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Metallocarboxypeptidases (MCPs) are involved in many biological processes such as fibrinolysis or inflammation, development, Alzheimer's disease, and various types of cancer. We describe the synthesis and kinetic characterization of a focused library of 22 thiirane- and oxirane-based potential mechanism-based inhibitors, which led to discovery of an inhibitor for the human pro-carboxypeptidase A1. Our structural analyses show that the thiirane-based small-molecule inhibitor penetrates the barrier of the pro-domain to bind within the active site. This binding leads to a chemical reaction that covalently modifies the catalytic Glu270. These results highlight the importance of combined structural, biophysical, and biochemical evaluation of inhibitors in design strategies for the development of spectroscopically nonsilent probes as effective beacons for in vitro, in cellulo, and/or in vivo localization in clinical and industrial applications. Fil: Testero, Sebastian Andres. University of Notre Dame; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Granados, Carla. Universitat Autònoma de Barcelona; España Fil: Fernández, Daniel. Universitat Autònoma de Barcelona; España Fil: Gallego, Pablo. Universitat Autònoma de Barcelona; España Fil: Covaleda, Giovanni. Universitat Autònoma de Barcelona; España Fil: Reverter, David. Universitat Autònoma de Barcelona; España Fil: Vendrell, Josep. Universitat Autònoma de Barcelona; España Fil: Avilés, Francesc X.. Universitat Autònoma de Barcelona; España Fil: Pallarès, Irantzu. Universitat Autònoma de Barcelona; España Fil: Mobashery, Shahriar. University of Notre Dame; Estados Unidos

A structure-activity relationship (SAR) for the oxadiazole class of antibacterials was evaluated by syntheses of 72 analogs and determination of the minimal-inhibitory concentrations (MICs) against the ESKAPE panel of bacteria. Selected compounds were further evaluated for in vitro toxicity, plasma protein binding, pharmacokinetics (PK), and a mouse model of methicillin-resistant Staphylococcus aureus (MRSA) infection. Oxadiazole 72c shows potent in vitro antibacterial activity, exhibits low clearance, a high volume of distribution, and 41% oral bioavailability, and shows efficacy in mouse models of MRSA infection. Fil: Boudreau, Marc A.. University of Notre Dame; Estados Unidos Fil: Ding, Derong. University of Notre Dame; Estados Unidos Fil: Meisel, Jayda E.. University of Notre Dame; Estados Unidos Fil: Janardhanan, Jeshina. University of Notre Dame; Estados Unidos Fil: Spink, Edward. University of Notre Dame; Estados Unidos Fil: Peng, Zhihong. University of Notre Dame; Estados Unidos Fil: Qian, Yuanyuan. University of Notre Dame; Estados Unidos Fil: Yamaguchi, Takao. University of Notre Dame; Estados Unidos Fil: Testero, Sebastian Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina. University of Notre Dame; Estados Unidos Fil: O'Daniel, Peter I.. University of Notre Dame; Estados Unidos Fil: Leemans, Erika. University of Notre Dame; Estados Unidos Fil: Lastochkin, Elena. University of Notre Dame; Estados Unidos Fil: Song, Wei. University of Notre Dame; Estados Unidos Fil: Schroeder, Valerie A.. University of Notre Dame; Estados Unidos Fil: Wolter, William R.. University of Notre Dame; Estados Unidos Fil: Suckow, Mark A.. University of Notre Dame; Estados Unidos Fil: Mobashery, Shahriar. University of Notre Dame; Estados Unidos Fil: Chang, Mayland. University of Notre Dame; Estados Unidos

The five-membered, nitrogen-containing pyrroline ring is a privileged structure. This ring is present in many bioactive compounds from natural sources. Pyrrolines - the dihydro derivatives of pyrroles - have three structural isomer classes, depending on the location of the double bond: 1-pyrrolines (3,4-dihydro-2H-pyrroles), 2-pyrrolines (2,3-dihydro-1H-pyrroles) and 3-pyrrolines (2,5-dihydro-1H-pyrroles). This review aims to describe the latest advances for the synthesis of pyrrolines by transition metal-catalyzed cyclizations. Only reactions in which the pyrroline ring is formed by metal promotion are described. Transformations of the pyrroline ring in other heterocycles, and the structural manipulations of the pyrroline itself are not discussed. The review is organized into three parts, each covering the metal-mediated synthesis of the three pyrroline isomers. Each part is subdivided according to the metal involved, and concludes with a brief description of notable biological activities within the class. Fil: Medran, Noelia Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: la Venia, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: Testero, Sebastian Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina

