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Melanin concentrating hormone (MCH) is a cyclic 19-amino-acid peptide expressed mainly in the hypothalamus. It is involved in the control of feeding behavior, energy homeostasis, and body weight. Administration of MCH-R1 antagonists has been proved to reduce food intake and cause weight loss in animal models. In the present study, a homology model of the human MCH-R1 was constructed using the crystal structure of bovine rhodopsin (PDB: 1u19) as a template. Based on the observation that MCH-R1 can bind ligands of high chemical diversity, the initial model was subjected to an extensive ligand-supported refinement using antagonists of different chemotypes. The refinement process involved stepwise energy minimizations and molecular dynamics simulations. The refined model was inserted into a pre-equilibrated DPPC/TIP3P membrane system and then simulated for 20 ns in complex with structurally diverse antagonists. This protocol was able to explain the SAR of MCH-R1 antagonists with diverse chemical structures. Moreover, it reveals new insights into the critical recognition sites within the receptor. This work represents the first detailed study of molecular dynamics of MCH-R1 inserted into a membrane-aqueous environment.

The objective of the present research was to evaluate the physicochemical characteristics of berberine chloride and to assess the complexation of drug with 2-hydroxypropyl-β-cyclodextrin (HPβCD), a first step towards solution dosage form development. The parameters such as log P value were determined experimentally and compared with predicted values. The pH-dependent aqueous solubility and stability were investigated following standard protocols at 25°C and 37°C. Drug solubility enhancement was attempted utilizing both surfactants and cyclodextrins (CDs), and the drug/CD complexation was studied employing various techniques such as differential scanning calorimetry, Fourier transform infrared, nuclear magnetic resonance, and scanning electron microscopy. The experimental log P value suggested that the compound is fairly hydrophilic. Berberine chloride was found to be very stable up to 6 months at all pH and temperature conditions tested. Aqueous solubility of the drug was temperature dependent and exhibited highest solubility of 4.05 ± 0.09 mM in phosphate buffer (pH 7.0) at 25°C, demonstrating the effect of buffer salts on drug solubility. Decreased drug solubility was observed with increasing concentrations of ionic surfactants such as sodium lauryl sulfate and cetyl trimethyl ammonium bromide. Phase solubility studies demonstrated the formation of berberine chloride-HPβCD inclusion complex with 1:1 stoichiometry, and the aqueous solubility of the drug improved almost 4.5-fold in the presence of 20% HPβCD. The complexation efficiency values indicated that the drug has at least threefold greater affinity for hydroxypropyl-β-CD compared to randomly methylated-β-CD. The characterization techniques confirmed inclusion complex formation between berberine chloride and HPβCD and demonstrated the feasibility of developing an oral solution dosage form of the drug.

Delta(9)-Tetrahydrocannabinol hemisuccinate (THC-HS), an ester prodrug of Delta(9)-tetrahydrocannabinol (THC) has been investigated for its potential to form inclusion complexes with modified synthetic beta-cyclodextrins (CDs). Phase solubility studies were performed to determine the stoichiometric ratio of complexation of THC-HS with random methylated beta-cyclodextrin (RAMEB) and 2-hydroxypropyl beta-cyclodextrin (HPBCD). THC-HS/RAMEB and THC-HS/HPBCD solid systems were prepared by lyophilization and the lyophilized complexes were characterized by Fourier transform infrared (FT-IR) spectroscopy, proton nuclear magnetic spectroscopy, and molecular modeling techniques. The formation of inclusion complexes of THC-HS/RAMEB and THC-HS/HPBCD was demonstrated by an A(L) type curve with the slopes less than unity by the phase solubility method. The association constants for THC-HS/RAMEB and THC-HS/HPBCD were found to be 562.48 and 238.83 M(-1), respectively. The stoichiometry of both of the complexes was found to be 1:1 as determined from the Job's plot. This was confirmed by (1)H NMR and FT-IR techniques. The results obtained from the molecular modeling studies were in accordance with the data obtained from nuclear magnetic resonance and FT-IR. The docking studies revealed the most probable mode of binding of THC-HS with RAMEB in which the alkyl chain was submerged in the hydrophobic pocket of the CD molecule and hydrogen bonding interactions were observed between the hemisuccinate ester side chain of THC-HS and the rim hydroxy groups of RAMEB. The solubility of THC-HS was significantly higher in RAMEB compared to HPBCD. Solid dispersions of THC-HS with CDs will be further utilized to develop oral formulations of THC-HS with enhanced bioavailability.

