R selection

Byatt. J.R., Selection of Primary Starters for Cage Motors and Secondary Starters for Slip-ring Motors, AOIP Electrical, UK. Kajiji, Y.H., Liquid Resistance Starting, AOYP Engineering Co. (P) Ltd, Mumbai, India. 

Moody, G. J., Thomas, J. D. R. Selective Ion Sensitive Electrodes, Watford, Merrow 1971... 

A few a/j/r -selective amide and imide enolates which arc able to provide high induced diastereo-selectivity have been uncovered very recently. The /V-propionylsultam 1 w hich opens a way to sryn-aldols as described in Section D.1.4.3.2.3.1. also allows the synthesis of r/nh-adducls. For this purpose. 1 is converted into the silyl-iV.O-ketene acetal 2 and subsequently added to aldehydes in a Mukaiyama-type aldol reaction106 to give awi-adducts 310<>f. 

However, deprotonation of rc-rf-butyldimethylsilyl-protected products 2 (prepared according to the classical Henry conditions )22, and consecutive reprotonation, provides the silylated nitroaldols 2 with high (R, R ) selectivity. Deprotonation of 2 by treatment with lithium diisopropylamide in tetrahydrofuran at — 78 C furnishes nitronates which are stable against / -elimination at that temperature. Protonation of these intermediates is achieved with an acetic acid/tetrahydrofuran (1 1) solution at —100 C. To achieve maximum yields, the mixture should be warmed up slowly before aqueous workup. 

To achieve reproducible (R. . ) selectivities in these nitroaldol reactions pure, distilled /m-butyldimcthylsilylnitronates and anhydrous tetrabutylammonium fluoride should be used22. The corresponding trimethylsilylnitronates furnish mixtures of (R, S )- and (R, R )-isomers22. 

Schrey, F., Gallagher, P., and Levy, R., Selective Silicide or Boride Film Formation by Reaction of Vapor Phase TiC with Silicon or Boron, J. Electrochem. Soc., 1137(5) 1647-1649 (May 1990)... 

Efforts were also made to invert the sense of enantioselectivity in the hydrolytic kinetic resolution of ester (1) using PAL with preferential formation of (R)-2 [40,411-Using epPCR and DNA shuffling, an (R)-selective mutant showing an E value of 30 was evolved by screening about 45 000 clones for the (R) enantiomer. The best mutant is characterized by 11 mutations, which are different from those of the best (S)-selective variant X [41]. 

Upon screening genomic libraries obtained from environmental samples, more than 200 new nitrilases that allow mild and selective hydrolysis of nitriles were discovered [56]. One of them catalyzes the (R)-selective hydrolysis of (16) with a value... 

The phosphotriesterase from Pseudomonas diminuta was shown to catalyze the enantioselective hydrolysis of several racemic phosphates (21), the Sp isomer reacting faster than the Rp compound [65,66]. Further improvements using directed evolution were achieved by first carrying out a restricted alanine-scan [67] (i.e. at predetermined amino acid positions alanine was introduced). Whenever an effect on activity/ enantioselectivity was observed, the position was defined as a hot spot. Subsequently, randomization at several hot spots was performed, which led to the identification of several highly (S)- or (R)-selective mutants [66]. A similar procedure was applied to the generation of mutant phosphotriesterases as catalysts in the kinetic resolution of racemic phosphonates [68]. 

In the directed evolution study, epPCR at various mutation rates was applied (10 000 clones). Some of the hits were (R) selective, and others were (S) selective. Eight of them were sequenced [89]. Of particular interest is mutant 1-K2-F5, characterized by a single mutation F432S, because it leads to reversal of enantioselectivity (79% ee in favor of (S)-37). 

The original library of 10 000 clones used in the Baeyer-Villiger reaction [89] was screened for performance as potential catalysts in the sulfoxidation [32]. This led to the discovery of at least 20 mutants having enantiomeric excess values in the range of 85-99%, some being (R) selective and others being (S) selective. Five mutants resulting in enantiomeric excess values of >95% were sequenced (Table 2.2) [32]. 

