Synthesis of seven- and eight-membered [1,2-a] alicyclic ring-fused benzimidazoles and 3-aziridinylazepino[1,2-a]benzimidazolequinone as a potential antitumour agent

Azepino and azocino[1,2-a]benzimidazoles were obtained either by treatment of 1-nitrophenyl-2-azacycloalkanes via a one-pot catalytic hydrogenation/acetylation or by treatment of the acetamides generated in the latter reaction with performic acid. This represents the first facile synthesis of eight-membered [1,2-a] alicyclic ring-fused benzimidazoles. 3-Methoxy-azepino[1,2-a]benzimidazole was elaborated to the novel potential cytotoxin, 3-(N-aziridinyl)-7,8,9,10-tetrahydro-6H-azepino[1,2-a]benzimidazole-1,4-dione. The synthesis included clarification of the reactivity of methoxy-substituted benzimidazoles towards nitration.     

Synthesis and relaxometric studies of a dendrimer-based pH-responsive MRI contrast agent

The design of effective pH responsive MRI contrast agents is a key goal in the development of new diagnostic methods for conditions such as kidney disease and cancer. A key factor determining the effectiveness of an agent is the difference between the relaxivity of the "on" state compared to that of the "off" state. In this paper, we demonstrate that it is possible to improve the pH-responsive action of a low molecular weight agent by conjugating it to a macromolecular construct. The synthesis of a bifunctional pH responsive agent is reported. As part of that synthetic pathway we examine the Ing-Manske reaction, identifying an undesirable by-product and establishing effective conditions for promoting a clean and effective reaction. Reaction of the bifunctional pH responsive agent with a G5-PAMAM dendrimer yielded a product with an average of 96 chelates per dendrimer. The relaxivity of the dendrimer conjugate rises from 10.8 mM(-1) s(-1) (pH 9) to 24.0 mM(-1) s(-1) (pH 6) per Gd(3+) ion. This more than doubles the relaxivity pH response, Deltar(1), of our agent from just 51 % for the original low molecular weight chelate to 122 % for the dendrimer.     

Synthesis of diaminopimelic acid containing peptidoglycan fragments and tracheal cytotoxin (TCT) and investigation of their biological functions

Bacterial cell wall peptidoglycan (PGN) is a potent immunostimulator and immune adjuvant. The PGN of Gram-negative bacteria and some Gram-positive bacteria contain meso-diaminopimelic acid (meso-DAP), and we have recently shown that the intracellular protein Nod1 is a PGN receptor and recognizes DAP-containing peptides. In this study, we achieved the synthesis of DAP-containing PGN fragments, including the first chemical synthesis of tracheal cytotoxin (TCT), GlcNAc-(beta1-4)-(anhydro)MurNAc-L-Ala-gamma-D-Glu-meso-DAP-D-Ala, and a repeating-unit of DAP-type PGN, GlcNAc-(beta1-4)-MurNAc-L-Ala-gamma-D-Glu-meso-DAP-D-Ala. For the synthesis of PGN fragments, we first established a new synthetic method for an orthogonally protected meso-DAP derivative, and then we constructed the glycopeptide structures. The ability of these fragments to stimulate human Nod1, as well as differences in Nod1 recognition of the variety of synthesized ligand structures were examined. The results showed that the substitution of the N terminus of iE-DAP is necessary for stronger Nod1 recognition, but the structure of the substituent seems not to be strictly recognized. The importance of the carboxyl group at the 2-position of DAP for human Nod1 stimulation was also shown.     

Purification and Characterization of Cytotoxin Produced by a Clinical Isolate of Vibrio cholerae O54 TV113

Vibrio cholerae O54 TV113 isolated from a diarrheal patient produces an extracellular cytotoxin that caused alteration in the morphology of Chinese hamster ovary cells manifested as cell shrinkage with intact cell boundaries and finally causing cell death. Syncase medium supplemented with lincomycin (50???g/ml), pH 7.2, and 18?h incubation with shaking at 37?°C supported optimal cytotoxin production. We isolated and purified this cytotoxin to homogeneity by ultrafiltration, 40?C80?% ammonium sulfate precipitation, gradient?Canion exchange chromatography, stepwise-anion exchange chromatography, and size exclusion chromatography increasing the specific activity by 866-fold. The cytotoxin is heat-labile, sensitive to protease and papain, and has a molecular weight of 64?kDa determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and enterotoxic activity in rabbit ileal loop assay. Both cytotoxic and enterotoxic activity could be inhibited or neutralized by antiserum raised against purified cytotoxin but not by preimmune serum. Immunodiffusion test between purified cytotoxin and its antiserum gave a single well-defined precipitin band showing reaction of complete identity and a well-defined single band in an immunoblot assay. This study thus indicate that the cytotoxin expressed by strain TV113 has both cytotoxic and enterotoxic activity and appears to contribute in pathogenesis of non-O1, non-O139 strains.     

