Lateral Side Chains Research Articles

Investigations of the Properties of l-Histidine in Aqueous NaCl Solutions at Different Temperatures

Density and viscosity experimental data for l-histidine in NaCl aqueous solutions were obtained at different salt and different amino acid concentrations in the range of temperatures between 293.15 and 323.15 K. The results have been correlated and analyzed in order to evaluate the influence of electrolyte concentration and temperature on the volumetric and viscometric properties of the solutions. The apparent molar volumes and the transfer volumes of l-histidine in aqueous NaCl solutions at different salt and amino acid molalities over entire temperature range were calculated from experimental density data. The viscosity experimental data have been analyzed with Jones–Dole equation and the Falkenhagen (A) and the Jones–Dole coefficient (B) have been calculated in order to evaluate the interactions occurring in the systems. The B viscosity coefficients were found to be positive for all conditions, showing a kosmotropic effect of solutes, indicating an alignment of zwitterions with ions/water dipoles. A comparison of standard partial molar volumes for some amino acids in water and NaCl aqueous solutions shows that they increase with molecular mass and complexity of the lateral side chain of the amino acid.

Role of the Comonomeric Units in Reaching Linear Backbone, High Solid-State Order and Charge Mobilities in Heptacyclic Arene-Based Alternating Copolymers

Unpredictable trends of charge mobility (μ) in multicyclic heteroarenes-contained polymers remain an obstacle in designing high performance polymers used in polymeric field effect transistors (PFETs). The roles of the comonomeric units in reaching high hole mobility (μh) of copolymers containing a heptacyclic arene unit, dithienocyclopentacarbazole (DTCC) were investigated in this study. A series of four DTCC-based alternating copolymers, PDTCC-1T, PDTCC-3T, PDTCC-BDT, and PDTCC-TT, were synthesized from the Pd-catalyzed copolymerizations between DTCC and comonomeric units including thiophene (1T), terthiophene (3T), benzodithiophene (BDT) and thienothiophene (TT) units. Among the four DTCC-based alternating copolymers, highest mobility of 1.36 × 10–2 cm2 V–1 s–1 was reached in PDTCC-3T. Optoelectronic and 2D-WAXD studies revealed that strong electronic interaction and highly ordered solid-state structure were only observed in PDTCC-3T. It is attributed to the combination of two axisymmertric units, DTCC and 3T, linearized the polymer backbone, leading to a compact solid-state packing and high μh, while centrosymmertic comonomeric units, BDT and TT curved the polymer backbones of PDTCC-BDT and PDTCC-TT, which decreases solid-state order and μh. Furthermore, the short axisymmeritric 1T although results in a linear backbone of PDTCC-1T, comparing to 3T, it is too short to effectively reduce interchain steric hindrance caused by the solubilizing octyl chains on DTCC. Thus, effective π–π stacking is hindered in PDTCC-1T, resulting in low μh. The macroscopic performances of μhs agreed well with the optoelectronic and 2D-WAXD studies. It is concluded that the linear backbone of DTCC copolymers is the prerequisite to reach ordered solid-state packing, which facilitate effective charge transport, and it depends on the prudent choose on the symmetry of the comonomeric unit. In addition, balance between the solubility and adequate crowdedness of lateral side chains is essential for a PFET material to be not only easily processed, but also effectively π–π stack.

Interaction of Imidazolium-Based Room-Temperature Ionic Liquids with DOPC Phospholipid Monolayers: Electrochemical Study

To test the biocompatible character of room-temperature ionic liquids (ILs), the interaction of various ILs with biological membrane (biomembrane) models was studied in this work. Dioleoyl phosphatidylcholine (DOPC) adsorbed on a mercury (Hg) electrode forms an impermeable defect-free monolayer which is a well established biomembrane model, prone to be studied by electrochemical techniques. We have monitored the modifications of the Hg supported monolayer caused by ILs using rapid cyclic voltammetry (RCV), alternating current voltammetry (ACV), and electrochemical impedance spectroscopy (EIS). A series of imidazolium-based ILs were investigated whose interaction highlighted the role of anion and lateral side chain of cation during the interaction with DOPC monolayers. It was shown that the hydrophobic and lipophilic character of the IL cations is a primary factor responsible for this interaction. Hg-supported monolayers provide an accurate analysis of the behavior of ILs at the interface of a biomembrane leading to a comprehensive understanding of the interaction mechanisms involved. At the same time, these experiments show that the Hg-phospholipid model is an effective toxicity sensing technique as shown by the correlation between literature in vivo toxicity data and the data from this study.

