The Plasmodium falciparum cysteine proteases falcipain-2 and falcipain-3 appear to be required for hemoglobin hydrolysis by intraerythrocytic malaria parasites. Previous studies showed that peptidyl vinyl sulfone inhibitors of falcipain-2 blocked the development of P. falciparum in culture and exerted antimalarial effects in vivo. We now report the structure-activity relationships for inhibition of falcipain-2, falcipain-3, and parasite development by 39 new vinyl sulfone, vinyl sulfonate ester, and vinyl sulfonamide cysteine protease inhibitors. Levels of inhibition of falcipain-2 and falcipain-3 were generally similar, and many potent compounds were identified. Optimal antimalarial compounds, which inhibited P. falciparum development at low nanomolar concentrations, were phenyl vinyl sulfones, vinyl sulfonate esters, and vinyl sulfonamides with P 2 leucine moieties. Our results identify independent structural correlates of falcipain inhibition and antiparasitic activity and suggest that peptidyl vinyl sulfones have promise as antimalarial agents.Malaria is one of the most important infectious diseases in the world. Plasmodium falciparum, the most virulent human malaria parasite, is estimated to cause over 300 million new cases and 1 million deaths annually (33). Further complicating this grim scenario is the emergence of the widespread resistance of P. falciparum to available antimalarial drugs (25). New drugs to combat malaria are urgently needed.Among potential new targets for antimalarial chemotherapy are enzymes that mediate hemoglobin hydrolysis. Intraerythrocytic P. falciparum trophozoites derive amino acids for protein synthesis from the hydrolysis of host cell hemoglobin in an acidic food vacuole (12,20,27). Proteases that hydrolyze hemoglobin in the food vacuole include members of the aspartic protease (1), cysteine protease (38, 39), and metalloprotease (9) families. Cysteine protease inhibitors arrested the erythrocytic life cycle of P. falciparum (26). Examination of inhibitortreated parasites revealed abnormally swollen food vacuoles filled with undigested hemoglobin, indicating that the block in parasite development was due to the inhibition of hemoglobin hydrolysis (26).P. falciparum contains three fairly typical papain family cysteine proteases, known as falcipains (28,38,39). Falcipain-2 and falcipain-3 appear to be the principal cysteine protease hemoglobinases (38, 39). Both of these proteases localize to vacuolar parasite fractions and readily hydrolyze hemoglobin under physiological reducing conditions at acidic pHs (37). Falcipain-2 is considerably more active against small peptide substrates, but the specificities of the two proteases are similar; both enzymes display a strong preference for leucine at the P 2 position (38, 39). The role of falcipain-1 in hemoglobin hydrolysis is unknown.In earlier studies, peptidyl vinyl sulfones inhibited falcipain-2 activity and parasite development at nanomolar concentrations and were active in vivo against murine malaria (22,29,30). We have now init...

We report the photophysical properties of new BODIPY derivatives monosubstituted at the central position. The presence of different functional groups induced the appearance of new photophysical processes in BODIPY dyes, such as intramolecular charge or energy transfer. These phenomena are sensitive to solvent properties (mainly the polarity) and have a potential use as fluorescent probes. Adequate modifications in their molecular structure or in the environment polarity can modulate the emission region of these fluorophores in the visible spectral region. Specifically, different processes and photophysical behaviors can be achieved depending on the excited chromophore and/or the solvent characteristics in a bichromophoric pyrene-BODIPY system.

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The preparation and full characterization of a variety of mono-([L1-H]), di-([L2-H 2 ], [L2A-H2]), and tri-([L3-H 3 ]) 1,2,3-triazolium salts constructed form "clicked" hydroxybenzene derivatives are reported. Deprotonation with potassium hexamethyldisilazide, followed by in situ metalation, allowed for the synthesis of a series of mono-(L1•[M]), di-(L2•[M] 2 , L2•[M] 2 ), and trinuclear (L3•[M] 3 ) group 9−11 (M = [Rh(CO) 2 Cl], [Pd(allyl)Cl], and [AuCl]) triazol-5-ylidene metal complexes. In solution, all metal complexes feature symmetrical patterns displaying C 2 and C 3 fold axes when supported by di-and tritriazol-5-ylidene ligands. The vibration frequencies of Ln•[Rh(CO) 2 Cl] n (n = 1−3) complexes indicate that the electron-donor properties of the new ligands are comparable to those for previously reported MIC complexes and superior to classical NHCs. Prompting coordination of the vicinal phenoxy group to the metal centers proved unsuccessful after treatment of the Ln•[Rh(CO) 2 Cl] n and Ln•[Pd(allyl)Cl] n (n = 1−3) precursors with AgBF 4 ; the expected chelated cationic complexes were highly unstable, indicating a weak or no coordination availability through the oxygen atom. Crystal structures of the complexes L1•[AuI] and L2A•[Pd(allyl)I] 2 illustrated the metal center geometrical environment and confirmed the lack of coordination through the phenoxy moiety of the ligand. Preliminary catalytic trials established the enhanced performance of di-and trimetallic palladium complexes in cross-coupling reactions and the intramolecular cyclization of enynes catalyzed by gold complexes.

