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J M Ostresh

Publications and source records attributed to J M Ostresh.

At least 19 recordsLinked to original sources
PubMed2001

Solid-phase synthesis of 1,7-disubstituted-1,3,5-triazepane-2,4-diones.

[reaction: see text]. The solid-phase synthesis of 1,7-disubstituted-1,3,5-triazepane-2,4-diones from resin-bound amino acids is described. The exhaustive reduction of solid-support bound amides with borane afforded the requisite secondary amines, which following treatment with phenyl isocyanatoformate and cleavage, provided the corresponding triazepane-2,4-diones.

Amino Acids↗
PubMed2001

An N-methyl-D-aspartate receptor channel blocker with neuroprotective activity.

Excitotoxicity, resulting from sustained activation of glutamate receptors of the N-methyl-d-aspartate (NMDA) subtype, is considered to play a causative role in the etiology of ischemic stroke and several neurodegenerative diseases. The NMDA receptor is therefore a target for the development of neuroprotective agents. Here, we identify an N-benzylated triamine (denoted as NBTA) as a highly selective and potent NMDA-receptor channel blocker selected by screening a reduced dipeptidomimetic synthetic combinatorial library. NBTA blocks recombinant NMDA receptors expressed in Xenopus laevis oocytes with a mean IC(50) of 80 nM; in contrast, it does not block GluR1, a glutamate receptor of the non-NMDA subtype. The blocking activity of NBTA on NMDA receptors exhibits the characteristics of an open-channel blocker: (i) no competition with agonists, (ii) voltage dependence, and (iii) use dependence. Significantly, NBTA protects rodent hippocampal neurons from NMDA receptor, but not kainate receptor-mediated excitotoxic cell death, in agreement with its selective action on the corresponding recombinant receptors. Mutagenesis data indicate that the N site, a key asparagine on the M2 transmembrane segment of the NR1 subunit, is the main determinant of the blocker action. The results highlight the potential of this compound as a neuroprotectant.

Amines↗
PubMed2001

Solid phase synthesis of mixture-based acyclic and heterocyclic small molecule combinatorial libraries from resin-bound polyamides.

The development of soluble mixture-based heterocyclic combinatorial libraries derived from amino acids and peptides is described. Starting with a "toolbox" of various chemical transformations, including alkylations, reductions, acylations, and the use of a variety of bifunctional reagents, the "libraries from libraries" concept has been expanded to encompass the development of more than fifty positional scanning combinatorial libraries each composed of tens of thousands of low molecular weight acyclic and heterocyclic compounds.

Combinatorial Chemistry Techniques↗
PubMed2000

Distal recognition site for classical pathway convertase located in the C345C/netrin module of complement component C5.

Previous studies focused on indels in the complement C345 protein family identified a number of potential protein-protein interaction sites in components C3 and C5. Here, one of these sites in C5, near the alpha-chain C terminus, was examined by alanine-scanning mutagenesis at 16 of the 18 non-alanine residues in the sequence KEALQIKYNFSF RYIYPLD. Alanine substitutions affected activities in the highly variable manner characteristic of binding sites. Substitutions at the lysine or either phenylalanine residue in the central KYNFSF sequence had the greatest effects, yielding mutants with <20% of the normal activity. These three mutants were also resistant to the classical pathway (CP) C5 convertase, with sensitivities roughly proportional to their hemolytic activities, but had normal susceptibilities to the cobra venom factor (CVF)-dependent convertase. Synthetic peptide MGKEALQIKYNFS-NH2 was found similarly to inhibit CP but not CVF convertase activation, and the effects of alanine substitutions in this peptide largely reflected those of the equivalent mutations in C5. These results indicate that residues KYNFSF form a novel, distal binding site for the CP, but not CVF convertase. This site lies approximately 880 residues downstream of the convertase cleavage site within a module that has been independently named C345C and NTR; this module is found in diverse proteins including netrins and tissue inhibitors of metalloproteinases.

Alanine↗
PubMed2000

Inhibition of beta-amyloid-induced neurotoxicity by imidazopyridoindoles derived from a synthetic combinatorial library.

