Carboxyl Fragment Research Articles

Total Synthesis of (−)‐Zampanolide and Structure–Activity Relationship Studies on (−)‐Dactylolide Derivatives

A new total synthesis of the marine macrolide (-)-zampanolide (1) and the structurally and stereochemically related non-natural levorotatory enantiomer of (+)-dactylolide (2), that is, ent-2, has been developed. The synthesis features a high-yielding, selective intramolecular Horner-Wadsworth-Emmons (HWE) reaction to close the 20-membered macrolactone ring of 1 and ent-2. The β-keto phosphonate/aldehyde precursor for the ring-closure reaction was obtained by esterification of a ω-diethylphosphono carboxylic acid fragment and a secondary alcohol fragment incorporating the THP ring that is embedded in the macrocyclic core structure of 1 and ent-2. THP ring formation was accomplished through a segment coupling Prins-type cyclization. Employing the same overall strategy, 13-desmethylene-ent-2 as well as the monocyclic desTHP derivatives of 1 and ent-2 were prepared. Synthetic 1 inhibited human cancer cell growth in vitro with nM IC(50) values, while ent-2, which lacks the diene-containing hemiaminal-linked side chain of 1, is 25- to 260-fold less active. 13-Desmethylene-ent-2 as well as the reduced versions of ent-2 and 13-desmethylene-ent-2 all showed similar cellular activity as ent-2 itself. The same activity level was attained by the monocyclic desTHP derivative of 1. Oxidation of the aldehyde functionality of ent-2 gave a carboxylic acid that was converted into the corresponding N-hexyl amide. The latter showed only μM antiproliferative activity, thus being several hundred-fold less potent than 1.

Investigations of human platelet-type 12-lipoxygenase: role of lipoxygenase products in platelet activation

Human platelet-type 12-lipoxygenase (12-LOX) has recently been shown to play an important role in regulation of human platelet function by reacting with arachidonic acid (AA). However, a number of other fatty acids are present on the platelet surface that, when cleaved from the phospholipid, can be oxidized by 12-LOX. We sought to characterize the substrate specificity of 12-LOX against six essential fatty acids: AA, dihomo-γ-linolenic acid (DGLA), eicosapentaenoic acid (EPA), α-linolenic acid (ALA), eicosadienoic acid (EDA), and linoleic acid (LA). Three fatty acids were comparable substrates (AA, DGLA, and EPA), one was 5-fold slower (ALA), and two showed no reactivity with 12-LOX (EDA and LA). The bioactive lipid products resulting from 12-LOX oxidation of DGLA, 12-(S)-hydroperoxy-8Z,10E,14Z-eicosatrienoic acid [12(S)-HPETrE], and its reduced product, 12(S)-HETrE, resulted in significant attenuation of agonist-mediated platelet aggregation, granule secretion, αIIbβ3 activation, Rap1 activation, and clot retraction. Treatment with DGLA similarly inhibited PAR1-mediated platelet activation as well as platelet clot retraction. These observations are in surprising contrast to our recent work showing 12(S)-HETE is a prothrombotic bioactive lipid and support our hypothesis that the overall effect of 12-LOX oxidation of fatty acids in the platelet is dependent on the fatty acid substrates available at the platelet membrane.

The Minimal Deneddylase Core of the COP9 Signalosome Excludes the Csn6 MPN− Domain

The COP9 signalosome (CSN) is a eukaryotic protein complex, which regulates a wide range of biological processes mainly through modulating the cullin ubiquitin E3 ligases in the ubiquitin-proteasome pathway. The CSN possesses a highly conserved deneddylase activity that centers at the JAMM motif of the Csn5 subunit but requires other subunits in a complex assembly. The classic CSN is composed of 8 subunits (Csn1–8), yet in several Ascomycota, the complex is smaller and lacks orthologs for a few CSN subunits, but nevertheless contains a conserved Csn5. This feature makes yeast a powerful model to determine the minimal assemblage required for deneddylation activity. Here we report, that Csi1, a diverged S. cerevisiae CSN subunit, displays significant homology with the carboxyl terminal domain of the canonical Csn6, but lacks the amino terminal MPN- domain. Through the comparative and experimental analyses of the budding yeast and the mammalian CSNs, we demonstrate that the MPN− domain of the canonical mouse Csn6 is not part of the CSN deneddylase core. We also show that the carboxyl domain of Csn6 has an indispensable role in maintaining the integrity of the CSN complex. The CSN complex assembled with the carboxyl fragment of Csn6, despite its lack of an MPN− domain, is fully active in deneddylation of cullins. We propose that the budding yeast Csi1 is a functional equivalent of the canonical Csn6, and thus the composition of the CSN across phyla is more conserved than hitherto appreciated.

