Home About us Contact
|
Home About us Contact | ||
|
|
||
Cyclic Imines (cyclic + imine)
Selected AbstractsThe structure of dihydrodipicolinate reductase (DapB) from Mycobacterium tuberculosis in three crystal formsACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2010Robert Janowski Dihydrodipicolinate reductase (DHDPR, DapB) is an enzyme that belongs to the l -lysine biosynthetic pathway. DHDPR reduces the ,,,-unsaturated cyclic imine 2,3-dihydrodipicolinic acid to yield the compound 2,3,4,5-tetrahydrodipicolinic acid in a pyridine nucleotide-dependent reaction. The substrate of this reaction is the unstable product of the preceding enzyme dihydrodipicolinate synthase (DHDPS, DapA). Here, the structure of apo-DHDPR from Mycobacterium tuberculosis is reported in two orthorhombic crystal forms, as well as the structure of DHDPR from M. tuberculosis in complex with NADH in a monoclinic crystal form. A comparison of the results with previously solved structures of this enzyme shows that DHDPR undergoes a major conformational change upon binding of its cofactor. This conformational change can be interpreted as one of the low-frequency normal modes of the structure. [source] The Chemistry of Escapin: Identification and Quantification of the Components in the Complex Mixture Generated by an L -Amino Acid Oxidase in the Defensive Secretion of the Sea Snail Aplysia californicaCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2009Michiya Kamio Dr. Abstract A complex mixture of products in an enzymatic reaction: Aplysia californica releases amino acid oxidase and its substrate lysine in defensive secretions to produce a mixture of multiple compounds (see figure). Escapin is an L -amino acid oxidase in the ink of a marine snail, the sea hare Aplysia californica, which oxidizes L -lysine (1) to produce a mixture of chemicals which is antipredatory and antimicrobial. The goal of our study was to determine the identity and relative abundance of the constituents of this mixture, using molecules generated enzymatically with escapin and also using products of organic syntheses. We examined this mixture under the natural range of pH values for ink,from ,5 at full strength to ,8 when fully diluted in sea water. The enzymatic reaction likely forms an equilibrium mixture containing the linear form ,-keto-,-aminocaproic acid (2), the cyclic imine ,1 -piperidine-2-carboxylic acid (3), the cyclic enamine ,2 -piperidine-2-carboxylic acid (4), possibly the linear enol 6-amino-2-hydroxy-hex-2-enoic acid (7), the ,-dihydroxy acid 6-amino-2,2-dihydroxy-hexanoic acid (8), and the cyclic aminol 2-hydroxy-piperidine-2-carboxylic acid (9). Using NMR and mass spectroscopy, we show that 3 is the major component of this enzymatic product at any pH, but at more basic conditions, the equilibrium shifts to produce relatively more 4, and at acidic conditions, the equilibrium shifts to produce relatively more 2, 7, and/or 9. Studies of escapin's enzyme kinetics demonstrate that because of the high concentrations of escapin and L -lysine in the ink secretion, millimolar concentrations of 3, H2O2, and ammonia are produced, and also lower concentrations of 2, 4, 7, and 9 as a result. We also show that reactions of this mixture with H2O2 produce ,-aminovaleric acid (5) and ,-valerolactam (6), with 6 being the dominant component under the naturally acidic conditions of ink. Thus, the product of escapin's action on L -lysine contains an equilibrium mixture that is more complex than previously known for any L -amino acid oxidase. [source] Stereodivergent Diversity Oriented Synthesis of Piperidine Alkaloids,,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2006Louis V. Adriaenssens Abstract Alkylidenetitanium reagents enable the reagent-controlled high throughput asymmetric synthesis of 2-substituted piperidines and rapid access to multiple cyclic imines using solid phase synthesis (SPS). The Schrock carbenes, generated by reduction of thioacetals, convert resin-bound esters into enol ethers. Treatment with acid releases amino ketones that are cyclized with TMSCl to give iminium salts. Reduction introduces a chiral centre at C-2, whose absolute stereochemistry is determined by a phenethylamine (PEA) chiral auxiliary. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Solid-phase synthesis of cyclic imines , potential for radiolabelling,JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 5-6 2007Carolyn A. Austin [source] Chemistry of Ru(& 6 -1,3,5-cyclooctatriene)(,2 -dimethyl fumarate)2THE CHEMICAL RECORD, Issue 3 2006Take-Aki Mitsudo Abstract The chemistry of a novel zerovalent Ru complex, Ru(,6 -cot)(,2 -dmfm)2 (1) (cot=1,3,5-cyclooctatriene; dmfm=dimethyl fumarate), is reviewed with a focus on its reactivity toward phosphines, amines, and H2O, as well as arenes and p -quinones. A variety of novel zerovalent Ru complexes were synthesized from Ru(,6 -cot)(,2 -dmfm)2 (1), and it was shown that the complexes preferably bear both electron-donating and -accepting ligands simultaneously to exhibit thermodynamic stability. The first isolable zerovalent Ru aqua complexes were successfully prepared, and in these complexes, the generation of a chiral center on the O atom of the coordinated H2O was disclosed. In addition, the characteristic catalytic activity of 1 in organic synthesis was considered by reviewing recently developed novel reactions: (i) dimerization of 2,5-norbornadiene to pentacyclo[6.6.0.02,6.03,13.010,14]tetradeca-4,11-diene (PCTD), (ii) intramolecular hydroamination of aminoalkynes to cyclic imines, (iii) formal [4+2] cycloaddition of alkynes with dmfm to trans -4-cyclohexene-1,2-dicarboxylates, and (iv) co-dimerization of dihydrofurans with ,,,-unsaturated esters to 2-alkylidenetetrahydrofurans. The products obtained here are expected to be used as novel functional organic monomers. © 2006 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 6: 107,116; 2006: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20076 [source] | ||||||||||