Synthesis of dimeric phenylethanoids isolated from olive oil mill wastewaters

Two dimeric phenylethanoids isolated from olive oil mill wastewaters have been synthesized from cathecol, tyrosol and 3,4-dihydroxyphenylacetic acid.

Concise synthesis of ether analogues of lysobisphosphatidic acid

We describe a versatile, efficient method for the preparation of ether analogues of (S,S)-lysobisphosphatidic acid (LBPA) and its enantiomer from (S)-solketal. Phosphorylation of a protected sn-2-O-octadecenyl glyceryl ether with 2-cyanoethyl bis-N,N-diisopropylamino phosphine and subsequent deprotection generated the bisether LBPA analogues. By simply changing the sequence of deprotection steps, we obtained the (R,R)- and (S,S)-enantiomers of 2,2'-bisether LBPA. An ELISA assay with anti-LBPA monoclonal antibodies showed that the bisether LBPAs were recognized with the same affinity as the natural 2,2'-bisoleolyl LBPA. [reaction: see text]

5-(Dimethoxymethyl)-2'-deoxyuridine: a novel gem diether nucleoside with anti-orthopoxvirus activity

To provide potential new leads for the treatment of orthopoxvirus infections, the 5-position of the pyrimidine nucleosides have been modified with a gem diether moiety to yield the following new nucleosides: 5-(dimethoxymethyl)-2'-deoxyuridine (2b), 5-(diethoxymethyl)-2'-deoxyuridine (3b), 5-formyl-2'-deoxyuridine ethylene acetal (4b), and 5-formyl-2'-deoxyuridine propylene acetal (5b). These were evaluated in human foreskin fibroblast cells challenged with the vaccinia virus or cowpox virus. Of the four gem diether nucleosides, only the dimethyl gem diether congener showed significant antiviral activity against both viruses. This antiviral activity did not appear to be related to the decomposition to the 5-formyl-2'-deoxyuridine, which was itself devoid of anti-orthopoxvirus activity in these assays. Moreover, at the pH of the in vitro assays, 2b was very stable with a decomposition (to aldehyde) half-life of >15 d. The anti-orthopoxvirus activity of pyrimidine may be favored by the introduction of hydrophilic moieties to the 5-position side chain.

Lewis Base Catalyzed Mannich-Type Reactions between Trimethylsilyl Enol Ethers and Aldimines

Lewis base catalyzed Mannich-type reaction between trimethylsilyl enol ethers and N-tosylaldimines is described. Nitrogen anions generated from amides or imides such as lithium benzamide or potassium phthalimide are found to be effective Lewis base catalysts in DMF at room temperature to afford the corresponding beta-amino carbonyl compounds in good to high yields; the oxygen anion generated from carboxylic acids such as lithium acetate was also found to be effective in dry DMF. The above-mentioned lithium acetate-catalyzed Mannich-type reaction between aldimines and various trimethylsilyl (TMS) enol ethers such as silyl ketene acetal proceeded smoothly even in water-containing DMF. Then, Lewis base catalyzed three-component Mannich-type reactions of TMS enol ether, tosylamide, and aromatic aldehyde having electron-withdrawing group such as p-nitrobenzaldehyde were investigated. The reaction proceeded smoothly to afford the corresponding beta-amino ester in good yield. Further, ammonium carboxylates such as tetrabutyl ammonium acetate or tetrabutyl ammonium benzoate were found to be more effective Lewis base catalysts in the above-mentioned Mannich-type reaction. The synthesis proceeded in various solvents at lower temperatures. The reaction between aldimines and TMS enol ethers generated from thioester and various ketones such as propiophenone or cyclohexanone also proceeded smoothly to afford the corresponding beta-amino carbonyl compounds in high yields with good to high anti-selectivities.

Simple, rapid procedure for the synthesis of chloromethyl methyl ether and other chloro alkyl ethers

[Reaction: see text]. Zinc(II) salts catalyze the reaction between acetals and acid halides to provide haloalkyl ethers in near-quantitative yield. Reactions from millimole to mole scale are typically complete in 1-4 h with 0.01 mol % catalyst. The solutions of haloalkyl ethers thus obtained can be utilized directly in reactions in which the presence of the ester byproduct does not interfere. Excess haloalkyl ether is destroyed on workup, thereby minimizing exposure to this class of carcinogenic compounds.

Asymmetric claisen rearrangements enabled by catalytic asymmetric Di(allyl) ether synthesis

Merging the catalytic asymmetric synthesis of di(allyl) ethers with ensuing olefin isomerization-Claisen rearrangement (ICR) reactions provides a convenient, two-step route to asymmetric aliphatic Claisen rearrangements from easily obtained starting materials. These reactions deliver the 2,3-disubstituted 4-pentenal derivatives characteristic of aliphatic Claisen rearrangements with excellent relative and absolute stereocontrol. A catalytic enantioselective synthesis of the (+)-calopin dimethyl ether demonstrates the utility of this reaction technology in asymmetric synthesis enterprises.

