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PubMed2002

A preliminary approach to nonenolizable beta,beta-tricarbonyls: assembly of a hyperevolutin prototype.

A synthetic approach to the hyperevolutin A acylated phloroglucinol ring system is described. Thus, intramolecular allene-nitrile oxide cycloaddition of 10 was used to construct the bicyclic framework and vicinal quaternary centers in cycloadduct 20 in the key bond-forming step. Treatment of 20 with Raney nickel and hydrogen gas produced primary enamine 21 which contains a nonenolizable beta,beta-tricarbonyl group in latent form.

Adamantane↗
PubMed2003

N-methylformamide-benzene complex as a prototypical peptide N-H...pi hydrogen-bonded system: density functional theory and MP2 studies.

Although the existence of peptide N-H...pi hydrogen bonds recently has been reported in protein structures, little is known about their strength and binding nature and, therefore, the relative importance of the interaction. To shed light on this binding, the N-methylformamide-benzene complex, as a model of the peptide N-H...pi hydrogen bonding, was studied by using density functional theory and Møller-Plesset second-order perturbation (MP2) methods. The geometry of the complex was fully optimized at the B3LYP/6-31G(d,p) and MP2/6-31G(d,p) levels. The optimized interaction distances are about 3.6 and 3.2 A, respectively, at the two levels. The binding energy corrected by basis set superposition error with the MP2/cc-pVTZ method based on the MP2/6-31G geometry is -4.37 kcal/mol, which is as strong as the conventional hydrogen bonding. The calculated results suggest that the peptide N-H...pi hydrogen bonding is of sufficient strength to play an important role in the stabilization of protein structures. These results are helpful to better understand the characteristics and nature of the peptide N-H...pi interaction as well as to modify current force fields to better represent this special interaction.

Benzene↗
PubMed2003

A prototype calix[4]arene-based receptor for carbohydrate recognition containing peptide and phosphate binding groups.

A novel class of macrobicyclic receptors for carbohydrate recognition based on upper rim, peptide-bridged calix[4]arenes has been designed and synthesized. Receptor 12, in which a charged phosphate group cooperates with peptide hydrogen-bonding donor and acceptor groups in the binding process, is the most efficient and selective in the complexation of simple carbohydrate derivatives. The selectivity observed is toward beta-glucoside 13a, which is better bound (DeltaG degrees = 19.6 kJ mol(-)(1)) compared to the corresponding alpha anomer 13b (DeltaG degrees = 17.0 kJ mol(-)(1)) and to the beta-galactoside 13c (DeltaG degrees = 17.7 kJ mol(-)(1)) in CDCl(3). A substantial drop in the stability constant is observed by esterification of the phosphate group in the host 12 or by alkylation of the OH groups in the 2 and 3 positions in the beta-glucoside and beta-galactoside derivatives. On the basis of a careful analysis of the (1)H NMR data available, a binding mode of the beta-octylglucoside 13a to receptor 12 is proposed.

Calixarenes↗
PubMed2005

Dispiro-1,2,4-trioxane analogues of a prototype dispiro-1,2,4-trioxolane: mechanistic comparators for artemisinin in the context of reaction pathways with iron(II).

Single electron reduction of the 1,2,4-trioxane heterocycle of artemisinin (1) forms primary and secondary carbon-centered radicals. The complex structure of 1 does not lend itself to a satisfactory dissection of the electronic and steric effects that influence the formation and subsequent reaction of these carbon-centered free radicals. To help demarcate these effects, we characterized the reactions of achiral dispiro-1,2,4-trioxolane 4 and dispiro-1,2,4-trioxanes 5-7 with ferrous bromide and 4-oxo-TEMPO. Our results suggest a small preference for attack of Fe(II) on the nonketal peroxide oxygen atom of 1. For 4, but not for 5 and 6, there was a strong preference for attack of Fe(II) on the less hindered peroxide bond oxygen atom. The steric hindrance afforded by a spiroadamantane in a five-membered trioxolane is evidently much greater than that for a corresponding six-membered trioxane. Unlike 1, 5-7 fragment by entropically favored beta-scission pathways forming relatively stable alpha-oxa carbon-centered radicals. These data suggest that formation of either primary or secondary carbon-centered radicals is a necessary but insufficient criterion for antimalarial activity of 1 and synthetic peroxides.