New method to analyze dielectric relaxation processes: a study on polymethacrylate series

The relaxation properties of polymethacrylates of the n-alkyl series with n = l, 2 and 4 (poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA) and poly(n-butyl methacrylate) (PnBMA)) have been measured and analyzed in order to relate their properties to the size of the lateral side chains. The n-alkyl series has been regarded as a model system and was used in this work to test a graphical data analysis method. Essentially, four relaxation processes were detected in the three polymers: the γ, β, α and αβ relaxations, in increasing order of temperature. It was found that the γ relaxation has a low activation energy, of around 36.3–38.5 kJ mol−1, independent of the side chain, exhibiting low entropy of activation values when referring to the Eyring description of the activation parameters. The β relaxation was found to be similar in PMMA and PEMA, showing an activation energy of 88.8 kJ mol−1, increasing to 112.8 kJ mol−1 in PnBMA. The activation entropy was also found to be low for this relaxation, although greater than that for the γ relaxation. In contrast, the α relaxation is quite different in these polymers. We observed a gradual shift in the glass transition temperature towards lower temperatures as the side chain increases in length. The manner in which the α transition makes its way into the dielectric spectra is more abrupt in PMMA than in PnBMA, denoting a higher fragility in the former polymer. Finally, there is a significant difference in the coalescence scenarios of the α and β relaxations for temperatures higher than the glass transition temperature, where they give rise to the so-called αβ relaxation. © 2013 Society of Chemical Industry

Synthesis and evaluation of some bioactive compounds having oxygen and nitrogen heteroatom

Some new 3,4–disubstituted isocoumarins were synthesized having bioactive pyrazole molecule at 3rd position of isocoumarin moiety (5a,b), from isocoumarin -3- carboxylic acid hydrazide (4a,b) followed by cyclization with acetyl acetone. A series of isocoumarin derivative having Schiff base as lateral side chain at 3rd position of isocoumarin moiety were also synthesized (7a,b), by condensing isocoumarin acid hydrazide and benzaldehyde derivative followed by dehydration. The chemical structures of all the compounds were determined by analytical and spectral method. The lead compounds were screened for antimicrobial and analgesic activities. The article presents the synthesis and characterization of different isocoumarin derivatives from Isocoumarin-3-carboxylic acid hydrazide. The compounds were also screened for their antimicrobial and analgesic activities.

Synthesis, Characterization, and Pharmacological Evaluation of Silicon-Containing Aminoquinoline Organometallic Complexes As Antiplasmodial, Antitumor, and Antimycobacterial Agents

Two silicon-containing analogues (1, 2) of chloroquine, modified in the lateral side chain with organosilicon moieties, were synthesized. Compounds 1 and 2 were further reacted with dinuclear half-sandwich transition metal precursors [Ru(Ar)(μ-Cl)Cl]2 (Ar = η6-p-iPrC6H4Me; η6-C6H6; η6-C6H5OCH2CH2OH), [Rh(COD)(μ-Cl)]2, and [RhCp*(μ-Cl)Cl]2, to yield a series of neutral mononuclear Ru(II), Rh(I), and Rh(III) silicon-aminoquinoline complexes (3–12). Compounds 1 and 2 act as monodentate donors that coordinate to the transition metals via the quinoline nitrogen of the aminoquinoline scaffold. All the compounds were characterized using various analytical and spectroscopic techniques, and the molecular structures of compounds 2 and 11 were elucidated by single-crystal X-ray diffraction analysis. Furthermore, the in vitro pharmacological activities of compounds 1–12 were established against chloroquine-sensitive (NF54) and chloroquine-resistant (Dd2) strains of the malarial parasite Plasmodium falciparum and agai...

