19887-32-2Relevant academic research and scientific papers
A Straightforward and High-Yielding Synthesis of 1,2,4-Oxadiazoles from Chiral N-Protected α-Amino Acids and Amidoximes in Acetone-Water: An Eco-Friendly Approach
Sauer, André C.,Wolf, Lucas,Quoos, Natália,Rodrigues, Mariele B.,Braga, Ant?nio L.,Rodrigues, Oscar E. D.,Dornelles, Luciano
, (2019/02/05)
A straightforward and high-yielding methodology for the synthesis of a high structural diversity of 1,2,4-oxadiazoles from different chiral N-protected α-amino acids and amidoximes under microwave (MW) irradiation is described herein. This greener approac
Convenient peptide synthesis without protection of C-Terminals
Noguchi, Takuya,Tehara, Naoka,Uesugi, Yuki,Jung, Seunghee,Imai, Nobuyuki
scheme or table, p. 42 - 43 (2012/03/11)
Condensation of carboxylic acids 1 and 5 with unprotected α-amino acids 2 via activation by ethyl chloroformate and triethylamine proceeded effectively to afford the corresponding amides in 5099% yields. Tripeptide 7c was obtained in 42% yield from the dipeptide 6c in a similar manner.
Practical synthesis of fluorous oxazolidinone chiral auxiliaries from α-amino acids
Hein, Jason E.,Geary, Laina M.,Jaworski, Ashley A.,Hultin, Philip G.
, p. 9940 - 9946 (2007/10/03)
A series of new fluorous-supported oxazolidinone chiral auxiliaries has been prepared using a versatile and general five-step pathway, starting from readily available chiral α-amino acids. The key feature of this synthesis is the efficient generation of a suitably active perfluoroalkyllithium species. By use of this protocol, the auxiliaries can be obtained in high enantiomeric purity and on multigram scales from L-phenylalanine and L-valine with overall yields as high as 55%. The new methodology also incorporates fluorous solid-phase extraction on the large scale, allowing bulk quantities (up to 25 g) of fluorous compounds to be purified from the crude reaction mixture.
Stereoselective conjugate radical additions: Application of a fluorous oxazolidinone chiral auxiliary for efficient tin removal
Hein, Jason E.,Zimmerman, Jake,Sibi, Mukund P.,Hultin, Philip G.
, p. 2755 - 2758 (2007/10/03)
(Chemical Equation Presented) A series of asymmetric free-radical-mediated intermolecular conjugate additions using a fluorous oxazolidinone chiral auxiliary has been completed. The fluorous auxiliary facilitated product isolation using fluorous solid phase extractions (FSPE), effectively removing excess organic and organometallic reagents. Parallel reactions carried out with a similar but nonfluorous norephedrine-derived oxazolidinone demonstrated the superior stereoselectivity and purification obtainable with the fluorous chiral auxiliary.
'One-pot' synthesis of chiral N-protected α-amino acid-derived 1,2,4-oxadiazoles
Braga, Antonio L.,Luedtke, Diogo S.,Alberto, Eduardo E.,Dornelles, Luciano,Severo Filho, Wolmar A.,Corbellini, Valeriano A.,Rosa, Daiane M.,Schwab, Ricardo S.
, p. 1589 - 1594 (2007/10/03)
A series of α-amino acid-derived 1,2,4-oxadiazoles have been synthesized via an easy, inexpensive and one-pot protocol. The heterocycles were obtained in good yields and in relatively short reaction times.
trans-(1S,2S)-1-substituted-2-(N,N-dialkylamino)-1-indanol derivatives as chiral ligands in the catalytic enantioselective addition of diethylzinc to aldehydes
Xu, Qianyong,Yang, Hongfang,Pan, Xinfu,Chan, Albert S.C.