Total Synthesis of (-)-Irciniastatin B and Structural Confirmation via Chemical Conversion to (+)-Irciniastatin A (Psymberin)

The total synthesis and structural confirmation of the marine sponge cytotoxin (-)-irciniastatin B has been achieved via a unified strategy employing a late-stage, selective deprotection/oxidation sequence that provides access to both (+)-irciniastatin A (psymberin) and (-)-irciniastatin B.     

Total synthesis of (+/-)fasicularin via a 2-amidoacrolein cycloaddition

The total synthesis of the cytotoxin fasicularin is described. The key steps include the following: (1) an intermolecular Diels-Alder cycloaddition of a 2-(triflamido)acrolein with the dioxolane ketal of trideca-1,3-dien-7-one to establish the trans-perhydroisoquinoline stereochemistry, (2) a stereoelectronically controlled hydride addition to a N(1)-C(2) iminium ion to introduce the equatorial hexyl substituent, and (3) elaboration of the pyrido ring by an internal aldol reaction.     

Steered molecular dynamics simulations of cobra cytotoxin interaction with zwitterionic lipid bilayer: no penetration of loop tips into membranes

Cobra cytotoxins, small proteins of three-fingered toxin family, unspecifically damage membranes in different cells and artificial vesicles. However, the molecular mechanism of this damage is not yet completely understood. We used steered molecular dynamics simulations to study the interaction of cardiotoxin A3 from Naja atra cobra venom with hydrated 1-palmitoyl-2-oleoyl-1-sn-3-phosphatidylcholine (POPC) bilayer. The studied system included one cytotoxin molecule, 64 lipid molecules (32 molecules in each monolayer) and 2500 water molecules. It was found that the toxin interacted with zwitterionic bilayer formed by POPC. During first nanosecond of simulation the toxin molecule was oriented toward membrane surface by loops' basement including cytotoxin regions Cys14-Asn19 and Cys38-Ser46. This orientation was stable enough and was not changed during next 6 ns of simulation. The obtained data suggest that cytotoxin molecule cannot penetrate into membrane composed of zwitterionic lipids without some auxiliary interaction.     

Structure and stereochemistry of a new cytotoxic polychlorinated sulfolipid from Adriatic shellfish

A detailed analysis of the causative toxins contained in the hepatopancreas of toxic mussels from the northern Adriatic sea has been carried out. Along with some DSP (diarrhetic shellfish poisoning) type toxins, such as okadaic acid, yessotoxin, and their derivatives, which are involved in a number of human intoxications throughout the world, we have now isolated a new cytotoxin, a polychlorinated sulfolipid 1, whose gross structure has been elucidated by spectral analysis, including various 2D NMR techniques. The relative stereochemistry of 1 was elucidated by successful application of the J-based configuration analysis developed for acyclic compounds using carbon-proton spin-coupling constants ((2,3)J(C,H)) and proton-proton spin-coupling constants ((3)J(H,H)); its absolute stereochemistry was established by the Mosher method. Compound 1 possesses in vitro cytotoxicity against WEHI 164 and RAW 264.7 cells.     

Total synthesis of floresolide B and Delta(6,7)-Z-floresolide B

The total syntheses of the cytotoxin marine natural product floresolide B (1) and its Delta(6,7)-Z isomer (2) have been achieved through an olefin metathesis-based strategy.     

Synthesis and characterization of chiral benzylic ether-bridged periodic mesoporous organosilicas

The first synthesis of a chiral periodic mesoporous organosilica (PMO) carrying benzylic ether bridging groups is reported. By hydrolysis and condensation of the new designed chiral organosilica precursor 1,4-bis(triethoxysilyl)-2-(1-methoxyethyl)benzene (BTEMEB) in the presence of the non-ionic oligomeric surfactant Brij 76 as supramolecular structure-directing agent under acidic conditions, an ordered mesoporous chiral benzylic ether-bridged hybrid material with a high specific surface area was obtained. The chiral PMO precursor was synthesized in a four-step reaction from 1,4-dibromobenzene as the starting compound. The evidence for the presence of the chiral units in the organosilica precursor as well as inside the PMO material is provided by optical activity measurements.     