New Angular-Shaped and Isomerically Pure Anthradithiophene with Lateral Aliphatic Side Chains for Conjugated Polymers: Synthesis, Characterization, and Implications for Solution-Prossessed Organic Field-Effect Transistors and Photovoltaics

An isomerically pure anti-anthradithiophene (aADT) arranged in an angular shape is developed. Formation of the framework of aADT incorporating four lateral alkyl substituents was accomplished by a one-pot benzannulation via multiple Suzuki coupling. This newly designed 2,8-stannylated aADT monomer was copolymerized with a ditheniodiketopyrrolopyrrole (DPP) unit and a bithiophene unit, respectively, to furnish an alternating donor–acceptor copolymer poly(anthradithiophene-alt-dithienyldiketopyrrolopyrrole) (PaADTDPP) and a thiophene-rich poly(anthradithiophene-alt-bithiophene) (PaADTT). PaADTT with crystalline nature achieved a high FET mobility of 7.9 × 10–2 cm2 V–1 s–1 with an on–off ratio of 1.1 × 107. The photovoltaic device based on the PaADTDPP:PC71BM (1:2.5, w/w) blend exhibited a Voc of 0.66 V, a Jsc of 9.49 mA/cm2, and a FF of 58.4%, delivering a power conversion efficiency (PCE) of 3.66%. By adding 1.5 vol % 1-chloronaphthalene (CN) as a processing additive, the PCE can be improved to 4.24%. We demonstrated that these angular-shaped and alkylated aADT-based polymers have better organic photovoltaic (OPVs) and field-effect transistor (FETs) characteristics than the linear-shaped ADT-containing polymers.

Deciphering the Resistance-Counteracting Functions of Ferroquine in Plasmodium falciparum-Infected Erythrocytes.

The aminoquinoline chloroquine (CQ) has been widely used for treating malaria since World War II. Resistance to CQ began to spread around 1957 and is now found in all malarious areas of the world. CQ resistance is caused by multiple mutations in the Plasmodium falciparum chloroquine resistance transporter (PfCRT). These mutations result in an increased efflux of CQ from the acidic digestive vacuole (DV) to the cytosol of the parasite. This year, we proposed a strategy to locate and quantify the aminoquinolines in situ within infected red blood cells (iRBCs) using synchrotron based X-ray nanoprobe fluorescence. Direct measurements of unlabeled CQ and ferroquine (FQ) (a ferrocene-CQ conjugate, extremely active against CQ-resistant strains) enabled us to evidence fundamentally different transport mechanisms from the cytosol to the DV between CQ and FQ in the CQ-susceptible strain HB3. These results inspired the present study of the localization of CQ and FQ in the CQ-resistant strain W2. The introduction of the ferrocene core in the lateral side chain of CQ has an important consequence: the transporter is unable to efflux FQ from the DV. We also found that resistant parasites treated by FQ accumulate a sulfur-containing compound, credibly glutathion, in their DV.

3,6‐Dialkylthieno[3,2‐b]thiophene moiety as a soluble and electron donating unit preserving the coplanarity of photovoltaic low band gap copolymers

AbstractIt has been shown recently, that the presence of alkyl side chains at the 3‐positions on the thiophene rings placed next to 2,1,3‐benzothiadiazole core in the backbone of several conjugated polymers results in severe steric hindrance and prevents efficient planarity of the thiophene‐2,1,3‐benzothiadiazole‐thiophene (TBzT) segment. Both properties have a strong influence on the optoelectronic properties of the polymer and need to be considered when the polymer is to be used for organic electronics applications. In this work, we modified a previously synthesized oligothiophene copolymer, consisting of two 3,4′‐dialkyl‐2,2′‐bithiophene units attached to a 2,1,3‐benzothiadiazole unit (TBzT segment) and a thieno[3,2‐b]thiophene unit, by optimizing the lateral alkyl side chains following a density functional theory investigation. It is demonstrated that eliminating the alkyl side chains from the 3‐positions of the TBzT segment and anchoring them onto the thieno[3,2‐b]thiophene, using an efficient synthesis of the 3,6‐dihexylthieno[3,2‐b]thiophene unit, allows us to reduce the energy band gap. In addition, the chemical modification leads to a better charge transport and to an enhanced photovoltaic efficiency of polymer/fullerene blends. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Opening up the advantages of the ruthenocenic bioprobes of ferroquine: distribution and localization in Plasmodium falciparum-infected erythrocytes

