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The compound ethyl-adenosyl monophosphate ester (ethyl-AMP) has been shown to effectively inhibit acetyl-CoA synthetase (ACS) enzymes and to facilitate the crystallization of fungal ACS enzymes in various contexts. In this study, the addition of ethyl-AMP to a bacterial ACS from Legionella pneumophila resulted in the determination of a co-crystal structure of this previously elusive structural genomics target. The dual functionality of ethyl-AMP in both inhibiting ACS enzymes and promoting crystallization establishes its significance as a valuable resource for advancing structural investigations of this class of proteins.

Praziquantel (PZQ) remains the only drug of choice for the treatment of schistosomiasis, caused by parasitic flatworms. The widespread use of PZQ in schistosomiasis endemic areas for about four decades raises concerns about the emergence of resistance of Schistosoma spp. to PZQ under drug selection pressure. This reinforces the urgency in finding alternative therapeutic options that could replace or complement PZQ. We explored the potential of medicinal plants commonly used by indigenes in Kenya for the treatment of various ailments including malaria, pneumonia, and diarrhoea for their antischistosomal properties. Employing the Soxhlet extraction method with different solvents, seven medicinal plants Artemisia annua, Ajuga remota, Bredilia micranta, Cordia africana, Physalis peruviana, Prunus africana and Senna didymobotrya were extracted. Qualitative phytochemical screening was performed to determine the presence of various phytochemicals in the plant extracts. Extracts were tested against Schistosoma mansoni newly transformed schistosomula (NTS) and adult worms and the schistosomicidal activity was determined by using the adenosine triphosphate quantitation assay. Phytochemical analysis of the extracts showed different classes of compounds such as alkaloids, tannins, terpenes, etc., in plant extracts active against S. mansoni worms. Seven extracts out of 22 resulted in 69.7% and ≥72.4% reduction in viability against adult worms after exposure for 24 and 48 h, respectively. This study provides encouraging preliminary evidence that extracts of Kenyan medicinal plants deserve further study as potential alternative therapeutics that may form the basis for the development of the new treatments for schistosomiasis.

Acetyl CoA synthetases (ACSs) are Acyl-CoA/NRPS/Luciferase (ANL) superfamily enzymes that couple acetate with CoA to generate acetyl CoA, a key component of central carbon metabolism in eukaryotes and prokaryotes. Normal mammalian cells are not dependent on ACSs, while tumor cells, fungi, and parasites rely on acetate as a precursor for acetyl CoA. Consequently, ACSs have emerged as a potential drug target. As part of a program to develop antifungal ACS inhibitors, we characterized fungal ACSs from five diverse human fungal pathogens using biochemical and structural studies. ACSs catalyze a two-step reaction involving adenylation of acetate followed by thioesterification with CoA. Our structural studies captured each step of these two half-reactions including the acetyl-adenylate intermediate of the first half-reaction in both the adenylation conformation and the thioesterification conformation and thus provide a detailed picture of the reaction mechanism. We also used a systematic series of increasingly larger alkyl adenosine esters as chemical probes to characterize the structural basis of the exquisite ACS specificity for acetate over larger carboxylic acid substrates. Consistent with previous biochemical and genetic data for other enzymes, structures of fungal ACSs with these probes bound show that a key tryptophan residue limits the size of the alkyl binding site and forces larger alkyl chains to adopt high energy conformers, disfavoring their efficient binding. Together, our analysis provides highly detailed structural models for both the reaction mechanism and substrate specificity that should be useful in designing selective inhibitors of eukaryotic ACSs as potential anticancer, antifungal, and antiparasitic drugs.

Infectious diseases are a major cause of morbidity and mortality around the world, accounting for approximately 50% of all deaths in tropical countries. Despite remarkable progress in the field of microbiology, inability to control or mitigate, epidemics caused by drug-resistant microorganisms pose a serious health hazard to the global population. New therapeutic strategies must be developed as a global initiative for the prevention and control of infectious diseases. This study focuses on Kenyan medicinal plants and their activity against bacteria. Plant extracts obtained from seven Kenyan plants used in traditional medicine, were screened for their antibacterial activity against Escherichia coli, Pseudomonas aeruginosa, Bacillus cereus, and Mycobacterium smegmatis. Extracts from all these plants showed antibacterial activity against at least one of the tested organisms at a concentration of 2 mg/mL. Chemical screening showed the presence of different classes of phytochemicals such as alkaloids, terpenes, tannins, in some active extracts.

