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  • 1
    Electronic Resource
    Electronic Resource
    Reversal of elution order of urea and thiourea derivatives of propranolol enantiomers on ionically versus covalently bound pirkle phases (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 120-123 
    Details
    ISSN: 0899-0042
    Keywords: Pirkle phases ; propranolol enantiomers ; urea derivatives ; thiourea derivatives ; chiral separation ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chromatographic performance of a series of urea and thiourea derivatives of (±)-propranolol has been evaluated on three different Pirkle stationary phases. Seven different isocyanate reagents were used to generate a range of both aliphatic and aromatic urea derivatives with the isothiocyanates yielding the corresponding thiourea analogues. The Pirkle phases employed consisted of 3,5-dinitrobenzoylphenylglycine and 3,5-dinitrobenzoylleucine, both ionically and covalently bound to aminopropyl silica as well as phenethylpropylurea (covalently attached only). The urea derivatives were consistently more strongly retained on covalently bound columns than their thiourea counterparts. This is in contrast to the situation observed for the ionic columns, where the thiourea derivatives were the more strongly retained on the phenylglycine column and the more strongly retained in four of seven instances on the leucine column. The underlying mechanisms giving rise to these differences in retention are as yet unidentified but appear to involve the urea group.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530020209
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  • 2
    Electronic Resource
    Electronic Resource
    Calmodulin discriminates between the two enantiomers of the receptor-operated calcium channel blocker sk&f 96365: A study using 1H-NMR and chiral HPLC (1990)
    New York, NY [u.a.] : Wiley-Blackwell
    Chirality 2 (1990), S. 229-232 
    Details
    ISSN: 0899-0042
    Keywords: receptor-operated calcium channel antagonist ; 1H NMR ; chiral HPLC ; calmodulin ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1H nuclear magnetic resonance at 360 MHz shows that SK&F 96365 (1-{β-[3-(p-methoxyphenyl)-propyloxy]-p-methoxyphenethyl}-1H- imidazole hydrochloride), an antagonist of mammalian receptor-operated calcium channels, interacts with the calcium-binding regulatory protein calmodulin (CaM). This may be inferred by a number of chemical shift changes in the spectrum of the calcium-saturated protein induced by addition of the compound. Moreover, two well-resolved singlets corresponding to the 2-proton of the SK&F 96365 imidazolium moiety are observed in the spectrum over a wide range of protein:compound ratios. Separation of rac SK&F 96365 into its two enantiomers by high-performance liquid chromatography on a cellulose tris (4-methylbenzoate) column enabled us to show that the doubling of this NMR signal in the presence of CaM is due to a propensity of the protein to distinguish between the two optical isomers of the compound.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chir.530020407
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis, Structure, and Antimalarial Activity of Some Enantiomerically Pure, cis-fused cyclopenteno-1,2,4-trioxanes (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 647-662 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two pairs of enantiomerically pure cis-fused cyclopenteno-1,2,4-trioxanes (7, ent-7 and 8, ent-8) are prepared (Schemes 1-3). Their identities are established by dye-sensitized photo-oxygenation of ent-7 and 8, ent-8 to the allylichydroperxides, reduction to the corresponding alcohols, and conversion to the (1S)-camphanates (Scheme 4), the structures of which are determined by X-ray analysis. The dynamic properties of ent-7 are investigated by NMR spectroscopy and PM3 calculations. Evidence for an easily accessible twist-boat conformation is obtained. The in vitro and in vivo antimalarial activities of 7, ent-7,8, and ent-8 as well as those of the racemic mixtures are evaluated against Plasmodium falciparum, P. berghei, and P. yoelii. No correlation is observed between configuration and activity. Racemates and pure enantiomers have commensurate activities. The mode of action on the intraerythrocytic parasite is rationalized in terms of close docking by the twist-boat conformer of the trioxane on the surface of a molecule of heme, single-electron transfer to the O—O σ* orbital, and scission to the acetal radical which then irreversibly isomerizes to a C-centered radical, the ultimate lethal agent (Scheme 5).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780312
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  • 4
    Electronic Resource
    Electronic Resource
    Protein-Loop Mimetics: A Diketopiperazine-Based Template to Stabilize Loop Conformations in Cyclic Peptides Containing the NPNA and RGD Motifs (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1825-1842 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We explore here an approach to mimic the structures and biological functions of protein loops in small synthetic molecules, by grafting the loop of interest onto an organic template comprising a bicyclic diketopiperazine, prepared by the formal coupling of (2S,4S)-4-aminoproline (Pro(NH2)) and aspartic acid (Asp). The Fmoc-protected template 4 is used to prepare cyclo(-Ala1-Asn2-Pro3-Asn4-Ala5- Ala6-Temp-) (5) and cyclo(-Ala1-Arg2-Gly3-Asp4-Temp-) (6) (where Temp = template derived from 4), containing the Asn-Pro-Asn-Ala (NPNA) and Arg-Gly-Asp (RGD) motifs. The conformational properties of these molecules are studied in aqueous solution by NMR and simulated-annealing methods. The NPNA motif, an immunodominant epitope on the circumsporozoite surface protein of the malaria parasite Plasmodium falciparum, is shown to adopt a stable type-I β-turn in 5. The template in 5 adopts a preferred conformation with Pro(NH2)χ1 ≍ -35° and the Asp moiety χ1 ≍ 70°. A different template conformation is inferred for 6, with Pro(NH2)χ1 ≍ 0°, but the ARGD loop appears by NMR to undergo rapid conformational averaging. Solid-phase binding assays reveal that 6 displays modest antagonist activity towards both the integrin αIIbβ3 and αvβ3 receptors.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790708
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  • 5
