Amine Side Chain Research Articles

Mutagenesis of the NaChBac sodium channel discloses a functional role for a conserved S6 asparagine

Asparagine is conserved in the S6 transmembrane segments of all voltage-gated sodium, calcium, and TRP channels identified to date. A broad spectrum of channelopathies including cardiac arrhythmias, epilepsy, muscle diseases, and pain disorders is associated with its mutation. To investigate its effects on sodium channel functional properties, we mutated the simple prokaryotic sodium channel NaChBac. Electrophysiological characterization of the N225D mutant reveals that this conservative substitution shifts the voltage-dependence of inactivation by 25 mV to more hyperpolarized potentials. The mutant also displays greater thermostability, as determined by synchrotron radiation circular dichroism spectroscopy studies of purified channels. Based on our analyses of high-resolution structures of NaChBac homologues, we suggest that the side-chain amine group of asparagine 225 forms one or more hydrogen bonds with different channel elements and that these interactions are important for normal channel function. The N225D mutation eliminates these hydrogen bonds and the structural consequences involve an enhanced channel inactivation.

Molecular dynamics simulations reveal a new role for a conserved active site asparagine in a ubiquitin-conjugating enzyme

The role of a highly conserved active site asparagine (N79) in the ubiquitin conjugating enzyme, Ubc13, is probed using molecular dynamics simulations. Both wild type and mutant enzymes (N79A and N79D) are studied. Contrary to a popular hypothesis, we show that it is unlikely that N79 stabilizes a reaction intermediate, but instead preferentially hydrogen bonds to a loop near the active site. This keeps the sidechain carboxylate of an aspartate in the loop (D119) near the sidechain amine of the substrate lysine. Our simulations show that this distance increases in the mutants. D119 has been hypothesized to play a variety of roles in the enzyme, including deprotonating the substrate lysine, so changing this distance can have an effect on the enzyme’s efficiency. Finally, we show that it is possible for the aspartate to deprotonate the substrate even across long distances if short water wires form that connect the proton donor and acceptor. Short water wires form with greater probability in the wild type than in mutant enzymes.

Abstract 4593: Glycoengineered antibodies for click chemistry applications

Abstract Antibody-drug conjugates (ADC) hold considerable promise as anticancer agents. A critical determinant of the effectiveness of ADCs is the chemistry that is used to conjugate the payload. Currently used approaches include primarily conjugation to either side-chain amine or carboxylic acid groups or conjugation to thiols. Because these reactions are not site specific and not easily controlled, these chemistries can result in reduced affinity for the target antigen. Further, these conjugation reactions lack selectivity and can result in heterogeneous mixtures of products that differ in the sites and stoichiometry of modification. We investigated a glycoengineering strategy that enables the introduction of artificial azide groups in the antibody without affecting their antigen affinity. This is based on the observation that glycosyltransferases can incorporate non-natural sugars (e.g., azido mannose) at different sites on an IgG molecule. The azide groups inthese artificial sugars are then available to react with alkynes through copper-catalyzed ‘click’ chemistry or with strained alkynes such as dibenzyl cyclooctyne (DBCO) allowing for biorthogonal, copper-free ‘click’ chemistry. Because the sugars are added reproducibly and at asite that does not affect antigen binding, the glycoengineering technology would overcome problems associated with traditional conjugation strategies. Using this approach, azide groups were introduced in anti-CD133 and anti-perlecan antibodies. Further, the azide groups were available to react with various DBCO conjugates including fluorophores, drug molecules and nanoparticles. Importantly, the addition of artificial sugar and subsequent azide-alkyne reactiondid not affect the affinity of the antibody for the target antigen. Conjugation of nanoparticles to antibodies using this approach resulted in enhanced cellular uptake of the nanoparticles. Similarly, conjugation of a cytotoxin to the antibody resulted in enhanced cell kill in vitro. Weexpect that this glycoengineering strategy will prove to be a unique platform technology that will have a significant impact on antibody-based therapeutics. Citation Format: Drishti Sehgal, Stephen Kalscheuer, Tanmoy Sadhukha, Jayanth Panyam. Glycoengineered antibodies for click chemistry applications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4593. doi:10.1158/1538-7445.AM2017-4593