Filth flies, including house flies, Musca domestica L., develop in animal manure. Adult house flies often are controlled with pesticides such as imidacloprid. How imidacloprid disseminates and persists after it contaminates manure was measured at a dairy farm. A week after application of imidacloprid via fly bait to cattle manure, a mean of approximately 4 ppm of imidacloprid, and as high as 15 ppm, was quantifiable up to 12 cm from the application site, but not farther. Laboratory experiments addressed the impact of 15 ppm of imidacloprid in manure on egg-to-adult development of house flies and on the biological control ability of a house fly pupal parasitoid, Spalangia endius Walker. In uncontaminated manure, 93% of eggs developed to adults, versus 7% in contaminated manure. In the parasitoid experiment, fly pupae were placed in contaminated or uncontaminated manure with or without S. endius. In the absence of S. endius, nearly 100% of flies emerged, with or without imidacloprid. In the presence of S. endius, only 11% of flies emerged from uncontaminated manure, versus 36% from contaminated manure; and parasitoids emerged from 82% of hosts in uncontaminated manure versus 53% in contaminated manure. These results suggest that realistic concentrations of imidacloprid in filth fly breeding habitat may interfere with house flies developing to the pupal stage, but also with parasitoids locating and utilizing house flies. However, after 1 wk, the effects on parasitoids will be low 12 cm beyond where bait was applied.

AIMS: Therapies that recapitulate the health benefits of caloric restriction in older adults are needed. Phosphodiesterase 4 inhibitors demonstrate such promise. We examined their effects on body weight and composition, physical and cognitive function in aged mice using Compound D159687 (D159687). METHODS: Nineteen 18 months old mice were randomized to receive either control (DMSO) or D159687 for seven weeks. We assessed food intake, body weight, and body composition over time and performed once the following tests: treadmill, inverted grip strength, rotarod, spontaneous Y maze tests and skeletal muscle mitochondrial biogenesis. RESULTS: Four of the D159687 treated mice died in the first week. Necropsy suggests acute lung injury. D159687 treated mice weighed more than control mice at baseline. After controlling for baseline weight, D159687 treated mice lost 4.2grams more weight than control mice, mainly from fat mass loss (p value < 0.001). Muscle mass was unchanged between the two mice groups. D159587 mice ate significantly more food than the control mice. We found no difference between the two groups in the results of treadmill, rotarod and spontaneous Y maze tests and in mitochondrial biogenesis. CONCLUSION: Compound D159687 induced weight loss, predominantly fat mass loss and increased food intake in aged mice. The caloric restriction and lean mass preservation potential of PDE4D inhibitors deserve further verification. Findings may have major therapeutic implications when translated to the older adult population. Although physical and cognitive parameters were unchanged in this study, further studies would be needed to verify these results. The high death rate in the D159687 treated mice may have been due to the technical aspects of oral gavage.

The enzyme 2-methylerythritol 2,4-cyclodiphosphate synthase, IspF, is essential for the biosynthesis of isoprenoids in most bacteria, some eukaryotic parasites, and the plastids of plant cells. The development of inhibitors that target IspF may lead to novel classes of anti-infective agents or herbicides. Enantiomers of tryptophan hydroxamate were synthesized and evaluated for binding to Burkholderia pseudomallei (Bp) IspF. The L-isomer possessed the highest potency, binding BpIspF with a KD of 36 µM and inhibited BpIspF activity 55% at 120 µM. The high-resolution crystal structure of the L-tryptophan hydroxamate (3)/BpIspF complex revealed a non-traditional mode of hydroxamate binding where the ligand interacts with the active site zinc ion through the primary amine. In addition, two hydrogen bonds are formed with active site groups, and the indole group is buried within the hydrophobic pocket composed of side chains from the 60 s/70 s loop. Along with the co-crystal structure, STD NMR studies suggest the methylene group and indole ring are potential positions for optimization to enhance binding potency.

