Intramolecular nitrone dipolar cycloadditions: control of regioselectivity and synthesis of naturally-occurring spirocyclic alkaloids.

The intramolecular nitrone dipolar cycloaddition of in situ-generated nitrones such as compound 26 has been used for the synthesis of cyclic isoxazolidines 27 and 29. The regioselectivity of the intramolecular cycloaddition depends on the nature of the terminal substituent on the dipolarophile. The influence of the substituent on the regioselectivity of the cycloaddition has been examined using several model systems and two methods of nitrone formation. These studies demonstrated that the cyano-substituent plays a special role in favouring the formation of the 6,6,5-ring fused adduct 27 under thermodynamically controlled conditions. The utility of the cyclo-adduct 57 (see Scheme 12) as a precursor for the naturally occurring histrionicotoxins is illustrated by the synthesis of three "unsymmetrical" (i.e. with each side chain bearing different functional groups) members of the histrionicotoxin family HTX-259A, HTX-285C and HTX-285E (2, 3 and 4 respectively).

Automated parallel freeze-evacuate-thaw degassing method for oxygen-sensitive reactions: RAFT polymerization.

An automated and parallel freeze-evacuate-thaw degassing method in a commercially available synthesizer is disclosed and tested for its applicability to reversible addition-fragmentation chain transfer (RAFT) polymerization. The effectiveness of this method to eliminate oxygen in polymerization reactions is demonstrated by directly comparing it against experiments performed using conventional laboratory techniques. Apart from the demonstrated accuracy, the proposed method has also shown significant precision when performing RAFT polymerizations. The reported experimental technique can be easily adapted to other chemical systems where the removal of oxygen is mandatory. This new high-throughput method has the potential to significantly increase the productivity and/or research outcomes in laboratories where oxygen-sensitive reactions are carried out.

Modeling the molecular basis for α4ß1 integrin antagonism.

We report a 3D QSAR study of almost 300 structurally diverse small molecule antagonists of the integrin α4ß1 whose biological activity spans six orders of magnitude. The alignment of the molecules was based on the conformation of a structurally related ligand bound to the αIIBß3 and αvß3 integrins in X-ray crystallographic studies. The molecular field method, CoMSIA, was used to generate the 3D QSAR models. The resulting models showed that the lipophilic properties were the most important, with hydrogen bond donor and steric properties less relevant. The models were highly significant (r(2)=0.89, q2(LOO)=0.67, r(2) (test set)=0.76), and could make robust predictions of the data (SEE=0.46, SEP=0.78, SEP (test set)=0.66). We predicted the antagonist activities of a further ten compounds with useful accuracy. The model appears capable of predicting α4ß1 integrin antagonist activity to within a factor of five for compounds within its domain of applicability. The implications for design of improved integrin antagonists will be discussed.

The influence of dipalmitoyl phosphatidylserine on phase behaviour of and cellular response to lyotropic liquid crystalline dispersions.

Lyotropic liquid crystalline nanoparticles (cubosomes) have the potential to act as amphiphilic scaffolds for the presentation of lipids and subsequent application in, for example, bioseparations and therapeutic delivery. In this work we have formulated lyotropic liquid crystalline systems based on the synthetic amphiphile 1,2,3-trihydroxy-3,7,11,15-tetramethylhexadecane (phytantriol) and containing the lipid dipalmitoyl phosphatidylserine (DPPS). We have prepared a range of DPPS-containing phytantriol cubosome formulations and characterized them using Small Angle X-ray Scattering and Cryo-transmission electron microscopy. These techniques show that increased DPPS content induces marked changes in lyotropic liquid crystalline phase behaviour, characterized by changes in crystallographic dimensions and increases in vesicle content. Furthermore, in vitro cell culture studies indicate that these changes correlate with lipid/surfactant cellular uptake and cytotoxicity. A model cell membrane based on a surface supported phospholipid bilayer was used to gain insights into cubosome-bilayer interactions using Quartz Crystal Microgravimetry. The data show that mass uptake at the supported bilayer increased with DPPS content. We propose that the cytotoxicity of the DPPS-containing dispersions results from changes in lipid/surfactant phase behaviour and the preferential attachment and fusion of vesicles at the cell membrane.

A gram-scale batch and flow total synthesis of perhydrohistrionicotoxin.

The total synthesis of the spiropiperidine alkaloid (-)-perhydrohistrionicotoxin (perhydro-HTX) 2 has been accomplished on a gram scale by employing both conventional batch chemistry as well as microreactor techniques. (S)-(-)-6-Pentyltetrahydro-pyran-2-one 8 underwent nucleophilic ring opening to afford the alcohol 10, which was elaborated to the nitrone 13. Protection of the nitrone as the 1,3-adduct of styrene and side-chain extension to the unsaturated nitrile afforded a precursor 17, which underwent dipolar cycloreversion and 1,3-dipolar cycloaddition to give the core spirocyclic precursor 18 that was converted into perhydro-HTX 2. The principal steps to the spirocycle 18 have successfully been transferred into flow mode by using different types of microreactors and in a telescoped fashion, allowing for a more rapid access to the histrionicotoxins and their analogues by continuous processing.

