Discovery of estrogen sulfotransferase inhibitors from a purine library screen

Triflimide-Promoted Nucleophilic C-Arylation of Halopurines to Access N7-Substituted Purine Biaryls

Functionalized nucleobases are utilized in a wide range of fields; therefore, the development of new synthesis methods is essential for their continued application. With respect to the C⁶-arylation of halopurines, which possess a substituent at the N⁷-position, only a small number of successful cases have been reported, which is predominately a result of large steric hinderance effects. Herein, we report efficient and metal-free C⁶-arylations and S_NAr reactions of N⁷-substituted chloropurines in aromatic and heteroatom nucleophiles promoted by triflimide (Tf₂NH) in fluoroalcohol.

Iodine-catalyzed oxidative functionalization of purines with (thio)ethers or methylarenes for the synthesis of purin-8-one analogues

An efficient oxidative functionalization of purine-like substrates with (thio)ethers or methylarenes under mild conditions is described. Using I2 as the catalyst, and TBHP as the oxidant, this protocol provides a valuable synthetic tool for the assembly of a wide range of 9-alkyl(benzyl)purin-8-one derivatives with high atom- and step-economy and exceptional functional group tolerance.

New tools for carbohydrate sulfation analysis: heparan sulfate 2-O-sulfotransferase (HS2ST) is a target for small-molecule protein kinase inhibitors

Sulfation of carbohydrate residues occurs on a variety of glycans destined for secretion, and this modification is essential for efficient matrix-based signal transduction. Heparan sulfate (HS) glycosaminoglycans control physiological functions ranging from blood coagulation to cell proliferation. HS biosynthesis involves membrane-bound Golgi sulfotransferases, including HS 2-O-sulfotransferase (HS2ST), which transfers sulfate from the cofactor PAPS (3'-phosphoadenosine 5'-phosphosulfate) to the 2-O position of α-l-iduronate in the maturing polysaccharide chain. The current lack of simple non-radioactive enzyme assays that can be used to quantify the levels of carbohydrate sulfation hampers kinetic analysis of this process and the discovery of HS2ST inhibitors. In the present paper, we describe a new procedure for thermal shift analysis of purified HS2ST. Using this approach, we quantify HS2ST-catalysed oligosaccharide sulfation using a novel synthetic fluorescent substrate and screen the Published Kinase Inhibitor Set, to evaluate compounds that inhibit catalysis. We report the susceptibility of HS2ST to a variety of cell-permeable compounds in vitro, including polyanionic polar molecules, the protein kinase inhibitor rottlerin and oxindole-based RAF kinase inhibitors. In a related study, published back-to-back with the present study, we demonstrated that tyrosyl protein sulfotranferases are also inhibited by a variety of protein kinase inhibitors. We propose that appropriately validated small-molecule compounds could become new tools for rapid inhibition of glycan (and protein) sulfation in cells, and that protein kinase inhibitors might be repurposed or redesigned for the specific inhibition of HS2ST.

A High-Throughput Screening-Compatible Strategy for the Identification of Inositol Pyrophosphate Kinase Inhibitors