Novel pyridine- and pyrimidine-based allosteric inhibitors are reported that achieve PDE4D subtype selectivity through recognition of a single amino acid difference on a key regulatory domain, known as UCR2, that opens and closes over the catalytic site for cAMP hydrolysis. The design and optimization of lead compounds was based on iterative analysis of X-ray crystal structures combined with metabolite identification. Selectivity for the activated, dimeric form of PDE4D provided potent memory enhancing effects in a mouse model of novel object recognition with improved tolerability and reduced vascular toxicity over earlier PDE4 inhibitors that lack subtype selectivity. The lead compound, 28 (BPN14770), has entered mid-stage, human Phase 2 clinical trials for the treatment of Fragile X Syndrome.

© 2016 Elsevier Ltd Methionine aminopeptidase (MetAP) is a class of ubiquitous enzymes essential for the survival of numerous bacterial species. These enzymes are responsible for the cleavage of N-terminal formyl-methionine initiators from nascent proteins to initiate post-translational modifications that are often essential to proper protein function. Thus, inhibition of MetAP activity has been implicated as a novel antibacterial target. We tested this idea in the present study by targeting the MetAP enzyme in the obligate intracellular pathogen Rickettsia prowazekii. We first identified potent RpMetAP inhibitory species by employing an in vitro enzymatic activity assay. The molecular docking program AutoDock was then utilized to compare published crystal structures of inhibited MetAP species to docked poses of RpMetAP. Based on these in silico and in vitro screens, a subset of 17 compounds was tested for inhibition of R. prowazekii growth in a pulmonary vascular endothelial cell (EC) culture infection model system. All compounds were tested over concentration ranges that were determined to be non-toxic to the ECs and 8 of the 17 compounds displayed substantial inhibition of R. prowazekii growth. These data highlight the therapeutic potential for inhibiting RpMetAP as a novel antimicrobial strategy and set the stage for future studies in pre-clinical animal models of infection.

The fragment FOL7185 (compound 17) was found to be a hit against IspD and IspE enzymes isolated from bacteria, and a series of analogs containing the pyrazolopyrimidine core were synthesized. The majority of these compounds inhibited the growth of Burkholderia thailandensis (Bt) and Pseudomonas aeruginosa (Pa) in the Kirby-Bauer disk diffusion susceptibility test. Compound 29 shows inhibitory activity at 0.1 mM (32.2 µg/mL), which is comparable to the control compound kanamycin (48.5 µg/mL). Compound 29 also shows inhibitory activity at 0.5 mM against kanamycin resistant P. aeruginosa. Saturation transfer difference NMR (STD-NMR) screening of these compounds against BtIspD and BtIspE indicated that most of these compounds significantly interact with BtIspE, suggesting that the compounds may inhibit the growth of Bt by disrupting isoprenoid biosynthesis. Ligand epitope mapping of compound 29 with BtIspE indicated that hydrogens on 2,4-dichlorophenyl group have higher proximity to the surface of the enzyme than hydrogens on the pyrazolopyrimidine ring.

A series of novel aminoalkylated quercetin analogs, prepared via the Mannich reaction of various primary and secondary amines with formaldehyde, were tested for antimalarial activity. The compounds were screened against three drug resistant malarial strains (D6, C235 and W2) and were found to exhibit sub-micromolar activity across all three strains (0.065-13.0μM). The structure-activity relationship determined from the antimalarial activity data suggests the inclusion of phenethyl amine sidechains on the quercetin scaffolding is necessary for potent activity. Additionally, the most active compounds ((5) and (6)) were tested for both early and late stage anti-gametocytocidal activity. Finally, the antimalarial activity data were utilized to construct comparative molecular field analysis (CoMFA) models to be used for further compound refinement.

Methionine aminopeptidase (MetAP) is a dinuclear metalloprotease responsible for the cleavage of methionine initiator residues from nascent proteins. MetAP activity is necessary for bacterial proliferation and is therefore a projected novel antibacterial target. A compound library consisting of 294 members containing metal-binding functional groups was screened against Rickettsia prowazekii MetAP to determine potential inhibitory motifs. The compounds were first screened against the target at a concentration of 10 µM and potential hits were determined to be those exhibiting greater than 50% inhibition of enzymatic activity. These hit compounds were then rescreened against the target in 8-point dose–response curves and 11 compounds were found to inhibit enzymatic activity with IC50 values of less than 10 µM. Finally, compounds (1–5) were docked against RpMetAP with AutoDock to determine potential binding mechanisms and the results were compared with crystal structures deposited within the PDB.