Apoptosis, or programmed cell death, forms an important part of the cellular regulation machinery. The Bcl-2 protein family, comprising of proapoptotic and antiapoptotic members, forms an important part of the cells internal apoptotic pathway. Overexpression of the antiapoptotic members of the family in a number of cancer cell lines renders them immune to apoptosis and the ability to survive under conditions of cellular stress. Inhibition of the antiapoptotic members of the Bcl-2 family are, therefore, an interesting target for the development of anticancer therapy. An innovative structure-based virtual screening strategy was developed to identify inhibitors of Bcl-xL, an antiapoptotic member of the Bcl-2 family. Various innovative filters, such as receptor-based pharmacophore, cascade docking approach, cross-docking, and composite scoring with docking pose based descriptors were designed through exhaustive validation studies and implemented in the screening funnel. The 1.8 million 'big-n-greasy' subset from ZINC was screened using the protocol, and 45 compounds were finally selected for biological evaluation against Bcl-xL. The evaluation led to the identification of one low-micromolar and two weaker inhibitors belonging to novel scaffolds. Further evaluation of structure-activity relationships around these scaffolds could help in the development of anticancer leads against Bcl-xL.

Cysteine proteases are implicated in a variety of human physiological processes and also form an essential component of the life cycle of a number of pathogenic protozoa and viruses. The present review highlights the drug design approaches utilized to understand the mechanism of inhibition and discovery of inhibitors against protozoal cysteine protease, falcipain (a cysteine protease of P. falciparum which causes malaria), and viral cysteine protease, SARS-CoV M(pro) (a cysteine protease of severe acute respiratory syndrome corona virus). The article describes rational approaches for the design of inhibitors and focuses on a variety of structure as well as ligand-based modeling strategies adopted for the discovery of the inhibitors. Also, the key features of ligand recognition against these targets are accentuated. Although no apparent similarities exist between viral and protozoal cysteine proteases discussed here, the goal is to provide examples of rational drug design approaches adopted to design inhibitors against these proteases. The current review would be of interest to scientists engaged in the development of drug design strategies to target the cysteine proteases present in mammals and other lower order organisms.

In addition to lowering blood pressure, telmisartan, an angiotensin (AT(1)) receptor blocker, has recently been shown to exert pleiotropic effects as a partial agonist of nuclear peroxisome proliferator-activated receptor gamma (PPAR gamma). On the basis of these findings and docking pose similarity between telmisartan and rosiglitazone in PPAR gamma active site, two classes of benzimidazole derivatives were designed and synthesized as dual PPAR gamma agonist/angiotensin II antagonists for the possible treatment of metabolic syndrome. Compound 4, a bisbenzimidazole derivative showed the best affinity for the AT(1) receptor with a K(i) = 13.4 nM, but it was devoid of PPAR gamma activity. On the other hand 9, a monobenzimidazole derivative, showed the highest activity in PPAR gamma transactivation assay (69% activation) with no affinity for the AT(1) receptor. Docking studies lead to the designing of a molecule with dual activity, 10, with moderate PPARgamma activity (29%) and affinity for the AT(1) receptor (K(i) = 2.5 microM).

Progress made in the past decade pertaining to the development of anti-parasitic agents based on artemisinin is presented. Apart from discussions on important derivatives obtained through functionalization at the C-3, C-9, C-10 and O-11 positions of artemisinin, an outline on its seco analogs and artemisinin bundles are given for a broader perspective on structure-activity relationships. Success with synthetic peroxides, drug-hybrid approaches, broad-spectrum anti-infective properties of peroxide compounds and a survey on peroxide-containing natural products other than artemisinin with available biological data are included to highlight recent trends and avenues for future research. A supplementary material with details on the biological properties of a larger collection of molecules belonging to the above structural classes is also given for reference.