(S)-4,5-dihydro-2-(2-hydroxy-4-hydroxyphenyl)-4-methyl-4-thiazolecarboxylic acid polyethers: a solution to nephrotoxicity

Previous studies revealed that within a family of ligands the more lipophilic chelators have better iron-clearing efficiency. The larger the log P(app) value of the compound, the better the iron-clearing efficiency. What is also clear from the data is that although the relative effects of log P(app) changes are essentially the same through different families, there are differences in absolute value between families. However, there also exists a second, albeit somewhat more disturbing, relationship. In all sets of ligands, the most lipophilic chelator is always the most toxic. The current study focuses on designing ligands that balance the lipophilicity/toxicity problem while iron-clearing efficiency is maintained. Earlier studies with (S)-4,5-dihydro-2-(2-hydroxy-4-methoxyphenyl)-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(CH(3)O)-DADFT, 6] indicated that this methyl ether was a ligand with excellent iron-clearing efficiency in both rodents and primates; however, it was too toxic. On the basis of this finding, a less lipophilic, more water-soluble ligand than 6 was assembled, (S)-4,5-dihydro-2-[2-hydroxy-4-(3,6,9-trioxadecyloxy)phenyl]-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(HO)-DADFT-PE, 11], a polyether analogue, along with its ethyl and isopropyl esters. The parent polyether and its isopropyl and ethyl esters were all shown to be highly efficient iron chelators in both rodents and primates. A comparison of 11 in rodents with the desferrithiocin analogue (S)-4,5-dihydro-2-(2,4-dihydroxyphenyl)-4-methyl-4-thiazolecarboxylic acid [(S)-4'-(HO)-DADFT, 1] revealed the polyether to be more tolerable, achieving higher concentrations in the liver and significantly lower concentrations in the kidney. The lower renal drug levels are in keeping with the profound difference in the architectural changes seen in the kidney of rodents given 1 versus those treated with 11.

Mild and Nonracemizing Conditions for Ullmann-type Diaryl Ether Formation between Aryl Iodides and Tyrosine Derivatives

CuI/N,N-dimethylglycine-catalyzed coupling reaction of L-tyrosine derivatives and L-phenylalanine-derived iodides in the presence of Cs2CO3 works at 90 degrees C to provide the corresponding diaryl ether. Partial racemization occurs when N-Boc- and N-Cbz-protected aromatic amino esters are used, while N-trityl- and N,N-dibenzyl-protected aromatic amino esters give rise to coupling products without loss of optical purity. Little racemization is also observed in cases of N-Boc- and N-Cbz-protected aromatic amino acids as substrates. But their reaction yields are moderate. On the basis of these studies, shorter protocols for assembling (S,S)-isodityrosine and K-13 are developed.

Palladium(II)-catalyzed aerobic hydroalkoxylation of styrenes containing a phenol

An intermolecular Pd-catalyzed hydroalkoxylation of styrenes that contain a phenol is presented. The reaction can be performed on terminal, disubstituted, and trisubstituted olefins in a variety of alcoholic solvents. Initial mechanistic data suggest a mechanism that involves oxidation of the alcoholic solvent to provide a Pd-hydride that inserts into an olefin. This is followed by formation of a quinone methide and subsequent addition of an alcohol to yield the hydroalkoxylated product.

Improved access to 2-O-monobenzyl ethers of β-cyclodextrin as precursors of catalysts for organophosphoryl esters hydrolysis

A comparative study of reaction conditions was performed for the synthesis of a 2-O-monobenzyl ether of cyclomaltoheptaose (beta-CD). Optimal conditions involved sodium ethoxide in Me(2)SO and benzyl bromide. The methodology was extended to the preparation of various 2(I)-O-iodobenzyl and 2(I)-O-carboxymethylbenzyl derivatives of beta-CD including a 3-carboxymethyl-4-iodobenzyl derivative of interest as precursor of an enzyme mimic to degrade the organophosphoryl ester diethyl 4-nitrophenyl phosphate (paraoxon).

Studies of photoinduced electron transfer and energy migration in a conjugated polymer system for fluorescence "turn-on" chemosensor applications

A series of poly[p-(phenyleneethynylene)-alt-(thienyleneethynylene)] (PPETE) polymers with variable percent loadings of the N,N,N'-trimethylethylenediamino group on the polymer backbone were synthesized and fully characterized. Photophysical studies show that changes in the loading of the amino group receptor on the backbone do not affect the polymer electronic structure in either the ground or excited states. The fluorescence quantum yields were found to be directly related to the loading of the amino groups and can be modeled by a Stern-Volmer type relationship. Photophysical studies related the total quenching efficiency to the inherent rate of photoinduced electron transfer (PET), the lifetime of the exciton, the rate of excitation energy migration along the polymer backbone, and the total loading of the receptor on the polymer. The role of the loading dependence on the application of these polymers as fluorescence "turn-on" sensors for toxic metal cations in dilute solution was also studied. Results showed that the fluorescence enhancement upon binding various cations was maintained even when the amino receptor loading along the polymer backbone was reduced.