Carnell et al. discovered that whole cells of Cunninghamella echinulata NRRL1384 were able to deracemize racemic N-(l-hydroxy-l-phenylethyl)benzamide (24) to produce the (R) enantiomer (Figure 5.17) [30]. The deracemization involves fast, highly (S)-selective oxidation, followed by slower, partially (R)-selective reduction of the ketone (25). Optimization by removing competing extracellular amidase/prote-ase activity resulted in 82% yield and 92% ee. 

DKR requires two catalysts one for resolution and one for racemization. We and others have developed a novel strategy using enzyme as the resolution catalyst and metal as the racemization catalyst as shown in Scheme 1. The R-selecfive DKR can be achieved by combining a R-selective enzyme with a proper metal catalyst and its counterpart by the combination of the metal catalyst with a -selective enzyme. This strategy has been demonstrated to be applicable to the DKR of secondary alcohols, allylic esters, and primary amines. Among them, the DKR of secondary alcohols has been the most successful. 

The purification of a product p from an impurity i by an ultrafiltration process is shown in Fig. 20-59 and Eq. (20-72), where Cjo and C o are the initial concentrations (g/L) of the two components, Y is the yield of product in the retentate, and r / = selectivity = S,/Sp, the ratio of passages. High yields are obtained in purifying out small solutes (high selectivity) but are compromised in removing larger impurities with similar passages to the product. 

Wood SJ, MacKenzie L, Maleeff B, Hurle MR, Wetzel R. Selective inhibition of Abeta fibril formation. J Biol Chem 1996 271 4086-4092. 

Cunnar, Eugene R. "Select alchemy and literature bibliography 1989-90." Cauda Pavonis, Spring 1992, 17-18. 

Karassik, I.J. Pump Performance Characteristics, Hydrocarbon Processing, June 1972, p. 101. Doyle, H.E. Highlights of API 610 Pump Standard, Hydrocarbon Processing, June 1972, p. 85. Polcak, R. Selecting Fans and Blowers, Chemical Engineering, Jan. 22, 1973, p. 86. 

Finley, P.R., Selective serotonin re-uptake inhibitors pharmacologic profiles and potential therapeutic distinctions, Ann. Pharmacother., 28(12), 1359-1369, 1994. 

Ni Q., Xu H., Partilla J., Costa B.D., Rice K., Rothman R. Selective labeling of K2 opioid receptors in rat brain by [125I]IOXY interactions of opioid peptides and other drugs with multiple K2a binding sites. Peptides. 14 1279, 1993. 

Andexer, J., von Langermann, J., Mell, A. et al. (2007) An R-selective hydroxynitrile lyase from Arabidopsis thaliana with an alpha/beta-hydrolase fold. Angewandte Chemie-International Edition, 46, 8679-8681. 

An (R)-selective counterpart was constructed in the same manner by using Escherichia coli DSM14 459 as host organism, but in this case two separate plasmids were used, which contain... 

Puvvada, G. V. K. Murthy, D. S. R. Selective precious metals leaching from a chalcopyrite concentrate using chloride/hypochlorite media. Hydrometallurgy 2000, 58, 185-191. 

Gatscha R. Selection of techniques. In A Guide to Cytopreparation, ed. KA Allen, pp. 43-57. Raleigh, NC American Society for Cytotechnology (ASCT), 1995. 

Rate Constants of Reactions R10 + RH R1OH + R (Selected Experimental Data)... 

Che and co-workers developed a catalytic r-selective aziridination of aromatic /V-arylirnincs with ethyl diazoacetate catalyzed by a ruthenium(ll) porphyrin complex (Scheme 75).364 The corresponding pyrrolidines were isolated as minor byproducts. 

Germolec, D.R., Selectivity and predictivity in immunotoxicity testing Immune endpoints and disease resistance, Toxicol. Letters, 149, 109, 2004. 

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