2018-61-3Relevant articles and documents
ENANTIOSELECTIVE CATALYSIS WITH TRANSITION METAL COMPLEXES
Brunner, Henri
, p. 39 - 56 (1986)
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A facile microwave-mediated drying process of thermally unstable / labile products
Pinchukova,Voloshko,Shyshkin,Chebanov,Van De Kruijs,Arts,Dressen,Meuldijk,Vekemans,Hulshof
, p. 1130 - 1139 (2010)
The drying behavior of (S)-N-acetylindoline-2-carboxylic acid, precipitated (1a, 17 wt %) and nonprecipitated (1b, 5 wt %), and N-acetyl-(S)-phenylalanine ((S)-2-acetamido-3-phenylpropanoic acid, 2), both pharmaceutical intermediates, and of cocarboxylase hydrochloride (thiamine pyrophosphate, 3), a coenzyme, a bioactive form of vitamin B1, being a thermolabile substance, has been determined in straightforward drying setups. The method of supplying energy to the system had a profound influence on the drying rate and on the internal temperature of the samples during drying. The drying time of (S)-N-acetylindoline-2-carboxylic acid (1b) with the low moisture content (5 wt %) could be reduced by a factor 4 using microwave irradiation instead of conventional heating, while keeping the sample temperature under 35 °C. N-Acetyl-(S)-phenylalanine (2) with a higher moisture content (22 wt %) demonstrated a decrease in drying time by a factor 2.5 to 4 depending on the applied microwave powers. A reduction in drying time of the precipitated (S)-N-acetylindoline-2-carboxylic acid (1a, 17 wt % moisture) by a factor 2 was demonstrated for drying at 150 W of microwave irradiation instead of using a water bath at 70 °C. A dramatically shorter drying time by a factor 10 was found for cocarboxylase hydrochloride (3, 15 wt % water) on lab-scale which could be reproduced on pilot-plant scale. To achieve with conventional heating similar drying times as under microwave irradiation for the four examples, extremely high energy inputs should be applied, necessitating extremely high temperature differences between the heating source and the sample. The results reveal that microwave irradiation is less energy-consuming and is particularly useful for effective drying of thermally unstable materials in short periods of time.
Chymotrypsin-catalyzed peptide synthesis in deep eutectic solvents
Maugeri, Zaira,Leitner, Walter,Dominguez De Maria, Pablo
, p. 4223 - 4228 (2013)
Deep eutectic solvents (DESs) are formed by mixing quaternary ammonium salts (e.g., choline chloride) and hydrogen-bond donors (e.g., glycerol or urea), which leads to biodegradable and readily available ionic solvents at room temperature. Analogous to other ionic liquids, DESs represent a promising reaction media if hydrophobic and hydrophilic substrates need to be combined. This paper assesses DESs as reaction media for chymotrypsin-catalyzed peptide synthesis. After careful determination of the reaction conditions (e.g., water content, enzyme loading), α-chymotrypsin displayed high activity for peptide synthesis in choline chloride/glycerol mixtures to afford productivities of ca. 20 g L-1 h-1 and with complete selectivity for the peptide, which is in contrast to the detrimental hydrolysis pathway observed in aqueous media. The nonimmobilized suspended enzyme could be reused several times by simple filtration with excellent to moderate activities. Overall, the results reported suggest that choline chloride based DESs may become promising neoteric solvents for peptide synthesis through biocatalysis. Copyright
Asymmetric transfer hydrogenation of prochiral carboxylic acids catalyzed by a five-coordinate Ru(II)-binap complex
Saburi,Ohnuki,Ogasawara,Takahashi,Uchida
, p. 5783 - 5786 (1992)
Asymmetric transfer hydrogenation of representative prochiral carboxylic acids was performed, using [RuH((S)-binap2]PF6 or a related complex as a catalyst and 2-propanol or ethanol as a hydrogen source, to achieve good to excellent enantioselectivities.
Novel chiral dendritic diphosphine ligands for Rh(I)-catalyzed asymmetric hydrogenation: Remarkable structural effects on catalytic properties
Yi, Bing,Fan, Qing-Hua,Deng, Guo-Jun,Li, Yue-Ming,Qiu, Li-Qin,Chan, Albert S. C.
, p. 1361 - 1364 (2004)
A series of dendritic ligands with a chiral diphosphine located at the focal point have been synthesized through coupling of pyrphos 2 with Frechet-type polyether dendron 3. The relationship between the primary structure of the dendrimer and its catalytic properties was established in the Rh-catalyzed asymmetric hydrogenation of α-acetamido cinnamic acid 4. A remarkable structural effect on catalytic activity was observed.