Adamantane↗
PubMed2006

Energetics of oxaspirocycle prototypes: 1,7-dioxaspiro[5.5]undecane and 1,7,9-trioxadispiro[5.1.5.3]hexadecane.

The relative gas-phase energetics of several low-lying isomers of 1,7-dioxaspiro[5.5]undecane and 1,7,9-trioxadispiro[5.1.5.3]hexadecane have been calculated with second-order Mller-Plesset perturbation theory and basis sets as large as aug-cc-pVQZ. Relative energies in THF, dichloromethane, acetone, and DMSO have been estimated with corrections from polarized continuum model calculations at the B3LYP/6-311+G(d) level. In the most stable conformation of 1,7-dioxaspiro[5.5]undecane, both rings adopt chair conformations, and both oxygens are axially disposed (2A). It is more than 2 kcal mol(-1) more stable than all the other conformers. In agreement with previous work, the "twist-boat" trans isomer (3A) is the most stable isomer of 1,7,9-trioxadispiro[5.1.5.3]hexadecane. However, in contrast to this earlier study, an "all-chair" conformation (3B) is found to be the most stable cis isomer of 1,7,9-trioxadispiro[5.1.5.3]hexadecane (E approximately 0.5 kcal mol(-1) in acetone and DMSO). Gauge-independent atomic orbital computations at the B3LYP/6-311+G(d) level indicate that this is the only cis isomer with (13)C NMR chemical shifts that are qualitatively consistent with the experimental spectra.

Cycloparaffins↗
PubMed2006

Theoretical determination of multiple exchange couplings and magnetic susceptibility data in inorganic solids: the prototypical case of Cu2(OH)3NO3.

Density functional theory based on hybrid functionals and localized atomic type basis sets is employed to calculate the exchange couplings in the layered three-dimensional compound Cu2(OH)3NO3. We assign accurate values to the six different in-plane exchange couplings. Interlayer exchange interactions through hydrogen bonds are also quantified. The calculated exchange coupling constants are then employed to perform quantum Monte Carlo simulations to yield magnetic susceptibility data, which compare successfully with experiments. Our approach sets the foundations of a viable methodology to extract reliable magnetic susceptibilities from density functional data.

Journal Article↗
PubMed2003

Marine natural products as novel antioxidant prototypes.

Pure natural products isolated from marine sponges, algae, and cyanobacteria were examined for antioxidant activity using a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) solution-based chemical assay and a 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) cellular-based assay. The DCFH system detects only antioxidants that penetrate cellular membranes. Potent antioxidants were identified and the results from each system compared. The algal metabolites cymopol (1), avrainvilleol (3), and fragilamide (4), and the invertebrate constituent puupehenone (5) showed strong antioxidant activity in both systems. Several compounds were active in the DPPH assay but significantly less active in the DCFH system. The green algal metabolite 7-hydroxycymopol (2) was isolated from Cymopolia barbataand its structure determined. Compound 2 was significantly less active in the DCFH system than cymopol (1). The sponge metabolites (1S)-(+)-curcuphenol (6), aaptamine (7), isoaaptamine (8), and curcudiol (9) and the cyanobacterial pigment scytonemin (10) showed strong antioxidant activity in the DPPH assay, but were relatively inactive in the DCFH system. Thus, cellular uptake dramatically affects the potential significance of antioxidants discovered using only the DPPH assay. The apparent "proantioxidants" hormothamnione A diacetate (11) and Laurencia monomer diacetate (12) require metabolic activation for antioxidant activity. Significant advantages are achieved using both a solution- and cellular-based assay to discover new antioxidants.

Animals↗
PubMed2001

Spirocyclic restriction of nucleosides. An analysis of protecting group feasibility while accessing prototype anti-1-oxaspiro[4.4]nonanyl mimics.

[reaction: see text] The first spirocyclic nucleoside featuring a beta-hydroxyl (anti) at C5' has yielded to synthesis. While the OMOM functionality proved to be sensitive to the conditions necessary to incorporate heterocyclic bases, PMB protection of the carbinol was readily accommodated. The remarkably similar minimum-energy conformations of the title compounds relative to natural thymidine as deduced by Amber calculations in the gas phase are noted.

DNA↗
PubMed2005

Efficient immobilization of a cadmium chemosensor in a thin film: generation of a cadmium sensor prototype.