A ferrocene-quinoline conjugate named ferroquine (FQ or SSR97193) is active against both chloroquine-susceptible and chloroquine-resistant Plasmodium falciparum and P. vivax strains and/or isolates. FQ was shown to be efficient for the treatment of uncomplicated malaria in humans (phase IIb of clinical trials). However, the molecular basis of FQ's mechanism of action is still unknown because few approaches (such as radioactive labelling or immunofluorescence) are available for that purpose. Previous reports from our laboratory suggest that the intramolecular hydrogen bond in the lateral side chain plays a crucial role in the antimalarial activity of the drug. We used two ruthenocenic bioprobes of FQ (with and without an intramolecular hydrogen bond) to study their localization and quantification in Plasmodium falciparum-infected erythrocytes. We first used Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) analysis to trace ruthenoquine (RQ, with an intramolecular hydrogen bond) and methylruthenoquine (Me-RQ, without an intramolecular hydrogen bond) in the infected red blood cells (iRBCs). We showed that RQ accumulates faster in the digestive vacuole of the iRBCs than Me-RQ. We next examined the ruthenium distribution at the ultrastructural level by transmission electron microscopy (TEM). We showed that RQ accumulates faster in the parasitic digestive vacuole (DV) close to its membranes than Me-RQ.

Amino Acid Precursor Supply in the Biosynthesis of the RNA Polymerase Inhibitor Streptolydigin by Streptomyces lydicus

Biosynthesis of the hybrid polyketide-nonribosomal peptide antibiotic streptolydigin, 3-methylaspartate, is utilized as precursor of the tetramic acid moiety. The three genes from the Streptomyces lydicus streptolydigin gene cluster slgE1-slgE2-slgE3 are involved in 3-methylaspartate supply. SlgE3, a ferredoxin-dependent glutamate synthase, is responsible for the biosynthesis of glutamate from glutamine and 2-oxoglutarate. In addition to slgE3, housekeeping NADPH- and ferredoxin-dependent glutamate synthase genes have been identified in S. lydicus. The expression of slgE3 is increased up to 9-fold at the onset of streptolydigin biosynthesis and later decreases to ∼2-fold over the basal level. In contrast, the expression of housekeeping glutamate synthases decreases when streptolydigin begins to be synthesized. SlgE1 and SlgE2 are the two subunits of a glutamate mutase that would convert glutamate into 3-methylaspartate. Deletion of slgE1-slgE2 led to the production of two compounds containing a lateral side chain derived from glutamate instead of 3-methylaspartate. Expression of this glutamate mutase also reaches a peak increase of up to 5.5-fold coinciding with the onset of antibiotic production. Overexpression of either slgE3 or slgE1-slgE2 in S. lydicus led to an increase in the yield of streptolydigin.

