Structure-activity relationships of novel anti-malarial agents. Part 2: cinnamic acid derivatives

We have described compound 1 as a lead structure for a novel class of anti-malarial agents. Replacement of the 3-phenylpropionyl moiety of the lead structure 1 by a 4-propoxycinnamic acid residue resulted in a significant improvement in antimalarial activity. Compound 3q represents an important step in the development of lead structure 1 into an anti-malarial drug candidate.     

二价铅离子与金属硫蛋白相互作用的研究

通过紫外吸收光谱和平衡透析法研究了二价铅离子同脱金属硫蛋白（ａｐｏ－ＭＴ）、锌－金属硫蛋白（Ｚｎ－ＭＴ）的相互作用,证实Ｐｂ（Ⅱ）是以金属巯基复合物（金属巯基比为１∶２）的形式同金属硫蛋白结合,表观离解常数（ＫＤ）为８．７１×１０－７ｍｏｌ／Ｌ．在自由铅浓度达到６．５２×１０－６ｍｏｌ／Ｌ的条件下,铅离子即可将Ｚｎ－ＭＴ上的Ｚｎ完全取代下来．通过ＥＤＴＡ、ＤＴＮＢ竞争反应、圆二色性（ＣＤ）光谱分析,认为Ｐｂ－ＭＴ的金属巯基复合物不同于Ｚｎ－ＭＴ中Ｚｎ与巯基形成的紧密的正四面体结构,而是可能形成一种三级结构相对松散、热力学上不稳定的Ｃｙｓ－Ｓ－Ｐｂ－Ｓ－Ｃｙｓ平面形结构．研究认为金属硫蛋白的两种亚型ＭＴ－Ⅰ、ＭＴ－Ⅱ与Ｐｂ（Ⅱ）的结合能力并无显著差异     

Discovery of potent and selective nonsteroidal indazolyl amide glucocorticoid receptor agonists

Modification of a phenolic lead structure based on lessons learned from increasing the potency of steroidal glucocorticoid agonists lead to the discovery of exceptionally potent, nonsteroidal, indazole GR agonists. SAR was developed to achieve good selectivity against other nuclear hormone receptors with the ultimate goal of achieving a dissociated GR agonist as measured by human in vitro assays. The specific interactions by which this class of compounds inhibits GR was elucidated by solving an X-ray co-crystal structure.     

Antimalarial activity of tetrahydro-β-carbolines targeting the ATP binding pocket of the Plasmodium falciparum heat shock 90 protein

A series of tetrahydro-β-carboline derivatives of a lead compound known to target the heat shock 90 protein of Plasmodium falciparum were synthesized and assayed for both potency against the parasite and toxicity against a human cell line. Using a rationalized structure based design strategy, a new lead compound with a potency two orders of magnitude greater than the original lead compound was found. Additional modeling of this new lead compound suggests multiple avenues to further increase potency against this target, potentially paving the path for a therapeutic with a mode of action different than any current clinical treatment.     

Antagonists of the human CCR5 receptor as anti-HIV-1 agents. part 1: discovery and initial structure-activity relationships for 1 -amino-2-phenyl-4-(piperidin-1-yl)butanes

Screening of the Merck sample collection for compounds with CCR5 receptor binding afforded (2S)-2-(3,4-dichlorophenyl)-1-[N-(methyl)-N-(phenylsulfonyl)amino]-4-[spiro(2,3-dihydrobenzthiophene-3,4'-piperidin-1'-yl)]butane S-oxide (4) as a potent lead structure having an IC50 binding affinity of 35 nM. Herein, we describe the discovery of this lead structure and our initial structure activity relationship studies directed toward the requirement for and optimization of the 1-amino fragment.     

Initial structure-activity relationship of a novel class of nonpeptidyl GnRH receptor antagonists: 2-arylindoles

A nonpeptidyl GnRH receptor antagonist (1), with a unique 2-arylindole core, was identified through the Merck in-house screening for binding affinity on the rat GnRH receptor. SAR studies directed toward the alkoxy-ethanolamine and 2-aryl groups resulted in a simpler lead structure with improved activity. This compound 50 exhibits a 60-fold improvement in binding activity over our initial lead 1.     

