- Enantioselective Desymmetrization of 2-Aryl-1,3-propanediols by Direct O-Alkylation with a Rationally Designed Chiral Hemiboronic Acid Catalyst That Mitigates Substrate Conformational Poisoning
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Enantioselective desymmetrization by direct monofunctionalization of prochiral diols is a powerful strategy to prepare valuable synthetic intermediates in high optical purity. Boron acids can activate diols toward nucleophilic additions; however, the design of stable chiral catalysts remains a challenge and highlights the need to identify new chemotypes for this purpose. Herein, the discovery and optimization of a bench-stable chiral 9-hydroxy-9,10-boroxarophenanthrene catalyst is described and applied in the highly enantioselective desymmetrization of 2-aryl-1,3-diols using benzylic electrophiles under operationally simple, ambient conditions. Nucleophilic activation and discrimination of the enantiotopic hydroxy groups on the diol substrate occurs via a defined chairlike six-membered anionic complex with the hemiboronic heterocycle. The optimal binaphthyl-based catalyst 1g features a large aryloxytrityl group to effectively shield one of the two prochiral hydroxy groups on the diol complex, whereas a strategically placed "methyl blocker"on the boroxarophenanthrene unit mitigates the deleterious effect of a competing conformation of the complexed diol that compromised the overall efficiency of the desymmetrization process. This methodology affords monoalkylated products in enantiomeric ratios equal or over 95:5 for a wide range of 1,3-propanediols with various 2-aryl/heteroaryl groups.
- Estrada, Carl D.,Ang, Hwee Ting,Vetter, Kim-Marie,Ponich, Ashley A.,Hall, Dennis G.
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- Controlling the Conformational Energy of a Phenyl Group by Tuning the Strength of a Nonclassical CH···O Hydrogen Bond: The Case of 5-Phenyl-1,3-dioxane
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Anancomeric 5-phenyl-1,3-dioxanes provide a unique opportunity to study factors that control conformation. Whereas one might expect an axial phenyl group at C(5) of 1,3-dioxane to adopt a conformation similar to that in axial phenylcyclohexane, a series of studies including X-ray crystallography, NOE measurements, and DFT calculations demonstrate that the phenyl prefers to lie over the dioxane ring in order to position an ortho-hydrogen to participate in a stabilizing, nonclassical CH···O hydrogen bond with a ring oxygen of the dioxane. Acid-catalyzed equilibration of a series of anancomeric 2-tert-butyl-5-aryl-1,3-dioxane isomers demonstrates that remote substituents on the phenyl ring affect the conformational energy of a 5-aryl-1,3-dioxane: electron-withdrawing substituents decrease the conformational energy of the aryl group, while electron-donating substituents increase the conformational energy of the group. This effect is correlated in a very linear way to Hammett substituent parameters. In short, the strength of the CH···O hydrogen bond may be tuned in a predictable way in response to the electron-withdrawing or electron-donating ability of substituents positioned remotely on the aryl ring. This effect may be profound: a 3,5-bis-CF3 phenyl group at C(5) in 1,3-dioxane displays a pronounced preference for the axial orientation. The results are relevant to broader conformational issues involving heterocyclic systems bearing aryl substituents.
- Bailey, William F.,Lambert, Kyle M.,Stempel, Zachary D.,Wiberg, Kenneth B.,Mercado, Brandon Q.
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p. 12116 - 12127
(2016/12/23)
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- LINCOMYCIN DERIVATIVES AND ANTIBACTERIAL AGENTS CONTAINING THE SAME AS THE ACTIVE INGREDIENT
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An objective of the present invention is to provide compounds of formula (1) or their pharmacologically acceptable salts or solvates wherein A represents aryl; R1 represents N-optionally substituted C1-6 alkyl-N-optionally substituted C1-6 alkylamino-C1-6 alkyl; R2 represents a hydrogen atom or optionally substituted C1-6 alkyl; R3 represents optionally substituted C1-6alkyl or C3-6 cycloalkyl-C1-4 alkyl; m is 1 to 3; n is 0; and p is 0 to 2. The compounds are novel lincomycin derivatives that have a potent activity against resistant Streptococcus pneumoniae, which have recently posed problems, in the treatment of infectious diseases. Further, the compounds are usable as antimicrobial agents and are useful for preventing or treating bacterial infectious diseases.
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Page/Page column 45-46
(2010/03/02)
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- 3-[1,4]OXAZEPANE-4-PYRIMIDONE DERIVATIVES
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A compound represented by the formula (I) or a pharmaceutically acceptable salt thereof: wherein Z represents nitrogen atom, C-F or the like; R1 represents a C1-C3 alkyl group; Y represents oxygen atom or N-R7; R2, R3, R4, R5, R6 and R7 each independently represents hydrogen atom, a C1-C6 alkyl group, or a group represented by the formula (II): which is used for preventive and/or therapeutic treatment of a disease caused by tau protein kinase 1 hyperactivity such as a neurodegenerative diseases (e.g. Alzheimer disease).
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Page/Page column 37-38
(2010/11/03)
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- Discovery of a novel class of 1,3-dioxane-2-carboxylic acid derivatives as subtype-selective peroxisome proliferator-activated receptor α (PPARα) agonists
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A new series of 1,3-dioxane-2-carboxylic acid derivatives was synthesized and evaluated for agonist activity at human peroxisome proliferator-activated receptor (PPAR) subtypes. Structure-activity relationship studies led to the identification of 2-methyl-c-5-[4-(5-methyl-2-phenyl-1,3-oxazol-4-yl)butyl]-1,3-dioxane-r-2-carboxylic acid 4b as a potent PPARα agonist with high subtype selectivity at human receptor subtypes. This compound exhibited a substantial hypolipidemic effect in type 2 diabetic KK-Ay mice.
- Aoki, Tomiyoshi,Asaki, Tetsuo,Hamamoto, Taisuke,Sugiyama, Yukiteru,Ohmachi, Shinji,Kuwabara, Kenji,Murakami, Kohji,Todo, Makoto
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p. 2128 - 2132
(2008/12/21)
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- Unusual Tethering Effects in the Schmidt Reaction of Hydroxyalkyl Azides with Ketones: Cation-π and Steric Stabilization of a Pseudoaxial Phenyl Group
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The Lewis acid-promoted reactions of chiral 2-aryl-3-azido-1-propanols with 4-substituted cyclohexanones lead to iminium ethers and ultimately caprolactams (following a hydrolysis step). In this study, it is shown that these reactions afford variable ratios of products, depending on the electronic nature of the phenyl group. These results are interpreted in the context of a cation?π stabilizing effect in the product-determining reaction intermediate. Remarkably, the best selectivity was obtained when an azidopropanol reagent containing a quaternary center was used; a control experiment showed that the high selectivity observed in this result depended upon the free rotation of the pseudoaxial aromatic group in the intermediate that affords the major product. Copyright
- Katz, Christopher E.,Aube, Jeffrey
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p. 13948 - 13949
(2007/10/03)
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- Cyclic imino derivatives and pharmaceutical compositions containing them
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The invention relates to cyclic imino compounds which have, inter alia, valuable pharmacological properties, especially inhibitory effects on cell aggregation, pharmaceutical compositions which contain these compounds and processes for preparing them.
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