Self-Assembly of T-Shaped Polyphilic Molecules in Solvent Mixtures

Coarse-grained molecular simulations of a model of a T-shaped polyphilic molecule in the presence of solvents are presented. The target molecules are liquid crystal bolaamphiphiles with grafted lateral side chains. The main core of the molecule corresponds to a rigid biphenyl unit, decorated at both ends with polar associating sites. A lateral flexible chain, whose character is mostly antagonistic with respect to the rest of the molecule, imparts unique self-assembly behavior to the pure fluid. In the case herein, the pure T-shaped bolaamphiphile (TsB) forms two-dimensional honeycomb-like columnar structures, and a study is performed on the effects of solvents added to this structure. Three model solvents are considered, each corresponding to the three different parts of the original molecule. We consider the whole concentration range and a temperature at which the pure TsB fluid shows a columnar liquid crystal behavior. All three solvents show different progressions and equilibrium mesophases. The solvent compatible with the end groups swells the structure at low concentrations and at higher concentrations forces a phase split between an essentially pure solvent phase and a structured LC phase. The solvent affine with the core of the TsB does not swell the structure at low concentrations. At higher concentrations, this solvent induces a phase separation where the TsB-rich phase forms a unique liquid crystal membrane. The solvent compatible with the lateral chain will not form stable phase separations, but transforms the columnar structure into a loose, worm-like micellar network. The results reported are generic in nature and describe the phase space for the entire family of TsB's.

Influence of the Alkyl Mantle on the Self-Assembly of Phenylene−Thienylene-Based Oligomers

The organization of a series of phenylene−thienylene-based oligomers solubilized with terminal (ω-hydroxyalkyl) and lateral (alkoxy) side chains was studied. The thermal behavior and self-assembly on the surface during solution and thermal processing are mainly affected by the position and length of the side chains. The molecules organize in different fashions, depending on the substitution pattern, as indicated by fiber X-ray scattering results. The oligomer with only lateral side chains behaves as a typical rigid rod arranged in lamella structures, while those with a homogeneous alkyl mantle around the aromatic system adapt a disklike character and form one-dimensional stacks. Because of the large aromatic rod, the role of the terminal hydroxy groups on the self-assembly can be neglected. The choice of the alkyl density around the aromatic core allows a control over the molecular organization, which is essential for the development of high-performance solution-processable organic semiconductors.

Luminescent mesogen jacketed poly(1‐alkyne) bearing lateral terphenyl with hexyloxy tail

AbstractMesogen jacketed liquid crystalline poly(1‐alkyne) and poly(1‐phenyl‐1‐alkyne) linked pendants of terphenyl mesogens with hexyloxy tails at the waist position ({RCC [(CH2)3OOC‐terpheyl‐(OC6H13)2]}n, where RH, PHATP(OC6)2; RC6H5, PPATP(OC6)2) were synthesized. The influences of structural variations on the thermal, mesomorphic, and luminescent properties were investigated. Polymerizations of all monomers are carried out by WCl6‐Ph4Sn catalysts successfully. The polymers are stable (Td ≥ 340 °C) and soluble in common solvents. The monomers and polymers show enantiotropic SmA phases in the heating and cooling processes, and the lateral side chains of the mesogenic units are perpendicular to the main chain. The “jacket effect” of chromophoric terphenyl core “shell” around the main chain also contributes to polymers with high photoluminescence, and the pendant‐to‐backbone energy transfer path is involved in the luminescence process of this polymers. In comparison with monosubstituted polyacetylene PHATP(OC6)2, the disubstituted polyacetylene PPATP(OC6)2 shows better photoluminescence in both THF solution and film, and exhibited about 40 nm red‐shifted than PHATP(OC6)2, indicating that the “jacket effect” of terphenyl mesogens forces poly(1‐phenyl‐1‐alkyne) backbone to extend in a more planar conformation with a better conjugation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

A 4-aminoquinoline derivative that markedly sensitizes tumor cell killing by Akt inhibitors with a minimum cytotoxicity to non-cancer cells

The purpose of this study was to evaluate the enhancement value of chloroquine analogs when used in combination with Akt inhibitors on the MDA-MB468, MDA-MB231 and MCF7 human breast cancer cell lines. The result showed that the combination of certain chloroquine analogs and Akt inhibitors are highly effective. In particular, the chloroquine analog N′-(7-fluoro-quinolin-4-yl)-N,N-dimethyl-ethane-1,2-diamine (compound 5) was highly effective in sensitizing cancer cell killing when combined with either Akt inhibitor 8 (1-{1-[4-(7-phenyl-1H-imidazo[4,5-g]quinoxalin-6-yl)-benzyl]-piperidin-4-yl}-1,3-dihydro-benzoimidazol-2-one) or 9 ([4-(2-chloro-4a,10a-dihydro-phenoxazin-10-yl)-butyl]-diethyl-amine hydrochloride). Importantly, the enhancement of chloroquine analogs 5 on cell killing by Akt inhibitors 8 and 9 was cancer-specific. Thus, this combinational approach is highly promising in controlling tumors with a minimum side effect. Structural analysis of effective and ineffective chloroquine analogs suggests that the 4-aminoquinoline scaffold and lateral side chain of dimethylamino functionality play an important role for the enhancement of cell killing by Akt inhibitors.