Molecular Basis of TyrA Substrate Specificity Underlying the Evolution of Alternative Tyrosine Biosynthetic Pathways

An aromatic amino acid, tyrosine, is essential for protein synthesis in all orders of life and also serves as a precursor to numerous specialized metabolites crucial for plant and human health (e.g., vitamin E, isoquinoline alkaloids, and plastoquinone). Most plants synthesize tyrosine via arogenate dehydrogenase (ADH/TyrAa) that is strongly feedback inhibited by tyrosine, whereas we recently found that soybean and Medicago truncatula have, besides ADHs, prephenate dehydrogenase (PDH/TyrAp) enzymes, which are completely insensitive to tyrosine. However, molecular and evolutionary mechanisms underlying TyrA substrate specificity and the two alternative tyrosine pathways are currently unknown. In this study, we identified non‐canonical ADHs (ncADHs), which are phylogenetically very similar to PDHs, but prefer arogenate substrate and are partially inhibited by tyrosine. By combining the x‐ray crystal structure of soybean PDH (GmPDH) and the phylogenetic distribution of PDH enzymes, we identified putative substrate specificity determining residues in the recently diverged PDH and ncADH homologs. Site‐directed mutagenesis of Asn222 on GmPDH, which corresponds to an Asp in soybean ncADH (GmncADH) resulted in loss of PDH and gain of ADH activity. Consistently, the reciprocal mutation on GmncADH, D218N, introduced PDH at the expense of ADH activity. The introduction of an Asp residue on GmPDH also resulted in gain of tyrosine inhibition, which allowed co‐crystallization of the GmPDH N222D mutant with tyrosine in the active site and demonstrated that Asp222 directly interacts with the side chain amine of tyrosine and likely arogenate. Furthermore, mutating the corresponding Asp on divergent plant ADHs resulted in a gain of PDH activity and relaxation of tyrosine inhibition. Thus, the corresponding Asn of PDHs and Asp of ADHs simultaneously control substrate specificity and tyrosine regulation, which can be altered in various plants to enhance the production of tyrosine and its derived plant natural products.

Reversible Macrocyclization of Peptides with a Conjugate Acceptor.

Macrocyclic peptides are an increasingly important class of biopharmaceuticals. A new method of macrocyclization is reported that involves reaction of the N-terminal amine and thiol side chain of cysteine with a Meldrum's acid derived conjugate acceptor. This reaction, which utilizes naturally occurring amino acids and requires no orthogonal protection of side chains, can also be reversed to yield the original linear peptide as desired.

GC-MS, GC-MS/MS and GC-IR differentiation of desoxy cathinone derivatives: Cyclic tertiary amines related to MDPV.

The desoxy phenethylamine analogues in this study represent a combination of alkyl side-chain and cyclic amines (azetidine, pyrrolidine, piperidine and azepane) to yield a set of molecules of identical elemental composition as well as major mass spectral fragment ions (base peaks) of identical elemental composition. These desoxy phenethylamine analogues of the aminoketone designer drug, 3,4-methylenedioxy-pyrrovalerone (MDPV) related to the natural product cathinone were prepared from piperonal (3,4-methylenedioxybenzaldehyde) via the intermediate precursor ketones. The aminoketones and the desoxy phenethylamine regioisomers were each separated in capillary gas chromatography experiments using an Rxi®-17Sil MS stationary phase with the aminoketones showing greater retention than the corresponding desoxyamines.

