- Design, synthesis, and evaluation of cystargolide-based β-lactones as potent proteasome inhibitors
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The peptidic β-lactone proteasome inhibitors (PIs) cystargolides A and B were used to conduct structure-activity relationship (SAR) studies in order to assess their anticancer potential. A total of 24 different analogs were designed, synthesized and evaluated for proteasome inhibition, for cytotoxicity towards several cancer cell lines, and for their ability to enter intact cells. X-ray crystallographic analysis and subunit selectivity was used to determine the specific subunit binding associated with the structural modification of the β-lactone (P1), peptidic core, (Px and Py), and end-cap (Pz) of our scaffold. The cystargolide derivative 5k, structurally unique at both Py and P1, exhibited the most promising inhibitory activity for the β5 subunit of human proteasomes (IC50 = 3.1 nM) and significant cytotoxicity towards MCF-7 (IC50 = 416 nM), MDA-MB-231 (IC50 = 74 nM) and RPMI 8226 (IC50 = 41 nM) cancer cell lines. Cellular infiltration assays revealed that minor structural modifications have significant effects on the ability of our PIs to inhibit intracellular proteasomes, and we identified 5k as a promising candidate for continued therapeutic studies. Our novel drug lead 5k is a more potent proteasome inhibitor than carfilzomib with mid-to-low nanomolar IC50 measurements and it is cytotoxic against multiple cancer cell lines at levels approaching those of carfilzomib.
- Niroula, Doleshwar,Hallada, Liam P.,Le Chapelain, Camille,Ganegamage, Susantha K.,Dotson, Devon,Rogelj, Snezna,Groll, Michael,Tello-Aburto, Rodolfo
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supporting information
p. 962 - 977
(2018/09/04)
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- One-step preparation of enantiopure l- or d-amino acid benzyl esters avoiding the use of banned solvents
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The enantiomers of amino acid benzyl esters are very important synthetic intermediates. Many of them are currently prepared by treatment with benzyl alcohol and p-toluenesulfonic acid in refluxing benzene or carbon tetrachloride, to azeotropically remove water, and then precipitated as tosylate salt by adding diethyl ether. Here, we report a very efficient preparation of eight l- or d-amino acid benzyl esters (Ala, Phe, Tyr, Phg, Val, Leu, Lys, Ser), in which these highly hazardous solvents are dismissed using cyclohexane as a water azeotroping solvent and ethyl acetate to precipitate the tosylate salt. With some work-up modifications and lower yield, the procedure can be applied also to methionine. Chiral HPLC analysis shows that all the benzyl esters, including the highly racemizable ones such as those of phenylglycine, tyrosine and methionine, are formed enantiomerically pure under these new reaction conditions thus validating the solvents replacement. Contrariwise, toluene cannot be used in place of benzene or carbon tetrachloride because leading to partially or totally racemized amino acid benzyl esters depending on the polar effect of the amino acid α-side chain as expressed by Taft’s substituent constant (σ*).
- Bolchi, Cristiano,Bavo, Francesco,Pallavicini, Marco
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p. 965 - 974
(2017/04/11)
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- Enantiomeric resolution of p-toluenesulfonate of valine benzyl ester by preferential crystallizaion
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Preferential crystallization of amino acid derivatives by seeding a pure enantiomer into racemic amino acid solutions has been studied for many years. However, few examples of valine derivatives have been reported so far. Although there have been some reports using valine hydrogen chloride with preferential crystallization, it is difficult to obtain optical isomers for valine derivatives using preferential crystallization. In this study, repeated preferential crystallization of p-toluenesulfonate valine benzyl ester with a 20% e.e. in 2-propanol gave a 94% e.e. on sonication. Sonication accelerated crystallization rate, but there was not a big difference in e.e. between with and without sonication. However, this research demonstrates the first preferential crystallization of p-toluenesulfonate of valine benzyl esters with an acceleration of crystallization using sonication.