Key elements for discriminating selective estrogen receptor modulators and selective receptor estrogen down regulators: a molecular approach to classify antiestrogens.

Abstract Abstract #3036 Breast cancer is the most common type of malignancy among women in the world. About 60% of breast tumours express the oestrogen receptor alpha (ERα) and are considered hormone-responsive. Thus endocrine therapies have been the treatment of choice. However, the estrogen-like agonist effect of the available selective estrogen receptor modulators such as tamoxifen and the development of resistances require the development of new treatments that act through different mechanisms.
 The objective of our study is to design new anti-estrogens and tools that can help to understand the molecular mechanisms involved in ligand dependent modulation or degradation of ERα. It has been proposed that ligand dependent ERα degradation of antagonist may result from the presence of an aliphatic side chain on a steroidal body. Our aim is to exploit the structural characteristics of anti-estrogens to create new compounds with different lateral side chains for the study of the relationship between structure and activity of antiestrogens.
 We selected the following compounds: RU 39411, RU 58668, which have similar structures of the steroid body, but different side-chain motifs: RU 39411 has a side chain similar to that of Tamoxifen, while RU 58668 has one similar to Faslodex. The third compound, EM 652, has a body of intermediate structure between stilbestrol and oestradiol while the side chain is similar to that of Raloxifen.
 First, we analysed the degradation of ERα in the presence of the different ligands: Fulvestrant and RU 58668 induce degradation of ERα,in a protasome dependent manner, while RU 39411 and EM 652 have the same effect as Tamoxifen and stabilize ERα. To further analyze the molecular mechanism we generated three mutants of ERα; L540Q (in H12 of ligand binding domain), K362A (interaction with co-activators,) and A350V-D351Y (interaction with side chain of antiestrogens).
 Using transient transfection of the different mutant constructs of MDA-MB231(ER-negative) cells, we tested the effect of the ligands on gene expression of a luciferase reporter gene under the control of an estrogen inducible promoter and ligand-induced degradation of ER. Our results demonstrate that antiestrogens can be classified into two groups based on structure and function: Tamoxifen and RU39411 fall into a first group, and Faslodex and RU58668 into a second group. However EM 652 has an intermediate behavior. Preliminary results on stable cell lines show that results from transient transfections can be reproduced.and confirm the importance of the integrity of H12 for antagonist activity. Molecular modelisation demonstrates that variations in the structure of the ER ligand binding domain in the presence of different antiestrogens correlate with functional differences.
 We have used molecular studies to screen and classify antiestrogen compounds into SERM or SERD with the aim to develop novel molecules for endocrine treatment of breast cancer. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3036.

Synthesis and Antimalarial Activity of Novel Side Chain Modified Antimalarial Agents Derived from 4-Aminoquinoline

Malaria is one of the foremost public health problems in developing countries affecting nearly 40% of the global population. Apart from this, the past two decade's emergence of drug resistance has severely limited the choice of available antimalarial drugs. Furthermore, the general trend emerging from the SAR-studies is that chloroquine resistance does not involve any change to the target of this class of drugs but involves compound specific efflux mechanism. Based on this premise a number of groups have developed short chain analogues of 4-aminoquinoline, which are active against CQ-resistant strains of P. falciparum in in vitro studies. However, these derivatives undergo biotransformation (de-alklyation) significantly affecting lipid solubility of the drug. In view of this background information, we thought that it would be interesting to study the effect of additional lipophilicity and cationic charge at the lateral side chain of 4-aminoquinoline. This prompted us to explore the cationic amino acid conjugates namely, lysine and ornithine of 4-aminoquinoline with a view to achieve improved antimalarial activity and to the best of our knowledge such amino acid conjugates have not been hitherto reported in the literature in the case of 4-aminoquinolines. In the present study, a new series of side-chain modified 4-aminoquinolines have been synthesized and found active against both susceptible and multidrug resistant strains of P. falciparum in vitro and P. yoelli in vivo. The seminal finding of the present study is that a new series of compounds having significantly more activity against CQ resistant parasites has been identified.