L-Malate dehydrogenase (PfMDH) from Plasmodium falciparum, the causative agent for the most severe form of malaria, has shown remarkable similarities to L: -lactate dehydrogenase (PfLDH). PfMDH is more closely related to [LDH-like] MDHs characterized in archae and other prokaryotes. Initial sequence analysis and identification of critical amino acid residues involved in inter-subunit salt-bridge interactions predict tetrameric structure for PfMDH. The catalytically active recombinant PfMDH was characterized as a tetramer. The enzyme is localized primarily in the parasites cytosol. To gain molecular insights into PfMDH/PfLDH relationships and to understand the quaternary structure of PfMDH, dimers were generated by mutation to the potential salt-bridge interacting sites. The R183A and R214G mutations, which snapped the salt bridges between the dimers and resulted in lower dimeric state, did not affect catalytic properties of the enzyme. The mutant dimers of PfMDH were active equally as the wild-type PfMDH. The studies reveal structure of PfMDH as a dimer of dimers. The tetrameric state of PfMDH was not essential for catalytic functions of the enzyme but may be an evolutionary adaptation for cytosolic localization to support its role in NAD/NADH coupling, an important metabolic function for survival of the malaria parasite.

A novel ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS-MS) method has been established for the determination of a newly synthesized epothilone D analog (AV-EPO-106) in human plasma. The plasma samples were prepared by liquid-liquid extraction with cold tert-butyl methyl ether. The chromatographic separation was achieved within 5 min on a C(18) column with water-methanol (10:90, v/v) as mobile phase at a flow-rate of 0.8 mL/min. Mass transition of m/z 568.2 to 386.1 was measured for AV-EPO-106 in positive atmospheric pressure chemical ionization mode. A detailed validation of the method was performed as per the USFDA guidelines. For AV-EPO-106 at the concentrations of 1.0, 5.0 and 10.0 microg/mL in human plasma, the absolute extraction recoveries were 86.17, 85.24 and 85.69%, respectively. The linear quantification range of the method was 0.10-20.0 microg/mL in human plasma with linear correlation coefficients greater than 0.999. The intra-day and inter-day accuracy for AV-EPO-106 at the levels of 1.0, 5.0 and 10.0 microg/mL in human plasma fell in the ranges of 98.25-100.47 and 94.19-97.25%, and the intra- and inter-day precision were in the ranges of 4.75-6.30% and 8.89-10.45%, respectively. The method was successfully applied to quantify AV-EPO-106 in human plasma to determine the half-life of this compound in human plasma., (2008 John Wiley & Sons, Ltd.)

The asymmetric unit of the title compound, C(22)H(26)O(8), contains two crystallographically independent mol-ecules with closely comparable conformations (r.m.s. overlay = 0.54 Å for 30 non-H atoms). All six-membered rings display chair conformations, with a slight distortion for the lactone ring. The mol-ecules are connected by O-H⋯O hydrogen bonds into chains along [010], with the independent mol-ecules segregated into separate chains. The two mol-ecules in the asymmetric unit face each other in a head-to-tail fashion, with the furan ring of one mol-ecule turned towards the carboxylic acid terminal of the other mol-ecule.

The title compound, C(22)H(30)O(7), is a fused five-ring system that is of inter-est for its anti-cancer and anti-malarial activity. The six-membered C(6) and C(5)O rings display chair conformations. The six-membered C(3)O(3) ring containing the ether and per-oxy functionalities has a distorted boat conformation, with a C-O-O-C torsion angle of 42.6 (1)° for the per-oxy group. The seven-membered C(6)O ring has a distorted boat-type conformation, while the seven-membered C(5)O(2) ring has a very distorted chair-type conformation. The structure contains inter-molecular O-H⋯O and O-H⋯(O,O) bonds that link the mol-ecules into sheets parallel to the (100) planes.

In the crystal structure of the title compound, C(28)H(36)O(4)S, the p-tolyl ring is inclined at 35.8° to the aromatic ring. The cyclohexene ring adopts a boat conformation and the heterocyclic ring is in a slightly distorted screw boat conformation.

A series of 53 nitro derivatives rationally designed were obtained by parallel synthesis and screened against Leishmania donovani. Six compounds exhibited IC(50) values lower than standard drugs. Brief SAR analysis revealed that substitution is important to the activity. Nitrothiophene analogues were more potent than the nitrofuran ones. This was attributed to the ability of sulfur atoms in accommodating electrons from nitro group, which facilitate its reduction and therefore the formation of free radicals lethal to parasites.

The salvinorin A analog dimethyl (2R,3aR,4R,6aR,7R,9S,9aS,9bS)-2-(3-fur-yl)-9,9a-dihydr-oxy-3a,6a-dimethyl-dodeca-hydro-benzo[de]chromene-4,7-dicarboxyl-ate, C(22)H(30)O(8), has a relatively simple spatial arrangement in which mol-ecules are linked into layers by two pairs of O-H⋯O hydrogen bonds. Each mol-ecule has as the central feature a dodeca-hydro-1H-phenalene ring system. Its three six-membered rings are in the chair conformation, with two axial methyl groups, one axial OH, and one equatorial OH, these OH groups being directly responsible for linking of the mol-ecules in the crystal structure.