- Munegumi, Toratane,Wakatsuki, Aiko,Takahashi, Yutaro
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experimental part
p. 188 - 192
(2012/03/27)
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- Esterification of unprotected a-Amino acids in ionic liquids as the reaction media
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Ionic liquid 1,3-dimethylimidazolium methanesulfonate was used to prepare a-amino acids benzylic esters from unprotected amino acids and benzyl chloride. Esterification of several amino acids was achieved with satisfactory yields: by-products can be removed by a simple work-up procedure to afford the pure product. The described method is simple, mild, rapid and save.
- Biondini, Daniele,Brinchi, Lucia,Germani, Raimondo,Goracci, Laura,Savelli, Gianfranco
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experimental part
p. 39 - 44
(2010/08/22)
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- A mild Boc deprotection and the importance of a free carboxylate
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We report a facile and rapid removal of Boc protecting groups using microwave heating in H2O, with deprotection only requiring a free carboxylic acid group in the starting material. Unlike previous approaches, no additional reagents are required.
- Thaqi, Ali,McCluskey, Adam,Scott, Janet L.
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supporting information; experimental part
p. 6962 - 6964
(2009/04/07)
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- Method for producing amides or esters
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The invention relates to a method for producing amides or esters from carboxylic acids and from an amine constituent or alcohol constituent in the presence of a 1,3,5-triazine and optionally in the presence of an organic solvent and of a tertiary amine. According to the invention, a (bi)cyclic diamine or an adduct formed therefrom with the triazine constituent is used as a tertiary amine in a preferred stoichiometric ratio of diamine to the triazine constituent ranging from 0.30 to 1.10; the stoichiometric ratio of carboxylic acid to the amine constituent or alcohol constituent should range from 0.2 to 5.0, and; the molar ratio of carboxylic acid to the triazine constituent ranges from 0.5 to 1.5. Amino acids such as N-protected amino acids and peptides serve as carboxylic acid constituents and (C-protected) amino acids or a C-protected peptide serve as the amine constituent. 2-chlorine-4,6-dimethoxy-1,3,5-triazine (CDMT) is used as the preferred 1,3,5-triazine, and the N,N′-dimethyl-1,4-piperazine is used as the cyclic diamine. In addition to this method, which can be carried out at temperatures ranging from ?80 to +150 ° C. and in the presence of an organic solvent, the invention also relates to adducts comprised of (bi)cyclic diamine and 1,3,5-triazine. Compared to the prior art, higher yields with shorter reaction times are achieved using the described method, and distinctly smaller waste quantities of tertiary amine bases accrue.
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- Stereocontrolled synthesis of β-lactams via staudinger reaction between phenoxyketenes and chiral imines
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Chiral Schiff bases derived from esters of valine and alanine have been shown to be useful intermediates for the stereoselective synthesis of β-lactams. Staudinger reaction between these compounds and phenoxyketenes, generated in situ, from the corresponding acid chlorides in the presence of triethylamine, provides a mixture of diastereomeric cis-β-lactams. Attempts have been made to separate them using column chromatography and their ratios determined through 1H NMR data.
- Kanwar, Seema,Saluja, Aarti,Khurana,Sharma
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p. 137 - 141
(2007/10/03)
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- PROCESS FOR PRODUCING L-VALINE BENZYL ESTER P-TOLUENESULFONATE
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A process for preparing L-valine benzyl ester p-toluenesulfonate comprising reacting L-valine with benzyl alcohol in the presence of p-toluenesulfonic acid in at least one aromatic solvent selected from the group consisting of toluene, monochlorobenzene and xylene under azeotropic dehydration conditions; and crystallizing L-valine benzyl ester p-toluenesulfonate from the resulting reaction solution. According to the process of the present invention, there can be safely, conveniently and industrially advantageously prepared L-valine benzyl ester p-toluenesulfonate which can be suitably used as an intermediate for pharmaceuticals such as antihypertensives.
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- Oxygen alkylation of Schiff base derivatives of amino acids
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Higher imine esters 1a-h and 7a-b of amino acids and dipeptides are prepared in 68-91% yield by saponification of the benzophenone Schiff base methyl esters 3a-d and 6 using phase-transfer techniques followed by O-alkylation with an alkyl halide. The procedure occurs with retention of configuration at the α-carbon except with phenylglycine derivatives.
- O'Donnell,Cook,Rusterholz
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p. 989 - 993
(2007/10/02)
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