Alzheimer's disease is a progressive neurodegenerative disorder characterized by the deposit of amyloid fibrils in the brain that result from the self-aggregative polymerization of the beta-amyloid peptide (Abeta). Evidence of a direct correlation between the ability of Abeta to form stable aggregates in aqueous solution and its neurotoxicity has been reported. The cytotoxic effects of Abeta have been attributed to the aggregation properties of a domain corresponding to the peptide fragment Abeta25-35. In an effort to generate novel inhibitors of Abeta neurotoxicity and/or aggregation, a mixture-based synthetic combinatorial library composed of 23 375 imidazopyridoindoles was generated and screened for inhibition of Abeta25-35 neurotoxicity toward the rat pheochromocytoma PC-12 cell line. The effect of the identified lead compounds on Abeta25-35 aggregation was then evaluated by means of circular dichroism (CD) and thioflavin-T fluorescence spectroscopy. Their activity against Abeta1-42 neurotoxicity toward the PC-12 cell line was also determined. The most active imidazopyridoindoles inhibited both Abeta25-35 and Abeta1-42 neurotoxicity in the low- to mid-micromolar range. Furthermore, inhibition of the random coil to beta-sheet transition and self-aggregation of Abeta25-35 was observed by CD and fluorescence spectroscopy, supporting the relationship between inhibition of the Abeta aggregation process and neurotoxicity.

Amyloid beta-Peptides↗
PubMed1999

Mixture-based heterocyclic combinatorial positional scanning libraries: discovery of bicyclic guanidines having potent antifungal activities against Candida albicans and Cryptococcus neoformans.

A mixture-based synthetic combinatorial library of more than 100,000 bicyclic guanidines was generated in a positional scanning format and assayed for activity against Candida albicans. Potent individual bicyclic guanidines were directly identified following the screening of the library. Time-kill curve studies indicated bactericidal activities for the individual bicyclic guanidines. These compounds also showed potent activity against Cryptococcus neoformans. These studies demonstrate the value of using mixture-based combinatorial positional scanning libraries made up of heterocyclic compounds for the rapid identification of novel classes of antifungal compounds.

Antifungal Agents↗
PubMed1998

Combinatorial chemistry: from peptides and peptidomimetics to small organic and heterocyclic compounds.

Modified dipeptides have been used successfully for the generation of a variety of small organic and heterocyclic combinatorial libraries, including linear urea, polyamine, hydantoin, thiohydantoin, cyclic urea, cyclic thiourea and bicyclic guanidine. The synthesis and screening results for a number of these libraries are described. The solid phase synthesis of heterocyclic compounds such as diazepine and thiomorpholinone are also described.

Chemistry, Organic↗
PubMed1996

Libraries from libraries: generation and comparison of screening profiles.

A positional scanning tetrapeptide library was chemically modified through alkylation and/or reduction of the amide bonds, thus generating three new combinatorial libraries with physico-chemical properties very different from the parent peptide library ('libraries from libraries'). Specific results were obtained with each of these libraries upon screening in kappa-opioid receptor binding and microdilution antimicrobial assays, illustrating the potential of the 'libraries from libraries' concept for the efficient generation of a variety of chemically diverse combinatorial libraries.

Animals↗
PubMed1996

The synthesis of peptidomimetic combinatorial libraries through successive amide alkylations.

A soluble peptidomimetic combinatorial library of 57,500 compounds was prepared. This library has a dipeptide scaffold with each amide hydrogen replaced with five different alkyl groups (methyl, ethyl, allyl, benzyl, or naphthylmethyl). Solid-phase methodology in combination with N-alkylation were used to synthesize the library, which incorporated 50 different L-, D-, and unnatural amino acids. Repetitive amide alkylations were carried out on the solid support following each amino acid coupling step. Individual model compounds were synthesized in order to optimize the alkylation conditions, to study potential amino acid side chain modifications, to determine the extent of racemization, and to provide analytical controls during the library synthesis.

Alkylation↗
PubMed1995

Induced conformational states of amphipathic peptides in aqueous/lipid environments.

Specific conformational effects have been reported for amphipathic model peptides upon binding of defined hydrophobic domains to nonpolar stationary phases during reversed-phase high performance liquid chromatography (RP-HPLC). Such induced conformations are found to be especially pronounced for peptides that are amphipathic in an alpha-helical conformation. Such induced amphipathic conformations resulted in substantially later elution than predicted using amino acid-based retention coefficients. In the present study, the induced conformational behavior of model peptides observed during RP-HPLC was correlated with their secondary structure as determined by circular dichroism (CD) spectroscopy in both aqueous solution and C18-mimetic environments. The experimental retention times of the peptides studied were found to correlate with their CD spectra in the presence of lipids, whereas a poor correlation was observed with their CD spectra in the presence of trifluoroethanol. A new approach was developed to evaluate the induction of secondary structure in peptides due to interactions at aqueous/lipid interfaces, which involves the measurement of the CD ellipticities of peptides bound to a set of C18-coated quartz plates. An excellent correlation was found in this environment between the RP-HPLC retention times and CD ellipticities of the bound peptides.

