Hydroxynaphthaldehyde phosphate derivatives as potent covalent Schiff base inhibitors of fructose-1,6-bisphosphate aldolase

Interactions of phosphate derivatives of 2,6-dihydroxynaphthalene (NA-P(2)) and 1,6-dihydroxy-2-naphthaldehyde (HNA-P, phosphate at position 6) with fructose-1,6-bisphosphate aldolase from rabbit muscle were analyzed by enzyme kinetics, difference spectroscopy, site-directed mutagenesis, mass spectrometry, and molecular dynamics. Enzyme activity was competitively inhibited by NA-P(2), whereas HNA-P exhibited slow-binding inhibition with an overall inhibition constant of approximately 24 nM. HNA-P inactivation was very slowly reversed with t(1/2) approximately 10 days. Mass spectrometry and spectrophotometric absorption indicated that HNA-P inactivation occurs by Schiff base formation. Rates of enzyme inactivation and Schiff base formation by HNA-P were identical and corresponded to approximately 4 HNA-P molecules bound par aldolase tetramer at maximal inhibition. Site-directed mutagenesis of conserved active site lysine residues 107, 146, and 229 and Asp-33 indicated that Schiff base formation by HNA-P involved Lys-107 and was promoted by Lys-146. Titration of Lys-107 by pyridoxal 5-phosphate yielded a microscopic pK(a) approximately 8 for Lys-107, corroborating a role as nucleophile at pH 7.6. Site-directed mutagenesis of Ser-271, an active site residue that binds the C(1)-phosphate of dihydroxyacetone phosphate, diminished HNA-P binding and enabled modeling of HNA-P in the active site. Molecular dynamics showed persistent HNA-P phosphate interactions with the C(1)-phosphate binding site in the noncovalent adduct. The naphthaldehyde hydroxyl, ortho to the HNA-P aldehyde, was essential for promoting carbinolamine precursor formation by intramolecular catalysis. The simulations indicate a slow rate of enzyme inactivation due to competitive inhibition by the phenate form of HNA-P, infrequent nucleophilic attack in the phenol form, and significant conformational barrier to bond formation as well as electrostatic destabilization of protonated ketimine intermediates. Solvent accessibility by Lys-107 Nz was reduced in the covalent Schiff base complex, and in those instances where water molecules interacted with Lys-107 in the simulations, Schiff base hydrolysis was not mechanistically favorable. The findings at the molecular level corroborate the observed mechanism of slow-binding tight inhibition by HNA-P of muscle aldolase and should serve as a blueprint for future aldolase inhibitor design.     

Thermodynamic studies of the mechanism of metal binding to the Escherichia coli zinc transporter YiiP

Sequence homology of the Escherichia coli YiiP places it within the family of cation diffusion facilitators, a family of membrane transporters that play a central role in regulating cellular zinc homeostasis. Here we describe the first thermodynamic and mechanistic studies of metal binding to a cation diffusion facilitator. Isothermal titration calorimetric analyses of the purified YiiP and binding competitions among Zn(2+), Cd(2+), and Hg(2+) revealed a mutually competitive binding site common to three metal ions and a set of noncompetitive binding sites, including one Cd(2+) site, one Hg(2+) site, and at least one Zn(2+) site, to which the binding of Zn(2+) exhibited partial inhibitions of both Cd(2+) and Hg(2+) bindings. Lowering the pH from 7.0 to 5.5 inhibited binding of Zn(2+) and Cd(2+) to the common site. Further, the enthalpy change of the Cd(2+) binding to the common site was found to be related linearly to the ionization enthalpy of the pH buffer with a slope corresponding to the release of 1.23 H(+) for each Cd(2+) binding. These H(+) effects are consistent with a coupled deprotonation process upon binding of Zn(2+) and Cd(2+). Modification of histidine residues by diethyl pyrocarbonate specifically inhibited Zn(2+) binding to the common binding site, indicating that the mechanism of binding-deprotonation coupling involves a histidine residue(s).     

N,N-dialkyl-4-[(8-azabicyclo[3.2.1]-oct-3-ylidene)phenylmethyl]benzamides, potent, selective delta opioid agonists

A series of N,N-dialkyl-4-(9-aryltropanylidenemethyl)benzamides was prepared. The lead compounds, 15a and 15c, exhibited extremely high affinity for the delta opioid receptor with excellent selectivity versus the micro opioid receptor. They were full agonists at the delta opioid receptor, as assessed by stimulation of GTPgammaS binding, and displayed antinociceptive activity.     

Transglycosylation reactions with a crude culture filtrate from Thermoascus aurantiacus

Some characteristics of regioselectivity and acceptor tolerance in transglycosylation reactions, catalysed by a crude culture filtrate from Thermoascus aurantiacus, were examined by employing methanol and monosaccharides as acceptors. When beta-D-mannopyranosyl fluoride was employed as the donor, the anomeric configuration of the newly formed bond was found to depend on the structure of the acceptor used.     