Cd、Pb及其复合污染对烤烟叶片生理生化及细胞亚显微结构的影响

本研究以水培的烤烟给予不同浓度的Cd、Pb及其复合物处理10d后的烟叶为材料,分析了烟叶过氧化氢酶、硝酸还原酶的活性变化,测试了烟叶可溶性糖含量的变化情况,通过透射电子显微镜观察到了Cd和Pb对烟叶叶肉细胞亚显微结构的改变,特别是对叶绿体、线粒体和细胞核结构的损伤情况进行了详细观察。并探讨其毒害机理。研究结果表明：1)烟叶过氧化氢酶的活性剧烈地被Cd抑制;而随着Pb浓度的增加,其活性则表现为先增加后减弱的变化。2)Cd对硝酸还原酶活性的影响表现为先刺激增强,当Cd浓度超过50mg·L-1后,Cd剧烈地抑制其活性,当Cd浓度为200mg·L-1时,其活性几乎为零;Pb抑制烟叶硝酸还原酶的活性,仅在1000mg·L-1时出现一个低于正常活性的抗性峰。3)烟叶可溶性糖含量对Cd、Pb及其复合污染非常敏感,在较低浓度的污染处理时,其含量就明显下降,烟叶可溶性糖含量的变化可作为监测Cd、Pb污染的指标。4)Cd对烟叶叶肉细胞亚显微结构具有较强的损伤诱变作用,对细胞核、叶绿体和线粒体造成不可逆转的伤害,破坏了细胞正常生理活动所需的结构基础。电镜观察表明Cd严重地破坏细胞的膜结构。这可能是由于Cd离子与蛋白质结合而使蛋白质变性,从而使得以蛋白质为重要组成成份之一的膜的结构改变,功能丧失。5)在细胞膜的外面可以看到大量的Pb沉积粒,细胞膜可以阻止部分Pb进入原生质体内部,但在细胞质和叶绿体中仍可看到Pb沉积粒。Pb同样的损伤叶绿体、线粒体、细胞核的亚显微结构。     

Timing Rhythms: Perceived Duration Increases with a Predictable Temporal Structure of Short Interval Fillers

Variations in the temporal structure of an interval can lead to remarkable differences in perceived duration. For example, it has previously been shown that isochronous intervals, that is, intervals filled with temporally regular stimuli, are perceived to last longer than intervals left empty or filled with randomly timed stimuli. Characterizing the extent of such distortions is crucial to understanding how duration perception works. One account to explain effects of temporal structure is a non-linear accumulator-counter mechanism reset at the beginning of every subinterval. An alternative explanation based on entrainment to regular stimulation posits that the neural response to each filler stimulus in an isochronous sequence is amplified and a higher neural response may lead to an overestimation of duration. If entrainment is the key that generates response amplification and the distortions in perceived duration, then any form of predictability in the temporal structure of interval fillers should lead to the perception of an interval that lasts longer than a randomly filled one. The present experiments confirm that intervals filled with fully predictable rhythmically grouped stimuli lead to longer perceived duration than anisochronous intervals. No general over- or underestimation is registered for rhythmically grouped compared to isochronous intervals. However, we find that the number of stimuli in each group composing the rhythm also influences perceived duration. Implications of these findings for a non-linear clock model as well as a neural response magnitude account of perceived duration are discussed.     

An approach to the analysis of the underlying structure of visual space using a generalized notion of visual pattern recognition

An approach is described by which certain deductions can be made concerning the natural underlying structure of visual space. The procedure is indirect and makes use of the notion of visual recognition defined with respect to an arbitrarily fixed structure. Consideration of the set of mappings associated with such recognition is shown to lead to a condition that must be satisfied by any proposed underlying structure.     

Synthesis and structure-activity relationships of second-generation hydroxamate botulinum neurotoxin A protease inhibitors

Botulinum neurotoxins are the most toxic proteins currently known. Based on a recently identified potent lead structure, 2,4-dichlorocinnamic acid hydroxamate, herein we report on the structure-activity relationship of a series of hydroxamate BoNT/A inhibitors. Among them, 2-bromo-4-chlorocinnamic acid hydroxamate, 2-methyl-4-chlorocinnamic acid hydroxamate, and 2-trifluoromethyl-4-chlorocinnamic acid hydroxamate displayed comparable inhibitory activity to that of the lead structure.     

Modeling an active conformation for linear peptides and design of a competitive inhibitor for HMG-CoA reductase

This study presents an approach that can be used to search for lead peptide candidates, including unconstrained structures in a recognized sequence. This approach was performed using the design of a competitive inhibitor for 3-hydroxy-3-methylglutaryl CoA reductase (HMGR). In a previous design for constrained peptides, a head-to-tail cyclic structure of peptide was used as a model of linear analog in searches for lead peptides with a structure close to an active conformation. Analysis of the conformational space occupied by the peptides suggests that an analogical approach can be applied for finding a lead peptide with an unconstrained structure in a recognized sequence via modeling a cycle using fixed residues of the peptide backbone. Using the space obtained by an analysis of the bioactive conformations of statins, eight cyclic peptides were selected for a peptide library based on the YVAE sequence as a recognized motif. For each cycle, the four models were assessed according to the design criterion ("V" parameter) applied for constrained peptides. Three cyclic peptides (FGYVAE, FPYVAE, and FFYVAE) were selected as lead cycles from the library. The linear FGYVAE peptide (IC(50) = 0.4 microM) showed a 1200-fold increase the inhibitory activity compared to the first isolated LPYP peptide (IC(50) = 484 microM) from soybean. Experimental analysis of the modeled peptide structures confirms the appropriateness of the proposed approach for the modeling of active conformations of peptides.     

Imidazo[1,5-a]quinoxalines as irreversible BTK inhibitors for the treatment of rheumatoid arthritis

Imidazo[1,5-a]quinoxalines were synthesized that function as irreversible Bruton's tyrosine kinase (BTK) inhibitors. The syntheses and SAR of this series of compounds are presented as well as the X-ray crystal structure of the lead compound 36 in complex with a gate-keeper variant of ITK enzyme. The lead compound showed good in vivo efficacy in preclinical RA models.     