Infections caused by hard-to-treat methicillin-resistant Staphylococcus aureus (MRSA) are a serious global public-health concern, as MRSA has become broadly resistant to many classes of antibiotics. We disclose herein the discovery of a new class of non-β-lactam antibiotics, the oxadiazoles, which inhibit penicillin-binding protein 2a (PBP2a) of MRSA. The oxadiazoles show bactericidal activity against vancomycin- and linezolid-resistant MRSA and other Gram-positive bacterial strains, in vivo efficacy in a mouse model of infection, and have 100% oral bioavailability.

An efficient and high-yielding solid phase synthesis of a small library of imidazolidin-2-ones and imidazol-2-ones was carried out employing a high chemo- and regioselective gold-catalyzed cycloisomerization as a key step. Polymer-supported amino acids derivatized with several alkyne functionalities combined with tosyl- and phenylureas have been subjected to gold-catalysis exhibiting exclusively C-N bond formation. The present work proves the potential of solid phase synthesis and homogeneous gold catalysis as an efficient and powerful synthetic tool for the generation of drug-like heterocycles. Fil: la Venia, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina. Palacky University; República Checa Fil: Medran, Noelia Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: Krchnak, Viktor. Palacky University; República Checa. University of Notre Dame-Indiana; Estados Unidos Fil: Testero, Sebastian Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina

A straightforward solid phase-based strategy for the rapid generation of two small libraries of trans 3-alkyl-substituted β-lactams is described. For the glycine-derived library, a controlled excess of nonactivated acid chlorides was used to prevent oxazinone formation. The second library involved the attachment of Fmoc-protected p -aminophenol to Wang resin for the preparation of structurally-closed analogues of known cholesterol absorption inhibitors. This strategy allowed us to introduce diversity in the three variable positions of the β-lactam ring.

The copper-mediated and non-basic oxidative cross-coupling of organotrifluoroborates with phenols was applied to elaboration of the structures of thiirane-based inhibitors of matrix metalloproteinases. By revision of the synthetic sequence to allow this cross-coupling as the final step, and taking advantage of the neutral nature of organotrifluoroborate cross-coupling, a focussed series of inhibitors showing aryloxy and alkenyloxy replacement of the phenoxy substitutent was prepared. This reaction shows exceptional promise as an alternative to the classic copper-mediated but strongly basic Ullmann reaction, for the diversification of ether segments within base-labile lead structures.

A series of 4-[(triazolyl)methoxy]phenyl analogs of the phenoxyphenyl-substituted thiirane SB-3CT 1 was evaluated for its ability to inhibit gelatinases, members of the matrix metalloproteinase family of enzymes. The triazole segment of these inhibitors was assembled using the Meldal-Sharpless copper-catalyzed Huisgen dipolar cycloaddition of an azide and a terminal alkyne. While these triazole derivatives possessed fair activity as gelatinase inhibitors, an intermediate used in the dipolar cycloaddition, 4-(propargyloxy)phenyl derivative 2, showed very good activity (

In the 80 years since their discovery the β-lactam antibiotics have progressed through structural generations, each in response to the progressive evolution of bacterial resistance mechanisms. The generational progression was driven by the ingenious, but largely empirical, manipulation of structure by medicinal chemists. Nonetheless, the true creative force in these efforts was Nature, and as the discovery of new β-lactams from Nature has atrophied while at the same time multi-resistant and opportunistic bacterial pathogens have burgeoned, the time for empirical drug discovery has passed. We concisely summarize recent developments with respect to bacterial resistance, the identity of the new β-lactams, and the emerging non-empirical strategies that will ensure that this incredible class of antibiotics has a future.

