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Enantiomeric Forms (enantiomeric + form)
Selected AbstractsAtropoisomeric Quinolinium Salt Promoting the Access to Both Enantiomeric Forms of Methyl Mandelate: A Versatile NADH Mimic.CHEMINFORM, Issue 6 2003Jean-Luc Vasse Abstract For Abstract see ChemInform Abstract in Full Text. [source] Stereoselective Synthesis of myo -, neo -, L - chiro, D - chiro, allo -, scyllo -, and epi -Inositol Systems via Conduritols Prepared from p -BenzoquinoneEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2003Michael Podeschwa Abstract A practical route is described for the flexible preparation of a wide variety of inositol stereoisomers and their polyphosphates. The potential of this approach is demonstrated by the synthesis of myo -, L - chiro -, D - chiro -, epi -, scyllo -, allo -, and neo -inositol systems. Optically pure compounds in either enantiomeric form can be prepared from p -benzoquinone via enzymatic resolution of a derived conduritol B key intermediate. High-performance anion-exchange chromatography with pulsed amperometric detection permits inositol stereoisomers to be resolved and detected with high sensitivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Enantioselective Preparation of 2-Aminomethyl Carboxylic Acid Derivatives: Solving the ,2 -Amino Acid Problem with the Chiral Auxiliary 4-Isopropyl-5,5-diphenyloxazolidin-2-one (DIOZ).HELVETICA CHIMICA ACTA, Issue 6 2003Preliminary Communication Multigram amounts of suitably protected ,2 -amino acids with 17 of the 20 proteinogenic side chains are prepared by diastereoselective reactions of Li, B, or Ti enolates of the corresponding 3-acyl-4-isopropyl-5,5-diphenyloxazolidin-2-ones (acyl-DIOZ; 1) with appropriate electrophiles (amidomethylation, hydroxyalkylation, (benzyloxycarbonyl)methylation) in yields of 55,90% and with diastereoselectivities of 80 to >97% (Scheme). The primary products 2,8 thus obtained are converted to protected ,2 -amino acids by standard procedures (Table,1). Many of the DIOZ derivatives are highly crystalline compounds (31 X-ray crystal structures in Table,2). The chiral auxiliary DIOZ, readily prepared in either enantiomeric form, is recovered with high yield. [source] A dipicolinate lanthanide complex for solving protein structures using anomalous diffractionACTA CRYSTALLOGRAPHICA SECTION D, Issue 7 2010Guillaume Pompidor Tris-dipicolinate lanthanide complexes were used to prepare derivative crystals of six proteins: hen egg-white lysozyme, turkey egg-white lysozyme, thaumatin from Thaumatococcus daniellii, urate oxidase from Aspergillus flavus, porcine pancreatic elastase and xylanase from Trichoderma reesei. Diffraction data were collected using either synchrotron radiation or X-rays from a laboratory source. In all cases, the complex turned out to be bound to the protein and the phases determined using the anomalous scattering of the lanthanide led to high-quality electron-density maps. The binding mode of the complex was characterized from the refined structures. The lanthanide tris-dipicolinate was found to bind through interactions between carboxylate groups of the dipicolinate ligands and hydrogen-bond donor groups of the protein. In each binding site, one enantiomeric form of the complex is selected from the racemic solution according to the specific site topology. For hen egg-white lysozyme and xylanase, derivative crystals obtained by cocrystallization belonged to a new monoclinic C2 crystal form that diffracted to high resolution. [source] The Enantiomer of Octreotate Binds to All Five Somatostatin Receptors with Almost Equal Micromolar Affinity , A Comparison with SANDOSTATIN®CHEMISTRY & BIODIVERSITY, Issue 7 2008James Gardiner Abstract Octreotate (1b) is the octreotide (SANDOSTATIN®; 1a) analogue, carrying a C-terminal CO2H (Thr) instead of the CH2OH (threoninol) group. In pursuit of our interest in unnatural peptides, we have now synthesized (by the solid-phase Fmoc method) the enantiomeric form 2 of octreotate and determined its affinity for the five human somatostatin (SRIF) receptors (hsst1,5). The binding was found to be 9.1, 4.1, 