Synthesis of a 3D photochromic coordination polymer with an interpenetrating arrangement: crystal engineering for electron transfer between donor and acceptor units

A new photochromic coordination network is constructed via the combination of viologen and carboxylate fragments. Close packing of the two-fold diamond-like interwoven mode creates electron transfer bridges for the acceptor and donor components. Radicals are generated upon photoirradiation and are accompanied by a color change from yellow to blue-green.

A short synthesis of nonracemic iodocyclohexene carboxylate fragment for kibdelone and congeners

A previously reported nonracemic iodocyclohexene carboxylate intermediate used in the asymmetric preparation of kibdelone C and its congeners was prepared in two synthetic steps from the product of microbial dihydroxylation of methyl 2-iodobenzoate.

Structural Controls on the Catalytic Polymerization of Hydroquinone by Birnessites

AbstractThe role of Mn oxide in the abiotic formation of humic substances has been well demonstrated. However, information on the effect of crystal structure and surface-chemical characteristics of Mn oxide on this process is limited. In the present study, hexagonal and triclinic birnessites, synthesized in acidic and alkali media, were used to study the influence of the crystal-structure properties of birnessites on the oxidative polymerization of hydroquinone and to elucidate the catalytic mechanism of birnessites in the abiotic formation of humic-like polymers in hydroquinone-birnessite systems. The intermediate and final products formed in solution and solid-residue phases were identified by UV/Visible spectroscopy, atomic absorption spectrometry, Fourier-transform infrared spectroscopy, X-ray diffraction, solid-phase microextraction-gaschromatography-mas ss pectrometry, ion chromatography, and ultrafiltration. The degree of oxidative polymerization of hydroquinone wasenhanced with increase in the interlayer hydrated H+, the average oxidation state (AOS), and the specific surface area of birnessites. The nature of the functional groups of the humic-like polymers formed was, however, almost identical when hydroquinone was catalyzed by hexagonal and triclinic birnessites with similar AOS of Mn. The results indicated that crystal structure and surface-chemistry characteristics have significant influence on the oxidative activity of birnessites and the degree of polymerization of hydroquinone, but have little effect on the abiotic formation mechanism of humic-like polymers. The proposed oxidative polymerization pathway for hydroquinone isthat, asit approachesthe birnessite, it formsp recursor surface complexes. Asa strong oxidant, birnessite accepts an electron from hydroquinone, which is oxidized to 1,4-benzoquinone. The coupling, cleavage, polymerization, and decarboxylation reactionsaccompany the generation of 1,4-benzoquinone, lead to the release of CO2 and carboxylic acid fragments, the generation of rhodochrosite, and the ultimate formation of humic-like polymers. These findings are of fundamental significance in understanding the catalytic role of birnessite and the mechanism for the abiotic formation of humic substances in nature.

4-Hydro-2-quinolones. 192.* relationship of xy structure and analgesic activity of 4-amino-2-oxo-1,2-dihydroquinoline-3-carboxylic acids and their derivatives

Some 4-N-R-2-Oxo-1,2-dihydroquinoline-3-carboxylic acids and their derivatives were synthesized as close structural analogs of the highly-active analgesic 4-benzylamino-2-oxo-1,2-dihydroquinoline-carboxylic acid. Pharmacological testing showed that manifestation of an analgesic effect depends on the presence of a carboxylic group and benzyl fragment in these molecules.

Signaling through LRP1: Protection from atherosclerosis and beyond

The low-density lipoprotein receptor-related protein (LRP1) is a multifunctional cell surface receptor that belongs to the LDL receptor (LDLR) gene family and that is widely expressed in several tissues. LRP1 consists of an 85-kDa membrane-bound carboxyl fragment (β chain) and a non-covalently attached 515-kDa (α chain) amino-terminal fragment. Through its extracellular domain, LRP1 binds at least 40 different ligands ranging from lipoprotein and protease inhibitor complex to growth factors and extracellular matrix proteins. LRP-1 has also been shown to interact with scaffolding and signaling proteins via its intracellular domain in a phosphorylation-dependent manner and to function as a co-receptor partnering with other cell surface or integral membrane proteins. LRP-1 is thus implicated in two major physiological processes: endocytosis and regulation of signaling pathways, which are both involved in diverse biological roles including lipid metabolism, cell growth/differentiation processes, degradation of proteases, and tissue invasion. The embryonic lethal phenotype obtained after target disruption of the LRP-1 gene in the mouse highlights the biological importance of this receptor and revealed a critical, but yet undefined role in development. Tissue-specific gene deletion studies also reveal an important contribution of LRP1 in vascular remodeling, foam cell biology, the central nervous system, and in the molecular mechanisms of atherosclerosis.