Two new cyclic hexapeptides, mollamides B (1) and C (2), were isolated from the Indonesian tunicate Didemnum molle along with the known peptide keenamide A (3). The structures were established using 1D and 2D NMR experiments. The relative configuration of mollamide B at the thiazoline moiety was determined using molecular modeling coupled with NMR-derived restraints. Their absolute configuration was determined using Marfey's method. The new peptides have been evaluated for their antimicrobial, antimalarial, anticancer, anti-HIV-1, anti-Mtb, and anti-inflammatory activities. Keenamide A and mollamide B show cytotoxicity against several cancer cell lines.

Leishmania donovani and Leishmania major farnesyl pyrophosphate synthase ( LdFPPS and LmFPPS) are potential targets for the development of antileishmanial therapy. The protein sequence for LdFPPS was recently elucidated in our laboratory. Highly refined homology models were generated using the protein sequences of LdFPPS and the closely related LmFPPS enzyme. A ligand-refined model of LmFPPS with a bound bisphosphonate ligand was generated using restraint-guided molecular mechanics followed by quantum mechanics/molecular mechanics refinement. The ligand-refined model of LmFPPS was further validated through extensive pose validation, enrichment, and other docking studies involving known bisphosphonate inhibitors. The model was able to explain the critical binding site interactions and site-directed mutagenesis data obtained from experimental studies on related FPPS enzymes. The ligand-refined model in conjunction with the validated docking protocol could be utilized in the future for structure-based virtual screening and rational drug design studies against these targets.

A method based on ultra-performance liquid chromatography mass spectrometry (UPLC-MS) applying atmospheric pressure chemical ionization in the positive ion mode is developed for the determination of coenzyme Q10 (CoQ10) in rat urine. The assay involves the extraction of crude urine, fast liquid chromatography on a Waters Acquity UPLC BEH C18 column (1.7 microm, 1.0 x 50 mm), and selected ion monitoring detection using mass transition. The calibration range is found to be 0.05-25 microg/mL, with the lower limit of quantitation of 0.05 microg/mL. Intra- and inter-day precision (relative standard deviation) for CoQ10 in rat urine range from 0.7% to 15%, and accuracy expressed in recovery rates in urine is between 83% and 118%. The recovery of this method is found to be between 80% and 95% at three concentrations. The total cumulative recovery of CoQ10 is 1.16 +/- 1.05% (percentage of dose intake, n = 4) from rat urine collected over 30 h after oral administration of the drug. The UPLC-MS method described allows the quick determination of CoQ10 in rat urine with good precision and accuracy. It is suitable for further excretion studies of CoQ10 in animals.

Synthesis of farnesyl pyrophosphate (FPP), a key intermediate of the isoprenoid biosynthesis pathway, is catalyzed by FPP synthase (FPPS). Antiprotozoal properties of bisphosphonates, which target FPPS, have generated interest in FPPS as a potential antiprotozoal drug target. The genes encoding FPPS from parasitic protozoa were assessed to analyze structural and functional features of the enzyme. Comparisons of the FPPS from the parasitic protozoa and search for conserved motifs revealed that FPPS from both apicomplexan and trypanosomatid parasites show characteristic conserved regions for example first aspartate rich motif (FARM) contained within II conserved domain and the second aspartate rich motif (SARM) contained within VI conserved domain. Phylogenetic analysis of FPPS generated a tree with three distinct clusters. Overall topology of the phylogenic tree constructed with small subunit ribosomal RNA sequences was almost similar to that constructed with FPPS sequences. Comparative homology modeling and structural comparisons of FPPS from the parasitic protozoa provided significant insights into common and distinct characteristics of the enzyme. The critical interacting residues of the isopentenyl pyrophosphate binding site are conserved across the enzymes from the family except for malarial FPPS where the C-terminal residues from the BXB motif of helix J were missing. Variations noticed in aromatic residue pairs at the fourth and fifth position upstream of the FARM, which play important role in determination of chain length of the polyprenyl products, may produce functional differences among protozoan FPPSs. The structural comparison of protozoan FPPS may be useful in designing common or selective FPPS inhibitors as potential broad spectrum or selective antiprotozoal agents.

