William W. Ogilvie

Total Synthesis of Brevetoxin A: Part 3: Construction of GHIJ and BCDE Ring Systems

Pivotal intermediates in the total synthesis of brevetoxin A are the BCDE and the GHIJ ring systems. Several of the previously developed methodologies such as hydroxy epoxide cyclizations, hydroxy dithioketal cyclizations, and Pd-catalyzed coupling with bis(cyclic ketene acetal phosphates) were employed to achieve these synthetic goals.

Discovery of the first series of inhibitors of human papillomavirus type 11: inhibition of the assembly of the E1-E2-Origin DNA complex.

We have discovered a series of inhibitors of the assembly of the HPV11 E1-E2-origin DNA complex, which incorporate an indandione fused to a substituted tetrahydrofuran.

Preparation of optically active stilbene oxides via sulfonium salts derived from C2 symmetric thiolanes.

Abstract Trans-stilbene oxides have been obtained in up to 83% enantiomeric excess via reaction of S-benzyl ylides prepared from optically active trans-2,5-disubstituted thiolanes.

Discovery of non-peptidic P2-P3 butanediamide renin inhibitors with high oral efficacy.

A new series of non-peptidic renin inhibitors having a 2-substituted butanediamide moiety at the P2 and P3 positions has been identified. The optimized inhibitors have IC50 values of 0.8 to 1.4 nM and 2.5 to 7.6 nM in plasma renin assays at pH 6.0 and 7.4, respectively. When evaluated in the normotensive cynomolgus monkey model, two of the most potent inhibitors were orally active at a dose as low as 3 mg/kg. These potent renin inhibitors are characterized by oral bioavailabilities of 40 and 89% in the cynomolgus monkey. Inhibitor 3z (BILA 2157 BS) was selected as candidate for pre-development.

Synthesis and antiviral activity of monobactams inhibiting the human cytomegalovirus protease.

A series of monobactam inhibitors of HCMV (N(o)) protease bearing a heterocycle linked by a methylene group at C-4 is described. Inhibitors containing a heterocycle such as a 2-furyl, 2-thiophenyl, 4-methyl-2-tetrazole and 2-benzothiazole were found to be active in a plaque reduction assay. Furthermore, 2-benzothiazole derivatives were shown to inhibit the HCMV protease activity inside cells by using a cell transfection assay, indicating that their antiviral activity in the plaque reduction assay could be attributed to protease inhibition.

Enzymatic generation of ceramide induces membrane restructuring: Correlated AFM and fluorescence imaging of supported bilayers.

The effect of enzymatic generation of ceramide on phase separated bilayers with a mixture of co-existing fluid and liquid-ordered phases has been examined using a combination of atomic force microscopy (AFM) and fluorescence imaging. Supported lipid bilayers prepared from a DOPC/sphingomyelin/cholesterol mixture were imaged prior to, during and after incubation with sphingomyelinase by total internal reflection fluorescence (TIRF) microscopy. Enzyme treatment resulted in the growth of large dye-excluded regions. The growth kinetics for these patches are consistent with activity of a variable number of enzyme molecules in different regions of the bilayer. Correlated AFM and fluorescence imaging shows that some of the large dye-excluded patches form around the original liquid-ordered domains, which become heterogeneous in height with many raised ceramide-rich regions around their periphery. However, some of the dye-excluded patches correspond to areas of the bilayer where the initial domains have largely or partially disappeared. The dye-excluded patches observed by fluorescence are shown to be areas of increased adhesion in lateral deflection AFM images and are postulated to form by incorporation of both cholesterol and ceramide in the original fluid phase and to vary in composition throughout the bilayer. This is evident from the observation that the dye-excluded areas are all detected as areas of increased friction, but do not always show a distinct height difference in topographic images. These results highlight the utility of a multi-modal imaging approach for understanding the complex membrane restructuring that occurs upon enzymatic generation of ceramide.

NBD-cholesterol probes to track cholesterol distribution in model membranes.