Pharmacological tools-'chemical probes'-that intervene in cell signaling cascades are important for complementing genetically-based experimental approaches. Probe development frequently begins with a high-throughput screen (HTS) of a chemical library. Herein, we describe the design, validation, and implementation of the first HTS-compatible strategy against any inositol phosphate kinase. Our target enzyme, PPIP5K, synthesizes 'high-energy' inositol pyrophosphates (PP-InsPs), which regulate cell function at the interface between cellular energy metabolism and signal transduction. We optimized a time-resolved, fluorescence resonance energy transfer ADP-assay to record PPIP5K-catalyzed, ATP-driven phosphorylation of 5-InsP7 to 1,5-InsP8 in 384-well format (Z' = 0.82 ± 0.06). We screened a library of 4745 compounds, all anticipated to be membrane-permeant, which are known-or conjectured based on their structures-to target the nucleotide binding site of protein kinases. At a screening concentration of 13 μM, fifteen compounds inhibited PPIP5K >50%. The potency of nine of these hits was confirmed by dose-response analyses. Three of these molecules were selected from different structural clusters for analysis of binding to PPIP5K, using isothermal calorimetry. Acceptable thermograms were obtained for two compounds, UNC10112646 (Kd = 7.30 ± 0.03 μM) and UNC10225498 (Kd = 1.37 ± 0.03 μM). These Kd values lie within the 1-10 μM range generally recognized as suitable for further probe development. In silico docking data rationalizes the difference in affinities. HPLC analysis confirmed that UNC10225498 and UNC10112646 directly inhibit PPIP5K-catalyzed phosphorylation of 5-InsP7 to 1,5-InsP8; kinetic experiments showed inhibition to be competitive with ATP. No other biological activity has previously been ascribed to either UNC10225498 or UNC10112646; moreover, at 10 μM, neither compound inhibits IP6K2, a structurally-unrelated PP-InsP kinase. Our screening strategy may be generally applicable to inhibitor discovery campaigns for other inositol phosphate kinases.

Discovery of Novel Selective ERα/ERβ Ligands by Multi-pharmacophore Modeling and Virtual Screening

Estrogen receptor α (ERα) and estrogen receptor β (ERβ) regulate different sets of gene expression, and have different ligand responses, which make the estrogen tissue-specific. Thus, the estrogen receptor (ER) subtype-selective ligands can improve the target-site selectivity and decrease the off-target effect. In order to discover the selective ER subtype ligands with novel scaffolds, in this work three-dimensional (3D) pharmacophore models of the ERα ligands (Hypo 1) and the ERβ ligands (Hypo 2) were established (correlation coefficients were 0.959 and 0.966) and validated (R=0.936 and 0.879; enrichment factors (EFs) at 2% were 16.2 and 8.4; areas under the concentration-time curve (AUC) of the receiver operating curve (ROC) were 0.88 and 0.91) using the Discovery Studio 4.0 software package. Hypo 1 and Hypo 2 were then employed for virtual screening and ten hits were found as potential candidate leads. Based on their ERα/ERβ binding affinity results by fluorescence polarization technology, two of these leads, AH-262/34334025 (AH) and AG-670/08803023 (AG) with novel scaffolds were identified as selective ERα ligands. A molecular docking study was also performed, which provided the explanation for the ER subtype preferences for AH and AG.

The Regulation of Steroid Action by Sulfation and Desulfation

Steroid sulfation and desulfation are fundamental pathways vital for a functional vertebrate endocrine system. After biosynthesis, hydrophobic steroids are sulfated to expedite circulatory transit. Target cells express transmembrane organic anion-transporting polypeptides that facilitate cellular uptake of sulfated steroids. Once intracellular, sulfatases hydrolyze these steroid sulfate esters to their unconjugated, and usually active, forms. Because most steroids can be sulfated, including cholesterol, pregnenolone, dehydroepiandrosterone, and estrone, understanding the function, tissue distribution, and regulation of sulfation and desulfation processes provides significant insights into normal endocrine function. Not surprisingly, dysregulation of these pathways is associated with numerous pathologies, including steroid-dependent cancers, polycystic ovary syndrome, and X-linked ichthyosis. Here we provide a comprehensive examination of our current knowledge of endocrine-related sulfation and desulfation pathways. We describe the interplay between sulfatases and sulfotransferases, showing how their expression and regulation influences steroid action. Furthermore, we address the role that organic anion-transporting polypeptides play in regulating intracellular steroid concentrations and how their expression patterns influence many pathologies, especially cancer. Finally, the recent advances in pharmacologically targeting steroidogenic pathways will be examined.

