The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
David M. Grant - One of the best experts on this subject based on the ideXlab platform.
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Experimental and theoretical investigation of the 13C and 15N chemical shift tensors in melanostatin-exploring the chemical shift tensor as a structural probe.
Journal of the American Chemical Society, 2004Co-Authors: Mark Strohmeier, David M. GrantAbstract:The determination of backbone conformations in powdered peptides using 13C and 15N shift tensor information is explored. The 13C and 15N principal shift values in natural abundance 13C and 15N melanostatin (l-Pro-l-Leu-Gly Amide) are measured using the FIREMAT technique. Furthermore, the orientation of the C−N bond in the 13C shift principal axis system for the backbone carbons is obtained from the presence of the 13C−14N dipolar coupling. The Ramachandran angles for the title compound are obtained from solid-state NMR data by comparing the experimentally determined shift tensor information to systematic theoretical shielding calculations on N-formyl-l-Amino Acid-Amide models. The effects of geometry optimization and neglect of intermolecular interactions on the theoretical shielding values in the model compounds are investigated. The sets of NMR derived Ramachandran angles are assembled in a set of test structures that are compared to the available single-crystal X-ray structure. Shift tensor calculation...
Mark Strohmeier - One of the best experts on this subject based on the ideXlab platform.
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Experimental and theoretical investigation of the 13C and 15N chemical shift tensors in melanostatin-exploring the chemical shift tensor as a structural probe.
Journal of the American Chemical Society, 2004Co-Authors: Mark Strohmeier, David M. GrantAbstract:The determination of backbone conformations in powdered peptides using 13C and 15N shift tensor information is explored. The 13C and 15N principal shift values in natural abundance 13C and 15N melanostatin (l-Pro-l-Leu-Gly Amide) are measured using the FIREMAT technique. Furthermore, the orientation of the C−N bond in the 13C shift principal axis system for the backbone carbons is obtained from the presence of the 13C−14N dipolar coupling. The Ramachandran angles for the title compound are obtained from solid-state NMR data by comparing the experimentally determined shift tensor information to systematic theoretical shielding calculations on N-formyl-l-Amino Acid-Amide models. The effects of geometry optimization and neglect of intermolecular interactions on the theoretical shielding values in the model compounds are investigated. The sets of NMR derived Ramachandran angles are assembled in a set of test structures that are compared to the available single-crystal X-ray structure. Shift tensor calculation...
Richard A. Houghten - One of the best experts on this subject based on the ideXlab platform.
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Determination of isokinetic ratios necessary for equimolar incorporation of carboxylic Acids in the solid-phase synthesis of mixture-based combinatorial libraries
Biopolymers, 2002Co-Authors: Achyuta N. Acharya, John M. Ostresh, Richard A. HoughtenAbstract:The methods used to study the relative reaction rates of 45 different aliphatic and aromatic carboxylic Acids when coupled to resin-bound Amino Acid Amides is described. Competition experiments involving the coupling of incoming carboxylic Acids to resin-bound Amino Acid Amides were performed. The relative composition of each N-acylated Amino Acid Amide in the resulting mixtures was compared to controls prepared by physically mixing equal aliquots of individual compounds in order to study the relative reaction rates of the incoming carboxylic Acids. The ratios of the incoming carboxylic Acids were then iteratively adjusted to yield as close to equimolar products as possible. As expected, the steric and electronic nature of the incoming carboxylic Acids was found to influence their relative reaction rates. The steric hindrance of the resin-bound Amino Acid appears to have a proportional effect on the reaction rates of the incoming carboxylic Acids. N-acylated Amino Acid Amides in the final mixtures, prepared using the final isokinetic ratios, were found to be approximately equimolar.
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Novel approaches for the solid-phase synthesis of biheterocyclic dihydroimidazole analogues.
Journal of combinatorial chemistry, 2002Co-Authors: Achyuta N. Acharya, And John M. Ostresh, Richard A. HoughtenAbstract:The solid-phase syntheses of dihydroimidazolyl 2-alkylthiobenzimidazoles, dihydroimidazolyl 2-alkylsulfonylbenzimidazoles, dihydroimidazolyl dihydroquinoxalin-2,3-diones, and dihydroimidazolyl dihydrobenzimidazol-2-imines are described. Following reduction of a resin-bound Amino Acid Amide, the primary amine of the resulting resin-bound diamine was N-acylated with 4-fluoro-3-nitrobenzoic Acid. Treatment with POCl3 led to formation of a dihydroimidazole derivative via dehydrative cyclization. The resin-bound dihydroimidazole derivative was then used as the key starting material for the synthesis of the aforementioned biheterocycles. Following cleavage, the resulting compounds, obtained in moderate yield and good purity, were characterized by LC−MS and 1H NMR and 13C NMR spectroscopy.