Novel ferulic amide derivatives with tertiary amine side chain as acetylcholinesterase and butyrylcholinesterase inhibitors: The influence of carbon spacer length, alkylamine and aromatic group

Based on our recent investigations on chalcone derivatives as AChE inhibitors, a series of ferulic acid (FA) tertiary amine derivatives similar to chalcone compounds were designed and synthesized. The results of bioactivity evaluation revealed that most of new synthesized compounds had comparable or more potent AChE inhibitory activity than the control drug Rivastigmine. The alteration of carbon chain linking tertiary amine groups and ferulic acid scaffold markedly influenced the inhibition activity against AChE. Among them the inhibitory activity of compound 6d (IC50: 0.71 ± 0.09 μmol/L) and 6e (IC50: 1.11 ± 0.17 μmol/L) was equal to 15-fold and 9-fold than that of Rivastigmine against AChE (IC50: 10.54 ± 0.86 μmol/L), respectively. Moreover, compound 6d shows the highest selectivity for AChE over butyrylcholinesterase(BuChE) (ratio: 18.3). The kinetic study suggested that compound 6d revealed a mixed-type inhibition against AChE. The result of molecular docking showed that compound 6d combines to AChE with three amino acid sites(Trp84, Tyr334 and Trp279), while combines to BuChE with two amino acid sites (Tyr67 and Gly66) in enzyme domains, respectively. Compound 6d might act as a potential agent for the treatment of Alzheimer's diseases (AD).

Enhanced Targeting of FLT3-ITD+AML Stem Cells through Combined Inhibition of SIRT1 and Autophagic Flux

Internal tandem duplication mutations of the Fms-like tyrosine kinase 3 (FLT3-ITD) are amongst the most common mutations in acute myeloid leukemia (AML) patients, and are associated with poor clinical outcome. Tyrosine kinase inhibitors (TKI) targeting FLT3 are only partially effective and fail to yield full and lasting responses in FLT3-ITD+ AML patients. Therefore, additional strategies to enhance eradication of FLT3-ITD+ AML cells are required to improve outcomes. We have previously shown that the NAD-dependent SIRT1 deacetylase is selectively overexpressed in human FLT3-ITD AML leukemia stem cells (LSC), which demonstrate increased sensitivity to the small molecule SIRT1 inhibitor Tenovin-6 (Li at al., Cell Stem Cell 15, 431, 2014). We have now determined that Tenovin-6, in addition to SIRT-1 inhibition and activation of p53 activity, also functions as an effective inhibitor of autophagic flux, mediated by an aliphatic tertiary amine side chain that mediates alkalization of lysosomes. Comparison of Tenovin (TV) analogs with or without SIRT1 or autophagy inhibitory properties revealed that TVs can kill melanoma cells independently of SIRT1 inhibition and that autophagy blockade correlates with ability to completely eliminate cancer cells. Autophagy is known to promote survival and facilitate tumorigenesis and drug resistance by degradation and recycling of intracellular proteins and organelles in lysosomes. In the present work, we investigated the roles of SIRT1 inhibition and autophagy inhibition in targeting AML cells. The TV analogs studied includedTV-39 (inhibits both SIRT1 and autophagy), TV-39OH (inhibits SIRT1 alone), TV-50 (inhibits autophagy alone), and TV-50OH (inhibits neither). We observed that FLT3-ITD + AML cell lines (MV4-11 and MOLM13) demonstrated increased sensitivity to TV analogs with either autophagy inhibitory (TV-50) or SIRT1 inhibitory (TV39OH) effects compared with FLT3-WT cell lines (OCI-AML3 and KG1A). The combination of TV50 and TV39OH resulted in synergistic cytotoxicity in FLT3-ITD+ AML cell lines, as well as in primary AML CD34+cells bearing the FLT3-ITD mutation (Table 1). Western blot analysis indicated that FLT3-ITD+ cells treated with TV39 showed accumulation of LC3B-II, consistent with blockade of a late stage of autophagy, as well as increased acetylated and total p53 expression, consistent with SIRT1 inhibition. Cells treated with TV39OH showed increased acetylated and total p53 without change of LC3B-II levels, whereas cells treated with TV50 alone showed only increase of LC3B-II and not in p53 levels. Knockdown (KD) of p53 using lentivirus-expressed shRNA constructs reversed the inhibitory effects of TVs with both SIRT1 and autophagy inhibitory properties. The combination of the FLT3 TKI AC220 with either TV39OH or TV50 resulted in synergistic cytotoxicity in MV4;11 and Molm-13 cells, indicating that these agents could induce enhance elimination of FLT3-ITD+ cells by TKIs. To confirm the interaction of SIRT1 and autophagy inhibition in targeting FLT3-ITD AML cells, we knocked down ATG5 and SIRT1 expression in MV4-11 and Molm13 cells using lentivirus expressed shRNA. KD of either ATG5 or SIRT1 individually resulted in significant induction of apoptosis and inhibition of proliferation in AML FLT3-ITD cell lines compared with shRNA controls (Table 2). The combined knockdown of SIRT1 and ATG5 induced further increase in apoptosis compared to KD of individual genes. KD of SIRT1 or ATG5 significantly enhanced levels of ROS in FLT3-ITD positive cell lines, measured using the CellROX® Deep Red Reagent (shCtrl vs. shATG5+shSirt1, 1 vs1.74 p=0.02; shCtrl vs shATG5, 1vs 1.83, p=0.009; shCtrl vs. shATG5, 1 vs. 1.85 p=0.008). In an ongoing experiment, we are checking the effect of KD of SIRT1, ATG5 or of both SIRT1 and ATG5 in Molm13 cells in their growth in NSG mice. We conclude that combined inhibition of SIRT1 activity and autophagic flow synergistically targets FLT3-ITD+ AML cell lines and primary CD34+ cells, and enhances their targeting by FLT3 kinase inhibitors. Combined targeting of autophagic flow and SIRT1 activity appears to be a promising strategy to enhance elimination of FLT3-ITD+ AML stem cells. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Tertiary amine derivatives of chlorochalcone as acetylcholinesterase (AChE) and buthylcholinesterase (BuChE) inhibitors: the influence of chlorine, alkyl amine side chain and α,β-unsaturated ketone group