Chemical transformation studies were conducted on (-)-8-hydroxymanzamine A ( 1), (-)-manzamine F ( 2), manzamine A ( 3), and (+)-8-hydroxymanzamine A ( 4), isolated from Indo-Pacific Acanthostrongylophora sponges. Thirteen new semisynthetic manzamine derivatives, including four Delta (34,35) manzamines ( 5, 6, 8, and 9) and the unprecedented manzamine derivative 17, are reported. The potent in vitro activities of the obtained semisynthetic manzamines against activated brain microglia and the AIDS opportunistic infection pathogen Mycobacterium tuberculosis are presented.

CRYSTALS OF THE TITLE COMPOUND [SYSTEMATIC NAME: (3R,6R,7S,8aR,9R,12aR)-7-hydr-oxy-3,6,9-trimethyl-octa-hydro-3,12-ep-oxy[1,2]dioxepino[4,3-i]isochromen-10(3H)-one], C(15)H(22)O(6), were obtained from microbial transformation of artemisinin by a culture of Cunninghamella elegans. The stereochemistry of the compound is consistent with the spectroscopic findings in previously published works. A weak O-H⋯O hydrogen bond occurs in the crystal structure, together with intermolecular C-H⋯O hydrogen bonds.

Type II diabetes is a heterogeneous disease where environment and genetics are important factors for the expression of the disease. The high cost for treating complications of diabetes is a burden for public health systems and governments worldwide. Type II diabetes has been causing debilitation worldwide for many decades, and a single drug that safely treats the disease has yet to be discovered. Sulfonylureas, biguanides, alpha-glucosidase, meglitinides, DPP-4 inhibitors and thiazolidinediones are among the classes of oral hypoglycemic drugs available to treat Type II diabetes, but concerns exist regarding safety and efficacy of these drugs. In this article we present the pros and cons of the six classes and discuss some of the latest advances towards the development of new drugs for the treatment of Type II diabetes.

Malaria, one of the major reemerging parasitic diseases, is caused by protozoal parasites belonging to the genus plasmodia. Antimalarial drugs have played a mainstream role in controlling the spread of malaria through the treatment of patients infected with the plasmodial parasites and controlling its transmissibility. The current line of therapy against malaria is faced with the hurdles of a low or total lack of efficacy due to the evolution of drug-resistant strains of the malarial parasites. Preventive vaccination against malaria is an ideal solution to this problem but is not expected to arrive for at least a decade. Development of antimalarial drugs involving novel mechanisms of action is therefore of imminent importance. Several novel drug candidates of synthetic and natural products origin as well as their combination therapies are currently being evaluated for their efficacy against the drug-resistant strains of the parasites. Various plasmodial targets/pathways, such as the Purine salvage pathway, Pyrimidine biosynthesis pathway as well as the processes in the apicoplast, have been identified and are being utilized for the discovery and development of novel antimalarial therapies. This review provides an overview of the latest developments in terms of drugs, combination therapies and novel plasmodial targets being carried out to counter the menace of drug-resistant malaria.

The absolute stereo structure of the natural product laurenditerpenol (1S, 6R, 7S, 10R, 11R, 14S, 15R) has been accomplished from eight plausible stereoisomers by its first asymmetric total synthesis in a highly convergent and flexible synthetic pathway. Six stereoisomers of laurenditerpenol were synthesized and evaluated for their biological activity.

Mycobacterium tuberculosis 1-deoxy-D: -xylulose-5-phosphate reductoisomerase (MtDXR) is a potential target for antitubercular chemotherapy. In the absence of its crystallographic structure, our aim was to develop a structural model of MtDXR. This will allow us to gain early insight into the structure and function of the enzyme and its likely binding to ligands and cofactors and thus, facilitate structure-based inhibitor design. To achieve this goal, initial models of MtDXR were generated using MODELER. The best quality model was refined using a series of minimizations and molecular dynamics simulations. A protein-ligand complex was also developed from the initial homology model of the target protein by including information about the known ligand as spatial restraints and optimizing the mutual interactions between the ligand and the binding site. The final model was evaluated on the basis of its ability to explain several site-directed mutagenesis data. Furthermore, a comparison of the homology model with the X-ray structure published in the final stages of the project shows excellent agreement and validates the approach. The knowledge gained from the current study should prove useful in the design and development of inhibitors as potential novel therapeutic agents against tuberculosis by either de novo drug design or virtual screening of large chemical databases.