Novel Potent and Efficacious Nonpeptidic Urotensin II Receptor Agonists

Six different series of nonpeptidic urotensin II receptor agonists have been synthesized and evaluated for their agonistic activity in a cell-based assay (R-SAT). The compounds are ring-opened analogues of the isochromanone-based agonist AC-7954 with different functionalities constituting the linker between the two aromatic ring moieties. Several of the compounds are highly potent and efficacious, with N-[1-(4-chlorophenyl)-3-(dimethylamino)-propyl]-4-phenylbenzamide oxalate (5d) being the most potent. The pure enantiomers of 5d were obtained from the corresponding diastereomeric amides. It was shown by a combination of X-ray crystallography and chemical correlation that the activity resides in the S-enantiomer of 5d (pEC(50) 7.49).

Diastereoselective Diels-Alder reactions of N-sulfonyl-1-aza-1,3-butadienes with optically active enol ethers: an asymmetric variant of the 1-azadiene Diels-Alder reaction

The first detailed study of a room-temperature asymmetric Diels-Alder reaction of N-sulfonyl-1-aza-1,3-butadienes is reported enlisting a series of 19 enol ethers bearing chiral auxiliaries, with many providing highly diastereoselective (endo and facial diastereoselection) reactions, largely the result of an exquisitely organized [4+2] cycloaddition transition state. Three new, readily accessible, and previously unexplored auxiliaries rationally emerged from the studies and provide remarkable selectivities (two of these give 49:1 endo:exo and 48:1 facial selectivity) that promise to be useful in systems beyond those detailed.

Piperazinyl oxime ethers as NK-1 receptor antagonists

The synthesis and structure-activity relations for a new class of centrally active NK-1 receptor antagonists are described. The new compounds are based on piperazine 2 and contain an oxime ether functionality. Several new compounds have high affinity for the NK-1 receptor and show good antagonistic activity in the gerbil foot-tapping assay.

Synthesis and in vitro cytotoxic activity of N-, F-, and S-ether derivatives of podophyllotoxin fatty acid adducts

This paper represents the first synthesis, spectroscopic characterization, and antitumor evaluation of F-, N-, and S-containing C4alpha-FA derivatives of podophyllotoxin. In a synthetic strategy, a FA unit of 4-O-podophyllotoxinyl 12-hydroxyoctadec-Z-9-enoate 2, a derivative of podophyllotoxin, was functionalized at the C-12 position by incorporating the F atom and N-containing moieties. The FA olefin (Z, C-9/C-10) of 2 was hydrogenated to produce a derivative possessing a hydroxy function (C-12) on a saturated C18 FA chain. In another synthetic strategy, two S-ethers of podophyllotoxin (C4alpha) were synthesized from a terminal unsaturated FA analog, 4-O-podophyllotoxinyl undec-10-enoate. Syntheses were achieved through effective synthetic procedures; 1H NMR, 13C NMR, IR, and high-resolution mass data proved excellent tools to characterize these derivatives. In vitro antitumor activity was investigated against a panel of five human neoplastic cell lines, SK-MEL (malignant, melanoma), KB (epidermal carcinoma, oral), BT-549 (ductal carcinoma, breast), SK-OV-3 (ovary carcinoma), and HL-60 (human leukemia). Keeping in view the severe lack of tumor selectivity of podophyllotoxin over normal cells, we assayed new analogs against noncancerous mammalian VERO (African green monkey kidney fibroblast) cell lines to gauge their extent of toxicity. Several of these compounds showed excellent moderation of antitumor activity. In general, we found excellent growth inhibition against the human leukemia cell line (HL-60), particularly for the analogs containing S-ethers and carbamates. None of the compounds were toxic to normal cell lines.

Total synthesis and cytotoxicity evaluation of syrinenin-4-O-farnesylether and its analogues

First synthesis of natural product, syrinenin-4-O-farnesylether (1), was carried out via two different paths. Four of its derivatives (9-12) were also prepared. Cytotoxicity screening of the selected compounds were performed on six tumour cell lines. Compound 12 exhibited prominent IC50 values of 1.9 microM and 0.8 microM on CNE and PC-3 cells, respectively.

Marine natural products: synthetic aspects

An overview of marine natural products synthesis during 2004 is provided. As with the previous installment of this series, the emphasis is on total syntheses of molecules of contemporary interest, new total syntheses, and syntheses that have resulted in structure confirmation or stereochemical assignments.

Synthesis and functionalization of a highly fluorescent and completely water-soluble poly(para-phenyleneethynylene) copolymer for bioconjugation

Bioconjugation of a highly fluorescent water-soluble poly(para-phenyleneethynylene) (PPE) copolymer with ionic and non-ionic side chains is achieved by means of chain-end modification, providing a design principle for biosensor development.

