- Enantioseparation of racemic organic ammonium perchlorates by a silica gel bound optically active di-tert-butylpyridino-18-crown-6 ligand
-
Both enantiomers of the novel chiral di-tert-butylpyridino-18-crown-6 ligand (R,R)-7 and (S,S)-7 containing an allyloxy group on the pyridine subcyclic unit were prepared by the reaction of 4-allyloxy-2,6-pyridinedimethyl ditosylate 9 and the enantiomers of di-tert-butyl-substituted tetraethylene glycol (R,R)-8 and (S,S)-8 in the presence of a strong base. One of them, (R,R)-7, was covalently attached to silica gel, and this chiral stationary phase (CSP) separated four selected racemic organic ammonium perchlorates into their enantiomers by column chromatography.
- Koentoes, Zoltan,Huszthy, Peter,Bradshaw, Jerald S.,Izatt, Reed M.
-
-
Read Online
- Stereoselective Modification of N-(α-Hydroxyacyl)-glycinesters via Palladium-Catalyzed Allylic Alkylation
-
N-(α-Hydroxyacyl)-glycinesters can be used as excellent nucleophiles in Pd-catalyzed allylic alkylation. The method allows for the stereoselective introduction of a wide range of side chains, including highly functionalized ones. Both diastereomers can be accessed through variation of the reaction conditions. Furthermore, the use of stannylated carbonates introduces vinylstannane motifs, which are eligible for subsequent C-C coupling reactions.
- Horn, Alexander,Kazmaier, Uli
-
supporting information
p. 4595 - 4599
(2019/06/27)
-
- Readily Accessible 1,2-Amino Ether Ligands for Enantioselective Intramolecular Carbolithiation
-
A new class of chiral 1,2-amino ether ligands, readily accessible from naturally occurring α-amino- or α-hydroxy acids, was found to provide high levels of both conversion and stereocontrol (up to 95:5 er) in intramolecular carbolithiation reactions, outperforming the benchmark ligand (?)-sparteine. The ligand could be used in a substoichiometric amount (0.25 equiv) without significant loss of enantioselectivity.
- Guyon, Hélène,Boussonnière, Anne,Castanet, Anne-Sophie
-
p. 4949 - 4957
(2017/05/12)
-
- Janadolide, a Cyclic Polyketide-Peptide Hybrid Possessing a tert-Butyl Group from an Okeania sp. Marine Cyanobacterium
-
Janadolide, a new cyclic polyketide-peptide hybrid possessing a tert-butyl group, was isolated from an Okeania sp. marine cyanobacterium. The gross structure was elucidated by spectroscopic analyses, and the absolute configurations of the amino acid moieties were determined by acid hydrolysis and chiral-phase HPLC analyses. The absolute configuration of the two stereogenic centers in the polyketide moiety was elucidated based on a combination of degradation reactions and spectroscopic analyses including the phenyl-glycine methyl ester method. Janadolide showed potent antitrypanosomal activity with an IC50 value of 47 nM without cytotoxicity against human cells at 10 μM.
- Ogawa, Hidetoshi,Iwasaki, Arihiro,Sumimoto, Shinpei,Kanamori, Yuki,Ohno, Osamu,Iwatsuki, Masato,Ishiyama, Aki,Hokari, Rei,Otoguro, Kazuhiko,Omura, Satoshi,Suenaga, Kiyotake
-
p. 1862 - 1866
(2016/08/02)
-
- Asymmetric hydrogenation reaction of alpha-ketoacids compound
-
The invention relates to the technical field of organic chemistry, especially to an asymmetric hydrogenation reaction of an alpha-ketoacids compound. The asymmetric hydrogenation reaction comprises a scheme shown in the description. In the scheme, R1 is phenyl, substituted phenyl, naphthyl, substituted naphthyl, C1-C6 alkyl, or aralkyl; a substituent group is C1-C6 alkyl, C1-C6 alkoxy, or halogen; and the number of the substituent group is 1-3. In the scheme, M is a chiral spiro-pyridylamino phosphine ligand iridium complex having a structure shown in the description. In the structure, R is hydrogen, 3-methyl, 4-tBu, or 6-methyl.
