) and L⁸ = 6-(4-methoxybenzylamino)purine (8); n = 0–4 and solv = H₂O, EtOH or MeOH. All the complexes have been fully characterized by elemental analysis, FTIR, UV–Vis and EPR spectroscopy, and by magnetic and conductivity measurements. Variable temperature (80–300 K) magnetic susceptibility data of 1–8 showed the presence of a strong antiferromagnetic exchange interaction between two Cu(II) (S = 1/2) atoms with J ranging from −150.0(1) to −160.3(2) cm⁻¹. The compound 6·4EtOH·H₂O was structurally characterized by single crystal X-ray analysis. The Cu?Cu separation has been found to be 2.9092(8) Å. The antiradical activity of the prepared compounds was tested by in vitro SOD-mimic assay with IC₅₀ in the range 8.67–41.45 μM. The results of an in vivo antidiabetic activity assay were inconclusive and the glycaemia in pre-treated animals did not differ significantly from the positive control.     

Two novel diterpenoids from Isodon rubescens var. lushanensis

Two novel diterpenoids, luanchunins A (1) and B (2), along with their precursor, kamebakaurin (3), had been isolated from the stems and leaves of Isodon rubescens var. lushanensis. Their structures were elucidated on the basis of extensive spectroscopic analyses. Compounds 1 and 2 showed potent cytotoxic activity against HL-60 with IC₅₀ values of 4.81 μM and 3.52 μM, respectively. Plausible pathways for the biosynthesis of 1 and 2 were also postulated.     

Organometallic diphenols: The importance of the organometallic moiety on the expression of a cytotoxic effect on breast cancer cells

We have recently reported that the ferrocenyl diphenol compound 1,1-di(4-hydroxyphenyl)-2-ferrocenyl-but-1-ene 1 exhibited strong in vitro anti-proliferative effects on both hormone dependent (MCF7, IC₅₀ = 0.7 μM) and hormone independent (MDA-MB231, IC₅₀ = 0.6 μM) breast cancer cells. In order to assess the importance of the ferrocenyl motif, we have prepared a series of analogs using the organometallic fragments (η⁵-C₅H₄)Cp^∗Fe (7), ((η⁵-C₅H₄)(CH₃)₂phospholyl)Fe (9), (η⁵-C₅H₄)CpRu (10), (η⁵-C₅H₄)Re(CO)₃ (11), and (η⁵-C₅H₄)Mn(CO)₃ (12), and the chlorinated ferrocenyl derivative 1,1-di(4-hydroxyphenyl)-2-ferrocenyl-4-chloro-but-1-ene (4). The nature of the organometallic moiety had a strong influence on estrogen receptor alpha (ERα) recognition, with relative binding affinity (RBA) values ranging from 0.55% to 10.8%. The second isoform of the estrogen receptor, ERβ, was better able to accommodate these compounds, with RBA values ranging from 8.9% to 17.1%. Molecular modeling studies suggest that the orientation of the compounds and their interactions with the residues of ERα and ERβ binding sites are very similar. A study on the MCF7 hormone dependent breast cancer cell line revealed an anti-proliferative effect for the ferrocenyl phenols 1 and 4, while the other compounds displayed either a proliferative effect (9-12), or no effect (7). The anti-proliferative effect of 1 and 4 is also evident in the MDA-MB231 hormone independent breast cancer cell line (IC₅₀(4) = 1 μM), and can be attributed to the cytotoxicity of these compounds, while the other compounds showed no effect on this cell line. The cytotoxicity of 1 and 4 may arise from electron delocalization in the radical cation in alkaline conditions, possibly resulting in a cytotoxic quinone methide formation, while the other complexes do not undergo the formation of this entity, as evidenced by the electrochemical results.