Neuropeptide F and the corn earworm, Helicoverpa zea: A midgut peptide revisited

The neuropeptide Y family of peptides is implicated in the regulation of feeding across a broad range of animals, including insects. Among vertebrates, neuropeptide Y exerts its actions mainly centrally, whereas peptide YY and pancreatic polypeptide arise from digestive tissues. Among invertebrates, neuropeptide F (NPF) is the sole counterpart of the NPY family. Shared features of NPF sequences derived for Lepidoptera indicate that the midgut peptide ( Hez-MP-I) of the corn earworm, Helicoverpa zea, characterized more than a decade ago, is a carboxyl fragment of a full-length NPF. An antibody to Hez-MP-I was used to characterize the peptide's distribution in tissues of larvae, pupae, and adults. Immunostaining demonstrated NPF-related material both in nervous tissues and in abundant endocrine cells of the midgut. Radioimmunoassay of Hez-MP-I in the head, midgut and hemolymph of fifth instar larvae revealed concentration changes corresponding to development and feeding state. As with the vertebrate homologs, NPF may arise both centrally and peripherally to modulate the physiology of feeding and digestion of Lepidoptera.

Enhanced expression of soluble recombinant tetanus neurotoxin Hc in Escherichia coli as a tetanus vaccine candidate

The expression of the carboxyl fragment of the heavy chain of tetanus neurotoxin (TeNT-Hc) in Escherichia coli has been hampered by the unusually high AT content and the presence of rarely used codons by Clostridium. The gene encoding TeNT-Hc was optimized for E. coli by replacing rare codons and decreasing the AT pairs from 72.57% to 52.47%. The reconstructed gene was expressed in E. coli BL21(DE3) and resulted in a soluble product which was about 46% of the total bacterial protein. TeNT-Hc produced in a 42 L fermentor was purified to >95% at 87 g/kg of cell paste (approximately 333 mg/L). BALB/c mice vaccinated with three bi-weekly doses of TeNT-Hc with Freund's adjuvant were fully protected against an intraperitoneally challenge of 2 × 10 3 50% lethal doses (LD 50s) of tetanus neurotoxin. NIH mice vaccinated with TeNT-Hc adsorbed to aluminum hydroxide gel adjuvant demonstrated a potency of 168 IU/mL, which was 2 times higher than the national standard for tetanus vaccines. These results suggest that TeNT-Hc may be a promising second-generation vaccine candidate for clinical use against tetanus neurotoxin.

ChemInform Abstract: A Tandem Aldol-Grob Reaction of Ketones with Aromatic Aldehydes.

Abstract Aromatic aldehydes react with ketones to produce(E)-1-aryl-1-alkenes via a tandem Aldol-Grob cleavage reaction sequence. The reaction, initiated by boron trifluoride, also produces a carboxylic acid fragment. Aromatic aldehydes react with ketones in the presence of boron trifluoride to produce(E)-1-aryl-1-alkenes via a tandem Aldol-Grob cleavage reaction sequence. Download : Download full-size image

The reactions of H3O+, NO+and O 2+ with several flavourant esters studied using selected ion flow tube mass spectrometry

The reactions of H(3)O(+), NO(+), and O(2) (+) with nineteen ester compounds occurring naturally in plants, and having important flavourant properties, were examined using selected ion flow tube mass spectrometry (SIFT-MS). The H(3)O(+) reactions primarily generate [R(1)COOR(2).H](+), and may also produce [R(2)](+) fragment ions and/or fragmentation within the ester linkage. Collisional association/adduct ions, [R(1)COOR(2).NO](+), are the main products formed in the NO(+) reactions, although the carboxyl fragment ion is also detected frequently. The identification of the parent compound may be made more easily in the H(3)O(+) and NO(+) reactions. The inclusion of O(2) (+) reactions in the analysis provides additional information, which may be applied when the identity of a parent compound cannot be determined solely from the H(3)O(+) and NO(+) analysis. Consideration of the product ions generated with the three precursors suggests that SIFT-MS can differentiate between many of the esters investigated, including isomers, although the product ions generated in the reactions with some esters are too similar to allow independent quantification. Our data therefore suggest that SIFT-MS may be a useful tool to rapidly analyse and quantify flavourant esters in complex gas mixtures.