The β-lactam classes of antibacterials are preeminent in the treatment of bacterial infection due to their unparalleled clinical efficacy and clinical safety. Following the discovery of the penicillins, successive β-lactam drug discovery has added the cephalosporin, penem cephamycin, clavulanate, monobactam, nocardicin, and carbapenem subclasses. The driving force behind much of this era of discovery is the staggering ability of pathogenic bacteria to adapt previous generations of the β-lactam by the acquisition and expression of resistance mechanisms. Although many factors contribute to β-lactam resistance, alterations to the molecular targets of the β-lactams (the penicillin binding proteins) and the use of enzymes (the β-lactamases) capable of the hydrolytic deactivation of the β-lactams are paramount. This review traces the historical development of β-lactam drug discovery, with emphasis on the most recent progress in the medicinal chemistry, biochemistry, and microbiology of the β-lactams leading to the discovery of new generation β-lactam antibacterials effective against the Gram-negative and -positive bacterial pathogens of current medical concern. Keywords: β-lactam; β-lactamase; penicillin; cephalosporin; monobactam

The oxadiazole antibacterials, a class of newly discovered compounds that are active against Gram-positive bacteria, target bacterial cell-wall biosynthesis by inhibition of a family of essential enzymes, the penicillin-binding proteins. Ligand-based 3D-QSAR analyses by comparative molecular field analysis (CoMFA), comparative molecular shape indices analysis (CoMSIA) and Field-Based 3D-QSAR evaluated a series of 102 members of this class. This series included inactive compounds as well as compounds that were moderately to strongly antibacterial against Staphylococcus aureus. Multiple models were constructed using different types of energy minimization and charge calculations. CoMFA derived contour maps successfully defined favored and disfavored regions of the molecules in terms of steric and electrostatic properties for substitution. Fil: Leemans, Erika. University of Notre Dame; Estados Unidos Fil: Mahasenan, Kiran V.. University of Notre Dame; Estados Unidos Fil: Kumarasiri, Malika. University of Notre Dame; Estados Unidos Fil: Spink, Edward. University of Notre Dame; Estados Unidos Fil: Ding, Derong. University of Notre Dame; Estados Unidos Fil: O'Daniel, Peter I.. University of Notre Dame; Estados Unidos Fil: Boudreau, Marc A.. University of Notre Dame; Estados Unidos Fil: Lastochkin, Elena. University of Notre Dame; Estados Unidos Fil: Testero, Sebastian Andres. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Notre Dame; Estados Unidos Fil: Yamaguchi, Takao. University of Notre Dame; Estados Unidos Fil: Lee, Mijoon. University of Notre Dame; Estados Unidos Fil: Hesek, Dusan. University of Notre Dame; Estados Unidos Fil: Fisher, Jed F.. University of Notre Dame; Estados Unidos Fil: Chang, Mayland. University of Notre Dame; Estados Unidos Fil: Mobashery, Shahriar. University of Notre Dame; Estados Unidos

The ozonolysis of carbohydrate derived norbornene systems in participating solvents demonstrated that different remote controlling factors could induce the regioselective fragmentation of the primary ozonide. The exo norbornene series afforded a complete regioselective process.

An efficient and selective procedure for a rapid access to polymer-supported carboxylic acids from their corresponding methyl esters using trimethyltin hydroxide is described. Silyl and benzyl ether, and Rink amide linkers are stable to the reaction conditions.

We have recently disclosed the discovery of the class of 1,2,4-oxadiazole antibiotics, which emerged from in silico docking and scoring efforts. This class of antibacterials exhibits Gram-positive activity, particularly against Staphylococcus aureus. We define the structure–activity relationship (SAR) of this class of antibiotics with the synthesis and evaluation of a series of 59 derivatives with variations in the C ring or C and D rings. A total of 17 compounds showed activity against S. aureus. Four derivatives were evaluated against a panel of 16 Gram-positive strains, inclusive of several methicillin-resistant S. aureus strains. These compounds are broadly active against Gram-positive bacteria. Fil: Ding, Derong. University Of Notre Dame-indiana; Estados Unidos Fil: Boudreau, Marc A.. University Of Notre Dame-indiana; Estados Unidos Fil: Leemans, Erika J.. University Of Notre Dame-indiana; Estados Unidos Fil: Spink, Edward. University Of Notre Dame-indiana; Estados Unidos Fil: Yamaguchi, Takao. University Of Notre Dame-indiana; Estados Unidos Fil: Testero, Sebastian Andres. University Of Notre Dame-indiana; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; Argentina Fil: O'Daniel, Peter I.. University Of Notre Dame-indiana; Estados Unidos Fil: Lastochkin, Elena. University Of Notre Dame-indiana; Estados Unidos Fil: Chang, Mayland. University Of Notre Dame-indiana; Estados Unidos Fil: Mobashery, Shahriar. University Of Notre Dame-indiana; Estados Unidos