Synthesis of deoxyfluoro sugars from carbohydrate precursors

Results obtained over the past decade concerning the introduction of the fluorine atom into carbohydrate molecules, either by nucleophilic substitution or electrophilic addition reactions, are summarised. The first section mainly deals with the triflate/fluoride tandem sequence and the DAST-reaction. In the discussion, emphasis is given to the dependency of the reaction course on the stereochemical and protecting group features. Possible reaction pathways are direct substitution (with inversion or retention of configuration), rearrangement (combined with substitution and inversion of configuration at both of the centres involved) and elimination. Based on the assumption of cyclic transition states or transient intermediates (formed through participation of neighbouring groups), far-reaching mechanistic generalisations were made. On this basis, isolated examples from the literature, which are not in accordance with these generalisations, are specifically brought to attention. Results from the recently introduced reaction of safe and easy to handle N-F fluorinating agents with glycals are also reported. This approach allows the simple and stereoselective access to a series of 2-deoxy-2-fluoro aldopyranoses, as well as the synthesis of various C-1-substituted derivatives by an easy one-pot reaction. However, the same method applied to furanoid glycals is rather poor with respect to stereoselectivity. Finally, considerations on the importance of fluorine-specific reactions of the S(N)-type in related fields of organic synthesis are made.     

Evolution of different subfamilies of mariner elements within the medfly genome inferred from abundance and chromosomal distribution

The abundance and distribution pattern of eight mariner elements from three different subfamilies in the genome of the medfly Ceratitis capitata were determined. The copy numbers, as determined by slot-blot analysis, were very different for these elements. Their abundance did not change significantly within the native, the ancient or the newly derived populations, indicating that the rapid colonization process of the medfly had not affected the copy number of mariner elements. The distribution of the mariner elements was analyzed using fluorescent in situ hybridization (FISH) with charge-coupled device (CCD) camera analysis. The pattern of distribution in euchromatin and heterochromatin varied greatly and was distinctive and specific for each element. The implications of these findings are discussed and it is concluded that they generally support the hypothesis of a transposition/selection model in which the abundance and distribution patterns of these elements are regulated primarily by selection against deleterious effects due to meiotic ectopic recombination, while genetic drift would have played a minor role. Received: 2 July 1999; in revised form: 15 November 1999 / Accepted: 16 November 1999     

Derivation of Neural Stem Cells from Human Adult Peripheral CD34+ Cells for an Autologous Model of Neuroinflammation

Proinflammatory factors from activated T cells inhibit neurogenesis in adult animal brain and cultured human fetal neural stem cells (NSC). However, the role of inhibition of neurogenesis in human neuroinflammatory diseases is still uncertain because of the difficulty in obtaining adult NSC from patients. Recent developments in cell reprogramming suggest that NSC may be derived directly from adult fibroblasts. We generated NSC from adult human peripheral CD34+ cells by transfecting the cells with Sendai virus constructs containing Sox2, Oct3/4, c-Myc and Klf4. The derived NSC could be differentiated to glial cells and action potential firing neurons. Co-culturing NSC with activated autologous T cells or treatment with recombinant granzyme B caused inhibition of neurogenesis as indicated by decreased NSC proliferation and neuronal differentiation. Thus, we have established a unique autologous in vitro model to study the pathophysiology of neuroinflammatory diseases that has potential for usage in personalized medicine.     

Bioavailability Studies of Stabilized Iron (II) Sulfate by Means of the Prophylactic-preventive Method

The bioavailability of stabilized ferrous sulfate was studied by means of the prophylactic-preventive test in rats. For comparative purposes, ferrous sulfate was used as reference standard. The test was performed in male weaned rats during 3 weeks, which were randomized into three groups of ten animals each. A control group received a basal diet of low iron content while the other groups received the same diet added with iron at a dose of 15 mg/kg as FeSO₄ 7H₂O and stabilized ferrous sulfate, respectively. Individual hemoglobin concentrations and weights were determined at the beginning and at the end of the study, and food intake was daily registered. Iron bioavailability (BioFe) of each source was calculated as the ratio between the amount of iron incorporated into hemoglobin during the treatment and the total iron intake per animal. A relative biological value was obtained as the ratio between the BioFe of stabilized ferrous sulfate and the reference standard given a value of 96%. Stabilized ferrous sulfate showed a high bioavailability, and when it is used to fortify dairy products as cheese and fluid milk in a dose of 15–20 mg of iron per kilogram, it behaved inertly in relation to the sensorial properties of the fortified food. These results suggest that this iron compound is a promising source to be use in food fortification.