Discovery of novel 3,6-disubstituted 2-pyridinecarboxamide derivatives as GK activators

A novel class of 3,6-disubstituted 2-pyridinecarboxamide derivatives was designed based on X-ray analysis of the 2-aminobenzamide lead class. Subsequent chemical modification led to the discovery of potent GK activators which eliminate potential toxicity concerns associated with an aniline group of the lead structure. Compound 7 demonstrated glucose lowering effect in a rat OGTT model.     

Discovery of pyrrolidine-based β-secretase inhibitors: lead advancement through conformational design for maintenance of ligand binding efficiency

We have developed a novel series of pyrrolidine derived BACE-1 inhibitors. The potency of the weak initial lead structure was enhanced using library-based SAR methods. The series was then further advanced by rational design while maintaining a minimal ligand binding efficiency threshold. Ultimately, the co-crystal structure was obtained revealing that these inhibitors interacted with the enzyme in a unique fashion. In all, the potency of the series was enhanced by 4 orders of magnitude from the HTS lead with concomitant increases in physical properties needed for series advancement. The progression of these developments in a systematic fashion is described.     

Polymorphic forms of 1,2-dipalmitoyl-sn-glycerol: a combined X-ray and electron diffraction study

Quantitative crystallographic structure analyses are carried out for two polymorphic forms of 1,2-dipalmitoyl-sn-glycerol. A single crystal X-ray determination on the higher melting beta'L-form reveals that the hairpin conformer structure is essentially identical to that of the dilauroyl homolog reported earlier (I. Pascher, S. Sundell and H. Hauser (1981) J. Mol. Biol. 153, 791-806) with inclined acyl chain packing in the O perpendicular methylene subcell. Lamellar electron diffraction intensity data from epitaxially crystallized samples were used to determine the structure of the lower melting alpha L-form. The chains pack in the hexagonal subcell and are perpendicular to the lamellar surface. An appropriately oriented molecular model based on the beta'L-polymorph does not lead to a satisfactory structure solution but models based on the conformationally different 1,2-diglyceride moiety of several phospholipid structures does lead to a closer match to the observed diffraction data. In this proposed packing model for the alpha L-form, the hydroxyl oxygens are somewhat farther away from the unit cell origin than in the beta'L-form crystal structure, and, in combination with the different molecular conformation, this might explain the observed stability of this crystal polymorph against acyl shifts.     

Biaryl guanidine inhibitors of in vitro HCV-IRES activity

A structure-activity relationship analysis was carried out on a high-throughput small molecule screening lead for HCV-IRES translation inhibition. The study led to the identification of a guanidine-based structure with low microM inhibitory activity.     

铅在日本沼虾体内的分布和积累

应用组织化学、透射电镜和原子吸收光谱分析等方法,研究了Pb在日本沼虾各主要器官和组织中的分布和积累情况。结果表明,在浓度为0．625mg·L^-1Pb溶液暴露10d后的日本沼虾触角腺内,具有大量的电子密度较高的Pb颗粒．在电镜下细胞内的溶酶体中沉积有大量的Pb颗粒,这些Pb通过积聚,在细胞顶端部位逐渐增多,从而出现外排现象．中肠细胞内含有Pb颗粒,细胞质出现空泡化,核膜和线粒体内嵴部分解体．肝胰脏细胞内除分布有少量Pb颗粒外,细胞结构基本完整．在沼虾鳃细胞内未发现Pb颗粒,但在鳃丝之间发现少量Pb颗粒吸附在鳃丝的表面原子吸收光谱分析结果表明,触角腺中Pb含量最高,达637．6mg·kg^-1;触角腺在Pb的解毒方面起着重要作用。     

Probing the structure of Leishmania major DHFR TS and structure based virtual screening of peptide library for the identification of anti-leishmanial leads

Leishmaniasis, a multi-faceted ethereal disease is considered to be one of the World's major communicable diseases that demands exhaustive research and control measures. The substantial data on these protozoan parasites has not been utilized completely to develop potential therapeutic strategies against Leishmaniasis. Dihydrofolate reductase thymidylate synthase (DHFR-TS) plays a major role in the infective state of the parasite and hence the DHFR-TS based drugs remains of much interest to researchers working on Leishmaniasis. Although, crystal structures of DHFR-TS from different species including Plasmodium falciparum and Trypanosoma cruzi are available, the experimentally determined structure of the Leishmania major DHFR-TS has not yet been reported in the Protein Data Bank. A high quality three dimensional structure of L.major DHFR-TS has been modeled through the homology modeling approach. Carefully refined and the energy minimized structure of the modeled protein was validated using a number of structure validation programs to confirm its structure quality. The modeled protein structure was used in the process of structure based virtual screening to figure out a potential lead structure against DHFR TS. The lead molecule identified has a binding affinity of 0.51?nM and clearly follows drug like properties.