Polyglutamylation Is a Post-translational Modification with a Broad Range of Substrates

Polyglutamylation is a post-translational modification that generates lateral acidic side chains on proteins by sequential addition of glutamate amino acids. This modification was first discovered on tubulins, and it is important for several microtubule functions. Besides tubulins, only the nucleosome assembly proteins NAP1 and NAP2 have been shown to be polyglutamylated. Here, using a proteomic approach, we identify a large number of putative substrates for polyglutamylation in HeLa cells. By analyzing a selection of these putative substrates, we show that several of them can serve as in vitro substrates for two of the recently discovered polyglutamylases, TTLL4 and TTLL5. We further show that TTLL4 is the main polyglutamylase enzyme present in HeLa cells and that new substrates of polyglutamylation are indeed modified by TTLL4 in a cellular context. No clear consensus polyglutamylation site could be defined from the primary sequence of the here-identified new substrates of polyglutamylation. However, we demonstrate that glutamate-rich stretches are important for a protein to become polyglutamylated. Most of the newly identified substrates of polyglutamylation are nucleocytoplasmic shuttling proteins, including many chromatin-binding proteins. Our work reveals that polyglutamylation is a much more widespread post-translational modification than initially thought and thus that it might be a regulator of many cellular processes.

Role of a tRNA Base Modification and Its Precursors in Frameshifting in Eukaryotes

Little is known about the role of specific base modifications of transfer RNAs. Wyosine bases are tRNA(Phe)-specific modifications that are distinguished by differentiated, lateral side chains and base methylations appended to the core ring structure of a universally conserved G37, adjacent to the anticodon of Phe tRNAs. Based on previous data, we hypothesized that this modification was needed for -1 frameshifting. Using a reporter system incorporating a SCV-LA yeast virus slippery site for detecting -1 frameshifts in vivo, yeast strains were created that enabled chemical-genetic dissection of the role of different functional groups of wyebutosine that are added in a three-step post-transcriptional set of reactions. With this system, hypomodification increased Phe-specific frameshifting, with incremental changes in frameshift efficiency after specific intermediates in the progression of wyebutosine synthesis. These data combined with investigations of wild-type and hypomodified tRNA binding to ribosomes suggest that frameshift efficiency is kinetically and not thermodynamically controlled. The progressive nature of frameshift efficiency with the stage of modification is consistent with a stepwise evolution and tuning of frameshift potential. The stepwise tuning of frameshift efficiency could explain why tRNA(Phe) in some eukaryotes is not fully modified but, rather, hypomodified to capture a specific frameshift potential.

Pyrrolidine Derivatives as New Inhibitors of ?-Mannosidases and Growth Inhibitors of Human Cancer Cells

New pyrrolidine-3,4-diol derivatives were prepared from D-(?)- and L-(+)-phenylglycinol and tested for their ability to inhibit 25 commercial glycosidases. The influence of the substitution of the lateral side chain and of the pyrrolidine ring on the enzyme inhibition was evaluated. (2R,3R,4S)-2-({[(1R)-2-Hydroxy-1-phenylethyl]amino} methyl)pyrrolidine-3,4-diol was a potent and selective inhibitor of ?-mannosidase from jack bean. This compound was derivatized into lipophilic esters in order to allow its internalization by human cancer cells. In particular, the 4-bromobenzoate derivative demonstrated promising inhibition of glioblastoma and melanoma cells whereas it was less effective on healthy human fibroblasts.