- -
-
Paragraph 0037; 0044
(2016/10/10)
-
- Direct asymmetric hydrogenation of α-keto acids by using the highly efficient chiral spiro iridium catalysts
-
A new efficient and highly enantioselective direct asymmetric hydrogenation of α-keto acids employing the Ir/SpiroPAP catalyst under mild reaction conditions has been developed. This method might be feasible for the preparation of a series of chiral α-hydroxy acids on a large scale.
- Yan, Pu-Cha,Xie, Jian-Hua,Zhang, Xiang-Dong,Chen, Kang,Li, Yuan-Qiang,Zhou, Qi-Lin,Che, Da-Qing
-
supporting information
p. 15987 - 15990
(2015/02/19)
-
- MACROCYCLIC INHIBITORS OF FLAVIVIRIDAE VIRUSES
-
Provided are compounds of Formula I and pharmaceutically acceptable salts and esters thereof. The compounds, compositions, and methods provided are useful for the treatment of virus infections, particularly hepatitis C infections.
- -
-
Page/Page column 261
(2014/01/08)
-
- Camphor-based Schiff base ligand SBAIB: An enantioselective catalyst for addition of phenylacetylene to aldehydes
-
A series of Schiff base ligands were synthesized from (1R)-camphor. Under the optimal conditions, (+)-SBAIB-a, 10 was found to be an excellent catalyst for the enantioselective addition of phenylacetylene to various aldehydes without utilizing either achiral additives or Ti(OiPr)4. This approach yielded (R)-propargylic alcohols in extremely high yields (up to 99%) and excellent enantioselectivities (up to 92%). The corresponding (S)-propargylic alcohols were synthesized in good to high enantioselectivities (up to 91%) and excellent yields (up to 99%) using (-)-SBAIB-a, 41.
- Boobalan, Ramalingam,Chen, Chinpiao,Lee, Gene-Hsian
-
scheme or table
p. 1625 - 1638
(2012/03/22)
-
- P2-P3 conformationally constrained ketoamide-based inhibitors of cathepsin K
-
An orally bioavailable series of ketoamide-based cathepsin K inhibitors with good pharmacokinetic properties has been identified. Starting from a potent inhibitor endowed with poor drug properties, conformational constraint of the P2-P3 linker and modifications to P1′ elements led to an enhancement in potency, solubility, clearance, and bioavailability. These optimized inhibitors attenuated bone resorption in a rat TPTX hypocalcemic bone resorption model.
- Barrett, David G.,Boncek, Virginia M.,Catalano, John G.,Deaton, David N.,Hassell, Anne M.,Jurgensen, Cynthia H.,Long, Stacey T.,McFadyen, Robert B.,Miller, Aaron B.,Miller, Larry R.,Payne, J. Alan,Ray, John A.,Samano, Vicente,Shewchuk, Lisa M.,Tavares, Francis X.,Wells-Knecht, Kevin J.,Willard Jr., Derril H.,Wright, Lois L.,Zhou, Hui-Qiang Q.
-
p. 3540 - 3546
(2007/10/03)
-
- α-Hydroxy carboxylic acids as ligands for enantioselective diethylzinc additions to aromatic and aliphatic aldehydes
-
The first examples of the enantioselective titanium-mediated diethylzinc additions to aromatic and aliphatic aldehydes catalyzed by optically active α-hydroxy acids are presented. The reactions proceed with very good yield and good asymmetric induction. Enantioselectivities up to 90% are obtained depending on ligand and aldehyde used. A stereochemical model for the reaction is proposed.
- Bauer, Tomasz,Gajewiak, Joanna
-
p. 9163 - 9170
(2007/10/03)
-
- Lithiated camphor-derived oxazolidinone S,N-acetals as chiral formyl anion synthons in additions to aldehydes. Asymmetric synthesis of α-hydroxy aldehydes and α-hydroxy acids
-
N-(Phenylthiomethyl)oxazolidinones derived from camphor can be lithiated and added to aldehydes in good yields and stereoselectivities. The adducts are crystalline, which simplifies isolation of the major diastereomer from the product mixture. Hydrolysis affords enantiopure α-hydroxy aldehydes, which can be oxidized to α-hydroxy acids in good yields. The steric course of the reaction is analyzed in detail and a mechanistic model is presented.