Historical overview of chemical library design

High-throughput chemistry (HTC) is approaching its 20-year anniversary. Since 1992, some 5,000 chemical libraries, prepared for the purpose of biological investigation and drug discovery, have been published in the scientific literature. This review highlights the key events in the history of HTC with emphasis on library design. A historical perspective on the design of screening, targeted, and optimization libraries and their application is presented. Design strategies pioneered in the 1990s remain viable in the twenty-first century.

Privileged scaffolds for library design and drug discovery

This review explores the concept of using privileged scaffolds to identify biologically active compounds through building chemical libraries. We hope to accomplish three main objectives: to provide one of the most comprehensive listings of privileged scaffolds; to reveal through four selected examples the present state of the art in privileged scaffold library synthesis (in hopes of inspiring new and even more creative approaches); and also to offer some thoughts on how new privileged scaffolds might be identified and exploited.

Inhibitory peptides of the sulfotransferase domain of the heparan sulfate enzyme, N-deacetylase-N-sulfotransferase-1

N-Deacetylase-N-sulfotransferase 1 (Ndst1) catalyzes the initial modification of heparan sulfate and heparin during their biosynthesis by removal of acetyl groups from subsets of N-acetylglucosamine units and subsequent sulfation of the resulting free amino groups. In this study, we used a phage display library to select peptides that interact with Ndst1, with the aim of finding inhibitors of the enzyme. The phage library consisted of cyclic random 10-mer peptides expressed in the phage capsid protein pIII. Selection was based on the ability of engineered phage to bind to recombinant murine Ndst1 (mNdst1) and displacement with heparin. Peptides that were enriched through multiple cycles of binding and disassociation displayed two specific sequences, CRGWRGEKIGNC and CNMQALSMPVTC. Both peptides inhibited mNdst1 activity in vitro, however, by distinct mechanisms. The peptide CRGWRGEKIGNC presents a chemokine-like repeat motif (BXX, where B represents a basic amino acid and X is a noncharged amino acid) and binds to heparan sulfate, thus blocking the binding of substrate to the enzyme. The peptide NMQALSMPVT inhibits mNdst1 activity by direct interaction with the enzyme near the active site. The discovery of inhibitory peptides in this way suggests a method for developing peptide inhibitors of heparan sulfate biosynthesis.

Monitoring enzyme reaction and screening of inhibitors of acetylcholinesterase by quantitative matrix-assisted laser desorption/ionization Fourier transform mass spectrometry

A matrix-assisted laser desorption/ionization Fourier transform mass spectrometry (MALDI-FTMS)-based assay was developed for kinetic measurements and inhibitor screening of acetylcholinesterase. Here, FTMS coupled to MALDI was applied to quantitative analysis of choline using the ratio of choline/acetylcholine without the use of additional internal standard, which simplified the experiment. The Michaelis constant (K(m)) of acetylcholinesterase (AChE) was determined to be 73.9 micromol L(-1) by this approach. For Huperzine A, the linear mixed inhibition of AChE reflected the presence of competitive and noncompetitive components. The half maximal inhibitory concentration (IC(50)) value of galantamine obtained for AChE was 2.39 micromol L(-1). Inhibitory potentials of Rhizoma Coptidis extracts were identified with the present method. In light of the results the referred extracts as a whole showed inhibitory action against AChE. The use of high-resolution FTMS largely eliminated the interference with the determination of ACh and Ch, produced by the low-mass compounds of chemical libraries for inhibitor screening. The excellent correlation with the reported kinetic parameters confirms that the MS-based assay is both accurate and precise for determining kinetic constants and for identifying enzyme inhibitors. The obvious advantages were demonstrated for quantitative analysis and also high-throughput characterization. This study offers a perspective into the utility of MALDI-FTMS as an alternate quantitative tool for inhibitor screening of AChE.