Regioselective synthesis of long-chain ethers and their sulfates derived from methyl beta-D-galactopyranoside and derivatives via dibutylstannylene acetal intermediates

A number of different conditions were investigated for the alkylation of the dibutylstannylene acetals of methyl beta-d-galactopyranoside with long-chain primary alkyl bromides, decyl, dodecyl, and tetradecyl bromide. The best yields of the major products, the 3-O-alkyl ethers, were obtained by reaction of the alkyl bromide with the monodibutylstannylene acetal in DMF in the presence of cesium fluoride for extended periods of time at moderate temperatures (65 degrees C). These products were always accompanied by minor amounts of the 3,6-di-O-alkyl derivative. Performing the reaction with excess alkyl halide on the bis(dibutylstannylene) acetal resulted in more of the 3,6-di-O-alkyl derivative, particularly for the shorter alkyl bromides, but this product was never predominant. Sulfation of the dibutylstannylene acetal of methyl 3-O-tetradecyl-beta-D-galactopyranoside resulted in the 6-sulfate in 96% yield.

Sulfoalkyl Ether-Alkyl Ether Cyclodextrin Derivatives, their Synthesis, NMR Characterization, and Binding of 6α-Methylprednisolone

The objective of this study is to see if random alkyl ethers of various sulfoalkyl ether cyclodextrins can be synthesized and characterized. The purpose of the alkylation was to test the hypothesis that an increase in the "height" of a cyclodextrins cavity would help in the binding/complexation of larger more structurally complex molecules. The synthesis of new cyclodextrin derivatives comprising a mixture of sulfoalkyl ether and alkyl ether substituents on the same cyclodextrin ring was performed in aqueous alkaline solutions using various sultones and alkylsulfates. The method presented provided an easy and efficient way to modify cyclodextrins avoiding the use of organic solvents and high quantities of alkylating agents and could be carried out in either a two step or "one pot" single step process. Purification was by neutralization followed by ultrafiltration. The derivatives were characterized by 1D, ((1)H and (13)C), and a 2D NMR technique (HMQC, Heteronuclear Multiple Quantum Coherence). The combination of these techniques allowed an analysis of the degree of substitution and the site of substitution on the cyclodextrin (CD) nucleus. For both beta- and gamma-CD, sulfoakylation was preferred on the 2 > 3 > 6 hydroxyls while alkylation was preferred 6 > 2 > 3. Due to the simultaneous presence of short alkyl ether chains and negatively charged sulfoalkyl ether chains, these mixed water-soluble cyclodextrin derivatives, especially those of gamma-cyclodextrin, should be able to bind more complex drugs. The improved binding capacity of these new modified CDs with the model drug 6alpha-methylprednisolone is reported.

Synthesis and Biological Activity of Anticancer Ether Lipids That Are Specifically Released by Phospholipase A2 in Tumor Tissue

The clinical use of anticancer lipids is severely limited by their ability to cause lysis of red blood cells prohibiting intravenous injection. Novel delivery systems are therefore required in order to develop anticancer ether lipids (AELs) into clinically useful anticancer drugs. In a recent article (J. Med. Chem. 2004, 47, 1694) we showed that it is possible to construct liposome systems composed of masked AELs that are activated by secretory phospholipase A2 in cancerous tissue. We present here the synthesis of six AELs and evaluate the biological activity of these bioactive lipids. The synthesized AEL 1-6 were tested against three different cancer cell lines. It was found that the stereochemistry of the glycerol headgroup in AEL-2 and 3 has a dramatic effect on the cytotoxicity of the lipids. AEL 1-4 were furthermore evaluated for their ability to prevent phosphorylation of the apoptosis regulating kinase Akt, and a correlation was found between their cytotoxic activity and their ability to inhibit Akt phosphorylation.

Toward an Understanding of the Catalytic Role of Hydrogen-Bond Donor Solvents in the Hetero-Diels−Alder Reaction between Acetone and Butadiene Derivative

A detailed theoretical investigation of the catalytic role of hydrogen-bond- (HB-) donor molecules (water, methanol, chloroform, dichloromethane, and chloromethane) in the hetero-Diels-Alder reaction between acetone and N,N-dimethyl-1-amino-3-methoxy-1,3-butadiene is presented. This work extends a previous study (Domingo, L. R.; Andres, J. J. Org. Chem. 2003, 68, 8662) in which the importance of weak HB-donor solvents to catalyze more effectively than solvents with a higher dielectric constant but no HB-donor capability was analyzed. Now, based on density functional theory (DFT) at B3LYP/6-31+G(d) level calculations, different techniques for analyzing the nature of HB interaction, namely, natural bond orbital (NBO) theory, topological analysis of the electron density (atoms in molecules, AIM, theory), and the electron localization function (ELF) and decomposition of the interaction energy between monomers (energy decomposition analysis, EDA), have been applied to understand why only some HB-donor solvents are able to catalyze the reaction. The catalytic effect of the solvent arises from the improved HB-acceptor capability of the oxygen atom at the transition structure (TS) due to the strong polarization of the carbonyl group. The HB acceptor presents three lone pairs (NBO analysis), and the ELF shows an increment of the electronic charge of the lone pairs of 0.50e with respect to the reactant. All solvent molecules form stronger HB interactions at the TS, but only those presenting larger charge-transfer interactions (water, methanol, chloroform) benefit more from the polarization of the carbonyl group than other solvents (dichloromethane, chloromethane) with less "covalent" character.