Plasmodium falciparum lactate dehydrogenase (pfLDH) is a key enzyme for energy generation of malarial parasites and is a potential antimalarial chemotherapeutic target. It is known that the oxamate moiety, a pyruvate analog, alone shows higher inhibition against pfLDH than human LDHs, suggesting that it can be used for the development of selective inhibitors. Oxamic acid derivatives were designed and synthesized. Derivatives 5 and 7 demonstrated activities against pfLDH with IC50 values of 3.13 and 1.75 muM, respectively, and have 59- and 7-fold selectivity over mammalian LDH, respectively. They also have micromolar range activities against Plasmodium falciparum malate dehydrogenase (pfMDH), which may fill the role of pfLDH when the activity of pfLDH is reduced. Thus, certain members of these oxamic acid derivatives may have dual inhibitory activities against both pfLDH and pfMDH. It is presumed that dual LDH/MDH inhibitors would have enhanced potential as antimalarial drugs.

A simple synthesis of sulfonamides 4-22 as novel histone deacetylase (HDAC) inhibitors is described. The key synthetic strategies involve N-sulfonylation of L-proline benzyl ester hydrochloride (2) and coupling reaction of N-sulfonyl chloride 3 with amines in high yields. It was found that several compounds showed good cellular potency with the most potent compound 20 exhibiting an IC50 = 2.8 microM in vitro.

Lactate dehydrogenase (LDH) is a key enzyme in the glycolytic pathway of Plasmodium falciparum (pf) and has several unique amino acids, related to other LDHs, at the active site, making it an attractive target for antimalarial agents. Oxamate, a competitive inhibitor, shows high substrate affinity for pfLDH. This class of compounds has been viewed as potential antimalarial agents. Thus, we have developed an effective automated synthetic strategy for the rapid synthesis of oxamic acid and ester libraries to screen for potential lead inhibitors. One hundred sixty-seven oxamic acids were synthesized using a "catch and release" method with overall yields of 20-70%. Most of the compounds synthesized had some inhibitory effects, but compounds 5 and 6 were the most active against both chloroquine- and mefloquine-resistant strains with IC50 values of 15.4 and 9.41 microM and 20.4 and 8.40 microM, respectively. Some oxamic acids showed activities against pfLDH and mammalian LDH (mLDH) at the micromolar range. These oxamic acids selectively inhibited pfLDH 2-5 fold over mLDH. Oxamic acid 21 was the most active against pfLDH at IC50 = 14 and mLDH at IC50 = 25 microM, suggesting that oxamic acid derivatives are potential inhibitors of pfLDH and that further study is required to develop selective inhibitors of pfLDH over mLDH.

Peroxisome proliferator-activated receptors (PPARs), members of the nuclear hormone receptor (NHR) family, are ligand-activated transcription factors. Ligands (agonists) of PPARgamma have been shown to inhibit growth, promote terminal differentiation, and induce apoptosis in human breast tumor cells. A cell-based reporter assay was developed to examine extracts of terrestrial and marine organisms for the ability to activate PPARgamma. Bioassay-guided fractionation and isolation of an active extract from Pseudoceratina rhax yielded the known histone deacetylase (HDAC) inhibitor psammaplin A (1). Compound 1 activates PPARgamma in a MCF-7 cell-based reporter assay and induces apoptosis in human breast tumor cells in vitro. Molecular modeling studies suggest that 1 may interact with binding sites within the PPARgamma ligand-binding pocket. Therefore, in addition to its known effects on HDAC-mediated processes, activation of PPARgamma-regulated gene expression may play a role in the ability of 1 to induce apoptosis.

Artemisinin (1) and its analogues have been well studied for their antimalarial activity. Here we present the antimalarial activity of some novel C-9-modified artemisinin analogues synthesized using artemisitene as the key intermediate. Further, antileishmanial activity of more than 70 artemisinin derivatives against Leishmania donovani promastigotes is described for the first time. A comprehensive structure-activity relationship study using CoMFA is discussed. These analogues exhibited leishmanicidal activity in micromolar concentrations, and the overall activity profile appears to be similar to that against malaria. Substitution at the C-9beta position was shown to improve the activity in both cases. The 10-deoxo derivatives showed better activity compared to the corresponding lactones. In general, compounds with C-9alpha substitution exhibited lower antimalarial as well as antileishmanial activities compared to the corresponding C-9beta analogues. The importance of the peroxide group for the observed activity of these analogues against leishmania was evident from the fact that 1-deoxyartemisinin analogues did not exhibit antileishmanial activity. The study suggests the possibility of developing artemisinin analogues as potential drug candidates against both malaria and leishmaniasis.