Identification of Novel Pigmentation Modulators by Chemical Genetic Screening

There is a continual need for compounds that effectively modulate melanin synthesis. To identify novel pigmentation modulators and their cellular targets, chemical genetic screenings were performed with triazine-based combinatorial libraries that include various linkers as intrinsic components of the small molecules in the library. The linker provides a ready means of attachment to beads, eliminating several common time-consuming downstream steps in the isolation of cellular targets for the small molecules of interest. Twelve compounds were identified as novel pigmentation modulators from various screenings performed in normal and albino murine melanocytes and zebrafish. Target identification by affinity chromatography revealed unexpected roles for prohibitin and mitochondrial F1F0-adenotriphosphatase in the regulation of mammalian pigmentation. The identification of prohibitin, a "scaffold protein", as a propigmentation effector represents a novel mechanism by which propigmentary signals are transduced. Results from our screenings provide potential active agents and targets for the medical and aesthetic treatment of disorders of pigmentation.

S(N)Ar displacements with 6-(fluoro, chloro, bromo, iodo, and alkylsulfonyl)purine nucleosides: synthesis, kinetics, and mechanism1

SNAr reactions with 6-(fluoro, chloro, bromo, iodo, and alkylsulfonyl)purine nucleosides and nitrogen, oxygen, and sulfur nucleophiles were studied. Pseudo-first-order kinetics were measured with 6-halopurine compounds, and comparative reactivities were determined versus a 6-(alkylsulfonyl)purine nucleoside. The displacement reactivity order was: F > Br > Cl > I (with BuNH2/MeCN), F > Cl approximately Br > I (with MeOH/1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)/MeCN), and F > Br > I > Cl [with K+ -SCOCH3/dimethyl sulfoxide (DMSO)]. The order of reactivity with a weakly basic arylamine (aniline) was: I > Br > Cl > F (with 5 equiv of aniline in MeCN at 70 degrees C). However, those reactions with aniline were autocatalytic and had significant induction periods ( approximately 50 min for the iodo compound and approximately 6 h for the fluoro analogue). Addition of trifluoroacetic acid (TFA) eliminated the induction period, and the order then was F > I > Br > Cl (with 5 equiv of aniline and 2 equiv of TFA in MeCN at 50 degrees C). The 6-(alkylsulfonyl)purine nucleoside analogue was more reactive than the 6-fluoropurine compound with both MeOH/DBU/MeCN and iPentSH/DBU/MeCN and was more reactive than the Cl, Br, and I compounds with BuNH2 and aniline/TFA. Titration of the 6-halopurine nucleosides in CDCl3 with TFA showed progressive downfield 1H NMR chemical shifts for H8 (larger) and H2 (smaller). The major site of protonation as N7 for both the 6-fluoro and 6-bromo analogues was confirmed by large upfield shifts ( approximately 16 ppm) of the 15N NMR signal for N7 upon addition of TFA (1.6 equiv). Mechanistic considerations and resolution of prior conflicting results are presented.

New thiopyrazolo[3,4-d]pyrimidine derivatives as anti-mycobacterial agents

The multiple parallel synthesis of a series of N,S-bis-alkylated thiopyrazolo[3,4-d]pyrimidines, based on sequential S- then N-alkylation, is reported. These compounds showed significant anti-mycobacterial activity (MICs down to 2mug/ml) and their potential as significant drug-like leads is substantiated through cytotoxicity evaluation and in silico profiling.

Chemical genetics: an evolving toolbox for target identification and lead optimization

Chemical genetics combines chemistry with biology as a means of exploring the function of unknown proteins or identifying the proteins responsible for a particular phenotype. Chemical genetics is thus a valuable tool in the identification of novel drug targets. This chapter describes the application of chemical genetics in traditional and systems-based approaches to drug target discovery and the tools/approaches that appear most promising for guiding future pharmaceutical development.