1.0, 1.4, and 4.2,,M, respectively. This almost equal one-digit micromolar affinity of ent -octreotate (2) to all five receptors contrasts with the behavior of most other somatostatin mimics including SANDOSTATIN® (octreotide; 1a) and [Tyr3]-octreotate (1c), which have affinities for the various receptors differing up to and above 104 -fold. Thus, the structure of the new compound does not prevent binding, albeit more weakly than its pseudo -enantiomer octreotide, and there is hardly any selectivity of the peptide,protein interaction (PPI) for any one of the five SRIF G-protein coupled receptors (GPCRs). Since the detailed structure(s) of these membrane-embedded receptors is unknown (no X-ray structure!), the result described here may be useful for modeling structures by comparing the affinities of the numerous known somatostatin mimics. [source] The Possible Influence of L -Histidine on the Origin of the First Peptides on the Primordial EarthCHEMISTRY & BIODIVERSITY, Issue 6 2006Hannes Reiner Abstract One of the most unsettled problems of prebiotic evolution and the origin of life is the explanation why one enantiomeric form of biomolecules prevailed. In the experiments presented in this paper, the influence of L -histidine on the peptide formation in the Salt-Induced Peptide Formation (SIPF) reaction of the enantiomeric forms of valine, proline, serine, lysine, and tryptophan, and the catalytic effects in this first step toward the first building blocks of proteins on the primordial earth were investigated. In the majority of the produced dipeptides, a remarkable increase of yields was shown, and the preference of the L - amino acids in the peptide formation in most cases cannot be denied. In summary, our data provide further experimental evidence for the plausibility of the SIPF reaction and point at a possible important role of L -histidine in the chemical evolution on the primordial earth. [source] Metal-Controlled Stereoselectivity in Complex Formation: Assembly of Tetranuclear Copper(I) Complexes with Four Stereogenic Nitrogen Donor Functions in all-(R) and all-(S) ConfigurationsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2003Jörg Schneider Abstract The reaction of N,N, -dialkyl-3,7-diazanonane-1,9-dithiolate (NR2S2) ligands (R = Me, Et) with monovalent copper resulted in the formation of the chiral complexes [Cu4(NMe2S2)2] (1) and [Cu4(NEt2S2)2] (2) which were characterised by means of X-ray diffraction and spectroscopic techniques. They contain copper atoms in both linear {S,Cu,S} fragments, which act as linkers between mononuclear [Cu(NR2S2)], subsites, and in {CuS2N2} units within these building blocks, which can be described as incomplete coordination octahedra of unusual design. Due to favourable interplay between the spatial demands of the ligand system and the electronic requirements of the copper atom, the nitrogen donor atoms within the [Cu(NR2S2)], metallo ligands are restricted to identical absolute configurations. The combination of two [Cu(NR2S2)], metallo ligands with two further CuI ions to give the tetranuclear complexes 1 or 2 via S,Cu,S bridges underlies stereochemical control, resulting in optically active systems with (R,R,R,R) and (S,S,S,S) configurations. Consequently, metallo ligands in their enantiomeric forms cannot combine via S,Cu,S bridges to form optically inactive meso complexes with the (R,R,S,S) configuration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Distribution of piperitone oxide stereoisomers in Mentha and Micromeria species and their chemical synthesesFLAVOUR AND FRAGRANCE JOURNAL, Issue 4 2007Olga Larkov Abstract Chiral GC,MS analyses of natural and synthetic trans- and cis- piperitone oxide were performed on an Rt- ,DEX-sm capillary column in order to clarify the stereochemistry of their enantiomeric forms. Only enantiomerically pure laevo-rotatory piperitone oxides, (1S,2S,4S)- trans- piperitone oxide and (1S,2S,4R)- cis- piperitone oxide, were detected by chiral analyses of Micromeria fruticosa (L.) Druce and Mentha longifolia L. The occurrence of the cis - and trans -piperitone oxides was dependent on the population of the