Several new cysteine proteases of the papain family have been discovered in the past few years. To help in the assignment of physiological roles and in the design of specific inhibitors, a clear picture of the specificities of these enzymes is needed. One of these novel enzymes, cathepsin X, displays a unique specificity, cleaving single amino acid residues at the C-terminus of substrates very efficiently. In this study, the carboxypeptidase activities and substrate specificity of cathepsins X and B have been investigated in detail and compared. Using quenched fluorogenic substrates and HPLC measurements, it was shown that cathepsin X preferentially cleaves substrates through a monopeptidyl carboxypeptidase pathway, while cathepsin B displays a preference for the dipeptidyl pathway. The preference for one or the other pathway is about the same for both enzymes, i.e., approximately 2 orders of magnitude, a result supported by molecular modeling of enzyme-substrate complexes. Cleavage of a C-terminal dipeptide of a substrate by cathepsin X can become more important under conditions that preclude efficient monopeptidyl carboxypeptidase activity, e.g., nonoptimal interactions in subsites S(2)-S(1). These results confirm that cathepsin X is designed to function as a monopeptidyl carboxypeptidase. Contrary to a recent report [Klemencic, I., et al. (2000) Eur. J. Biochem. 267, 5404-5412], it is shown that cathepsins X and B do not share similar activity profiles, and that reagents are available to clearly distinguish the two enzymes. In particular, CA074 was found to inactivate cathepsin B at least 34000-fold more efficiently than cathepsin X. The insights obtained from this and previous studies have been used to produce an inhibitor designed to exploit the unique structural features responsible for the carboxypeptidase activity of cathepsin X. Although of moderate potency, this E-64 derivative is the first reported example of a cathepsin X-specific inhibitor.

A regioselective synthesis of N-carbomethoxy-2,3,5-tribromoindole (6) via a sequential one-pot bromination-aromatization-bromination of N-carbomethoxyindoline (2) is described. The process for the transformation of 2 into 6 permitted the isolation of stable reaction intermediates N-carbomethoxy-5-bromoindoline (3), N-carbomethoxy-5-bromoindole (4), and N-carbomethoxy-3,5-dibromoindole (5). Compound 6 was used to complete the total synthesis of the natural products 1b and 1c. In addition, bromination of N-carbomethoxyindole (11) afforded N-carbomethoxy-2,3,6-tribromoindole (13), from which the natural product 1a was synthesized.

Following a copper catalyzed alkyne azide cycloaddition (CuAAC) and N-alkylation protocols, we report the preparation of a hybrid N-heterocyclic/mesoionic [NHC(H)-MIC(H)][2I] salt (1) in high yields. The treatment of salt 1 with CuO and KI yields a second hybrid NHC/MIC proligand featuring a tetraiodocuprate anion [NHC(H)-MIC(H)][CuI] (2). Through selective deprotonation and metalation, both salts 1 and 2 can generate either the chelate heterodicarbene complexes (3) with the rare [NHC·(M)·MIC][MX] general formula (M = Pd, Rh) or NHC-anchored/pendent triazolium species (4) [NHC·(M)-MIC(H)]. If the triazolium moiety of type 4 complexes is deprotonated with KHMDS in the presence of a second metal center, a series of heterobimetallic complexes of the type [NHC·(M)-MIC·(M')] (5) are achieved. Interestingly, the reaction of salt 2 with KHMDS yields the bimetallic copper heterodicarbene (6) which can be a useful transfer reagent for the preparation of type 3 complexes. A variety of synthetic routes for the preparation of complexes 3-5 and their full characterization in solution and in the solid state will be discussed.

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