Development and validation of a fluorescence HPLC-based screening assay for inhibition of human estrogen sulfotransferase

Human estrogen sulfotransferase (SULT1E1) is involved in the regulation of 17beta-estradiol responsiveness and is believed to protect peripheral tissues from excessive estrogenic effects. Several assays already have been developed to investigate the inhibitory effect of endocrine-disrupting compounds (EDCs) on SULT1E1. However, most of these assays make use of the radiolabeled cofactor [(35)S]3'-phosphoadenosine 5'-phosphosulfate (PAPS) or radiolabeled substrate [(3)H]estradiol. In this article, we describe the development and validation of an assay for the inhibition of human SULT1E1 that is rapid and simple and that uses the nonradioactive and noncarcinogenic 1-hydroxypyrene. A gradient HPLC separation of 15 min using a C18-RP column was developed to detect 1-hydroxypyrene and its metabolite pyrene 1-sulfate fluorescently. Time- and protein-dependent formation of pyrene 1-sulfate was investigated, and enzyme kinetics was determined (K(m)=6.4+/-0.8 nM and V(max)=158+/-19 pmol/min/microg SULT1E1). At higher 1-hydroxypyrene concentrations, the assay displayed non-Michaelis-Menten kinetics involving substrate inhibition. IC(50) values have been determined for eight known SULT1E1 inhibitors or competing substrates (17beta-estradiol, 17alpha-estradiol, genistein, 17alpha-ethynylestradiol, estrone, diethylstilbestrol, estriol, and hexestrol) and two previously unknown SULT1E1 inhibitors (zearalenone and dienestrol). The method was demonstrated to be easy, feasible, and highly reproducible for SULT1E1 screening assay inhibition studies.

Selective Magnesiation of Chloro-iodopurines: An Efficient Approach to New Purine Derivatives

[reaction: see text] Both 6-chloro-2-iodo-9-isopropylpurine (1) and 2-chloro-6-iodo-9-benzylpurine (4) undergo a selective I/Mg exchange reaction with iPrMgCl at -80 degrees C. The reaction course at 0 degrees C is different. Magnesiation of 1 proceeds with the migration of magnesium to the 8 position of the purine nuclei. In the case of 4, substitution of iodine with an alkyl group from the Grignard reagent accompanied with a Cl/Mg exchange reaction takes place, and 6-alkyl-2-magnesiated purines (9) are formed. Thus prepared Grignard reagents afford the corresponding alcohols by the reaction with aldehydes.

High-Temperature Liquid Chromatography Coupled On-Line to a Continuous-Flow Biochemical Screening Assay with Electrospray Ionization Mass Spectrometric Detection

The potential of high-temperature liquid chromatography (HTLC) was investigated in an on-line combination with a screening system for bioactive compounds against the enzyme cathepsin B. Samples were separated by HTLC and subsequently analyzed by an on-line continuous-flow enzymatic assay. Detection was performed by electrospray ionization mass spectrometry, revealing both the bioactivity and the molecular mass of the bioactive compounds. Compared to conventional reversed-phase liquid chromatography, the amount of methanol necessary for separation could be decreased to only 10%, which improved the compatibility of LC with a biochemical assay. Sufficient preheating of the mobile phase prior to the separation and postcolumn cooling to prevent deactivation of the enzyme, even at column temperatures as high as 208 degrees C, was achieved as indicated by the reliable peak shapes obtained. The sensitivity was comparable with previously described systems operating at ambient temperatures as similar IC50 values were obtained. Exposing the inhibitors to high temperatures did not lead to thermal decomposition. The separation of inhibitors and the subsequent biochemical assay was performed either isothermally at various temperatures or by applying various temperature gradients as well as at various flow rates. The results obtained clearly show the compatibility of HTLC with an enzymatic screening assay.

Parallel Solution-Phase Synthesis of a 2,6,8,9-Tetrasubstituted Purine Library via a Sulfur Intermediate