Effect of the site of hydrogen-bonding on the liquid crystalline behaviour of supramolecular complexes

Two series of hydrogen-bonded side-chain liquid crystal polymers have been prepared by mixing components containing carboxyl acid and pyridyl-based fragments. We have focused our attention on the effect that the position of the hydrogen bond donor or acceptor site attached to the side-chain backbone has on the hydrogen-bonding interactions and liquid crystalline phase transitions of the system. The liquid crystalline behaviour of the complexes is studied using Fourier transform infrared spectroscopy, differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The results indicate that the phase transition temperatures of the complexes are influenced by the site of hydrogen-bonding.

Synthesis of (S)-Jamaicamide C Carboxylic Acid

The jamaicamides are natural product sodium channel blockers derived from the cyanobacterium Lyngbya majuscula. The carboxylic acid fragment of jamaicamide C contains a methyl stereocenter and a trisubstituted E chloroolefin. Herein, we present the nonracemic synthesis of the aliphatic chain of jamaicamide C. The methyl stereocenter was installed using Evans' oxazolidinone methodology, and the trisubstituted chloroolefin was set by silylstannylation of a triple bond.

Transgenic Expression of Insulin-Response Element Binding Protein-1 in β-Cells Reproduces Type 2 Diabetes

Recent evidence supports the idea that insulin signaling through the insulin receptor substrate/phosphatidyl-inositol 3-kinase/Akt pathway is involved in the maintenance of beta-cell mass and function. We previously identified the insulin-response element binding protein-1 (IRE-BP1) as an effector of insulin-induced Akt signaling in the liver, and showed that the 50-kDa carboxyl fragment confers the transcriptional activity of this factor. In this investigation we found that IRE-BP1 is expressed in the alpha, beta, and delta-cells of the islets of Langerhans, and is localized to the cytoplasm in beta-cells in normal rats, but is reduced and redistributed to the islet cell nuclei in obese Zucker rats. To test whether IRE-BP1 modulates beta-cell function and insulin secretion, we used the rat insulin II promoter to drive expression of the carboxyl fragment in beta-cells. Transgenic expression of IRE-BP1 in FVB mice increases nuclear IRE-BP1 expression, and produces a phenotype similar to that of type 2 diabetes, with hyperinsulinemia, hyperglycemia, and increased body weight. IRE-BP1 increased islet type I IGF receptor expression, potentially contributing to the development of islet hypertrophy. Our findings suggest that increased gene transcription mediated through IRE-BP1 may contribute to beta-cell dysfunction in insulin resistance, and allow for the hypothesis that IRE-BP1 plays a role in the pathophysiology of type 2 diabetes.

Analysis of the molecular mimicry between HLA-B27 and a bacterialOmpAprotein using synthetic peptides

In spite of a lack of sequence 'homology' between HLA-B27 and the bacterial OmpA outer membrane proteins, they both react with the Ye-2 monoclonal anti-HLA-B27 antibody. The Ye-2 antibody also reacted positively in ELISA with a synthetic peptide derived from the segment spanning residues 63-84 of B*2705. The critical peptide residues were determined by testing first with overlapping peptides, followed by a replacement set made according to the determined epitope. The results were compared with those with overlapping eight mers made to span a carboxyl fragment of the Escherichia coli OmpA protein. They indicate the reason why Ye-2 reacts with both sets of peptides is because it has a preference for polymers of arginine.

Effects of phthalate and sulphonic acid ester plasticisers on TiO2 catalysed photodegradation of PVC

The effects of two plasticisers, one phthalate and one sulphonic acid ester, on the photodegradation of TiO2 pigmented polyvinylchloride films are reported. The loading of each plasticiser was altered in the range 0–70% relative to the polyvinylchloride and the effects on the rates of photomineralisation were determined using a closed loop flow system to detect the carbon dioxide evolution. All plasticiser additions lead to an initial acceleration in CO2 evolution over the non-plasticised cases. Non-plasticised films show a marked acid catalysis due to HCl evolution which leads to an acceleration in the rate of oxidation with time. Following initial rapid oxidation of preadsorbed plasticiser, the phthalate systems demonstrated a reduced rate of CO2 production and no acid catalysis. The sulphonic acid ester plasticiser is broken down to produce sulphonic acid and sulphuric acid fragments which are sufficiently acidic to catalyse the TiO2 when plasticiser loadings are >50%. The carboxylic acid fragments from the phthalates seem incapable of catalysis even at the highest levels used in the present work.