Synthesis and antiamoebic activity of new oxime ether derivatives containing 2-acetylpyridine/2-acetylfuran

Various oxime ether derivatives of 2-acetylpyridine and 2-acetylfuran series have been synthesised. O-Alkylation of the oximes by various alkylaminoethyl halides gave the corresponding oxime ether derivatives. The structures of these compounds were elucidated by UV, IR, 1H NMR, 13C NMR spectroscopic methods and elemental analyses. All the compounds were screened in vitro against the HM1:IMSS strain of Entamoeba histolytica. Based on the 50% inhibitory concentration (IC50) data of the 12 compounds evaluated, two of the 2-acetylpyridine series and two in the 2-acetylfuran series showed better IC50 values in vitro when compared with the standard amoebicidal drug, metronidazole. Moreover, one compound showed the most promising antiamoebic activity (IC50=0.5 microM vs IC50=1.9 microM of metronidazole).

Androsterone 3alpha-ether-3beta-substituted and androsterone 3beta-substituted derivatives as inhibitors of type 3 17beta-hydroxysteroid dehydrogenase: chemical synthesis and structure-activity relationship

Type 3 17beta-hydroxysteroid dehydrogenase (17beta-HSD) is involved in the biosynthesis of androgen testosterone. To produce potent inhibitors of this key steroidogenic enzyme, we prepared a series of androsterone (ADT) derivatives by adding a variety of substituents at position 3. The 3beta-substituted ADT derivatives proved to be good inhibitors (IC(50) = 57-147 nM) with better inhibitory activities obtained for compounds bearing a propyl, s-butyl, cyclohexylalkyl, or phenylalkyl group. With an IC(50) value of 57 nM, the 3beta-phenylmethyl-ADT was 6-fold more potent than ADT, the lead compound, and 13-fold more potent than 4-androstene-3,17-dione, the natural enzyme substrate used itself as inhibitor. The 3alpha-ether-3beta-substituted ADT derivatives had a lower inhibitory activity compared to the 3beta-substituted ADT analogues except for the 3beta-phenylethyl-3alpha-methl-O-ADT (IC(50) = 73 nM), which proved to be a more potent inhibitor than 3beta-phenylethyl-ADT (IC(50) = 99 nM). The results of our study identified potent type 3 17beta-HSD inhibitors for potential use in the treatment of androgen-sensitive diseases.

Approaches to improving the biocompatibility of porous perfluoropolyethers for ophthalmic applications

Porous perfluoropolyether (PFPE) membranes for ophthalmic applications were prepared with a zwitterion monomer, 3-[[2-(methacryloxy) ethyl](N,N-dimethyl)ammonio]-propane-1-sulphonate, copolymerized in weight ratios of 0-10%. The polymer samples were assessed for a range of physical properties, including equilibrium water content, bovine serum albumin permeability, transparency, refractive index and the ability to support corneal epithelial cell and tissue attachment, growth and migration. In vitro assessment of the polymers using bovine corneal epithelial cells and tissue showed that a zwitterion incorporation level of between 0% and 6% in the PFPE membranes supported the migration of an intact sheet of epithelial tissue without compromising epithelial cell attachment and growth, with 4-6% being the optimal level for these properties. Binding patterns of the cell adhesion glycoprotein fibronectin were also found to reflect the cell and tissue response. Effective nutrient permeability, refractive index and optical transparency were also maintained by the porous PFPE polymers containing this concentration of zwitterionic monomer. The presence of amounts of zwitterion greater than 6% was inhibitory to both tissue migration and cell growth and was associated with increased optical haze. These results demonstrated that it is possible to achieve the potential for increased biocompatibility in zwitterion-containing PFPE polymers without compromising existing beneficial characteristics.

Synthesis and in vivo analgesic and anti-inflammatory activity of some bi heterocyclic coumarin derivatives

Sets of coumarinyl ethers having chromone, benzofuranyl and 4-hydroxy coumarins (4, 5, 6) were prepared and tested for analgesic and antiinflammatory activity. The 4-(4'-acetyl-3'-hydroxy-phenoxymethyl)-coumarin 3 were synthesised by the reaction of 4-bromo methyl coumarin with 2, 4-dihydroxy acetophenones, were found to less active. Further compound 3 having the ortho hydroxy moiety was cyclised to chromones 4 and benzofurans 5 were found to enhance the analgesic and anti-inflammatory activity. The cyclisation to 4-hydroxy coumarin 6 was found to be reducing the anti-inflammatory and analgesic activity in this series. These newly synthesized compounds were found to produce less toxicity and less ulcerogenic effects.