species. In all cases (1S,2S,4S)- trans- piperitone oxide was detected together with (4S)-piperitone, while (1S,2S,4R)- cis- piperitone oxide was detected together with (4R)-piperitone in the plants analysed. The four stereoisomers of trans - and cis -piperitone oxide were obtained by alkaline epoxidation of both (4R)- and (4S)-piperitone. The formation of the 1,2-epoxide can take place on either side of the 1,4-substituted six-membered ring. Racemization at C4 was observed under alkaline epoxidation reaction conditions due to keto-enol tautomerism. Copyright © 2007 John Wiley & Sons, Ltd. [source] Separation and measurement of plant alkaloid enantiomers by RP-HPLC analysis of their Fmoc-Alanine analogs ,PHYTOCHEMICAL ANALYSIS, Issue 5 2008Stephen T. Lee Abstract Introduction. Ammodendrine (1), anabasine (2) and coniine (3) can cause congenital malformations in livestock. They appear naturally in both enantiomeric forms, and can cause variable physiological responses. A method to measure the enantiomeric ratio of these natural toxins is needed. Objective. To develop a simple and economical method in order to determine the enantiomeric ratios of piperidine and pyrrolidine alkaloids in small samples of plant material. Methodology. Mixtures of isolated or purified plant alkaloids were converted to their Fmoc- l -Ala-alkaloid analogues forming diastereomeric mixtures, which were then analysed by high pressure liquid chromatography (HPLC) with mass spectrometry (MS) and ultraviolet (UV) detection to determine enantiomeric ratios. Results. The diastereomeric analogs for ammodendrine, anabasine and nornicotine could be separated and the enantiomeric ratios determined. The Fmoc- l -Ala-coniine analogue was not resolved under the HPLC conditions studied. The enantiomeric ratios of the selected plant alkaloids were measured and found to differ between both location within a species and location between species. Conclusion. A low-cost HPLC method to analyse the enantiomeric ratio of plant alkaloids containing primary or secondary amine nitrogens via conversion to their respective diastereomeric analogues has been developed. Published in 2008 by John Wiley & Sons. [source] Reductive detoxification of the acetophenone skeleton of the carnation phytoanticipin by Fusarium oxysporum f.sp. dianthiPLANT PATHOLOGY, Issue 6 2000P. Curir The skeleton of the carnation phytoanticipin, acetophenone, was detoxified by Fusarium oxysporum f.sp. dianthi, the main fungal parasite of carnation. This process consisted of the reduction to ethanol of the acetyl group, leading to the formation of phenylethanol, which has lower fungitoxic activity than the parent molecule. The conversion took place through the activity of an adaptive fungal oxidoreductase, which was NADH-dependent and was released by the fungus as two enzymatic forms within the culture substrate in the presence of acetophenone. Reduction was stereospecific and gave rise to only one of the two possible enantiomeric forms. [source] Comparative disposition of ricobendazole enantiomers after intravenous and subcutaneous administration of a racemic formulation to calvesBIOPHARMACEUTICS AND DRUG DISPOSITION, Issue 8 2000Carles Cristòfol Abstract The enantioselective disposition kinetics of the benzimidazole anthelmintic, ricobendazole (RBZ), have been characterized after its intravenous (iv) and subcutaneous (sc) administration as a racemic formulation to cattle. The (+) and (,) RBZ enantiomeric forms were recovered in plasma after iv and sc administration of the racemic RBZ formulation, using a chiral phase based HPLC method. A biexponential plasma concentration versus time curve was observed for both RBZ enantiomers following the iv treatment. Total body clearance was higher for (,) RBZ (150.4 mL/h,·,kg) compared with that obtained for the (+) RBZ antipode (78.1 mL/h,·,kg). The elimination half-life of the (,) RBZ enantiomer was shorter (T1/2,: 2.67 h) compared with the (+) enantiomer (T1/2,: 5.41 h). The plasma availability (expressed as AUC) was significantly higher for (+) RBZ compared with that obtained for the (,) antipode following both treatments. The