    Electronic Resource
    Electronic Resource
    A Tricyclic Template Derived from (2S,4R)-4-Hydroxyproline for the Synthesis of Protein Loop Mimetics (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 2235-2248 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A tricyclic diketopiperazine, formally derived by coupling (2S,4S)-4-aminoproline (Pro(NH2)) and (2S,4R)-4-(carboxymethyl)proline (Pro(CH2COOH)), is synthesized starting from readily available (2S,4R)-4-hydroxyproline. The resulting tricyclic template has carboxy and amino groups to which a peptide chain may be attached. The Fmoc-protected template 5 is incorporated into the cyclic molecule cyclo(-Ala1-Asn2-Pro3-Asn4-Ala5-) (6) where Pro(NH2)7 = Pro(CH2COOH)8 represents the template, using solid-phase peptide synthesis with cyclization in solution. The molecule is shown by NMR and dynamic simulated annealing methods to adopt a preferred conformation in aqueous solution, which includes an extended backbone at the residues Asn2-Pro3-Asn4, and a type-Iβ-turn at . These studies show that this novel template may be used in the synthesis of cyclic peptide and protein mimetics having defined secondary structure in aqueous environments.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790817
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  • 6
    Electronic Resource
    Electronic Resource
    Synthesis of a Novel Tricyclic Dipeptide Template and Its Incorporation into a Cyclic Peptide Mimetic Containing an NPNA Motif (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 1513-1527 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel tricyclic dipeptide template, formally derived by coupling (2S,4S)-4-aminoproline (Pro(NH2)) and (S)-2-(carboxymethyl)proline (Pro(CH2COOH)) as a diketopiperazine, has been synthesized in a form suitable for solid-phase peptide synthesis using Fmoc chemistry. This template was incorporated into the cyclic molecule cyclo(-Ala1-Asn2-Pro3-Asn4-Ala5-Ala6-Temp-) (Temp = template), whose conformation in H2O was studied by NMR methods. Average solution structures derived by restrained simulated annealing point to a highly populated βI-turn within the Asn-Pro-Asn-Ala motif and also indicate which conformations are likely to be preferred by the template.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800514
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis of New 1,2,4-Trioxanes and their Antimalarial Activity (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1805-1812 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The three dihydronaphtho[1,2,4]trioxines 9-11 have been synthesized and two of them converted to the five carbamate and ester derivatives 12-16 (Schemes 1 and 2). The resulting new trioxanes together with two already known and ascaridole (7) were tested for antimalarial activity against the sensitive N strain of Plasmodium berghei in mice. On comparison with artemisinin (1) and dihydroartemisinin (2), modest activity was found. The four most active compounds were some 12-18 times less potent than 1.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710722
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  • 8
    Electronic Resource
    Electronic Resource
    Synthesis of a Type-VIβ-Turn Peptide Mimetic and Its Incorporation into a High-Affinity Somatostatin Receptor Ligand (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 1588-1606 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of a cis-Phe-Pro dipeptide mimetic is described, which adopts a type-VIβ-turn conformation. In this mimetic, the α-positions of Phe and Pro are joined by a CH2CH2 bridge, thereby forming a fused bicyclic system, and fixing a geometry similar to that seen in cis-Phe-Pro units in protein crystal structures. The dipeptide mimetic 20 was synthesized in optically pure form starting from (R)-α-allylproline (6; Schemes 1, 3, and 4), with a free carboxylic acid and an Fmoc-protected N-terminus, thereby allowing its incorporation into linear and cyclic peptides using standard solid-phase methods. The mimetic 20 was incorporated into the cyclic somatostatin analogue cyclo(-Phe = Pro-Phe-D-Trp-Lys-Thr-), where Phe = Pro represents the mimetic. This analogue shows a high affinity (pIC50 8.6) for somatostatin receptors on rat-brain cortex membranes. Based on NMR studies in aqueous solution, likely low-energy conformations for this analogue were deduced using restrained dynamic simulated annealing. The conformations found, which include a distorted type-II′ turn at D-Trp-Lys, are similar to low-energy conformations deduced elsewhere for cyclo(-Phe-Pro-Phe-D-Trp-Lys-Thr-), as well as to those seen in crystal structures of the somatostatin analogue octreotide.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780614
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  • 9
    Electronic Resource
    Electronic Resource
    Ein neuer Typ von Sesquiterpenlactonen aus Lychnophora salicifolia (1983)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1983 (1983), S. 1455-1458 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A New Type of Sesquiterpene Lactones from Lychnophora sallicifoliaFrom the polar fractions of Lychnophora salicifolia two new sesquiterpene lactones were isolated, the structures of which have been elucidated by high field 1H-NMR spectroscopy and by partial synthesis of one of the epimeric lactones which are derived from caryophyllene.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198319830820
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  • 10
    Electronic Resource
    Electronic Resource
    Ein weiteres Germacranolid mit β-Lactonring aus Grazielia serrata (1983)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1983 (1983), S. 2045-2048 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Further Germacranolide with a β-Lactone Ring from Grazielia serrataThe reinvestigation of the aerial parts of Grazielia serrata afforded in addition to compounds isolated previously two germacranolides, 8β-angeloyloxy-9β-hydroxycostunolide and a further germacranolide with a β-lactone ring. The structure - 8β-tiglioyloxygrazielolide (1) - was elucidated by spectroscopic methods and by chemical transformation into the trans,trans-cyclodecadiene derivative 3.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198319831122
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