A new series of tertiary amine derivatives of chlorochalcone (4a∼4l) were designed, synthesized and evaluated for the effect on acetylcholinesterase (AChE) and buthylcholinesterase (BuChE). The results indicated that all compounds revealed moderate or potent inhibitory activity against AChE, and some possessed high selectivity for AChE over BuChE. The structure–activity investigation showed that the substituted position of chlorine significantly influenced the activity and selectivity. The alteration of tertiary amine group also leads to obvious change in bioactivity. Among them, IC50 of compound 4l against AChE was 0.17 ± 0.06 µmol/L, and the selectivity was 667.2 fold for AChE over BuChE. Molecular docking and enzyme kinetic study on compound 4l suggested that it simultaneously binds to the catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. Further study showed that the pyrazoline derivatives synthesized from chlorochalcones had weaker activity and lower selectivity in inhibiting AChE compared to that of chlorochalcone derivatives.

ChemInform Abstract: Exploiting Alkylquinone Tautomerization: Amine Benzylation.

A general protocol for the synthesis of benzylic amines via side-chain amination of alkylquinones is reported. The reactions are initiated by the tautomerization of an alkylquinone to the corresponding quinone methide, which is subsequently trapped in situ by an amine nucleophile. This process is promoted by tertiary amines in protic solvents under mild conditions and is compatible with many functional groups. 1,2- and 1,4-benzoquinones, as well as naphthoquinones, participate in this reaction using a wide range of primary and secondary amines/anilines. The synthetic utility of this transformation is also explored.

Amino Acid Specific Effects on RNA Tertiary Interactions: Single-Molecule Kinetic and Thermodynamic Studies.