The structure-activity relationship (SAR) for the newly discovered oxadiazole class of antibiotics is described with evaluation of 120 derivatives of the lead structure. This class of antibiotics was discovered by in silico docking and scoring against the crystal structure of a penicillin-binding protein. They impair cell-wall biosynthesis and exhibit activities against the Gram-positive bacterium Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA) and vancomycin-resistant and linezolid-resistant S. aureus. 5-(1H-Indol-5-yl)-3-(4-(4-(trifluoromethyl)phenoxy)phenyl)-1,2,4-oxadiazole (antibiotic 75b) was efficacious in a mouse model of MRSA infection, exhibiting a long half-life, a high volume of distribution, and low clearance. This antibiotic is bactericidal and is orally bioavailable in mice. This class of antibiotics holds great promise in recourse against infections by MRSA. Fil: Spink, Edward. University of Notre Dame-Indiana; Estados Unidos Fil: Ding, Derong. University of Notre Dame-Indiana; Estados Unidos Fil: Peng, Zhihong. University of Notre Dame-Indiana; Estados Unidos Fil: Boudreau, Marc A.. University of Notre Dame-Indiana; Estados Unidos Fil: Leemans, Erika. University of Notre Dame-Indiana; Estados Unidos Fil: Lastochkin, Elena. University of Notre Dame-Indiana; Estados Unidos Fil: Song, Wei. University of Notre Dame-Indiana; Estados Unidos Fil: Lichtenwalter, Katerina. University of Notre Dame-Indiana; Estados Unidos Fil: O’Daniel, Peter I.. University of Notre Dame-Indiana; Estados Unidos Fil: Testero, Sebastian Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina. University of Notre Dame-Indiana; Estados Unidos Fil: Pi, Hualiang. University of Notre Dame-Indiana; Estados Unidos Fil: Schroeder, Valerie A.. University of Notre Dame-Indiana; Estados Unidos Fil: Wolter, William R.. University of Notre Dame-Indiana; Estados Unidos Fil: Antunes, Nuno T.. University of Notre Dame-Indiana; Estados Unidos Fil: Suckow, Mark A.. University of Notre Dame-Indiana; Estados Unidos Fil: Vakulenko, Sergei. University of Notre Dame-Indiana; Estados Unidos Fil: Chang, Mayland. University of Notre Dame-Indiana; Estados Unidos Fil: Mobashery, Shahriar. University of Notre Dame-Indiana; Estados Unidos

Ozonolysis of a carbohydrate derived norbornene system afforded a stable intramolecular cross-ozonide through a stereocontrolled pathway involving a regioselective fragmentation of the primary ozonide.

A gold-catalyzed cyclization of immobilized 2-alkynylanilines was developed as the key step in the synthetic sequence for the preparation of 2-substituted indoles. These results demonstrate the potential of the unexplored combination of gold catalysis and solid-phase organic synthesis.