- Gawley, Robert E.,Campagna, Silvio A.,Santiago, Marcelina,Ren, Tong
-
-
- Protocols for the Preparation of Each of the Four Possible Stereoisomeric α-Alkyl-β-hydroxy Carboxylic Acids from a Single Chiral Aldol Reagent
-
Protocols have been devised whereby all four possible stereoisomeric α-alkyl-β-hydroxy carboxylic acids can be derived from a single aldol reagent, hydroxy ketone 3.Compound 3, obtained in enantiomerically homogeneous form in 50percent overall yield from tert-butylglycine (1), is used for aldol reactions in the form of its trimethylsilyl and tert-butyldimethylsilyl derivatives, 4 and 5.The Z lithium and Z boron enolates of 4 react with various aldehydes to give aldols 8 and 9, respectively.Deprotonation of 4 by bromomagnesium 2,2,6,6-tetramethylpiperidide (MTMP) gives the E enolate, which may be trapped by trimethylsilyl chloride to obtain the E silyl enol ether 11.The E bromomagnesium enolate of 4 reacts with aldehydes to give aldols of structure 15.Transmetalation of the bromomagnesium enolate of keto ether 5 is accomplished by reaction with (triisopropoxy)titanium chloride.The resulting E (triisopropoxy)titanium enolate reacts with aldehydes to provide aldols of structure 17.The aldols resulting from the foregoing reactions are hydrolyzed to keto diols 19-22, which are oxidized to the stereoisomeric α-methyl-β-hydroxy carboxylic acids 23-26.
- Draanen, Nanine A. Van,Arseniyadis, Simeon,Crimmins, Michael T.,Heathcock, Clayton H.
-
p. 2499 - 2506
(2007/10/02)
-
- Synthesis of a Chiral, Nonracemic Aziridinone (α-Lactam)
-
(S)-tert-Leucine is diazotized affording a mixture of the expected α-chloro and α-hydroxy acids (S)-15 and (S)-16 and the rearranged β-chloro and β-hydroxy acids (R)-12 and (S)-11.Separation produces a 51percent yield of pure (S)-15 (e.e. >= 97.4percent) which is converted via the acid chloride (S)-17 into the α-chloro amides (S)-18a and b (e.e. = 99.0 and 95.2percent, respectively).On treatment with tBuOK, the latter is converted into the α-lactam (R)-22b (59percent, e.e. >= 91.0percent, D20 = -293.7), which is accompanied by small amounts of its ring opening product (R)-23b.Only the α-amino ester (R)-23a is formed from the α-chloro amide (S)-18a and tBuOK.While the enantiomers of the halo amides 13, 18a, b, 24a, b and of the 3-pentyl esters of the hydroxy acid 16 are separated by GC on chiral columns, the α-lactam 22b and the α-amino esters 23a, b require conversion into separable derivatives without involving the stereogenic center.Thus, alkaline hydrolysis of 22b as well as acidic cleavage of 23 yield the α-amino acids 25 which are cyclized to the oxazolidine-2,5-diones 26 by means of bis(trichloromethyl)carbonate ("triphosgene").As shown by the high enantiomeric excess of the products derived from (S)-tert-leucine none of the reactions described results in a considerable degree of racemization.Authentic samples of 11 and 12 are synthesized from the Reformatzky product 21.The absolute configurations of the major enantiomers derived from (S)-14 are based on the retention on chiral GC columns, the signs of optical rotations, and CD spectra.The mechanism of the rearrangement leading to the β-hydroxy and β-chloro acids (S)-11 and (R)-12 is interpreted in terms of a stereospecific 1,2-methyl shift occurring simultaneously with the ring cleavage of the (protonated) α-lactone (R)-2 (R = tBu) which is the crucial intermediate formed in the diazotization of (S)-14.
- Quast, Helmut,Leybach, Holger
-
p. 849 - 859
(2007/10/02)
-