The effect of enzymatic reaction on dissolution rate: Theoretical analysis and experimental test
Johnson,Amidon
, p. 195 - 203 (1986)
The dissolution behavior of N-acetylphenylalanine ethyl ester (1) and N-benzoyltyrosine ethyl ester (2) from a rotating disk into aqueous solutions containing the enzyme α-chymotrypsin was investigated. The effect of the bulk enzymatic reaction on the dissolution rates is modeled using the continuity equation where the reaction term is considered a constant throughout the reaction zone. Dimensional analysis on the continuity equation defines the important parameter R* = K(cat)E0h2/(C(s)D) which is the ratio of the diffusion time to the reaction time. This parameter correctly predicted the fact that the enzymatic reaction had only a slight impact on the dissolution of the highly soluble 1 while the effect on the less soluble 2 was large. Also predicted by R* is the dissolution dependence on the catalytic rate constant. The variation of this rate constant with pH is consistent with the dependence on pH found for the dissolution rate of 2. It is further demonstrated that the decrease in dissolution rate with solubility can be significantly reduced when the dissolving compound is an enzyme substrate. For the two compounds used in this study the dissolution rate decreased with the square root of solubility, as predicted by the theoretical analysis in the presence of enzyme. Other experiments included the variation of the enzyme concentration and the rotational speed on the spinning disk. All experiments were designed to show how R* could correctly predict the relative importance of the convective, diffusive, and reactive processes.
From 2H-phospholes to BIPNOR, a new efficient biphosphine for asymmetric catalysis
Mathey, Francois,Mercier, Francois,Robin, Frederic,Ricard, Louis
, p. 117 - 120 (1998)
For many years now, we have studied the 1H-/2H-phosphole equilibrium and its synthetic applications. On reaction with alkynes, 2H-phospholes yield the corresponding 1-phosphanorbornadienes. As ligands of rhodium(I), these phosphines show some potential in catalytic hydrogenation and hydroformylation of alkenes. Starting from 3,3′,4,4′-tetramethyl-1,1′-biphospholyl and tolan, we have similarly obtained the corresponding 2,2′-bis-(1-phosphanorbornadienyl) (BIPNOR) with two chiral, non-racemisable, phosphorus atoms at the bridgeheads. The pure enantiomers of BIPNOR appear to be efficient ligands in asymmetric hydrogenation of C=C and C=O double bonds.
A versatile synthesis of phosphine-aminophosphine ligands for asymmetric catalysis
Boaz, Neil W.,Ponasik Jr., James A.,Large, Shannon E.
, p. 2063 - 2066 (2005)
A new and versatile synthesis of phosphine-aminophosphine ligands allows the incorporation of a wide range of nitrogen and phosphorus substituents into these ligands, several of which exhibit improved properties for rhodium-catalyzed asymmetric hydrogenation reactions. This synthesis also allows the preparation of mixed phosphine-phosphoramidite species.
Structure-activity relationship studies of dipeptide-based hepsin inhibitors with Arg bioisosteres
Kwon, Hongmok,Ha, Hyunsoo,Jeon, Hayoung,Jang, Jaebong,Son, Sang-Hyun,Lee, Kiho,Park, Song-Kyu,Byun, Youngjoo
supporting information, (2020/12/25)
Hepsin is a type II transmembrane serine protease (TTSP) associated with cell proliferation and overexpressed in several types of cancer including prostate cancer (PCa). Because of its significant role in cancer progression and metastasis, hepsin is an attractive protein as a potential therapeutic and diagnostic biomarker for PCa. Based on the reported Leu-Arg dipeptide-based hepsin inhibitors, we performed structural modification and determined in vitro hepsin- and matriptase-inhibitory activities. Comprehensive structure-activity relationship studies identified that the p-guanidinophenylalanine-based dipeptide analog 22a exhibited a strong hepsin-inhibitory activity (Ki = 50.5 nM) and 22-fold hepsin selectivity over matriptase. Compound 22a could be a prototype molecule for structural optimization of dipeptide-based hepsin inhibitors.
P-chirogenic diphosphazanes with axially chiral substituents and their use in rh-catalyzed asymmetric hydrogenation
Moritz, Jan-Ole,Chakrabortty, Soumyadeep,Bernd H. Mu.ller,Spannenberg, Anke,Kamer, Paul C. J.
, p. 14537 - 14544 (2020/12/29)
A convenient synthesis of enantiopure P-chirogenic diphosphazanes incorporating bulky bisphenol and 1,1′-bi-2-naphtholderived substituents via the functionalization of a readily accessible enantiopure lithium phosphinoamide with chlorophosphoridites was developed. Since the product requires no subsequent deprotection, the protocol provides an easy, convenient synthesis of P-chirogenic ligands on the gram scale. The ligands were applied in the Rh-catalyzed asymmetric hydrogenation of benchmark substrates furnishing enantiomeric excess values up to 96%.
The effect of imidazolium salts with amino acids as counterions on the reactivity of 4-nitrophenyl acetate: A kinetic study
Figueroa, Roberto,Orth, Elisa,Pavez, Paulina,Rojas, Mabel,Santos, José G.
, (2020/04/29)
As a first approach to improve the “green character” of the surfactants based on imidazolium cations, three surfactants using 1-tetradecyl-3-methylimidazolium [C14mim]+ as cation and different amino acids (AA) as counterion, were syn