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At least 379 records · Page 21Linked to original sources
PubMed2006

Liphagal, a Selective inhibitor of PI3 kinase alpha isolated from the sponge akacoralliphaga: structure elucidation and biomimetic synthesis.

[structure: see text] Liphagal (1), a selective inhibitor of PI3K alpha, has been isolated from the marine sponge Aka coralliphaga collected in Dominica. The "liphagane" meroterpenoid carbon skeleton of liphagal (1) is new. A biomimetic total synthesis has been used to confirm the constitution of liphagal (1) and support a proposed biogenesis.

Androstadienes↗
PubMed2006

Biomimetic approach to perophoramidine and communesin via an intramolecular cyclopropanation reaction.

[reaction: see text] Starting from tryptamine 4 and isatin 5, a biomimetic approach to the pentacyclic substructure 1 of perophoramidine and communesin was developed. The key steps were to create a stable three/six bicyclic system 2 on the 2,3-double bond of an indole derivative 3 by an intramolecular cyclopropanation, followed by ring opening of the resulting cyclopropane ring with the in situ generated amine group of an aniline.

Cyclopropanes↗
PubMed2006

A magnetic biomimetic nanocatalyst for cleaving phosphoester and carboxylic ester bonds under mild conditions.

[Structure: see text] As a result of the unique surface structure of nanospheres, Asp and His residues supported on a 12 nm maghemite nanoparticle worked collaboratively as a biomimetic nanocatalyst for hydrolyzing paraoxon (phosphoester) and 4-nitrophenyl acetate (carboxylic ester) in Milli-Q water (pH 7.0) at 37 degrees C, without employing extremes of pH or heavy metals. Our nanocatalyst could be facilely recovered via magnetic concentration. The isolated catalyst exhibited long-term stability, showing no significant loss of its catalytic activity for repeated uses after 3 months.

Amino Acid Sequence↗
PubMed2000

Biomimetic total syntheses of (-)-TAN1251A, (+)-TAN1251B, (+)-TAN1251C, and (+)-TAN1251D.

[reaction: see text] The muscarinic antagonists (-)-TAN1251A (1), (+)-TAN1251B (2), (+)-TAN1251C (3), and (+)-TAN1251D (4) have been synthesized biomimetically by enamine formation from an amino aldehyde to give TAN1251C ketal 18. Oxidation and reduction lead to TAN1251A (1), which has been hydroxylated to give TAN1251B (2). Stereospecific reduction of TAN1251C ketal 18 leads to TAN1251D (4).

Molecular Mimicry↗
PubMed2002

In situ polymerization into porous ceramics: a novel route to tough biomimetic materials.

A hydroxyapatite-based biomimetic composite, which is henceforth referred to as a synthetic bony material with high toughness characteristics, was prepared. It was obtained from a hydroxyapatite (HAp) skeleton with a relative porosity fraction of approximately 32 vol %, prepared by cold-isostatic-press compaction, followed by a sintering process, leading to a hydroxyapatite structure containing percolated submicrometer porosity channels. The percolated pores were infiltrated with a liquid mixture of epsilon-caprolactam monomer and an initiator, before homogeneous in situ polymerization to 6-nylon within the fully percolated pore structure was induced thermally. The final composite consisted of a dense interpenetrated hydroxyapatite/6-nylon network in a fraction approximately 68/30 vol %. The work of fracture value of the hybrid composite was found to be comparable with those found in two natural materials (bovine femur and nacre), which were also investigated under the same testing conditions.

Journal Article↗
PubMed2002

Trabecular bone scaffolding using a biomimetic approach.