Purine analogues exhibiting a wide range of pharmacological activities have been considered a privileged structure in medicinal chemistry. In addition, the purine core consisting of four points of structural diversity is a well-sought scaffold in combinatorial chemistry. Although most of the efforts have been focused on 2,6,9-, 6,8,9-, or 2,8,9-trisubstituted purines, syntheses of 2,6,8,9-tetrasubstituted purines are rare. This paper presents a parallel solution phase approach for the synthesis of fully substituted purines via a 6-sulfur-substituted pyrimidine as the key intermediate. This strategy combining construction and modification of the purine ring thus increases the structural diversity of the final products. Sequential substitution of chlorines in 4,6-dichloro-2-methyl-5-nitropyrimidine with primary amine and benzylmercaptan afforded the 4-(substituted)amino-6-benzylthio-5-nitropyrimidine, which was readily converted to its diaminopyrimidine analogue by reduction of the nitro group. The diaminopyrimidine intermediate was cyclized to construct the purine ring with a C-8 substituent. Eventual oxidation of sulfur to sulfone and subsequent displacement by a primary or secondary amine provided the desired 2,6,8,9-tetrasubstituted purine analogues. This synthetic methodology was validated with the synthesis of a 216-member purine library.

Identification of the F1F0 mitochondrial ATPase as a target for modulating skin pigmentation by screening a tagged triazine library in zebrafish

A triazine-based combinatorial library of small molecules was screened in zebrafish to identify compounds that produced interesting phenotypes. One compound (of 1536 screened) induced a dramatic increase in the pigmentation of early stage zebrafish embryos. This compound, PPA, was also found to increase pigmentation in cultured mammalian melanocytes. The cellular target was identified as the mitochondrial F1F0-ATP synthase (ATPase) by affinity chromatography. Oligomycin, a small molecule known to inhibit the mitochondrial ATPase, competed with PPA for its cellular target in melanocytes. In addition, PPA was shown to alter the membrane potential of mitochondria, consistent with inhibition of the mitochondrial ATPase. Thus, PPA has been successfully used as a chemical probe in a forward chemical genetic approach to establish a link between the phenotype and the protein. The results attest to the power of screening small molecule libraries in zebrafish as a means of identifying mammalian targets and suggest the mitochondrial ATPase as a target for modulating pigmentation in both melanocytes and melanoma cells.

Sulfotransferase structural biology and inhibitor discovery

Sulfotransferases catalyze the transfer of a sulfuryl group from 3'-phosphoadenosine 5'-phosphosulfate (PAPS) to proteins, carbohydrates and small molecules. The sulfotransferases comprise cytosolic and Golgi-resident enzymes; Golgi-resident enzymes represent fertile territory for identifying pharmaceutical targets. Structure-based sequence alignments indicate that the structural fold, and the PAPS-binding site, is conserved between the two classes. Initial efforts to identify sulfotransferase inhibitors by screening kinase inhibitor libraries yielded competitive inhibitors of PAPS with muM IC(50) values. Within particular classes of Golgi-resident sulfotransferases that show tight in vitro specificity, the substrate-binding site might be a suitable drug target, although sulfotransferases are generally assumed to be difficult to inhibit as a result of the expected size and chemical character of the substrate-binding site.

Identification of Compounds that Bind Mitochondrial F1F0 ATPase by Screening a Triazine Library for Correction of Albinism

A triazine-based combinatorial library of small molecules was screened in albino murine melanocytes to identify compounds that induce pigmentation. Six compounds (of 1536 screened) produced at least 3-fold increases in pigmentation. Immunohistochemical studies demonstrated that the compounds conferred correct routing of the mistrafficked enzyme tyrosinase, which is critical to normal melanogenesis. Affinity matrices of the immobilized compounds allowed the cellular target to be identified as the mitochondrial F1F0-ATP synthase. Oligomycin and aurovertin B, small molecules known to inhibit the mitochondrial ATP synthase, were shown to compete with the triazine-based compounds for their cellular target in albino melanocytes and confer similar effects on pigmentation and tyrosinase rerouting. This is the first demonstration of the mitochondrial ATP synthase as a potential therapeutic target for restoring pigmentation in albino melanocytes.