Enzymes in the methylerythritol phosphate pathway make attractive targets for antibacterial activity due to their importance in isoprenoid biosynthesis and the absence of the pathway in mammals. The fifth enzyme in the pathway, 2-C-methyl-d-erythritol-2,4-cyclodiphosphate synthase (IspF), contains a catalytically important zinc ion in the active site. A series of de novo designed compounds containing a zinc binding group was synthesized and evaluated for antibacterial activity and interaction with IspF from Burkholderia pseudomallei, the causative agent of Whitmore's disease. The series demonstrated antibacterial activity as well as protein stabilization in fluorescence-based thermal shift assays. Finally, the binding of one compound to Burkholderia pseudomallei IspF was evaluated through group epitope mapping by saturation transfer difference NMR.

Drug design and discovery remains a popular topic of study to many students interested in visible, real-world applications of the chemical sciences. It is important that laboratory experiments detailing the early stages of drug discovery incorporate both compound design and an exploration of ligand/receptor interactions. Molecular modeling is widely employed in research endeavors seeking to predict the activity of potential compounds prior to synthesis and can therefore be used to illustrate these concepts. The following activity therefore details the use of AutoDock to predict the binding affinity and docked pose of a series of CDK2 inhibitors. Students can then compare their docking output to experimentally determined inhibitory activities and crystal structures. Finally, the AutoDock workflow detailed in this activity can be used in research settings, provided the receptor crystal structure is known.

We have optimized the Pd-catalyzed intramolecular α-arylation of 2-(2-halo-benzyl)-cyclohexanones and found that the use of 2-(dicyclohexylphosphino)-2′,4′,6′-tri-i-propyl-1,1′-biphenyl (X-Phos) as an added ligand led to a reproducible, efficient, and scalable synthesis of tricycle-[7.3.1.02,7]-trideca-2,4,6-trien-13-ones.

The relationship between chirality and biological activity has been of increasing importance to the pharmaceutical and biopharmaceutical areas as evidenced by a growing number of chiral drugs that have been developed within the last two decades. This chapter covers several areas of importance in the design and synthesis of novel small molecule chiral drugs for medicinal chemists. The focus of this chapter is to provide an overview of the impact of chirality in medicinal chemistry and pharmaceutical sciences, and this should not be considered an exhaustive review of the topic. Several examples reported in the recent literature have been used to highlight the impact of chirality on development of therapeutics for various molecular targets. Chirality, as used in this chapter, also includes examples of atropisomers. The effects of chirality on pharmacological activities, absorption, distribution, metabolism, and excretion and toxicity are exemplified. In addition to chirality at carbon, examples of chiral compounds involving chirality at noncarbon atoms are included. A section on chirality in drug design provides several examples from recent literature covering diverse target classes. Regulatory considerations that apply to chiral drugs are addressed briefly. Section 10 covers recent drug development and marketed single enantiomers. Multiple synthetic approaches to produce chiral compounds with high enantiomeric purity, including chromatographic separation and enantioselective syntheses, were covered adequately in the 6th edition, and thus these areas and general definitions of chirality are not repeated in this chapter. Keywords: biological activity; chirality

Methionine aminopeptidases (MetAPs) are metalloenzymes that cleave the N-terminal methionine from newly synthesized peptides and proteins. These MetAP enzymes are present in bacteria, and knockout experiments have shown that MetAP activity is essential for cell life, suggesting that MetAPs are good antibacterial drug targets. MetAP enzymes are also present in the human host and selectivity is essential. There have been significant structural biology efforts and over 65 protein crystal structures of bacterial MetAPs are deposited into the PDB. This review highlights the available crystallographic data for bacterial MetAPs. Structural comparison of bacterial MetAPs with human MetAPs highlights differences that can lead to selectivity. In addition, this review includes the chemical diversity of molecules that bind and inhibit the bacterial MetAP enzymes. Analysis of the structural biology and chemical space of known bacterial MetAP inhibitors leads to a greater understanding of this antibacterial target and the likely development of potential antibacterial agents.

The optimization and synthesis of biaryl PDE4D allosteric modulator D159687 was achieved on gram scale via a concise two-step process. The synthesis features sequential chemoselective Suzuki coupling reactions taking advantage of different reactivity profiles of benzyl versus aryl halides. The method was then applied to the synthesis of two additional PDE4D allosteric modulators, D159404 and D159153. The efficient synthesis of these PDE4 allosteric modulators will allow for further biological evaluation of these compounds and the method developed will empower rapid analog formation through combinatorial chemical means.