Hydroxypropyl-beta-cyclodextrin (HPBCD) was investigated as a possible solubilizer for a series of poorly water-soluble antimalarial drugs. The solubilities of artemisinin, artether, dihydroartemisinin, and 10-deoxoartemisinin in HPBCD solutions were studied. The phase-solubility profile of these drugs in HPBCD solutions, in the concentration range studied, can be classified as type A(L) or soluble 1:1 complexes. The solubilities of artemisinin, artether, dihydroartemisinin, and 10-deoxoartemisinin in 20% w/v solutions of HPBCD are 4.5, 1.3, 6.0, and 5.2 mg/mL, respectively. The stability constants of artemisinin, dihydroartemisinin, artether, and 10-deoxoartemisinin complexes with HPBCD are 475, 405, 327, and 146 M(-1), respectively. Three different docking methods, SYBYL DOCK, FlexiDock, and DOCK 4.0.1 were evaluated to further understand the complexation modes and applicability of the docking programs for the modeling of inclusion complexes. The results showed that DOCK 4.0.1 offers a better correlation in terms of orientation of molecules inside the cyclodextrin cavity and also in terms of docking scores., (Copyright 2003 Wiley-Liss, Inc. and the American Pharmaceutical Association)

Increasing resistance of malaria parasites to conventional antimalarial drugs is an important factor contributing to the persistence of the disease as a major health threat. The ongoing search for novel targets has resulted in identification and expression of several enzymes including cysteine proteases that are implicated in hemoglobin degradation. Falcipain-2 and falcipain-3 are considered to be the two principal cysteine proteases in this degradation, and hence, are potential drug targets. A homology model of falcipain-3 was built and validated by various structure/geometry verification tools as well as docking studies of known substrates. The correlation coefficient of 0.975 between interaction energies and K(m) values of these substrates provided additional support for the model. On comparison with the previously reported falcipain-2 homology model, the currently constructed falcipain-3 structure showed important differences between the S2 pockets that might explain the variations in the K(m) values of various substrates for these enzymes. Further, docking studies also provided insight into possible binding modes and interactions of ligands with falcipain-3. Results of the current study could be employed in de novo drug design leading to development of new antimalarial agents.

Giardiasis is a protozoal disease infecting 200 million people throughout the world. Giardiasis is widespread primarily in developing countries. Infections are correlated with poor hygienic conditions, poor water quality control, and overcrowding. There are very few therapeutics currently available, and drug development to treat giardiasis is hampered mainly by socioeconomic obstacles. This article presents the history of antigiardial chemotherapy and current state of therapeutic availability along with the future prospectus of development of antigiardial agents. In addition to accumulated knowledge about the previous and current antigiardial drugs, advanced technologies including computer-aided drug design and combinatorial synthetic chemistry, as well as high throughput screening techniques, accelerate understanding of the disease and further research toward a suitable antigiardial agent.

On the basis of earlier reported quantitative structure-activity relationship studies, a series of 9beta-16-(arylalkyl)-10-deoxoartemisinins were proposed for synthesis. Several of the new compounds 7 and 10-14 were synthesized employing the key synthetic intermediate 23. In a second approach, the natural product (+)-artemisinic acid was utilized as an acceptor for conjugate addition, and the resultant homologated acids were subjected to singlet oxygenation and acid treatment to provide artemisinin analogues. Under a new approach, we developed a one step reaction for the interconversion of artemisinin 1 into artemisitene 22 that did not employ selenium-based reagents and found that 2-arylethyliodides would undergo facile radical-induced conjugate addition to the exomethylene lactone of 22 in good yield. The lactone carbonyls were removed sequentially by diisobutylaluminum hydride reduction followed directly by a second reduction (BF(3)-etherate/Et(3)SiH) to afford the desired corresponding pyrans. Six additional halogen-substituted aromatic side chains were installed via 22 furnishing the bioassay candidates 15-20. The analogues were examined for in vitro antimalarial activity in the W-2 and D-6 clones of Plasmodium falciparum and were additionally tested in vivo in Plasmodium berghei- and/or Plasmodium yoelii-infected mice. Several of the compounds emerged as highly potent orally active candidates without obvious toxicity. Of these, two were chosen for pharmacokinetic evaluation, 14 and 17.