The current treatment of large bone defects has several disadvantages. An alternative for using grafts or bone cement for the filling of bone cavities is the use of a bone scaffold that provides a temporary load-bearing function. This paper describes a biomechanical design procedure for a personalized implant with a geometry that has a good fit inside the defect and an internal architecture that provides a scaffold with optimized mechanical properties. These properties are optimized for a load-bearing application, for avoiding stress shielding in the bone surrounding the implant and for activation of osteoblasts seeded inside the scaffold. The design is based on medical images both of the defect and of healthy bone tissue that is representative for the tissue being replaced by the scaffold. Evaluation of the scaffold's mechanical properties is done with high-resolution finite element analyzes of the scaffold and healthy bone. This allows matching of the scaffold and bone mechanical properties, thus giving the scaffold its biomimetic properties.

Journal Article↗
PubMed2000

Biomimetic synthesis of ordered silica structures mediated by block copolypeptides.

In biological systems such as diatoms and sponges, the formation of solid silica structures with precisely controlled morphologies is directed by proteins and polysaccharides and occurs in water at neutral pH and ambient temperature. Laboratory methods, in contrast, have to rely on extreme pH conditions and/or surfactants to induce the condensation of silica precursors into specific morphologies or patterned structures. This contrast in processing conditions and the growing demand for benign synthesis methods that minimize adverse environmental effects have spurred much interest in biomimetic approaches in materials science. The recent demonstration that silicatein-a protein found in the silica spicules of the sponge Tethya aurantia--can hydrolyse and condense the precursor molecule tetraethoxysilane to form silica structures with controlled shapes at ambient conditions seems particularly promising in this context. Here we describe synthetic cysteine-lysine block copolypeptides that mimic the properties of silicatein: the copolypeptides self-assemble into structured aggregates that hydrolyse tetraethoxysilane while simultaneously directing the formation of ordered silica morphologies. We find that oxidation of the cysteine sulphydryl groups, which is known to affect the assembly of the block copolypeptide, allows us to produce different structures: hard silica spheres and well-defined columns of amorphous silica are produced using the fully reduced and the oxidized forms of the copolymer, respectively.

Cysteine↗
PubMed2002

Biomimetic synthesis and optimization of cyclic peptide antibiotics.

Molecules in nature are often brought to a bioactive conformation by ring formation (macrocyclization). A recurrent theme in the enzymatic synthesis of macrocyclic compounds by non-ribosomal and polyketide synthetases is the tethering of activated linear intermediates through thioester linkages to carrier proteins, in a natural analogy to solid-phase synthesis. A terminal thioesterase domain of the synthetase catalyses release from the tether and cyclization. Here we show that an isolated thioesterase can catalyse the cyclization of linear peptides immobilized on a solid-phase support modified with a biomimetic linker, offering the possibility of merging natural-product biosynthesis with combinatorial solid-phase chemistry. Starting from the cyclic decapeptide antibiotic tyrocidine A, this chemoenzymatic approach allows us to diversify the linear peptide both to probe the enzymology of the macrocyclizing enzyme, TycC thioesterase, and to create a library of cyclic peptide antibiotic products. We have used this method to reveal natural-product analogues of potential therapeutic utility; these compounds have an increased preference for bacterial over eukaryotic membranes and an improved spectrum of activity against some common bacterial pathogens.

Amino Acid Sequence↗
PubMed2001

A piezoelectric biomimetic sensor for aminopyrine with a molecularly imprinted polymer coating.

A molecularly imprinted polymer for aminopyrine was synthesized using methacrylic acid as functional monomer. The polymer was employed as the recognition element of a piezoelectric bulk acoustic wave biomimetic sensor for aminopyrine. Influencing factors were investigated in detail and optimized. This sensor exhibited high selectivity and sensitivity to aminopyrine. The response range of the sensor was between 5.0 x 10(-8) and 1.0 x 10(-4) M with a detection limit of 2.5 x 10(-8) M in the aqueous system. Scatchard analysis with UV spectrophotometry showed that the same class of binding sites was formed in the molecularly imprinted polymer in the studied concentration range, and the dissociation constant and the apparent maximum number of these binding sites were estimated to be 2.29 mM and 165.0 mumol g-1 dry polymer, respectively. Impedance analysis was employed to verify the imprinting effect and lack of variation in the viscoelasticity of the polymer coating during detection.