N-tetrahydrothiochromenoisoxazole-1-carboxamides as selective antagonists of cloned human 5-HT2B.

The serendipitous discovery of N-cyclohexyl-8-fluoro-3,3a,4,9b-tetrahydro-1H-thiochromeno[4,3-c]isoxazole-1-carboxamide as a selective human serotonin 5-HT2B antagonist with Ki of 42+/-5 nM is reported herein. A subsequent functional assay indicated little agonist activity compared to 5-HT itself.

Antiviral activity of gliotoxin, gentian violet and brilliant green against Nipah and Hendra virus in vitro.

BACKGROUND: Using a recently described monolayer assay amenable to high throughput screening format for the identification of potential Nipah virus and Hendra virus antivirals, we have partially screened a low molecular weight compound library (>8,000 compounds) directly against live virus infection and identified twenty eight promising lead molecules. Initial single blind screens were conducted with 10 microM compound in triplicate with a minimum efficacy of 90% required for lead selection. Lead compounds were then further characterised to determine the median efficacy (IC50), cytotoxicity (CC50) and the in vitro therapeutic index in live virus and pseudotype assay formats. RESULTS: While a number of leads were identified, the current work describes three commercially available compounds: brilliant green, gentian violet and gliotoxin, identified as having potent antiviral activity against Nipah and Hendra virus. Similar efficacy was observed against pseudotyped Nipah and Hendra virus, vesicular stomatitis virus and human parainfluenza virus type 3 while only gliotoxin inhibited an influenza A virus suggesting a non-specific, broad spectrum activity for this compound. CONCLUSION: All three of these compounds have been used previously for various aspects of anti-bacterial and anti-fungal therapy and the current results suggest that while unsuitable for internal administration, they may be amenable to topical antiviral applications, or as disinfectants and provide excellent positive controls for future studies.

Characteristics of Nipah virus and Hendra virus replication in different cell lines and their suitability for antiviral screening.

We have recently described the development and validation of a high throughput screening assay suitable for henipavirus antiviral identification. While we are confident this assay is robust and effective, we wished to investigate assay performance in a range of alternative cell lines to determine if assay sensitivity and specificity could be improved. We evaluated ten different cell lines for their susceptibility to Hendra and Nipah virus infection and their sensitivity of detection of the effects of the broad spectrum antiviral, ribavirin and nine novel antivirals identified using our initial screening approach. Cell lines were grouped into three categories with respect to viral replication. Virus replicated best in Vero and BSR cells, followed by Hep-2, HeLa, BHK-21 and M17 cells. The lowest levels of RNA replication and viral protein expression were observed in BAEC, MMEC, A549 and ECV304 cells. Eight cell lines appeared to be similarly effective at discriminating the antiviral effects of ribavirin (<2.7-fold difference). The two cells lines most sensitive to the effect of ribavirin (ECV304 and BAEC) also displayed the lowest levels of viral replication while Vero cells were the least sensitive suggesting excess viral replication may limit drug efficacy and cell lines which limit viral replication may result in enhanced antiviral efficacy. However, there was no consistent trend observed with the other nine antivirals tested. While improvements in antiviral sensitivity in other cell lines may indicate an important role in future HTS assays, the slightly lower sensitivity to antiviral detection in Vero cells has inherent advantages in reducing the number of partially effective lead molecules identified during initial screens. Comparison of a panel of 54 novel antiviral compounds identified during routine screening of an in-house compound library in Vero, BHK-21 and BSR cells suggests no clear advantage of screening in either cell type.

Diaryl ether synthesis in supercritical carbon dioxide in batch and continuous flow modes.

A high yielding, batch mode synthesis of diaryl ethers and sulfides by an S(N)Ar fluoride-mediated process in scCO(2) has been developed; the use of a polymer-supported imidazolium fluoride reagent in batch mode led to the development of a fixed-bed continuous flow process, with high conversions.

Total synthesis of (-)-histrionicotoxin 285A and (-)-perhydrohistrionicotoxin.

Starting from commercially available ( S)-glycidol, and via a common intermediate, the total synthesis of (-)-histrionicotoxin 285A and (-)-perhydrohistrionicotoxin has been achieved. Key to this synthesis was the efficient construction of a six-membered, chiral, cyclic nitrone.

Clean and efficient synthesis of O-silylcarbamates and ureas in supercritical carbon dioxide.

The synthesis of a family of O-silylcarbamates from the corresponding silylamines has been achieved simply by heating the silylamine in supercritical carbon dioxide (scCO2), and these O-silylcarbamates have been shown to be effective precursors for the synthesis of a range of symmetrical and unsymmetrical ureas.

Discovery of (Z)-2-phenyl-3-(1H-pyrrol-2-yl)acrylonitrile derivatives active against Haemonchus contortus and Ctenocephalides felis (cat flea).

A series of 2-phenyl-3-(1H-pyrrol-2-yl)acrylonitrile derivatives were synthesized and evaluated for in vitro activity against the endoparasite Haemonchus contortus and the ectoparasite Ctenocephalides felis. Some compounds had significant in vitro activity against these parasites.