Extracts of the root and trunk barks of the Chinese tree Pseudolarix kaempferi, which contain pseudolaric acids, are used in Chinese medicine for treatment of fungal infections. Pseudolaric acid B (PLAB) is the major constituent that exhibits anti-fungal activity. The nuclear peroxisome proliferator-activator receptors (PPAR) were proposed as a cellular target for the action of PLAB and its analogs. PLAB and two derivatives were tested for the activation of PPAR isoforms in two mammalian cell lines. CV-1 and H4IIEC3 cells were transfected with phorbol ester response element or PPAR response element reporter constructs, and CV-1 cells were co-transfected with the individual PPAR isoform expression plasmids. PLAB showed similar concentration-dependent effects for the activation of PPAR alpha, gamma and delta isoforms in CV-1 and H4IIEC3 cells. O-Deacetylation of PLAB (PLAC) or esterification of the free carboxy group of PLAB with beta-D-O-glucopyranoside (PLAG) markedly reduced or abolished the activation of these PPAR isoforms. In H4IIEC3 cells, PLAB increased the activation of endogenous PPARalpha and the phospholipase C signaling pathway; and stimulated peroxisomal fatty acyl-CoA oxidase activity. These effects of PLAB on the activation of endogenous PPARalpha and phospholipase C-dependent pathway were blocked by staurosporine. These results suggest that the action of PLAB on PPARalpha in H4IIEC3 cells is mediated by a protein kinase C dependent phosphorylation. Based upon these findings, the chemical class of biologically active diterpene acids related to PLAB may have promise for the treatment of metabolic and pathophysiological disorders that are regulated by these nuclear receptor isoforms.

Increasing resistance of malaria parasites, in particular Plasmodium falciparum, demands a serious search for novel targets. Cysteine protease in P. falciparum, encoded by a previously unidentified gene falcipain 2, provides one such target to design chemotherapeutic agents for treatment of malaria. In fact, a few cysteine protease inhibitors have been shown to inhibit growth of cultured malarial parasites. In absence of a crystal structure for this enzyme, homology modeling proved to be a reasonable alternative to study binding requirements of the enzyme. A homology model for falcipain 2 was developed and validated by docking of known vinyl sulfone inhibitors. Further, based on the observations of these studies, novel isoquinoline inhibitors were designed and synthesized, which exhibited in vitro enzyme inhibition at micromolar concentrations.

Artemisinin (1) is a unique sesquiterpene peroxide occurring as a constituent of Artemisia annua L. Because of the effectiveness of Artemisinin in the treatment of drug-resistant Plasmodium falciparum and its rapid clearance of cerebral malaria, development of clinically useful semisynthetic drugs for severe and complicated malaria (artemether, artesunate) was prompt. However, recent reports of fatal neurotoxicity in animals with dihydroartemisinin derivatives such as artemether have spawned a renewed effort to develop nontoxic analogues of artemisinin. In our effort to develop more potent, less neurotoxic agents for the oral treatment of drug-resistant malaria, we utilized comparative molecular field analysis (CoMFA) and hologram QSAR (HQSAR), beginning with a series of 211 artemisinin analogues with known in vitro antimalarial activity. CoMFA models were based on two conformational hypotheses: (a) that the X-ray structure of artemisinin represents the bioactive shape of the molecule or (b) that the hemin-docked conformation is the bioactive form of the drug. In addition, we examined the effect of inclusion or exclusion of racemates in the partial least squares (pls) analysis. Databases derived from the original 211 were split into chiral (n = 157), achiral (n = 34), and mixed databases (n = 191) after leaving out a test set of 20 compounds. HQSAR and CoMFA models were compared in terms of their potential to generate robust QSAR models. The r(2) and q(2) (cross-validated r(2)) were used to assess the statistical quality of our models. Another statistical parameter, the ratio of the standard error to the activity range (s/AR), was also generated. CoMFA and HQSAR models were developed having statistically excellent properties, which also possessed good predictive ability for test set compounds. The best model was obtained when racemates were excluded from QSAR analysis. Thus, CoMFA of the n = 157 database gave excellent predictions with outstanding statistical properties. HQSAR did an outstanding job in statistical analysis and also handled predictions well.