In light of the current models for an early RNA-based universe, the potential influence of simple amino acids on tertiary folding of ribozymal RNA into biochemically competent structures is speculated to be of significant evolutionary importance. In the present work, the folding-unfolding kinetics of a ubiquitous tertiary interaction motif, the GAAA tetraloop-tetraloop receptor (TL-TLR), is investigated by single-molecule fluorescence resonance energy transfer spectroscopy in the presence of natural amino acids both with (e.g., lysine, arginine) and without (e.g., glycine) protonated side chain residues. By way of control, we also investigate the effects of a special amino acid (e.g., proline) and amino acid mimetic (e.g., betaine) that contain secondary or quaternary amine groups rather than a primary amine group. This combination permits systematic study of amino acid induced (or amino acid like) RNA folding dynamics as a function of side chain complexity, pKa, charge state, and amine group content. Most importantly, each of the naturally occurring amino acids is found to destabilize the TL-TLR tertiary folding equilibrium, the kinetic origin of which is dominated by a decrease in the folding rate constant (kdock), also affected by a strongly amino acid selective increase in the unfolding rate constant (kundock). To further elucidate the underlying thermodynamics, single-molecule equilibrium constants (Keq) for TL-TLR folding have been probed as a function of temperature, which reveal an amino acid dependent decrease in both overall exothermicity (ΔΔH° > 0) and entropic cost (-TΔΔS° < 0) for the overall folding process. Temperature-dependent studies on the folding/unfolding kinetic rate constants reveal analogous amino acid specific changes in both enthalpy (ΔΔH⧧) and entropy (ΔΔS⧧) for accessing the transition state barrier. The maximum destabilization of the TL-TLR tertiary interaction is observed for arginine, which is consistent with early studies of arginine and guanidine ion-inhibited self-splicing kinetics for the full Tetrahymena ribozyme [ Yarus , M. ; Christian , E. L. Nature 1989 , 342 , 349 - 350 ; Yarus , M. Science 1988 , 240 , 1751 - 1758 ].

Effect of pH on the Binding of Sodium, Lysine, and Arginine Counterions to l‐Undecyl Leucinate Micelles

AbstractMicelle formation by the amino acid‐based surfactant undecylenyl l‐leucine was investigated as a function of solution pH with NMR, dynamic light scattering, and fluorescence spectroscopy. NMR and dynamic light scattering showed that 50 mM undecylenyl l‐leucine and 50 mM NaHCO3 solutions contained micelles approximately 20 Å in diameter and that micelle radius and the mole fraction of surfactant molecules associated with micelles changed very little with solution pH. The binding of the amino acids arginine and lysine to the anionic micelles was also investigated from pH 7.0 to 11.5. Below pH 9.0, the mole fraction of arginine cations bound to the micelles was approximately 0.4. Above pH 9.0, the arginine counterions became zwitterionic, and the mole fraction of bound arginine molecules decreased steadily to less than 0.1 at pH 11. When arginine dissociated from the micelles, their radii decreased from 14 to 10 Å. Similar behavior was observed with lysine; however, when lysine dissociated from the micelle surface, little change in micelle radius was observed. Two‐dimensional NMR experiments suggested that below pH 9.0, l‐arginine bound perpendicular to the micelle surface primarily though its side chain amine while l‐lysine bound parallel to the surface through both of its amine functional groups. Finally, the rate at which the amide protons on the surfactant headgoup exchanged with solvent was investigated with NMR spectroscopy. The exchange reaction was faster in solutions containing only surfactant monomers and slower when the surfactants were in micellar form and the headgoup amide protons were less exposed to solvent.

Degradable Amine-Reactive Coatings Fabricated by the Covalent Layer-by-Layer Assembly of Poly(2-vinyl-4,4-dimethylazlactone) with Degradable Polyamine Building Blocks.