[reaction: see text] The development of an ion-selective chemosensor for Cd(2+) allows generation of a "real-time" sensor. Immobilization of the chemosensor on quartz was achieved in a simple monolayer and in a thin film using a polymer intermediary. As intended, the thin film contains much more chemosensor than the monolayer and provides measurable responses to aqueous Cd(2+) concentrations below 1 microM. Alkali and alkaline earth ions do not interfere with Cd(2+) sensing; Zn(2+) and Cu(2+) are potential interferents.

Journal Article↗
PubMed2006

180 degree unidirectional bond rotation in a biaryl lactone artificial molecular motor prototype.

A bifunctional biaryl lactone has been synthesized that should be capable of iterative unidirectional aryl-aryl bond rotation via: (1) a diastereoselective lactone ring opening, (S)-1 to (P,S)-2 or (M,S)-2; (2) a chemoselective lactonization, (P,S)-2 or (M,S)-2 to (S)-3; and (3) a chemoselective hydrolysis, (S)-3 to (S)-1. Preliminary results of a racemic sample have indicated unidirectional 180 degrees rotation with very high directional selectivity per individual artificial molecular motor molecule through the first two steps of this sequence. [reaction: see text]

Borohydrides↗
PubMed2000

Ligand tuning in asymmetric catalysis: mono- and bis-phospholanes for a prototypical Pd-catalyzed asymmetric allylation reaction

[structures: see text] Enantioselectivities and yields comparable to the best catalysts reported previously can be achieved in the addition of potassium dimethyl malonate to diphenylallyl acetate by the use of Pd(0) complexes of bis-phospholanes prepared from D-mannitol. By appropriate changes in the C2-C5 substituents, rare example of a useful monophosphine can also be prepared by a similar route. In both instances chirality of C3 and C5 oxygen seems to play a crucial role in the asymmetric induction.

Journal Article↗
PubMed1997

Binding and distribution of three prototype calcium channel blockers in perfused rat liver.

This work represents a study of the binding and distribution of three different calcium channel blockers in the Sprague-Dawley rat liver, using an in situ perfusion technique. For this purpose, [3H] desmethoxyverapamil, [3H] PN200-110 (isradipine) and [3H] azidopine were used as binding probes interacting with calcium channels. The perfusion steps of the liver involved both portal vein and thoracic inferior vena cava cannulations as inlet and outlet respectively. The subhepatic inferior vena cava was ligated to prevent leakage of the perfusate. Buffer, containing the tracer drug, was administered via the portal vein at a rate of 1 mL/min and perfusate collected at the same rate within specified time intervals during 50 min. The concentration of the tracer solutes in the perfusate's outlet increased with time, and steady state was observed for all tracers at > or = 40 min. The effect of adding cold isradipine to tracer desmethoxyverapamil, or cold verapamil to tracer PN200-110 were also assessed. First order rate constants for hepatocellular influx, efflux and calcium channel binding of the tracer substances were obtained using a simplified model from Goresky et al. These constants were mathematically manipulated and changed into permeability constants, second order binding constants, and residency times. Tracer solute influx across hepatocellular membranes is solubility-diffusion controlled, is inversely related to the molecular weights and is different in value from the efflux constants. Cold isradipine reduced the binding constant of desmethoxyverapamil by 36%, while cold verapamil reduced the binding constant of PN200-110 by 23%. Azidopine cellular distribution was low, however, binding to its receptor was analogous to desmethoxyverapamil and PN200-110. Moreover, PN200-110 had the highest residency time with no effect of cold verapamil on its receptor binding, while desmethoxyverapamil had the lowest residency time which significantly increased in the presence of cold isradipine.

Animals↗
PubMed2001

Receptor-mediated targeting of spray-dried lipid particles coformulated with immunoglobulin and loaded with a prototype vaccine.