Competitive Stereochemical Control Operative during Conrotatory Electrocyclization of Helically Equilibrating Diquinanyl-Substituted 1,3,5,7-Octatetraenyl Bisenolates

[Carbohydrate structure: see text] Activation of the squarate ester cascade by adding the lithiated bicyclo[3.3.0]octene 20 and vinyllithium sequentially to 1 results in the isolation of the four tetracyclic products 21-24. The structures of the topographically complex products were deduced by 2D NMR spectroscopy and X-ray diffraction studies. The mechanistic insights gained by these findings are discussed. The product distribution is telltale evidence for predominant 1,2-addition of the second alkenyl anion. Product stereochemistry is in turn diagnostic of the preferred mode of conrotatory ring closure operating within equilibrating helical intermediates of opposite pitch. A competing pathway for the elimination of methanol in these highly functionalized intermediates has been observed for the first time.

Synthesis of ferrocene-grafted poly(p-phenylene-ethynylenes) and control of electrochemical behaviors of their thin films

New ferrocene-coated poly(p-phenylene-ethynylenes) (PPEs) with end capping groups of protected thiol were prepared by a palladium-catalyzed Sonogashira coupling reaction. Ferrocene groups were covalently attached to polymers A and B through ethylene oxide tethers and to polymer C through methylene tethers. Polymers A and B are soluble in common solvents such as tetrahydrofuran (THF), chloroform, methylene chloride, acetone, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), and polymer C is soluble in toluene, THF, chloroform, and methylene chloride. Polymers A-C display low quantum yield, caused by electron-transfer quenching of ferrocene groups as electron donors. The polymer thin films were prepared through incubation of gold electrodes in THF solutions containing the polymers for 2 days. Ferrocene in thin films of polymers A and B display significantly faster electron-transfer rate than that of polymer C. Hydrophilic ethylene oxide side chains of polymers A and B decrease formal potential of tethered ferrocene groups because of electron-donating effect from ethylene oxide side chains, which stabilizes the ferrocenium ion and leads to a cathodic shift of the redox wave.

Nonspecific interactions of a carboxylate-substituted PPE with proteins. A cautionary tale for biosensor applications

Two carboxylate-substituted, fluorescent (Phi = 0.08), water-soluble poly(p-phenyleneethynylene)s (PPE) and a water-soluble model compound were exposed to a series of proteins and bovine serum. While the anionic PPEs do not have any specific binding sites, they form stable complexes with histone, lysozyme, myoglobin, and hemoglobin. The complex formation was evidenced by fluorescence quenching. Bovine serum albumin does not quench the fluorescence of the PPEs but enhances it, probably due to its surfactant character. These results imply that the use of charged conjugated polymers as biosensors, while an attractive proposition, has to take into account strong nonspecific interactions between conjugated polymers and the host of proteins that is found in cells and complex biological fluids.

Design and synthesis of low molecular weight compounds with complement inhibition activity

An attempt was made to synthesize a series of non-cytotoxic low molecular weight compounds of varying substitutions and functionalities having pharmacophore activity like carbonyl compounds, carboxylic acid and bioisosteres like tetrazole and phenyl acrylic acid. The in vitro assay of these analogues for the inhibition of complement activity revealed significant inhibitory activity for varying substituents and, particularly, for bioisosteres, that is, tetrazole and phenyl acrylic acid derivatives.

Use of tunable ligands allows for intermolecular Pd-catalyzed C--O bond formation

Bulky biaryl phosphine ligands facilitate Pd-catalyzed C-O coupling reactions of aryl halides with primary and secondary alcohols by promoting reductive elimination at the expense of beta-hydride elimination. The key to their success is the ability to match the size of the ligand to that of the combination of substrates. The efficient coupling of a number of unactivated aryl chlorides and bromides with cyclic and acyclic secondary alcohols was achieved. This included the coupling of allylic alcohols for the first time in a Pd-catalyzed coupling process.

Catalytic, Enantioselective, Vinylogous Aldol Reactions

In 1935, R. C. Fuson formulated the principle of vinylogy to explain how the influence of a functional group may be felt at a distant point in the molecule when this position is connected by conjugated double-bond linkages to the group. In polar reactions, this concept allows the extension of the electrophilic or nucleophilic character of a functional group through the pi system of a carbon-carbon double bond. This vinylogous extension has been applied to the aldol reaction by employing "extended" dienol ethers derived from gamma-enolizable alpha,beta-unsaturated carbonyl compounds. Since 1994, several methods for the catalytic, enantioselective, vinylogous aldol reaction have appeared, with which varying degrees of regio- (site), enantio-, and diastereoselectivity can be attained. In this Review, the current scope and limitations of this transformation, as well as its application in natural product synthesis, are discussed.

Total synthesis and complete assignment of the stereostructure of a cytotoxic bromotriterpene polyether (+)-aurilol

The plane structure and partial stereochemistry of a cytotoxic bromotriterpene polyether (+)-aurilol (1), isolated from the sea hare Dolabella auricularia, were mainly elucidated by NMR methods; however, determination of the entire stereochemistry has not been reached. Although there have also been many other types of triterpene polyethers, it is often difficult to determine their stereostructures even by the current highly advanced spectroscopic methods, especially in acyclic systems including quaternary carbon centers such as C10-C11, C14-C15, and C18-C19 in 1. In this paper, we report that the total assignment of the incomplete stereostructure of (+)-aurilol (1) to the structural formula 2 has been accomplished through its first asymmetric total synthesis featuring the highly regio- and stereocontrolled biogenetic-like A-D ether ring formations.