SNAr Iodination of 6-Chloropurine Nucleosides: Aromatic Finkelstein Reactions at Temperatures Below −40 °C1

Mesitoyl or toluoyl esters of inosine and 2'-deoxyinosine were deoxychlorinated at C6 to give the crystalline 6-chloropurine nucleoside derivatives, which underwent quantitative conversion to the 6-iodo analogues with NaI/TFA/butanone at -50 to -40 degrees C. The 6-iodo compounds were efficient substrates for SNAr, Sonogashira, and Suzuki-Miyaura reactions, in contrast with the 6-chloro analogues, and gave good to high yields of C-N and C-C coupled products.

Identification, function and structure of the mycobacterial sulfotransferase that initiates sulfolipid-1 biosynthesis

Sulfolipid-1 (SL-1) is an abundant sulfated glycolipid and potential virulence factor found in Mycobacterium tuberculosis. SL-1 consists of a trehalose-2-sulfate (T2S) disaccharide elaborated with four lipids. We identified and characterized a conserved mycobacterial sulfotransferase, Stf0, which generates the T2S moiety of SL-1. Biochemical studies demonstrated that the enzyme requires unmodified trehalose as substrate and is sensitive to small structural perturbations of the disaccharide. Disruption of stf0 in Mycobacterium smegmatis and M. tuberculosis resulted in the loss of T2S and SL-1 formation, respectively. The structure of Stf0 at a resolution of 2.6 A reveals the molecular basis of trehalose recognition and a unique dimer configuration that encloses the substrate into a bipartite active site. These data provide strong evidence that Stf0 carries out the first committed step in the biosynthesis of SL-1 and establish a system for probing the role of SL-1 in M. tuberculosis infection.

Rapid Discovery of Potent Sulfotransferase Inhibitors by Diversity-Oriented Reaction in Microplates Followed by in situ Screening

Rapid diversity-oriented microplate library synthesis and in situ screening with a high-throughput fluorescence-based assay were used to develop potent inhibitors of beta-arylsulfotransferase IV (beta-AST-IV). This strategy leads to facile inhibitor synthesis and study as it allows protecting-group manipulation and product isolation from other library components to be avoided. Through repeated library formation, three aspects of inhibitor makeup, the identities of the two binding groups and the length of the linker between them, were independently optimized. Several potent inhibitors were obtained, one of which was determined to have an inhibition constant K(i) of 5 nM. This compound is the most potent beta-AST-IV inhibitor developed to date, with a K(i) value more than five orders of magnitude lower than the Michaelis constant K(m) for the substrate whose binding it inhibits.

Safety-Catch Approach to Orthogonal Synthesis of a Triazine Library

A novel safety-catch method for orthogonal synthesis of highly pure trisubstituted triazines was developed. Since the polymer-support used in this method is not acid-labile, this strategy can be uniquely applied to the synthesis of acid-sensitive triazine library compounds. This method will dramatically increase the diversity of triazine and other related heterocyclic library compounds.

Catalysis of nucleophilic aromatic substitutions in the 2,6,8-trisubstituted purines and application in the synthesis of combinatorial libraries

The following paper summarizes our work on compound libraries of 2,6,8-trisubstituted purines. This synthesis route on a polystyrene support begins with 2,6-dichloro purine making extensive use of catalysis. During the synthesis the polymer bound purines were brominated selectively on C8. The substitution reaction of C6-Cl by amines was found to be acid catalyzed. The substitution of C2-Cl by amines and aryls, as well as the substitution of a C8-Br by aryls, alkenyl and alkynyl groups can be catalyzed by transition metals. Under some bromination conditions novel selective oxidative transformations of 2-amino groups in 2,6-diamino purines have been found.

Facilitated forward chemical genetics using a tagged triazine library and zebrafish embryo screening

An improved forward chemical genetics approach was successfully demonstrated using a tagged library concept. A small-molecule triazine library with linkers was used to screen for brain/eye developmental phenotypes in a zebrafish embryo system. This approach enabled the rapid isolation of the target proteins by facile affinity matrix preparation and elucidated the first small-molecule inhibitors for several ribosomal accessory proteins or their complex as the target.