PURPOSE: Spray-dried lipid-based microparticles (SDLM) serve as a platform for delivery of a wide variety of compounds including peptides, proteins, and vaccines to the respiratory mucosa. In the present study, we assessed the impact of IgG-mediated targeting to phagocytic cells of inactivated influenza virus formulated in SDLM, on subsequent immune responses. METHODS: SDLM were produced containing inactivated influenza virus strain A/WSN/32/H1N1 (WSN), with or without IgG. Using phagocytic antigen presenting cells (APC) and a T cell hybridoma (TcH) line specific for a dominant influenza virus epitope, we compared the in vitro responses elicited by ligand-formulated (SDLM-IgG-WSN) and non-ligand particles (SDLM-WSN). The effect of including the IgG ligand in the formulation was further characterized by measuring the immune responses of rodents vaccinated with SDLM. RESULTS: SDLM-IgG-WSN were internalized in an Fc receptor (FcR)-dependent manner by phagocytic APC that were then able to effectively present a dominant, class II-restricted epitope to specific T cells. While SDLM-WSN elicited a lower response than administration of plain inactivated virus in saline, the level of the T cell response was restored both in vitro and in vivo by incorporating the APC FcR ligand, IgG, in the SDLM. CONCLUSIONS: Incorporation of FcR ligand (IgG) in SDLM restored the limited ability of formulated virus to elicit T-cell immunity, by receptor-mediated targeting to phagocytes.

Administration, Inhalation↗
PubMed1992

The development of a microwave fluid-bed processor. I. Construction and qualification of a prototype laboratory unit.

The static bed- and planetary-type microwave dryers currently available to process pharmaceutical materials are not designed to use hot-air fluidization for the purpose of maximizing microwave energy inputs and particle drying. To take advantage of the benefits offered by fluidization, a 1-kg Uni-Gatt laboratory fluid bed processor was modified to support microwave-assisted fluid bed drying of several representative pharmaceutical granulations. The construction, design features, and validation of this new microwave fluid bed processor are presented.

Calibration↗
PubMed2003

Prototype symbolization in hooded crows.

Studies were undertaken to determine whether four crows previously trained to an image-based abstract selection rule could establish a relationship between the number of elements in a group and initially indifferent symbols (arabic numerals) and operate with these symbols, i.e., studies addressed the ability of these birds to symbolize. Unlike other similar studies, there was no use of special development of associative connections between the symbols and the corresponding arrays of elements, but conditions were created in which birds could observe these relationships on the basis of comparison with previously obtained information. Demonstration series were performed for this purpose, in which correct solutions by the crow resulted in receipt of a number of larvae corresponding to the number of elements in the array pictured or numeral imaged on the stimulus selected by the crow. Images belonged to the same category as the corresponding stimulus for selection (the second stimulus was another category): if the image was an array, then the corresponding picture for selection also bore an array, and vice versa. Crows could solve the task successfully by using an image-based selection rule. In test series, the image and both selection stimuli were initially from different categories: if the image was a numeral, then both selection stimuli were arrays, and vice versa. All four crows successfully coped with this task. Despite the absence of any similarity between the image and "correct" stimulus, they selected the array corresponding to the numeral and vice versa. It is suggested that the birds could achieve this result by comparing the information obtained during the presentation series--about the number of reinforcement units corresponding to each stimulus. Similar experiments showed that crows could use numbers to perform operations analogous to arithmetic addition.

Animals↗
PubMed2004

The potential of photochemical transition metal reactions in prebiotic organic synthesis. I. Observed conversion of methanol into ethylene glycol as possible prototype for sugar alcohol formation.

Photochemical processes involving redox reactions between metal ions and organic substrates possess the versatile potential for having harnessed solar energy for prebiotic organic synthesis. The present study in our Laboratory has shown that ultraviolet irradiation of transition metal ions such as of Ni, Co, Fe, Cu and Ti dissolved in primary or secondary alcohols causes photoreduction of the metal ions with the concomitant oxidation of the alcohol to aldehyde or ketone. An observed accompaniment of this novel 'light' reaction has been the known 'dark' pinacol reaction, whereby the carbonyl derivative underwent bimolecular coupling to the diol by the photogenerated reduced transition metal reagent. These tandem 'light-dark' processes possess the potential for the stepwise synthesis of dimeric 1,2-diols from simpler alcohols under conditions that might have prevailed on the prebiotic earth. Experiments reported here have demonstrated that such a tandem 'light-dark' conversion of methanol into ethylene glycol, via formaldehyde, does in fact occur, when nickel(II) acetylacetonate solutions in methanol undergo prolonged irradiation at 185-254 nm. Since ethylene glycol can be considered as the simplest sugar alcohol, these findings may provide novel insight into the prebiotic oligomerization of formaldehyde into higher sugar alcohols or even sugars.

Ethylene Glycol↗