A series of cholesterol (Chol) probes with NBD and Dansyl fluorophores attached to the 3-hydroxyl position via carbamate linkers has been designed and synthesized and their ability to mimic the behavior of natural cholesterol in bilayer membranes has been examined. Fluorescence spectroscopy data indicate that the NBD-labeled lipids are located in the polar headgroup region of the bilayer with their position varying with the method of fluorophore attachment and the linker length. The partitioning of the Chol probes between liquid-ordered (L(o)) and liquid-disordered (L(o)) phases in supported bilayers prepared from ternary lipid mixtures of DOPC, Chol and either egg sphingomyelin or DPPC was examined by fluorescence microscopy. The carbamate-linked NBD-Chols show a stronger preference for partitioning into L(o) domains than does a structurally similar probe with an ester linkage, indicating the importance of careful optimization of probe and linker to provide the best Chol mimic. Comparison of the partitioning of NBD probes to literature data for native Chol indicates that the probes reproduce well the modest enrichment of Chol in L(o) domains as well as the ceramide-induced displacement of Chol. One NBD probe was used to follow the dynamic redistribution of Chol in phase separated membranes in response to in situ ceramide generation. This provides the first direct optical visualization of Chol redistribution during enzymatic ceramide generation and allows the assignment of new bilayer regions that exclude dye and have high lateral adhesion to ceramide-rich regions.

Lewis acids in diastereoselective processes involving acyclic radicals

The radical reductions and allylations of a series of a-halo-P-alkoxy esters under bidentate chelation-controlled conditions are reported and compared with the analogous reactions under non-chelating conditions. The addition of Lewis acids is shown to give excellent selectivity for the syn products in the case of reduction, and the anti products in the case of allylation. In some cases, ratios greater than 1OO:l are obtained. The reactions require initiation with EbB and can be inhibited by m- and p-dinitrobenzene, which imply a radical-based mechanism. Iodides, bromides and phenyl selenides are all suitable substrates. Investigations also provide a rationale for the large excess of MgBr2.OEt2 which is apparently required in these reactions. Competition experiments provide a more detailed explanation of substrate reactivity. Traditionally radicals derived from acyclic precursors have seldom been considered as intermediates for the generation of asymmetric centers. Recently however, it has been discovered that radicals can indeed react with high levels of diastereoselectivity (1). This has been achieved mainly through the use of chiral auxiliaries (2) or by the influence of a stereogenic center adjacent to a carbonyl (1,2-asymmetric induction) (3,4, 5). The scope of these reactions has also been expanded by the use of Lewis acids (6, 7), solvent complexation (8) and intramolecular hydrogen bonding (9) to enhance and even reverse the facial bias. In this paper, we describe results we have obtained in chelation-controlled reductions, allylations and atom transfer reactions of a-halo-P-alkoxy esters, and present evidence for radical-based processes. Preliminary experiments designed to elucidate further mechanistic details will also be discussed. Scheme 1 X Ph -. *Et

Potent β-Lactam Inhibitors of Human Cytomegalovirus Protease:

A series of novel monobactam inhibitors of human cytomegalovirus (HCMV) protease has been described that possess a heterocyclic thiomethyl side chain at C-4. Changes to the heterocycle did not significantly change the inhibitory activity of these compounds in an enzymatic assay, although improvements in solubility and cell culture activity were noted. A number of permutations between C-4 substitutions and N-1 derivatives led to the identification of several β-lactams with antiviral activity in a plaque reduction assay. N-methyl thiotetrazole-containing compounds were found to be the most potent inhibitors in the enzymatic assay.

Single-Isomer Trisubstituted Olefins from a Novel Reaction of (E)-β-Chloro-α-iodo-α,β-unsaturated Esters and Amides

(E)-beta-chloro-alpha-iodo-alpha,beta-unsaturated esters are converted to single isomer trisubstituted olefins bearing three different carbon substituents by cross-coupling under reflux. Mechanistic investigations suggest that this process transfers a hydrogen from the boronic acid to the alpha-position of the substrate and then introduces an aryl group to the beta-position of the intermediate template while replacing chloride. The reaction is highly stereoselective, showing preference for the E-isomer. The process proceeds through (E)-beta-chloro-alpha-aryl-alpha,beta-unsaturated esters that are transformed efficiently into the corresponding E-products through stereoselective Suzuki-type reactions giving single isomers. The observed stereochemistry is apparently enabled by the intermediacy of a palladium allenoate. The reaction involves a catalytic cycle in which Pd(II) is reduced to Pd(0) through the formation of biaryl-coupled products.