Highly Sensitive in Vitro Selections for DNA-Linked Synthetic Small Molecules with Protein Binding Affinity and Specificity

We have developed in vitro selections for DNA-linked synthetic small molecules with protein binding affinity and specificity. These selections require only generally accessible equipment, offer high degrees of enrichment of active molecules from mixtures of predominantly inactive species, can be applied to a variety of unrelated proteins, and require approximately 108-fold less material than existing synthetic molecule screening methods. Iterating these selections multiplies the net enrichment of active molecules, enabling enormous overall enrichment factors exceeding 106 to be achieved. Further, the selections can be adapted to select for binding specificity in addition to binding affinity. The application of methods described in this work may play a key role in the discovery of desired molecules from DNA-templated synthetic libraries.

Multiplex inhibitor screening and kinetic constant determinations for yeast hexokinase using mass spectrometry based assays

An electrospray ionization mass spectrometry based assay was developed for kinetic measurements and inhibitor screening of yeast hexokinase. There is considerable discrepancy in the literature as to the accuracy of kinetic data obtained for hexokinase. In the assay described herein, the product, glucose 6-phosphate was directly monitored by ion trap mass spectrometry and quantified using an internal standard, 2 deoxy-glucose 6-phosphate. The kinetic parameters, K(M) and V(max) for the two substrates were determined without using a coupling enzyme as is normally employed in the traditional spectrophotometric assay for systems lacking a chromophore. In addition, hexokinase was successfully immobilized onto an amino-link gel, and a mock library was screened against the immobilized enzyme for the identification of possible inhibitors. After comparing the mass spectra of the library before and after incubation, trehalose 6-phosphate, ADP, and oxidized glutathione were differentiated from other weak or non-inhibitors. Inhibition behavior of ADP with respect to ATP was further evaluated with the ESI-MS assay and the value of K(i) was determined. This ESI-MS assay was demonstrated to be both accurate and precise for determining kinetic constants and for identifying enzyme inhibitors.

Protein Structure Similarity as Guiding Principle for Combinatorial Library Design

Proteins are modularly built from a limited set of approximately 1000 structural domains. The evolutionary relationship within a domain family suggests that the knowledge about a common fold structure can be exploited for the design of small molecule libraries in the development of inhibitors and ligands. This principle has been used for the synthesis of inhibitors for kinases sharing the same fold. It can also be applied for proteins which share the same fold architecture yet belong to different functional classes. Bestatin--originally known as an aminopeptidase inhibitor--was employed as guiding structure for the development of leukotriene A4 hydrolase inhibitors. A combinatorial approach helped to identify inhibitors for sulfotransferases which share structural similarity with nucleotide kinases using a kinase inhibitor core structure as guiding principle.

Synthesis of a bisubstrate analogue targeting estrogen sulfotransferase

Sulfotransferases catalyze the transfer of a sulfuryl group from the eukaryotic sulfate donor 3'-phosphoadenosine 5'-phosphosulfate to an acceptor biomolecule. Sulfotransferases have been linked with several disease states, prompting our investigation of specific sulfotransferase inhibitors. Presented herein is the synthesis and evaluation of a bisubstrate analogue designed to inhibit estrogen sulfotransferase. The synthesis utilizes a novel, orthogonally protected 3'-phosphoadenosine 5'-phosphate (PAP) derivative allowing the selective functionalization of the 5'-phosphate with a sulfate acceptor mimic. Kinetic studies revealed significant inhibitory activity and provide guidance for improved inhibitor design.

A potent and highly selective sulfotransferase inhibitor

In the present work, we have used a newly developed, fluorescence-based assay to screen a library of >30 000 compounds as potential beta-arylsulfotransferase-IV inhibitors. A total of 11 inhibitors were discovered. Most of the compounds discovered showed low micromolar inhibition, but one of the compounds showed potent inhibition (Ki = 96 nM). The most potent of these inhibitors was tested against a variety of other purine binding enzymes and showed remarkable specificity.