Study on the Synthesis and Antitumor Activity of New Indolocarbazole Compounds

A series of new antitumor compounds having indolecarbazole structures were designed and synthesized. The methoxy substituted indolecarbazole parent nucleus, which was firstly synthesized, is condensed with bromine substituted amino acid methyl ester to produce the target compounds. The target compounds were performed with methylthiazolyldiphenyl-tetrazolium bromide(MTT) in vitro cytotoxin activity test and the results showed that compounds CZ-1, CZ-3 and CZ-6 have higher activity against human colon cancer(HT-29) and(HCT-8), hepatocellular carcinoma(Bel-7402), NSCLC(A549) and breast cancer(MCF-7) cells as compared to the positive control JDC-108.     

Relaxometric and modelling studies of the binding of a lipophilic Gd-AAZTA complex to fatted and defatted human serum albumin

A new lipophilic gadolinium chelate consisting of a long aliphatic chain bound to the AAZTA coordination cage (Gd-AAZTAC17) has been synthesised. It possesses two coordinated water molecules (q=2) in fast exchange with the solvent (tau298(M) = 67 ns), which yields a relaxivity of 10.2 mM(-1) s(-1). At concentrations greater than 0.1 mM, it forms micelles (average diameter 5.5 nm) characterised by a relaxivity of approximately 30 mM(-1) s(-1) at 20 MHz and 298 K. The latter value appears to be "quenched" by magnetic interactions among the Gd(III) ions on the surface of the micelle that cause a decrease in the electronic relaxation time. A relaxivity of 41 mM(-1) s(-1) was recorded for this micellar system when 98 % of the Gd(III) ions were replaced by diamagnetic Y(III). Gd-AAZTAC17 exhibits a better affinity for fatted human serum albumin (HSA) than for defatted HSA, whereas the relaxivities of the supramolecular adducts are reversed. The relaxivity shown by Gd-AAZTAC17/defatted HSA ({r b(1) (20 MHz, 298 K)=84 mM(-1) s(-1)) is by far the highest relaxivity reported so far for non-covalent paramagnetic adducts with slow-moving substrates. As shown by molecular docking calculations, the gadolinium complex enters a hydrophobic pocket present in fatted HSA more extensively than the corresponding adduct with defatted HSA. Interestingly, no marked difference was observed in either the relaxation enhancement or the binding affinity between fatted and defatted HSA when the binding titrations were carried out at a Gd-AAZTAC17 concentration higher than its critical micellar concentration (cmc). This behaviour has been attributed to the formation of an association between the negatively charged micelle of the lipophilic metal complexes and the positive residues on the surface of the protein.     

An investigation of the interaction of cobra venom cytotoxins with liposomes by the fluorescent-probe method

The interaction of cytotoxins V_c1, V_c5, and V_c6 of the venom of the Central Asian cobra with liposomes having a negative surface charge prepared from a mixture of phosphatidylcholine and palmitic acid (1:1, molar) has been investigated with the aid of a pyrene fluorescent probe. It has been shown that on interacting with liposomes a cytotoxin increases the microviscosity of the hydrophobic region of membranes. This effect depends on the phase state of the lipids. Observations on the kinetics of the transfer of energy between pyrene probes and diphenylhexatriene have shown that on the addition of a cytotoxin to samples of liposomes with a negative surface charge an aggregation of the liposomes takes place without a disturbance of their integrity.     

A novel method for time-resolved fluorimetric determination and imaging of the activity of peroxidase, and its application to an enzyme-linked immunosorbent assay