Photochemical Release of Aldehydes from α-Acetoxy Nitroveratryl Ethers

Photolabile aldehyde-releasing precursors (alpha-acetoxy ethers) were prepared by reduction of the corresponding esters with DIBAL and quenching the intermediate aluminum hemiacetal with acetic anhydride. These species smoothly released aldehydes upon irradiation with UV light at 350 nm. Using this method, not only simple model aliphatic aldehydes were liberated but also specimens relevant for the flavor and fragrance industry (methional, phenylacetaldehyde, and (R)-citronellal). [reaction: see text]

Synthesis of Homoleptic Barium Alkoxides and Aryloxides and Their Reactions with Al(CH3)3: a Convenient Route to Heterometallic Species

Reactions of metallic Ba with benzofuranol (dbbfoH) or diethylene glycol give homoleptic and homonuclear complexes Ba(dbbfo)(2)(dbbfoH)(2).3dbbfoH and Ba{O(CH(2)CH(2)O)(2)}{O(CH(2)CH(2)OH)(2)}(2) (60-89%). Both compounds and formerly described Ba{O(CH(2)CH(2)O)(2)Me}(2) react with Al(CH(3))(3) to yield trinuclear heterobimetallic low-coordinated barium compounds with structure and geometry depending on the reaction stoichiometry and crystallization procedure.

Sol-gel-based solid-phase microextraction and gas chromatography-mass spectrometry determination of dextromethorphan and dextrorphan in human plasma

A novel solid-phase microextraction (SPME) method was developed for isolation of dextromethorphan (DM) and its main metabolite dextrorphan (DP) from human plasma followed by GC-MS determination. Three different polymers, poly(dimethylsiloxane) (PDMS), poly(ethylenepropyleneglycol) monobutyl ether (Ucon) and polyethylene glycol (PEG) were synthesized as coated fibers using sol-gel methodologies. DP was converted to its acetyl-derivative prior to extraction and subsequent determination. The porosity of coated fibers was examined by SEM technique. Effects of different parameters such as fiber coating type, extraction mode, agitation method, sample volume, extraction time, and desorption condition, were investigated and optimized. The method is rapid, simple, easy and inexpensive and offers high sensitivity and reproducibility. The limits of detection are 0.010 and 0.015 ng/ml for DM and DP, respectively. The precisions for both analytes are below 5% (n=5). The correlation coefficient was satisfactory (r(2)>0.99) for both DM and DP. Linear ranges were obtained from 0.03 ng/ml to 2 microg/ml for DM and from 0.05 ng/ml to 2 microg/ml for DP.

Photorelease of Alcohols from 2-Nitrobenzyl Ethers Proceeds via Hemiacetals and May Be Further Retarded by Buffers Intercepting the Primary aci-Nitro Intermediates

The mechanism for the photoinduced release of glycolic acid from its 2-nitrobenzyl ether was reinvestigated. The pH-dependent rate constants of the thermal reactions initiated by irradiation are similar to those reported previously for 2-nitrobenzyl methyl ether. A hemiacetal intermediate that limits the release rate of glycolic acid at pH values </=7 was identified by time-resolved IR and UV measurements. Furthermore, 2-(2'-nitrosophenyl)-1,3-dioxolan-4-one, a long-lived intermediate formed by intramolecular trapping of the aci-tautomer, was observed and characterized.

Fabrication of Carbon Nanotube−Molecule−Silicon Junctions

A hybridization strategy for the covalent connection of single wall carbon nanotubes to silicon surfaces via oligo(phenylene ethynylene)s has been demonstrated using an orthogonal bisdiazonium functionalization protocol.

Synthesis of spiroketal enol ethers related to tonghaosu and their insecticidal activities

This paper describes the syntheses and biological activities of a number of spiroketal enol ethers which are analogues of the plant extract tonghaosu. The insecticidal potential of this spiroketal system is assessed.

Thyroid Receptor Ligands. 3. Design and Synthesis of 3,5-Dihalo-4-alkoxyphenylalkanoic Acids as Indirect Antagonists of the Thyroid Hormone Receptor

Based on the recently described concept of "indirect antagonism" of nuclear receptors, a series of thyroid hormone receptor (TR) antagonists were prepared, in which the outer ring of a thyromimetic was replaced with alkyl chains of variable length and branch. The results of a binding assay for the human TR and reporter cell assay revealed, within this series, a positive correlation between increasing bulk of the alkyl group and affinity to TRs. Compared with already reported TR antagonists, their affinities are within the same range, thus potentially representing a useful approach to novel and high affinity TR-antagonists.