, p. 945 - 951 (2007/10/03)
A series of optically active trans-(1S,2S)-1-substituted-2-(N,N-dialkylamino)-1-indanol derivatives 1-6 were synthesized and applied in the catalytic enantioselective addition of diethylzinc to aldehydes. The enantiomeric purity of the addition products i
Stereoselective intramolecular copper(I)--catalyzed [2 + 2]-photocycloadditions. Enantioselective synthesis of (+)- and (-)-grandisol
Langer,Mattay
, p. 7256 - 7266 (2007/10/03)
This work deals with copper(I)-catalyzed intramolecular [2 + 2]-photocycloadditions of 1,6-diene derivatives. The bridgehead carbons C-1 and C-5 of the resulting bicyclo[3.2.0]heptanes are generated stereoselectively by using chiral starting material, chiral catalysts, or chiral auxiliaries. The irradiation of (S)-3 leads to enantiomerically pure 4 and 5 which opens a new synthetic route to enantiomerically pure (+)- and (-)-grandisol 9. The use of chiral copper complexes as catalysts delivers enantiomeric excesses below 5%. The reason for these small excesses is a low reactivity of the chiral copper complexes, as confirmed by CD-spectroscopic measurements. Malic acid or amino carboxylic acid derivatives as chiral auxiliaries yield the bicyclic alcohols 4 and 5 with enantiomeric excesses up to 15%. The employment of a chiral diol as an auxiliary delivers a chiral ketal 36, and the resulting ketone 7 exhibits enantiomeric excesses up to 60%.
Enantioselective cleavage of esters by histidine-containing tripeptides in micellar solutions of various hexadecyltrialkylammonium bromide surfactants
Cleij, Marco C.,Drenth, Wiendelt,Nolte, Roeland J. M.
, p. 1 - 6 (2007/10/02)
Cleavage of chiral p-nitrophenyl esters derived from the amino acid phenylalanine by histidine-containing tripeptides has been studied in micellar solutions of four quaternary ammonium surfactants.Enzyme-like enantioselectivities up to kL/kD = 131 (at 0 deg C) are observed.The enantioselectivity can be rationalized by assuming a hydrophobically driven stabilizing hydrogen bond between the L enantiomer of the ester and the tripeptide in the transition state of the reaction.This hydrogen bond is absent in the reaction with the D enantiomer of the ester.The transition state has an amphipolar character and is stabilized by the micellar environment.The hydrophilic-hydrophobic balance of the reactants, which affects the transition state, was optimized by varying the composition of the tripeptide and the length of the N-protecting groups in the tripeptide and the substrate.The activities and enantioselectivities depend on the structure of the quaternary ammonium surfactant headgroup.Increasing the size of this headgroup leads to an increase in rate of hydrolysis of the L ester and hence to an increase in enantioselectivity.This effect is attributed to a change in the degree of ion-pair formation with a carboxylate group that is present in the peptides.Compared to previous studies the results indicate that a chiral surfactant is not required for obtaining high enantioselectivities.
Mechanism of enantioselective ester cleavage by histidine-containing peptides at a micellar interface. 2. Effect of changing peptide chain length
Cleij, Marco C.,Drenth, Wiendelt,Nolte, Roeland J. M.
, p. 459 - 468 (2007/10/02)
Chiral p-nitrophenyl esters derived from the amino acid phenylalanine are cleaved by various histidine-containing tripeptides and higher oligopeptides as catalysts at a micellar interface.It is assumed that the oligopeptides adopt an internally hydrogen-b
Mechanism of Enantioselective Ester Cleavage by Histidine-Containing Dipeptides at a Micellar Interface
Cleij, Marco C.,Drenth, Wiendelt,Nolte, Roeland J. M.
, p. 3883 - 3891 (2007/10/02)
Chiral p-nitrophenyl esters derived from the amino acid phenylalanine are cleaved by histidine-containing dipeptides at a micellar interface.High enantioselectivities (up to kL/kD = 30.4 at 0 deg C) are observed.Both the substrates and the catalysts contain an alternating sequence of hydrophobic and hydrophilic groups.Due to the need for hydration of the hydrophilic groups, the hydrophobic groups cannot dissolve completely into the micellar hydrocarbon phase.The kinetic data suggest that the micellar interface is capable of discriminating between transition states that have different hydrophilic and hydrophobic properties.One of the diastereomeric transition states is characterized by a hydrogen bond between the amide CO group of the ester and an NH group of the histidine-containing dipeptide.Upon formation of this hydrogen bond these polar CO and NH groups lose their hydrophilicity which allows the transfer of the adjacent apolar groups to the micellar hydrocarbon phase.The other diastereomeric transition state cannot form this hydrogen bond and the hydrophobic groups remain hydrated.Consequently, the latter transition state is of higher energy.The kinetic data reveal that it is important to prevent steric hinderance between the reactants in order to allow the unhindered formation of the hydrogen bond.