We report the fabrication of reactive and degradable cross-linked polymer multilayers by the reactive/covalent layer-by-layer assembly of a non-degradable azlactone-functionalized polymer [poly(2-vinyl-4,4-dimethylazlactone), PVDMA] with hydrolytically or enzymatically degradable polyamine building blocks. Fabrication of multilayers using PVDMA and a hydrolytically degradable poly(β-amino ester) (PBAE) containing primary amine side chains yielded multilayers (∼100 nm thick) that degraded over ∼12 days in physiologically relevant media. Physicochemical characterization and studies on stable films fabricated using PVDMA and an analogous non-degradable poly(amidoamine) suggested that erosion occurred by chemical hydrolysis of backbone esters in the PBAE components of these assemblies. These degradable assemblies also contained residual amine-reactive azlactone functionality that could be used to impart new functionality to the coatings post-fabrication. Cross-linked multilayers fabricated using PVDMA and the enzymatically degradable polymer poly(l-lysine) were structurally stable for prolonged periods in physiological media, but degraded over ∼24 h when the enzyme trypsin was added. Past studies demonstrate that multilayers fabricated using PVDMA and non-degradable polyamines [e.g., poly(ethylenimine)] enable the design and patterning of useful nano/biointerfaces and other materials that are structurally stable in physiological media. The introduction of degradable functionality into PVDMA-based multilayers creates opportunities to exploit the reactivity of azlactone groups for the design of reactive materials and functional coatings that degrade or erode in environments that are relevant in biomedical, biotechnological, and environmental contexts. This "degradable building block" strategy should be general; we anticipate that this approach can also be extended to the design of amine-reactive multilayers that degrade upon exposure to specific chemical triggers, selective enzymes, or contact with cells by judicious design of the degradable polyamine building blocks used to fabricate the coatings.

Cisplatin-Protein Interactions: Unexpected Drug Binding to N-Terminal Amine and Lysine Side Chains.

Literature studies carried out by mass spectrometry and X-ray crystallography have demonstrated that cisplatin is able to bind proteins mainly close to Met, His, and free Cys side chains. To identify possible alternative modes of cisplatin binding to proteins at the molecular level, here we have solved the high-resolution X-ray structure of the adduct formed in the reaction between the drug and the model protein thaumatin, which does not contain any His and free Cys residues and possesses just one buried Met. Our data reveal unexpected cisplatin binding sites on the protein surface that could have general significance: cisplatin fragments -[Pt(NH3)2Cl](+), -[Pt(NH3)Cl2], and -[Pt(NH3)2(OH2)](2+) bind to a protein N-terminus and close to Lys and Glu side chains.

Abstract 2914: Biphenylene and bipyridine connected benzofuran compounds as novel regulators of kRAS transcription

Abstract Pancreatic cancer is the fourth most deadly cancer with 5 year survival rate of ∼6%. One of the major attributes of pancreatic cancer is kRAS mutations. kRAS is a proto-oncogene with intrinsic GTPase activity, and is responsible for cell proliferation, division, and apoptosis. kRAS mutations are observed in &amp;gt;95% of pancreatic adenocarcinoma and in 30% all human tumors. When mutated it leads to continuous activity and uncontrolled proliferation which results in increased tumorigenicity and poor prognosis. Downregulating kRAS expression has shown to halt proliferation and leads to cellular death in pancreatic cancer models, but to date no small molecule capable of such transcriptional silencing has been described. A novel series of molecules with either biphenylene or bipyridine spacer connecting the terminal benzofuran ring was synthesized using solution phase chemistry. Tertiary amine side chains were incorporated to the C2-position of the benzofuran ring to improve the DNA binding affinity of these compounds. The synthesized compounds were purified using a “catch and release” method employing the sulfonic acid based resins. The eleven novel compounds were screened in parallel for their ability to stabilize G-quadruplex structures in the kRAS promoter, and to downregulate kRAS promoter activity. Two of the compounds increased the thermal profile of non-canonical DNA formations in the promoter region by &amp;gt;5 °C; however, on the whole these compounds did not seem to function as G-quadruplex-stabilizing agents. Eight compounds significantly decreased luciferase expression under the explicit control of the kRAS promoter by up to 75%, by compound BF 4.3, through an as-yet unknown mechanism of action. The compound series was examined for the inhibition of cellular viability in two mutant kRAS pancreatic cancer cell lines - Panc-1 and MIA PaCa-2; in both cell lines the compounds containing the bipyridine spacer had greater cytotoxic effects with IC50's of ∼30 μM, consistently. qPCR is being used to confirm the decrease in promoter activity in native cellular conditions. These agents are intriguing in both their novel scaffold and their unexpected activity decreasing kRAS expression in a mechanism unrelated to higher order DNA structures. Ultimately, down regulation of kRAS transcription will provide a novel therapeutic approach for pancreatic cancer and improve the prognosis of this highly lethal disease. Citation Format: Harshul Batra, Mohammad K. Islam, David E. Thurston, Khondaker M. Rahman, Tracy A. Brooks. Biphenylene and bipyridine connected benzofuran compounds as novel regulators of kRAS transcription. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2914.