The efficient syntheses of two new types of conformationally constrained S-[2-[(1-iminoethyl)amino]ethyl]homocysteine derivatives, 1-amino-3-[2[(1-iminoethyl)amino]ethylthio]cyclobutane carboxylic Acid (5) and (4S)-4-[[2-[(1-Iminoethyl)amino]ethyl]thio]-L-proline (6), are reported. These molecules represent the first attempts to probe conformational constraint near the α-amino acid moiety of known homocysteine-based inhibitors of nitric oxide synthase. Targets 5 and 6 were evaluated as potential inhibitors of the three human isoforms of nitric oxide synthase. © 2002 John Wiley & Sons, Inc. Heteroatom Chem 13:77–83, 2002; DOI 10.1002/hc.1109

A series of substituted 2-iminopyrrolidines has been prepared and shown to be potent and selective inhibitors of the human inducible nitric oxide synthase (hiNOS) isoform versus the human endothelial nitric oxide synthase (heNOS) and the human neuronal nitric oxide synthase (hnNOS). Simple substitutions at the 3-, 4-, or 5-position afforded more potent analogues than the parent 2-iminopyrrolidine 1. The effect of ring substitutions on both potency and selectivity for the different NOS isoforms is described. Substitution at the 4- and 5-positions of the 2-iminopyrrolidine yielded both potent and selective inhibitors of hiNOS. In particular, (+)-cis-4-methyl-5-pentylpyrrolidin-2-imine, monohydrochloride (20), displayed potent inhibition of hiNOS (IC50 = 0.25 microM) and selectivities of 897 (heNOS IC50/hiNOS IC50) and 13 (hnNOS IC50/hiNOS IC50). Example 20 was shown to be an efficacious inhibitor of NO production in the mouse endotoxin assay. Furthermore, 20 displayed in vivo selectivity, versus heNOS isoform, by not elevating blood pressure at multiples of the effective dose in the mouse.

A series of analogues of 2-iminopiperidine have been prepared and shown to be potent inhibitors of the human nitric oxide synthase (NOS) isoforms. Methyl substitutions on the 4-position (3) or 4- and 6-positions (8) afforded the most potent analogues. These compounds exhibited IC50 values of 0.1 and 0.08 microM, respectively, for hiNOS inhibition. Substitution with cyclohexylmethyl at the 6-position (13) afforded an inhibitor that showed the best selectivity for hiNOS versus heNOS (heNOS IC50/hiNOS IC50 = 64). Following oral administration, inhibitors were found to decrease serum nitrite/nitrate levels in an in vivo rat endotoxin assay. This series of 2-iminopiperidines were prepared via the described synthetic methodologies. The effect of ring substitutions on potency and selectivity for this class of cyclic amidines as NOS inhibitors is described.

In this study we report a series of triazine derivatives that are potent inhibitors of PDE4B. We also provide a series of structure activity relationships that demonstrate the triazine core can be used to generate subtype selective inhibitors of PDE4B versus PDE4D. A high resolution co-crystal structure shows that the inhibitors interact with a C-terminal regulatory helix (CR3) locking the enzyme in an inactive ‘closed’ conformation. The results show that the compounds interact with both catalytic domain and CR3 residues. This provides the first structure-based approach to engineer PDE4B-selective inhibitors.

Published biological data suggest that the methyl erythritol phosphate (MEP) pathway, a non-mevalonate isoprenoid biosynthetic pathway, is essential for certain bacteria and other infectious disease organisms. One highly conserved enzyme in the MEP pathway is 2C-methyl-d-erythritol 2,4-cyclodiphosphate synthase (IspF). Fragment-bound complexes of IspF from Burkholderia pseudomallei were used to design and synthesize a series of molecules linking the cytidine moiety to different zinc pocket fragment binders. Testing by surface plasmon resonance (SPR) found one molecule in the series to possess binding affinity equal to that of cytidine diphosphate, despite lacking any metal-coordinating phosphate groups. Close inspection of the SPR data suggest different binding stoichiometries between IspF and test compounds. Crystallographic analysis shows important variations between the binding mode of one synthesized compound and the pose of the bound fragment from which it was designed. The binding modes of these molecules add to our structural knowledge base for IspF and suggest future refinements in this compound series.