Aminopyrine↗
PubMed2004

A versatile, non-biomimetic route to the preussomerins: syntheses of (+/-)-preussomerins F, K and L.

The first total syntheses of the title fungal metabolites preussomerins F, K and L are described and their structures confirmed thereby. The syntheses were achieved following a versatile, unified, non-biomimetic approach, which is easily extendable to prepare other known and novel members of this family. Key steps include the functionalisation of a 2-arylacetal anion, tandem one-pot Friedel-Crafts cyclisation-deprotection, regioselective substrate-directable hydrogenation and reductive-opening of epoxides.

Epoxy Compounds↗
PubMed2004

Biomimetic thermo-responsive star diblock gelators.

We report the synthesis of novel biomimetic gelators with star diblock copolymer architectures by sequential monomer addition via alcoholic ATRP at 20 degrees C; free-standing gels can be formed from 5% aqueous copolymer solutions at 37 degrees C.

Journal Article↗
PubMed2003

Lipid binding and membrane penetration of polymyxin B derivatives studied in a biomimetic vesicle system.

Understanding membrane interactions and cell-wall permeation of Gram-negative bacteria is of great importance, owing to increasing bacterial resistance to existing drugs and therapeutic treatments. Here we use biomimetic lipid vesicles to analyse membrane association and penetration by synthetic derivatives of polymyxin B (PMB), a potent naturally occurring antibacterial cyclic peptide. The PMB analogues studied were PMB nonapeptide (PMBN), in which the hydrophobic alkyl residue was cleaved, PMBN diastereomer containing D-instead of L-amino acids within the cyclic ring (dPMBN) and PMBN where the hydrophobic alkyl chain was replaced with an Ala6 repeat (Ala6-PMBN). Peptide binding measurements, colorimetric transitions induced within the vesicles, fluorescence quenching experiments and ESR spectroscopy were applied to investigate the structural parameters underlying the different membrane-permeation profiles and biological activities of the analogues. The experiments point to the role of negatively charged lipids in membrane binding and confirm the prominence of lipopolisaccharide (LPS) in promoting membrane association and penetration by the peptides. Examination of the lipid interactions of the PMB derivatives shows that the cyclic moiety of PMB is not only implicated in lipid attachment and LPS binding, but also affects penetration into the inner bilayer core. The addition of the Ala6 peptide moiety, however, does not significantly promote peptide insertion into the hydrophobic lipid environment. The data also indicate that the extent of penetration into the lipid bilayer is not related to the overall affinity of the peptides to the membrane.

Binding, Competitive↗
PubMed2003

Biomimetic mineralization of charged collagen matrices: in vitro and in vivo study.

Polyanionic collagen matrix prepared by hydrolysis side chain amides of asparagine and glutamine was mineralized in vivo, without inflammatory response, biodegradation, or resorption, with calcium phosphate deposited in close resemblance to the D-periodicity of collagen fibrils assembly. In vitro results with the same material produced mineralized collagen fibers with a similar morphology and chemical characteristics, suggesting that amide hydrolysis may have introduced into this matrix, signs for the controlled mineralization of collagen fiber. TEM indicated that amide hydrolysis occurred near the OVERLAP and GAP zones, as suggested by the significant reduction in inter-band distances in these regions. The lack of an inflammatory response associated to the similar mineralization pattern observed in vivo and in vitro suggests not only the biomimetic behavior of polyanionic collagen matrix, but also its potential uses as scaffold for bone tissue reconstruction. Based on these results, a model for the in vitro mineralization was also proposed.

Animals↗
PubMed1995

Transport of proteins dissolved in organic solvents across biomimetic membranes.