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Solid-phase parallel synthesis of trisubstituted dihydroimidazolyl dihydroquinoxalin-2(1H)-ones
Tetrahedron, 2002Co-Authors: Achyuta N. Acharya, John M. Ostresh, Richard A. HoughtenAbstract:Abstract An efficient approach for the solid-phase synthesis of dihydroimidazolyl dihydroquinoxalin-2(1 H )-ones is described. Following reduction of a resin-bound Amino Acid Amide, the primary amine of the resulting di-amine was selectively N-acylated with 4-fluoro-3-nitrobenzoic Acid. Treatment with POCl 3 led to formation of a dihydroimidazolyl derivative via dehydrative cyclization. Following displacement of the aryl fluoro group with an α-Amino Acid methyl ester, the dihydroimidazolyl moiety was alkylated with an alkyl halide. Reduction of aromatic nitro group with concomitant intramolecular cyclization using tin(II) chloride dihydrate led to formation of the dihydroimidazolyl dihydroquinoxalin-2(1 H )-one. The compound was characterized by LC–MS, and 1 H and 13 C NMR spectroscopy.
Shigenori Yamaguchi - One of the best experts on this subject based on the ideXlab platform.
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Dynamic Kinetic Resolution of Amino Acid Amide Catalyzed by d-Aminopeptidase and α-Amino-ε-caprolactam Racemase
Journal of the American Chemical Society, 2005Co-Authors: Yasuhisa Asano, Shigenori YamaguchiAbstract:Amino Acid Amide racemizing activity was discovered in α-Amino-e-caprolactam (ACL) racemase (EC 5. 1. 1. 15) from Achromobacter obae. The enzymatic synthesis of d-alanine from l-alanine Amide has been demonstrated by use of d-Aminopeptidase (DAP; EC 3. 4. 11. 19) from Ochrobactrum anthropi C1-38 and ACL racemase. The conversion of 45 mM l-alanine Amide was carried out at 30 °C for 7 h; l-alanine Amide was completely converted to d-alanine, and no l-alanine was detected. The result of successive enzymatic reaction shows that the combination of ACL racemase and DAP can be applied for dynamic kinetic resolution of dl-Amino Acid Amides to yield d-Amino Acids.
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dynamic kinetic resolution of Amino Acid Amide catalyzed by d Aminopeptidase and α Amino e caprolactam racemase
Journal of the American Chemical Society, 2005Co-Authors: Yasuhisa Asano, Shigenori YamaguchiAbstract:Amino Acid Amide racemizing activity was discovered in α-Amino-e-caprolactam (ACL) racemase (EC 5. 1. 1. 15) from Achromobacter obae. The enzymatic synthesis of d-alanine from l-alanine Amide has been demonstrated by use of d-Aminopeptidase (DAP; EC 3. 4. 11. 19) from Ochrobactrum anthropi C1-38 and ACL racemase. The conversion of 45 mM l-alanine Amide was carried out at 30 °C for 7 h; l-alanine Amide was completely converted to d-alanine, and no l-alanine was detected. The result of successive enzymatic reaction shows that the combination of ACL racemase and DAP can be applied for dynamic kinetic resolution of dl-Amino Acid Amides to yield d-Amino Acids.
Stephen F Martin - One of the best experts on this subject based on the ideXlab platform.
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Applications of the Ugi reaction with ketones.
Tetrahedron letters, 2008Co-Authors: Suvi T M Simila, Stephen F MartinAbstract:A convenient synthesis of highly functionalized, α,α-disubstituted Amino Acid Amide derivatives has been accomplished by using cyclic and acyclic ketones as the carbonyl inputs in the Ugi multicomponent reaction. An application of this extension of the Ugi reaction to the synthesis of α,α-divinyl Amino Acids that may be cyclized via ring-closing metathesis to provide highly substituted pyrrolidines is described.