A new type of fluorescence assay for the determination of peroxidase (POx) activity is presented. The assay is based on the indication of the enzymatic consumption of H(2)O(2) (HP), using a fluorescent europium-tetracycline (Eu(3)TC) complex as indicator. On addition of HP, this complex forms a highly fluorescent adduct (Eu(3)TC-HP), which is decomposed in the presence of POx to form the weakly fluorescent europium-tetracycline (Eu(3)TC). Hence, the activity of the enzyme can be directly determined by means of the luminescent Eu(3)TC complex as indicator. The POx assay demonstrated herein was elaborated starting from a spectral characterization of the complex systems involved. Due to the long lifetime of lanthanide luminescence, both steady-state and time-resolved luminescence assays can easily be performed. The time-resolved assay can quantify POx in the range from 4.0 x 10(-5) to 5.9 x 10(-3) U mL(-1), with a limit of detection of 1.0 x 10(-5) U mL(-1). The effects of POx inhibitors such as cyanide, hydroxylamine, and azide have also been studied. In addition, a time-resolved fluorescent detection method for a POx-based enzyme-linked immunosorbent assay (ELISA) has been developed, which is demonstrated in a sandwich model assay with bovine IgG serving as analyte. Furthermore, a time-resolved fluorescent imaging method is demonstrated that makes use of a straightforward imaging set-up adjusted to the optical properties of the europium reagent.     

Total Synthesis of Rapamycin

Rapamycin (1) is a macrocyclic natural product, established as a potent immunosuppressant and currently of interest to the scientific community as the framework for a series of novel anticancer drugs. Extensive studies have culminated in a new convergent total synthesis of 1 , which features a number of group‐derived methodologies and an unusual catechol‐templating strategy for the construction of the challenging macrocyclic core.

     

Towards Binuclear Polyaminocarboxylate MRI Contrast Agents? Spectroscopic and MD Study of the Peculiar Aqueous Behavior of the LnIII Chelates of OHEC (Ln=Eu,Gd, and Tb): Implications for Relaxivity

We report the study of binuclear Ln(III) chelates of OHEC (OHEC=octaazacyclohexacosane-1,4,7,10,14,17,20,23-octaacetate). The interconversion between two isomeric forms, which occurs in aqueous solution, has been studied by NMR, UV/Vis, EPR, and luminescence spectroscopy, as well as by classical molecular dynamics (MD) simulations. For the first time we have characterized an isomerization equilibrium for a Ln(III) polyaminocarboxylate complex (Ln(III)=Y, Eu, Gd and Tb) in which the metal centre changes its coordination number from nine to eight, such that: [Ln(2)(ohec)(H(2)O)(2)](2-) r<==>[Ln(2)(ohec)](2-)+2 H(2)O. The variable temperature and pressure NMR measurements conducted on this isomerization reaction give the following thermodynamic parameters for Eu(III): K(298)=0.42+/-0.01, DeltaH(0)=+4.0+/-0.2 kJ mol(-1), DeltaS(0)=+6.1+/-0.5 J K(-1) mol(-1) and DeltaV(0)=+3.2+/-0.2 cm(3) mol(-1). The isomerization is slow and the corresponding kinetic parameters obtained by NMR spectroscopy are: k(298)(is)=73.0+/-0.5 s(-1), DeltaH++(is)=75.3+/-1.9 kJ mol(-1), DeltaS++(is)= +43.1+/-5.8 J K(-1) mol(-1) and DeltaV++(is)=+7.9+/-0.7 cm(3) mol(-1). Variable temperature and pressure (17)O NMR studies have shown that water exchange in [Gd(2)(ohec)(H(2)O)(2)](2-) is slow, k(298)(ex)=(0.40+/-0.02)x10(6) s(-1), and that it proceeds through a dissociative interchange I(d) mechanism, DeltaV( not equal )=+7.3+/-0.3 cm(3) mol(-1). The anisotropy of this oblong binuclear complex has been highlighted by MD simulation calculations of different rotational correlation times. The rotational correlation time directed on the Gd-Gd axis is 24 % longer than those based on the axes orthogonal to the Gd-Gd axis. The relaxivity of this binuclear complex has been found to be low, since 1) only [Gd(2)(ohec)(H(2)O)(2)](2-), which constitutes 70 % of the binuclear complex, contributes to the inner-sphere relaxivity and 2) the anisotropy of the complex prevents water molecules from having complete access to both Gd(III) cages; this decreases the outer-sphere relaxivity. Moreover, EPR measurements for the Gd(III) and for the mixed Gd(III)/Y(III) binuclear complexes have clearly shown that the two Gd(III) centres interact intramolecularly; this enhances the electronic relaxation of the Gd(III) electron spins.     