Carbapenem-hydrolyzing class D β-lactamases (CHDLs) represent an emerging antibiotic resistance mechanism encountered among the most opportunistic Gram-negative bacterial pathogens. We report here the substrate kinetics and mechanistic characterization of a prominent CHDL, the OXA-58 enzyme, from Acinetobacter baumannii. OXA-58 uses a carbamylated lysine to activate the nucleophilic serine used for β-lactam hydrolysis. The deacylating water molecule approaches the acyl-enzyme species, anchored at this serine (Ser-83), from the α-face. Our data show that OXA-58 retains the catalytic machinery found in class D β-lactamases, of which OXA-10 is representative. Comparison of the homology model of OXA-58 and the recently solved crystal structures of OXA-24 and OXA-48 with the OXA-10 crystal structure suggests that these CHDLs have evolved the ability to hydrolyze imipenem, an important carbapenem in clinical use, by subtle structural changes in the active site. These changes may contribute to tighter binding of imipenem to the active site and removal of steric hindrances from the path of the deacylating water molecule. Fil: Verma, Vidhu. University of York; Reino Unido Fil: Testero, Sebastian Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina Fil: Amini, Kaveh. University of York; Reino Unido Fil: Wei, William. University of Toronto; Canadá Fil: Liu, Jerome. University of York; Reino Unido Fil: Balachandran, Naresh. University of York; Reino Unido Fil: Monoharan, Tharseekan. University of York; Reino Unido Fil: Stynes, Siobhan. University of York; Reino Unido Fil: Kotra, Lakshmi P.. University of Toronto; Canadá Fil: Golemi-Kotra, Dasantila. University of York; Reino Unido

An efficient and high-yielding "hydrogen-free" reduction of α,β-unsaturated alkenes was carried out employing Grubbs' catalyst in a non-metathetic role and Et(3)SiH. Conditions were optimized under microwave irradiation. Application to the solid-phase organic synthesis allows a facile construction of sp(3)-sp(3) carbon bonds through a sequential cross metathesis/olefin reduction.

Matrix metalloproteinases (MMPs) are important zinc-dependent endopeptidases. Two members of this family of enzymes called gelatinases (MMP-2 and MMP-9) have been implicated in a number of human diseases, including cancer, neurological and cardiovascular diseases, and inflammation, to name a few. We describe in this report the preparation and evaluation of two structural types of thiirane inhibitors that show selectivity toward gelatinases. The biphenyl series targets both gelatinases, whereas the monophenyl analogues exhibit potent inhibition of only MMP-2. The latter structural type also exhibits improved water solubility and metabolic stability, both traits desirable for progress of these molecules forward in gelatinase-dependent animal models of disease.

The three-dimensional X-ray crystal structure of carboxypeptidase A, a zinc-dependent hydrolase, covalently modified by a mechanism-based thiirane inactivator, 2-benzyl-3,4-epithiobutanoic acid, has been solved to 1.38 Å resolution. The interaction of the thiirane moiety of the inhibitor with the active site zinc ion promotes its covalent modification of Glu-270 with the attendant opening of the thiirane ring. The crystal structure determination at high resolution allowed for the clear visualization of the covalent ester bond to the glutamate side chain. The newly generated thiol from the inhibitor binds to the catalytic zinc ion in a monodentate manner, inducing a change in the zinc ion geometry and coordination, while its benzyl group fits into the S1' specificity pocket of the enzyme. The inhibitor molecule is distorted at the position of the carbon atom that is involved in the ester bond linkage on one side and the zinc coordination on the other. This particular type of thiirane-based metalloprotease inhibitor is for the first time analyzed in complex to the target protease at high resolution and may be used as a general model for zinc-dependent proteases. Fil: Fernández, Daniel. Universitat Autònoma de Barcelona; España Fil: Testero, Sebastian Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Química Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Química Rosario; Argentina. University of Notre Dame; Estados Unidos Fil: Vendrell, Josep. Universitat Autònoma de Barcelona; España Fil: Avilés, Francesc X.. Universitat Autònoma de Barcelona; España Fil: Mobashery, Shahriar. University of Notre Dame; Estados Unidos