Evaluation of a series of MetAP inhibitors in an in vitro enzyme activity assay led to the first identification of potent molecules that show significant growth inhibition against Burkholderia pseudomallei. Nitroxoline analogues show excellent inhibition potency in the BpMetAP1 enzyme activity assay with the lowest IC50 of 30 nM and inhibit the growth of B. pseudomallei and B. thailandensis at concentrations ≥31 μM.

The X-ray crystal and molecular structures of the three benzodiazepine (BZD) receptor ligands are presented and the electronic character of inverse agonist ligands is probed through molecular orbital calculations. Two of the ligands have a 6-benzylamino substituent: 6-benzylamino-β-carboline-3-carboxylic acid methyl ester, 1, which is a high affinity antagonist with IC50 = 10 nM, and 6-benzylamino-β-carboline, 2, which is a moderate affinity inverse agonist with IC50 = 106 nM. The third compound, 3-ethoxy-β-carboline hydrochloride, 3, displays partial inverse agonist activity with an IC50of 24 nM. Intermolecular interactions, including extensive hydrogen bonding involving both the pyridyl nitrogen atom and the indole N—H as well as π stacking of aromatic rings, are characteristic of β-carbolines and are found in these three structures. In addition, two of these compounds are protonated in the crystalline state, thereby providing a model for interactions in the absence of the 3-carboxylic acid ester function. Electronic calculations show that (1) the partial inverse agonist ligand has the highest charge on the N(2) atom and (2) high affinity β-carbolines possess two neighboring sites that have high electrostatic attraction for a hydrogen atom in an intermolecular interaction. These findings suggest that modifications to the 3-position side chain to enhance the charge on the pyridyl N atom and provide a hydrogen bond acceptor site will facilitate the development of partial inverse agonist ligands. Keywords: β-carbolines, benzodiazepine receptor, crystallography, structure–activity relationships.

Lithiation of 8-chlorodibenz[b,f][1,4]oxazepine-10-tert-butylcarbamate (1) is described. Electrophilic substitution of the resulting N-Boc dibenzoxazepine α- lithioamine 2 with ketones, aldehydes, nitriles, iso-cyanates and imines, followed by an in-situ cyclization, gave fused carbamates 5–26, fused 2H-imidazol-2-ones 27–29, fused hydantoins 30–32, and fused ureas 33–35, respectively, in 11–66% yield.

8-Chlorodibenz[b,f][1,4]oxazepine-10(11H)-carboxylic acid, 2-acetylhydrazide (1, SC-19220) has been previously reported by us and others to be a PGE2 antagonist selective for the EP1 receptor subtype with antinociceptive activities. Analogs of SC-19220, in which the acetyl moiety has been replaced with pyridylpropionyl groups and their homologs, have been synthesized as illustrated by compounds 13 and 29. These and other members of this series have been shown to be efficacious analgesics and PGE2 antagonists of the EP1 subtype. This report discusses the structure activity relationships within this series.

The synthesis and affinities of six new 3-substituted beta-carbolines (6-10, 12) for the benzodiazepine receptor (BzR) are described. These analogs were used both to probe the dimensions of the hydrophobic pocket in the benzodiazepine receptor and to test the predictive ability of a previously reported 3D-QSAR regression model. Of the new analogs synthesized, the gamma-branched derivatives (isobutoxy, 7, IC50 = 93 nM; isopentoxy, 9, IC50 = 104 nM) display significantly higher affinity for the BzR than either the beta-branched (sec-butoxy, 6, IC50 = 471 nM; tert-butyl ketone, 12, IC50 = 358 nM) or delta-branched (isopentoxy, 8, IC50 = 535 nM) analogs. An exception to this rule is the gamma-branched 3-benzyloxy derivative 10 (IC50 > 1000 nM) which appears to have a chain length that is too long to be accommodated by the BzR. The standard error of prediction for these six new beta-carbolines using the original regression model is significantly lower than the standard error estimate of the cross validation runs on the training set, hence the predictions made using this model are much better than expected. In order to obtain more credible predictions, a new procedure called GOLPE (generating optimal linear PLS estimates) was used to eliminate irrelevant electrostatic and steric descriptors from the regression equation. A substantial reduction in the standard error estimate resulted. The predictions from this new regression equation were somewhat less accurate than the ones obtained with the original regression equation; however the standard error of prediction and the standard error estimate are in much closer agreement. Finally, to probe the effect that the quality of the steric and electrostatic potentials has on 3D-QSAR analyses, the semiempirical MNDO parallel PRDDOE geometries and Mulliken charges used in the original analyses were replaced with ab initio 3-21G parallel 6-31G* geometries and electrostatic potential fit charges. A modest decrease in the standard error estimate and increase in cross validated R2 resulted.