Bisaryloxime ethers as potent inhibitors of transthyretin amyloid fibril formation

Amyloid fibril formation by the plasma protein transthyretin (TTR), requiring rate-limiting tetramer dissociation and monomer misfolding, is implicated in several human diseases. Amyloidogenesis can be inhibited through native state stabilization, mediated by small molecule binding to TTR's primarily unoccupied thyroid hormone binding sites. New native state stabilizers have been discovered herein by the facile condensation of arylaldehydes with aryloxyamines affording a bisarylaldoxime ether library. Of the library's 95 compounds, 31 were active inhibitors of TTR amyloid formation in vitro. The bisaryloxime ethers selectively stabilize the native tetrameric state of TTR over the dissociative transition state under amyloidogenic conditions, leading to an increase in the dissociation activation barrier. Several bisaryloxime ethers bind selectively to TTR in human blood plasma over the plethora of other plasma proteins, a necessary attribute for efficacy in vivo. While bisarylaldoxime ethers are susceptible to degradation by N-O bond cleavage, this process is slowed by their binding to TTR. Furthermore, the degradation rate of many of the bisarylaldoxime ethers is slow relative to the half-life of plasma TTR. The bisaryloxime ether library provides valuable structure-activity relationship insight for the development of structurally analogous inhibitors with superior stability profiles, should that prove necessary.

Efficient synthesis of alkynylsilyl ethers and silaketals via base-induced alkynylsilane alcoholysis

The efficient silylation of alcohols with di- and trialkynylsilanes was achieved under base-catalyzed conditions to afford alkynyl silyl ethers and symmetrical alkynyl silaketals in good yield. A selective alcoholysis of dialkynyl silyl ethers to mixed silaketals was also demonstrated. These products served as substrates for enyne ring-closing metathesis and, consequently, as precursors to stereochemically defined 1,3-dienes.

Nonpolar and Short Side Chain Groups at C-11β of Estradiol Result in Antiestrogens

We have previously found that esters of 11beta-estradiol carboxylates are transformed from an estrogen into an antiestrogen when the 11beta-side chain is increased in length from four to five non-hydrogen atoms (n > or = 5). To understand the structural requirements for this transformation and obtain metabolically stable analogues that are not susceptible to esterase cleavage, we have synthesized other compounds having an 11beta-side chain composed of other functional groups: ketones, amides, ethers, and thiono esters. With the exception of amides, which bind poorly to the estrogen receptor (ER), all of these compounds exhibit antiestrogenic action when the side chain length is n > or = 5. Ethers (n > or = 5), studied in more detail, inhibit the action of estradiol with either ERalpha or ERbeta. In rat uteri they are estrogen antagonists/weak agonists and decrease the concentration of cholesterol in blood (an hepatic estrogenic action). Thus, these short chain and nonpolar 11beta-analogues of estradiol have tissue specific antiestrogenic/estrogenic actions, characteristics of selective estrogen receptor modulators.

Radical α-C−H Hydroxyalkylation of Ethers and Acetal

[reaction: see text] Epsilonthers and an acetal were found to undergo direct intermolecular addition to aldehydes under the Et(3)B/air conditions. This study presents a very unique and simple means for the radical alpha-C-H hydroxyalkylation of oxygen-containing compounds.

Mannose-substituted PPEs detect lectins: A model for Ricin sensing

The interaction of a mannose-substituted poly(para phenyleneethynylene) (mPPE) with a lectin, Concanavalin A (ConA), is reported; the ConA causes fluorescence quenching of the mPPE with a K(SV) of 5.6 x 10(5).

Evaluation of substituted oxime ethers for growth regulatory activity against Spodoptera litura (F.)

Insect growth regulatory activity (IGR) of fifty-two substituted oxime ethers were evaluated against an important polyphagous lepidopteran crop pest, Spodoptera litura (F.). A number of compounds produced symptoms comparable to exogenously applied juvenile hormone. Maximum IGR activity was exhibited by 4'-(2,6,6-trimethyl-2-cyclohexen- -yl)-3'-buten-2'(E)-ketoxime-N-O-alkyl ether with an ED50 (morphological) of 40 microg g(-1) body weight, compared to 20 microg g(-1) of JH III. Two more compounds namely 4'-(2,6,6-trimethyl-2-cyclohexen-1-yl)-3'-buten-2'(Z)-ketoxime-N-O-methyl propyl ether (ED50 192 microg g(-1)) and 4'-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3'-buten-2'(E)-ketoxime-N-O-pentyl ether (ED50 380 microg g(-1)) showed considerable IGR activity, whereas 4'-(2,6,6-trimethyl-2-cyclohexen-1-yl)-3'-buten-2'(E)-ketoxime-N-O-pentyl ether was found to be toxic to the larvae (ED50 268 microg g(-1)). Three compounds used in this study were also synergised by piperonyl butoxide (PBO). The synergistic ratios were found in the range of 1.33 to 4.605. The ovicidal activity of the oxime ethers is not significant.

Marine natural products: synthetic aspects

An overview of marine natural products synthesis during 2003 is provided. The emphasis on total syntheses of molecules of contemporary interest, new total syntheses, and syntheses that have resulted in structure conformation or stereochemical assignments.