enantiomeric ratio in plasma at T0 was close to unity (50% of each enantiomer); the analysis of the concentration ratios (+) RBZ/(,) RBZ, demonstrated an increase in the proportion of (+) RBZ during the time course of the kinetics after both iv and sc treatments. The results presented herein show the enantioselective disposition kinetics of RBZ in cattle and are a further contribution to the understanding of the kinetic behaviour of these sulphoxide-containing benzimidazole anthelmintics in ruminants. Copyright © 2000 John Wiley & Sons, Ltd. [source] Stereochemical Integrity of Oxazolone Ring-Containing JadomycinsCHEMBIOCHEM, Issue 10 2007Charles N. Borissow Dr. Abstract The jadomycins are a series of natural products produced by Streptomyces venzuelae ISP5230 in response to ethanol shock. A unique structural feature of these angucyclines is the oxazolone ring, the formation of which is catalyzed by condensation of a biosynthetic aldehyde intermediate and an amino acid. The feeding of enantiomeric forms of ,-amino acids indicates that the amino acid is incorporated by S. venezuelae ISP5230 without isomerization at the ,-carbon. The characterization of the first two six-membered E-ring-containing jadomycins is reported. These precursor-directed biosynthesis studies indicate flexibility in the acceptor substrate specificity of the glycosyltransferase, JadS. Analysis of cytotoxicity data against two human breast cancer cell lines indicates that the nature of the substitution at the ,-carbon, rather than the stereochemistry, influences biological activity. [source] The Possible Influence of L -Histidine on the Origin of the First Peptides on the Primordial EarthCHEMISTRY & BIODIVERSITY, Issue 6 2006Hannes Reiner Abstract One of the most unsettled problems of prebiotic evolution and the origin of life is the explanation why one enantiomeric form of biomolecules prevailed. In the experiments presented in this paper, the influence of L -histidine on the peptide formation in the Salt-Induced Peptide Formation (SIPF) reaction of the enantiomeric forms of valine, proline, serine, lysine, and tryptophan, and the catalytic effects in this first step toward the first building blocks of proteins on the primordial earth were investigated. In the majority of the produced dipeptides, a remarkable increase of yields was shown, and the preference of the L - amino acids in the peptide formation in most cases cannot be denied. In summary, our data provide further experimental evidence for the plausibility of the SIPF reaction and point at a possible important role of L -histidine in the chemical evolution on the primordial earth. [source] Synthesis and characterization of novel chiral ionic liquids and investigation of their enantiomeric recognition propertiesCHIRALITY, Issue 2 2008David K. Bwambok Abstract We report the synthesis and characterization of amino acid ester based chiral ionic liquids, derived from L - and D -alanine tert butyl ester chloride. The synthesis was accomplished via an anion metathesis reaction between commercially available L - and D -alanine tert butyl ester chloride using a variety of counterions such as lithium bis (trifluoromethane) sulfonimide, silver nitrate, silver lactate, and silver tetrafluoroborate. Both enantiomeric forms were obtained as confirmed by bands of opposite sign in the circular dichroism spectra. The L - and D -alanine tert butyl ester bis (trifluoromethane) sulfonimide were obtained as liquids at room temperature and intriguingly exhibited the highest thermal stability (up to 263°C). In addition, the ionic liquids demonstrated enantiomeric recognition ability as evidenced by splitting of racemic Mosher's sodium salt signal using a liquid state 19F nuclear magnetic resonance (NMR) and fluorescence spectroscopy. The L - and D -alanine tert butyl ester chloride resulted in solid salts with nitrate, lactate, and tetrafluoroborate anions. This illustrates the previously observed tunability of ionic liquid synthesis, resulting in ionic liquids of varying properties as a function of varying the anion. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] | ||||||||||