A major mechanism of bacterial resistance to beta-lactam antibiotics (penicillins, cephalosporins, carbapenems, etc.) is the production of beta-lactamases. A handful of class A beta-lactamases have been discovered that have acquired the ability to turn over carbapenem antibiotics. This is a disconcerting development, as carbapenems are often considered last resort antibiotics in the treatment of difficult infections. The GES family of beta-lactamases constitutes a group of extended spectrum resistance enzymes that hydrolyze penicillins and cephalosporins avidly. A single amino acid substitution at position 170 has expanded the breadth of activity to include carbapenems. The basis for this expansion of activity is investigated in this first report of detailed steady-state and pre-steady-state kinetics of carbapenem hydrolysis, performed with a class A carbapenemase. Monitoring the turnover of imipenem (a carbapenem) by GES-1 (Gly-170) revealed the acylation step as rate-limiting. GES-2 (Asn-170) has an enhanced rate of acylation, compared with GES-1, and no longer has a single rate-determining step. Both the acylation and deacylation steps are of equal magnitude. GES-5 (Ser-170) exhibits an enhancement of the rate constant for acylation by a remarkable 5000-fold, whereby the enzyme acylation event is no longer rate-limiting. This carbapenemase exhibits k(cat)/K(m) of 3 x 10(5) m(-1)s(-1), which is sufficient for manifestation of resistance against imipenem.

The unique hydrophobic surface patches in class D beta-lactamases presented an opportunity for designing two compounds, 6alpha-(1R-hydroxyoctyl)penicillanic acid and 6beta-(1R-hydroxyoctyl)penicillanic acid, as mechanistic probes of these enzymes. In a sequence of three synthetic steps from benzhydryl 6,6-dibromopenicillanate, the targeted compounds were prepared in a stereospecific manner.

Four positional isomers of Thiastearate (TS) and Isoxyl (Thiocarlide) were assayed as fatty acid desaturase inhibitors in Trypanosoma cruzi epimastigotes. 9-TS did not exert a significant effect on growth of T. cruzi, nor on the fatty acid profile of the parasite cells. One hundred micromolars of 10-TS totally inhibited growth, with an effective concentration for 50% growth inhibition (EC(50)) of 3.0+/-0.2microM. Growth inhibition was reverted by supplementing the culture media with oleate. The fatty acid profile of treated cells revealed that conversion of stearate to oleate and palmitate to palmitoleate were drastically reduced and, as a consequence, the total level of unsaturated fatty acids decreased from 60% to 32%. Isoxyl, a known inhibitor of stearoyl-CoA Delta9 desaturase in mycobacteria, had similar effects on T. cruzi growth (EC(50) 2.0+/-0.3microM) and fatty acid content, indicating that Delta9 desaturase was the target of both drugs. 12- and 13-TS were inhibitors of growth with EC(50) values of 50+/-2 and 10+/-3microM, respectively, but oleate or linoleate were unable to revert the effect. Both drugs increased the percentage of oleate and palmitate in the cell membrane and drastically reduced the content of linoleate from 38% to 16% and 12%, respectively, which is in agreement with a specific inhibition of oleate Delta12 desaturase. The absence of corresponding enzyme activity in mammalian cells and the significant structural differences between trypanosome and mammalian Delta9 desaturases, together with our results, highlight these enzymes as promising targets for selective chemotherapeutic intervention.

We have prepared immobilized olefins as models for the cross metathesis using different olefin partners in the presence of second generation Grubbs and Hoveyda-Grubbs precatalysts. We have demonstrated that solid-phase cross metathesis is strongly dependent on the degree of homodimerization of the non-immobilized olefin and the reactivity of such a homodimer. As in the homogeneous phase, the Hoveyda-Grubbs precatalyst was better for immobilized alpha,beta-unsaturated carbonyl compounds.

[reaction: see text] An efficient cross-metathesis on solid support for the synthesis of beta-lactam analogues of cholesterol absorption inhibitors is described. The applied strategy allows the introduction of diversity in positions 3 and 4 of the beta-lactam ring with excellent 3,4-trans selectivity and complete E selectivity at the C-3 side chain.

[reaction: see text] The enantiospecific assembly of the pentalenolactones' carbon skeleton was achieved in 17 steps and 16% overall yield from methyl alpha-D-glucopyranoside. The synthetic strategy relies on two highly efficient key steps: an exo-diastereoselective Diels-Alder reaction and a nonsymmetric ozonolysis.

The synthesis of a 4,5-cyclopropanated carbohydrate was achieved in five steps from methyl α- d -mannopyranoside under mild conditions that avoid the use of carbene chemistry.