Fragmentation pathways of acetic acid upon adsorption on Si(1 0 0)2 × 1

The reaction of acetic acid on the Si(1 0 0)2 × 1 surface has been investigated by density functional calculations on a two-dimers cluster model. We found that, once in the physisorbed state, acetic acid can proceed to react via two different pathways. In the first one, the cleavage of the hydroxylic bond is followed by a number of migrations of the dissociated hydrogen as well as structural rearrangements that eventually lead to the incorporation of an oxygen atom into the silicon surface, with a Si–O–Si structure. The second reaction pathway involves an initial C–H bond breakage, and evolves into a C–C bond cleavage and binding of the separate methyl and carboxylic fragments on top of a silicon dimer.

Bis(guanidinium) bis-(4-hydroxy-pyridine-2,6-dicarboxyl-ato-κO,N,O)nickel-ate(II) dihydrate.

The reaction of nickel(II) nitrate hexa­hydrate, guanidine (G) and 4-hydroxy­pyridine-2,6-dicarboxylic acid (hypydcH2) in a 1:2:2 molar ratio in aqueous solution resulted in the formation of the title compound, (CH6N3)2[Ni(C7H3NO5)2]·2H2O or (GH)2[Ni(hypydc)2]·2H2O. The six donor atoms of the two 4-hydroxy­pyridine-2,6-dicarboxyl­ate or (hypydc)2− ligands form a distorted octa­hedral arrangement around the NiII centre. Considerable C—O⋯π stacking inter­actions between the CO groups of carboxyl­ate fragments and the pyridine rings of (hypydc)2− with a distance of 3.3212 (8) Å are observed. In the crystal structure, a wide range of noncovalent inter­actions consisting of hydrogen bonding (of the types O—H⋯O and N—H⋯O), ion pairing, and π–π [centroid–centroid distance 3.8037 (5) Å], N—H⋯π and C—O⋯π stacking inter­actions connect the various components into a supra­molecular structure.

Establishment and Characterization of Monoclonal and Polyclonal Antibodies Against Human Intestinal Fatty Acid‐Binding Protein (I‐FABP) using Synthetic Regional Peptides and Recombinant I‐FABP

We have succeeded in raising highly specific anti‐human intestinal fatty acid‐binding protein (I‐FABP) monoclonal antibodies by immunizing animals with three synthetic regional peptides, i.e., the amino terminal (RP‐1: N‐acetylated 1‐19‐cysteine), middle portion (RP‐2: cysteinyl‐91‐107) and carboxylic terminal (RP‐3: cysteinyl‐121‐131) regions of human I‐FABP, and the whole I‐FABP molecule as antigens. We also raised a polyclonal antibody by immunizing with a recombinant (r) I‐FABP. To ascertain the specificity of these antibodies for human I‐FABP, the immunological reactivity of each was examined by a binding assay using rI‐FABP, partially purified native I‐FABP and related proteins such as liver‐type (L)‐FABP, heart‐type (H)‐FABP, as well as the regional peptides as reactants, and by Western blot analysis. In addition, the expression and distribution of I‐FABP in the human gastrointestinal tract were investigated by an immunohistochemical technique using a carboxylic terminal region‐specific monoclonal antibody, 8F9, and a polyclonal antibody, DN‐R2. Our results indicated that both the monoclonal and polyclonal antibodies established in this study were highly specific for I‐FABP, but not for L‐FABP and H‐FABP. Especially, the monoclonal antibodies raised against the regional peptides, showed regional specificity for the I‐FABP molecule. Immunoreactivity of I‐FABP was demonstrated in the mucosal epithelium of the jejunum and ileum by immunohistochemical staining, and the immunoreactivity was based on the presence of the whole I‐FABP molecule but not the presence of any precursors or degradation products containing a carboxylic terminal fragment. It is concluded that some of these monoclonal and polyclonal antibodies, such as 8F9, 4205, and DN‐R2, will be suitable for use in research on the immunochemistry and clinical chemistry of I‐FABP because those antibodies can recognize both types of native and denatured I‐FABP. In order to detect I‐FABP in blood samples, it is essential to use this type of antibody, reactive to native type of I‐FABP. It is anticipated that, in the near future, such a method for measuring I‐FABP will be developed as a useful tool for diagnosing intestinal ischemia by using some of these antibodies.