Phosphodiesterase 4 (PDE4), the primary cAMP-hydrolyzing enzyme in cells, is a promising drug target for a wide range of conditions. Here we present seven co-crystal structures of PDE4 and bound inhibitors that show the regulatory domain closed across the active site, thereby revealing the structural basis of PDE4 regulation. This structural insight, together with supporting mutagenesis and kinetic studies, allowed us to design small-molecule allosteric modulators of PDE4D that do not completely inhibit enzymatic activity (I(max) approximately 80-90%). These allosteric modulators have reduced potential to cause emesis, a dose-limiting side effect of existing active site-directed PDE4 inhibitors, while maintaining biological activity in cellular and in vivo models. Our results may facilitate the design of CNS therapeutics modulating cAMP signaling for the treatment of Alzheimer's disease, Huntington's disease, schizophrenia and depression, where brain distribution is desired for therapeutic benefit.

In order to employ rational drug design in the discovery of selective benzodiazepine receptor agonists and inverse agonists, pharmacophore/receptor models for both these activities must first be established. Recently, a pharmacophore for the inverse agonist site has been formulated employing the most recent receptor mapping techniques (22). The continuation of this approach to the pharmacophore for agonist ligands has permitted a definition of this site independently of the inverse agonist model. The agonist pharmacophore/receptor contains two hydrogen bond donating sites of interaction (H1 and H2) located about 6.5 A from each other, as well as three areas of lipophilic interaction (L1 – L3). The areas L1 and L2 are critical for agonist activity; moreover, some ligands also require an interaction in a third lipophilic area termed L3. This is in agreement with previous work (12-23). In addition, an area of negative steric interaction (S1) between the ligand and receptor-binding protein is defined. In regard to the pharmacophore, it was established that the alignment rule for agonist β-carbolines is different from that which elicits inverse agonist activity. Consideration of the pharmacophore has resulted in the synthesis of a new β-carboline 16 which elicits agonist activity. This ligand 16 not only satisfied the requirements of the pharmacophore, but more importantly it elicited both anticonvulsant and anxiolytic activity, but was devoid of the myorelaxant/ataxic properties associated with the benzodiazepines.

5(S)-Fluoro-N6-(iminoethyl)-l-lysine (14), an analogue of the potent, selective induced nitric oxide synthase (iNOS) inhibitor iminoethyl-l-lysine (1), was synthesized and found to be a selective iNOS inhibitor.

(3S,4S,5R)-2-Imino-4-methyl-5-pentyl-3-pyrrolidinol hydrochloride (1) is a potent inducible nitric oxide synthase (i-NOS) inhibitor that has three times the selectivity of its parent, (+)-cis-4-methyl-5-pentylpyrrolidin-2-imine hydrochloride (2).

8-Chlorodibenz[b,f][1,4]oxazepine-10(11H)-carboxylic acid, 2-[1-oxo-3-(4-pyridinyl)propyl]hydrazide, monohydrochloride ( 1 , SC-51089) is a functional PGE 2 antagonist selective for the EP 1 receptor subtype with antinociceptive activity. 1,2 Analogues of SC-51089, in which the diacylhydrazine moiety has been replaced with 2,4-disubstituted-oxazoles and-thiazoles, are described.