ChemInform Abstract: Dual Catalysis: Proton/Metal‐Catalyzed Tandem Benzofuran Annulation/Carbene Transfer Reaction.

Abstracto‐Hydroxyl‐benzylalcohols bearing an acetylenic amine side chain are subjected to conditions A).

Exploiting Alkylquinone Tautomerization: Amine Benzylation

A general protocol for the synthesis of benzylic amines via side-chain amination of alkylquinones is reported. The reactions are initiated by the tautomerization of an alkylquinone to the corresponding quinone methide, which is subsequently trapped in situ by an amine nucleophile. This process is promoted by tertiary amines in protic solvents under mild conditions and is compatible with many functional groups. 1,2- and 1,4-benzoquinones, as well as naphthoquinones, participate in this reaction using a wide range of primary and secondary amines/anilines. The synthetic utility of this transformation is also explored.

Identification and SAR Evaluation of Hemozoin-Inhibiting Benzamides Active against Plasmodium falciparum.

Quinoline antimalarials target hemozoin formation causing a cytotoxic accumulation of ferriprotoporphyrin IX (Fe(III)PPIX). Well-developed SAR models exist for β-hematin inhibition, parasite activity, and cellular mechanisms for this compound class, but no comparably detailed investigations exist for other hemozoin inhibiting chemotypes. Here, benzamide analogues based on previous HTS hits have been purchased or synthesized. Only derivatives containing an electron deficient aromatic ring and capable of adopting flat conformations, optimal for π-π interactions with Fe(III)PPIX, inhibited β-hematin formation. The two most potent analogues showed nanomolar parasite activity, with little CQ cross-resistance, low cytotoxicity, and high in vitro microsomal stability. Selected analogues inhibited hemozoin formation in Plasmodium falciparum causing high levels of free heme. In contrast to quinolines, introduction of amine side chains did not lead to benzamide accumulation in the parasite. These data reveal complex relationships between heme binding, free heme levels, cellular accumulation, and in vitro activity of potential novel antimalarials.

Protein Complexation and pH Dependent Release Using Boronic Acid Containing PEG-Polypeptide Copolymers.

New poly(L-lysine)-b-poly(ethylene glycol) copolypeptides have been prepared, where the side-chain amine groups of lysine residues are modified to contain ortho-amine substituted phenylboronic acid, i.e., Wulff-type phenylboronic acid (WBA), groups to improve their pH responsive, carbohydrate binding properties. These block copolymers form nanoscale complexes with glycosylated proteins that are stable at physiological pH, yet dissociate and release the glycoproteins under acidic conditions, similar to those found in endosomal and lysosomal compartments within cells. These results suggest that WBA modified polypeptide copolymers are promising for further development as degradable carriers for intracellular protein delivery.

Lysine-Capped Silica Nanoparticles: A Solid-State NMR Spectroscopy Study

ABSTRACTTo achieve the goal of biocompatibility in nano-based materials we must first obtain a fundamental understanding of the physical and chemical behavior of biomolecules at the interfaces of nanomaterials. A first step towards understanding protein interactions with nanomaterials is to understand how individual amino acids interact at the interfaces. In this paper, we investigated the lysine adsorption behavior on fumed silica nanoparticles by solid-state NMR spectroscopy. We use 1H, 13C and 15N solid-state magic angle spinning (MAS) NMR techniques to elucidate how lysine is adsorbed on silica nanoparticles surfaces via strong hydrogen-bonding interaction between the protonated side-chain amine group and silanol group on silica nanoparticles surfaces.*