Using lipid-impregnated porous cellulose membranes as biomimetic barriers, we tested the hypothesis that to afford effective transmembrane transfer of proteins and nucleic acids, the vehicle solvent should be able to dissolve both the biopolymers and the lipids. While the majority of solvents dissolve one or the other, ethanol and methanol were found to dissolve both, especially if the protein had been lyophilized from an aqueous solution of a pH remote from the protein's isoelectric point. A number of proteins, as well as RNA and DNA, dissolved in these alcohols readily crossed the lipidized membranes, whereas the same biopolymers placed in nondissolving solvents (e.g., hexane and ethyl acetate) or in those unable to dissolve lipids (e.g., water and dimethyl sulfoxide) exhibited little transmembrane transport. The solubility of biopolymers in ethanol and methanol was further enhanced by complexation with detergents and poly(ethylene glycol); significant protein and nucleic acid transport through the lipidized membranes was observed from these solvents but not from water.

Biological Transport↗
PubMed1999

Simulation of biomimetic recognition between polymers and surfaces.

Many biological processes, such as transmembrane signaling and pathogen-host interactions, are initiated by a protein recognizing a specific pattern of binding sites on part of a membrane or cell surface. By recognition, we imply that the polymer quickly finds and then adsorbs strongly on the pattern-matched region and not on others. The development of synthetic systems that can mimic such recognition between polymers and surfaces could have significant impact on advanced applications such as the development of sensors, molecular-scale separation processes, and synthetic viral inhibition agents. Attempting to affect recognition in synthetic systems by copying the detailed chemistries to which nature has been led over millenia of evolution does not seem practical for most applications. This leads us to the following question: Are there any universal strategies that can affect recognition between polymers and surfaces? Such generic strategies may be easier to implement in abiotic applications. We describe results that suggest that biomimetic recognition between synthetic polymers and surfaces is possible by exploiting certain generic strategies, and we elucidate the kinetic mechanisms by which this occurs. Our results suggest convenient model systems for experimental studies of dynamics in free energy landscapes characteristic of frustrated systems.

Algorithms↗
PubMed2003

Interactions of mouse Paneth cell alpha-defensins and alpha-defensin precursors with membranes. Prosegment inhibition of peptide association with biomimetic membranes.

The bactericidal activity of mouse alpha-defensins (cryptdins) requires proteolytic activation of inactive precursors by matrix metalloproteinase-7 (matrilysin, EC, MMP-7(a)). To investigate mechanisms of cryptdin-4 (Crp4) peptide interactions with membrane bilayers and to determine whether MMP-7-mediated proteolysis activates the membrane disruptive activity of Crp4, associations of Crp4 and melittin with biomimetic lipid/polydiacetylene chromatic vesicles were characterized. The peptides differ in their sensitivity to vesicle lipid composition and their depth of bilayer penetration. Crp4 undergoes strong interfacial binding onto lipid bilayers with disruption of the bilayer head group region, unlike melittin, which inserts more deeply into the hydrophobic core of the bilayer. Colorimetric and tryptophan fluorescence studies showed that Crp4 insertion is favored by negatively charged phospholipids and that zwitterionic and Escherichia coli phospholipids promote stronger interfacial binding; melittin-membrane interactions were independent of either variable. In contrast to the membrane disruptive activity of Crp4, pro-Crp4 did not perturb vesicular membranes, consistent with the lack of bactericidal activity of the precursor, and incubation of Crp4 with prosegment in trans blocked Crp4 and G1W-Crp4 membrane interactions at concentrations that inhibit Crp4 bactericidal activity. CD measurements showed that Crp4 has an expected beta-sheet structure that is not evident in the pro-Crp4 CD trace or when Crp4 is incubated with prosegment, indicating that the beta-sheet signal is attenuated by proregion interactions or possibly disrupted by the prosegment. Collectively, the results suggest that the prosegment inhibits Crp4 bactericidal activity by blocking peptide-mediated perturbation of target cell membranes, a constraint that is relieved when MMP-7 cleaves the prosegment.

Amino Acid Sequence↗