Amino Acid Sequence↗
PubMed1994

"Libraries from libraries": chemical transformation of combinatorial libraries to extend the range and repertoire of chemical diversity.

The generation of diverse chemical libraries using a "libraries from libraries" concept is described. The central features of the approaches presented are the use of well-established solid-phase synthesis methods for the generation of combinatorial libraries, combined with the chemical transformation of such libraries while they remain attached to the solid support. The chemical libraries that are generated by this process have very different physical, chemical, and biological properties compared to the libraries from which they were derived. A wide range of chemical transformations are possible for peptide-based or other libraries, and an almost unlimited range of useful chemical diversities can be envisioned. In the example presented, the amide functionalities in an existing combinatorial library made up of peptides were permethylated while the library remained attached to the solid-phase support used in its synthesis. After removal of the permethylated mixtures from their solid support, this library, now lacking the typical -CONH- amide bonds of peptides, can be tested in solution with virtually all existing assay systems to identify individual compounds having specific biological activities of interest. An illustration of the use of such libraries is presented, in which the described permethylated library was used to identify individual permethylated compounds having potent antimicrobial activity against Gram-positive bacteria.

Amino Acid Sequence↗
PubMed1994

Peptide libraries: determination of relative reaction rates of protected amino acids in competitive couplings.

In the solid phase preparation of synthetic peptide libraries, equimolarity of the resultant peptides in the mixture simplifies the identification of active compounds. Two primary methods for the preparation of combinatorial peptide mixtures are currently used. In the first method, the starting resin is divided into equal aliquots, individual amino acids are coupled to each aliquot, and the resin is then recombined. This process is repeated for each position. However, due to the physical process, each resin bead contains only one peptide sequence. Statistically, for mixtures of longer sequences, an ever-increasing amount of resin is necessary to ensure complete representation of each peptide in the library. Thus, each peptide will be represented in the library if a sufficient number of resin beads are used. In addition, the concentration of each peptide in the library depends on both the number of mixture positions in the library and the amount of resin used. In the second method, mixtures of amino acids are coupled simultaneously at each addition step. The proportion of each amino acid in the reaction mixture is varied inversely to its reaction rate such that, ideally, an equimolar mixture of each peptide is synthesized. An advantage of this method over the previous method is that each peptide is ensured to be represented in the library, although not necessarily in equimolar amounts. It is known that not only do the coupling rates of each amino acid vary, but the coupling rates of individual amino acids also change when coupled to different amino acid resins.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1992

Conformation and dynamics of an Fab'-bound peptide by isotope-edited NMR spectroscopy.

The dynamics and conformation of the peptide antigen MHKDFLEKIGGL bound to the Fab' fragment of the monoclonal antipeptide antibody B13A2, raised against a peptide from myohemerythrin, have been investigated by isotope-edited NMR techniques. The peptides were labeled with 15N (98%) or 13C (99%) at the backbone of individual amino acid residues. Well-resolved amide proton and nitrogen backbone resonances were obtained and assigned for eight of the 12 residues of this bound peptide. Significant resonance line width and chemical shift differences were observed. The 15N and 1H line width variations are attributed to differential backbone mobilities among the bound peptide residues which are consistent with the previously mapped epitope of this peptide antigen. Local structural information was obtained from isotope-directed NOE studies. The approximate distances associated with the experimental NOEs were estimated on the basis of a theoretical NOE analysis involving the relative integrated intensities of the NOE and source peaks. In this way, the sequential NH-NH NOEs obtained for seven of the Fab'-bound peptide residues were shown to correspond to interproton separations of approximately 3 A or less. Such short distances indicate that the backbone dihedral angles of these residues are in the alpha rather than the beta region of phi,psi conformational space; the peptide most likely adopts a helical conformation from F5 to G11 within the antibody combining site. The significance of these results with respect to the type and extent of conformational information obtainable from studies of high molecular weight systems is discussed.

Amino Acid Sequence↗