The structural requirements for ligand binding to the benzodiazepine receptor (BzR) inverse agonist site were probed through the synthesis and in vitro evaluation of 3-substituted beta-carbolines 6, 7, 11, 12, gamma-carboline 13, and diindoles 18-21, 23-25, 27, 28, and 34. On the basis of the apparent binding affinities of these and other analogues, a hydrogen bond acceptor site (A2) on the receptor is proposed to interact with the N(9) hydrogen atom of the beta-carbolines or the N(7) hydrogen nuclei of the diindoles. Likewise, a proposed hydrogen bond donating site (H1) interacts with the N(2) nitrogen atom of the beta-carbolines or the N(5) nitrogen atom of the diindoles. It appears that interaction with both sites is a prerequisite for high affinity since analogues which have either one or both of these positions blocked exhibit substantial reduction in affinity. Moreover, H1 appears to be capable of engaging in a three-centered hydrogen bond with appropriately functionalized ligands, which explains the increase in potency observed in the following series of 3-substituted beta-carbolines: the n-butyl (12, IC50 = 245 nM), n-propoxy (9, IC50 = 11 nM), and propyl ketone (11, IC50 = 2.8 nM) congeners. In addition to H1 and A2, there appears to be a relatively narrow hydrophobic pocket in the binding cleft that can accommodate substituents at the 3-position of the beta-carbolines which have chain lengths less than or equal to C5. There is a 1 order of magnitude decrease in affinity between n-propoxy analogue 9 (IC50 = 11 nM, chain length = 4) and n-butoxy derivative 7 (IC50 = 98 nM, chain length = 5). Furthermore, alpha- and gamma-branching [e.g. ethoxycarbonyl (2), IC50 = 5 nM and tert-butoxycarbonyl (31) IC50 = 10 nM] but not beta- and delta-branching [e.g. isopropoxy (6), IC50 = 500 nM and (neopentyloxy) carbonyl (48), IC50 = 750 nM] at position 3 are tolerated. Occupation of this hydrophobic pocket is clearly important for high affinity as evidenced by the relatively low affinity of 30, a beta-carboline which possesses a hydrogen atom at the 3-position. This same hydrophobic pocket is partially filled by the D and E rings of the diindoles, which accounts for the high affinity of several members of this series. An excluded volume analysis using selected 3-substituted beta-carbolines and ring-E substituted pyridodiindoles is consistent with the presence of this hydrophobic pocket (see Figure 1).(ABSTRACT TRUNCATED AT 400 WORDS)

A series of 11-substituted dibenzoxazepines was prepared via α-lithiation utilizing the N-Boc group as an activator. The N-Boc group directs metalation of 5 by n-BuLi to the benzylic C-11 carbon. For 6 which contains 1,3 interrelated directed metalation groups, metalation with n-BuLi occurs at both the 11- and 9- positions. The regioselectivity for the lithiation of 6 can be increased to a ratio of 97:3, by employing LDA as the base, thus providing a convenient and general route to 11-substituted 8-chloro-dibenzoxazepines. By the proper choice of the base, the regioselectivity of lithiation-substitution reactions in the pharmaceutically important heteroaromatic ring systems (5) and (6) can be controlled. The N-Boc group can be readily removed with mild acid treatment

The six step synthesis of the cytotoxic antileukemic alkaloid 1-methoxy canthine-6-one 2 is described. The pivotal steps are represented by the oxidation (DDQ) of 9 to afford the 3-acylindole 14 and the conversion of 11 into the 4-methoxy-1-alkyl β-carboline 15 .

Rats were trained to respond under 3-min fixed-interval schedules of food presentation, and effects of the benzodiazepine-receptor ligands, flumazenil, 2-(4-methoxy-phenyl)-pyrazolo[4,3-c]quinolin-3(5H)-one (CGS 9895), 3-carbo-t-butoxy-beta-carboline (beta-CCtB), and beta-carboline-3-carboxylic acid ethyl ester (beta-CCE) were assessed before and after the induction of tolerance to chlordiazepoxide. Before daily administration of chlordiazepoxide, none of the antagonists produced appreciable effects on rates of responding up to doses of 32.0 mg/kg i.p. beta-CCE was the only antagonist studied at a higher dose (100.0 mg/kg i.p.), which decreased response rates. After 23 days of daily chlordiazepoxide administration (oral doses started at 10 and increased to 100 mg/kg/day by the 17th day), dose-effect curves for chlordiazepoxide were shifted to the right by about one-half log unit. Subjects were also more sensitive to the flumazenil, CGS 9895, and beta-CCtB, however, since these drugs produced only small effects in non-tolerant subjects, precise estimates of the degree of the shift in dose-effect curves could not be estimated. However, there were differences in the changes in the dose-effect curves induced by chlordiazepoxide tolerance. These results suggest differences in mechanism of action of antagonists in tolerant and non-tolerant subjects, and further that the sensitivity that is induced to antagonists in tolerant subjects is not conferred equally to all drugs having benzodiazepine antagonist activity.