Synthesis of new 6-substituted purinyl-5′-nor-1′-homocarbanucleosides based on indanol

A series of new 6-substituted purinyl-5′-nor-1′-homocarbanucleosides based on indanol were synthesized from (±)-cis-3-hydroxymethyl-1-indanol, an appropriately functionalized derivative of which was reacted with 6-chloropurine in the presence of NaH and 18-crown-6 ether to prepare a key intermediate that gave access to the target molecules, purinylcarbanucleosides in which position 6 is occupied by a chloro, hydroxy, methoxy, amino or substituted phenyl group.     

Isolation and structure of providencin: a highly oxygenated diterpene possessing a unique bicyclo[12.2.0]hexadecane ring system from the sea plume Pseudopterogorgia kallos

[structure: see text] Providencin (1) is a naturally occurring cytotoxin isolated from the Caribbean gorgonian octocoral Pseudopterogorgia kallos. Its highly oxygenated hexacyclic structure is based on a previously undescribed bicyclo[12.2.0]hexadecane ring system and was established through spectroscopic analysis and X-ray crystallographic analysis. Providencin (1) was shown to exhibit modest anticancer activity against human breast (MCF7), lung (NCI-H460), and CNS (SF-268) cancer cell lines.     

Structure, stability, dynamics, high-field relaxivity and ternary-complex formation of a new tris(aquo) gadolinium complex

The tripodal hexadentate picolinate ligand dpaa3- (H3dpaa=N,N'-bis[(6-carboxypyridin-2-yl)methyl]glycine) has been synthesised. It can form 1:1 and 1:2 lanthanide/ligand complexes. The crystal structure of the bis(aquo) lutetium complex [Lu(dpaa)(H2O)2] has been determined by X-ray diffraction studies. The number of water molecules was determined by luminescence lifetime studies of the terbium and europium complexes. The tris(aquo) terbium complex shows a fairly high luminescence quantum yield (22 %). The [Gd(dpaa)(H2O)3] complex displays a high water solubility and an increased stability (pGd=12.3) with respect to the analogous bis(aquo) complex [Gd(tpaa)(H2O)2] (pGd=11.2). Potentiometric and relaxometric studies show the formation of a soluble GdIII hydroxo complex at high pH values. A unique aquohydroxo gadolinium complex has been isolated and its crystal structure determined. This complex crystallises as a 1D polymeric chain consisting of square-shaped tetrameric units. In heavy water, the [Gd(dpaa)-(D2O)3] complex shows a quite high HOD proton relaxivity at high field (11.93 s(-1) mM(-1) at 200 MHz and 298 K) because of the three inner-sphere water molecules. The formation of ternary complexes with physiological anions has been monitored by relaxometric studies, which indicate that even under conditions favourable to the formation of adducts with oxyanions, the mean relaxivity remains higher than those of most of the currently used commercial contrast agents except for the citrate. However, the measured relaxivity (r1=7.9 s(-1) mM(-1)) in a solution containing equimolar concentrations of [Gd(dpaa)(D2O)3] and citrate is still high. The interaction with albumin has been investigated by relaxometric and luminescence studies. Finally, a new versatile method to unravel the geometric and dynamic molecular factors that explain the high-field relaxivities has been developed. This approach uses a small, uncharged non-coordinating probe solute, the outer-sphere relaxivity of which mimics that of the water proton. Only a routine NMR spectrometer and simple mathematical analysis are required.     

Allylamine Derivatives—a New Class of Active Substances in Antifungal Chemotherapy

Fungal infections (mycoses) are found throughout the world. Only a few structural classes of compounds currently satisfy the demands of modern chemotherapy in their treatment; hence, the quest for new types of active substances is of major scientific and therapeutic importance. The first representative of a new class of substances–the allylamine derivatives–namely naftifine ((E)-N-methyl-N-(1-naphthylmethyl)-3-phenylallylamine) was discovered by accident and has recently become commercially available as a topical antimycotic. The exploration of structure-activity relationships on the basis of naftifine and new synthetic strategies led to the discovery of the currently most active compound of this type, terbinafine, the first pharmaceutical agent to contain a (E)-1, 3-enyne structural element. Terbinafine exhibits considerably higher activity than the original “lead” structure naftifine both in vitro and in vivo; it is also up to one order of magnitude more effective than standard preparations in various chemotherapeutic animal tests after topical or oral administration. According to clinical experience gained so far, terbinafine is well tolerated and shows promising activity against various types of mycoses. Allylamines act as potent, selective inhibitors of fungal squalene epoxidase via a novel mechanism, which, unlike in the case of other inhibitors of steroid biosynthesis, does not depend on cytochrome P450.