The Range of Substrates

Maximal speed (Vmax) and supposed Michaelis constant (K ) of pectin hydrolysis reaction (catalyzed by the studied pectinesterase) were determined in Zinewedwer — Berk coordinated, They were determined in the range of substrate concentration values that was below optimum one V = 14.7 10 M min K = 5.56 10 M. The value of dissociated constant (KJ of the triple enzyme—substrate complex was determined from the experimental data at high substrate concentration. It was the following Kj= 0.22 M. Bunting and Murphy method was used for determination. 

Azotobacters. Burk and Winogradsky in the 1930s showed that these could readily be obtained from soil samples by elective enrichment with benzoate. The degradative pathway for benzoate has been elucidated (Hardisson et al. 1969), and the range of substrates extended to 2,4,6-trichlorophenol (Li et al. 1992 Latus et al. 1995). The enzyme from Azotobacter sp. strain GPl that catalyzes the formation of 2,6-dichlorohydroquinone from... 

Nickel catalysts promote the hydroalumination of alkenes using trialkylalanes R3AI and dialkylalanes such as BU2AIH as the aluminum hydride sources [9, 29, 30, 33]. However, exhaustive studies of the range of substrates capable of hydroalumination with these reagents has not been carried out. Linear terminal alkenes like 1-octene react quantitatively with BU3AI at 0°C within 1-2 h in the presence of catalytic amounts of Ni(COD)2 [30]. Internal double bonds are inert under these conditions, whereas with 1,5-hexadiene cycHzation occurs. 

Attempts to expand the range of substrates to include cyclopropenes20 and norbornene-derived meso-bicyclic hydrazines25 have recently been reported. A further noteworthy contribution has been the development of a recyclable hydroboration process by the group of Fernandez26-28 These and other approaches toward... 

Inverting the electronic sense of the small ring conjunctive reagent expands the range of substrates that would be suitable reaction partners. The aldehydes 37a 88> and 38 89) are available by the formylation of the corresponding lithium salt with DMF. 

The AD has been developed into an extremely useful reaction, and Sharpless states that probably its synthetic utility surpasses that of titanium tartrate-catalysed asymmetric epoxidation [16], since the range of substrates is much larger for AD. 

Next, in chronological order, Acheson and his group, in his series Addition reactions of heterocyclic compounds (cf. 63AHC(1)125), extended the range of substrates to pyridine derivatives and initially believed to have found numerous pyridoazepines. The contents of six experimental articles (1968-1975), however, were for the most part revised... 

The aminoxyl radicals lend themselves to synthetically interesting procedures of oxidation, both in the radical form itself and in the oxoammonium form (from TEMPO). Major advantages appear to be the mild operating conditions, the range of substrates susceptible to transformation and the selectivity in the oxidation of specific structural motifs. 

Esterases have a catalytic function and mechanism similar to those of lipases, but some structural aspects and the range of substrates differ 7-11). Most important, they lack the so-called lid prominent in almost all lipases. Nevertheless, one can expect that the lessons learned from the directed evolution of lipases also apply to esterases. So far, few efforts have been investigated in the directed evolution of enantioselective esterases, although earlier work by Arnold 17,32,139) had shown that the activity of esterases as catalysts in the hydrolysis of achiral esters can be enhanced. The first example involving the improvement of enantioselectivity concerned the hydrolytic kinetic resolution of the sterically hindered ester rac-19 catalyzed by the esterase from P. fluorescens (PFE) 140). 

Since the range of substrates of aldolases are rather limited they are primarily useful for synthesis of carbohydrate like compounds. Their utility carmot be compared to the wide range of aldol reactions known in organic chemical synthesis. Thus it may be concluded that aldolases may be used for synthesis of... 

Enzymes that make NPs necessarily act on complex molecules. Such chemicals can be very hard for chemists to synthesise hence, the range of substrates available to the biochemist to assess substrate specificity was often limited. 

The reaction failed without addition of the salts. The range of substrate reactivity formed was ... 

The nitrosyl complex [Rh(NO)(PPh3)3] (36) catalyzes the hydrogenation of both 1-hexene and cyclohexene in dichloromethane as solvent and was also found to add deuterium to cyclohexene without H/D scrambling.138 A further study extended the range of substrates hydrogenated to internal alkenes, to conjugated and non-conjugated dienes, activated alkenes and terminal and internal alkynes.139... 

The generalizations in the following discussion are based on reports of reactions carried out under ideal conditions, i.e. liquid ammonia or DMSO as solvent, photostimulation rather than dark reactions, most appropriate nucleofuge, etc. The range of nucleophiles which can be used are itemized in Section 2.2.3, which also contains several extensive tables in which the range of substrates can be clearly seen. It must be noted, however, that reactions which proceed in high yield with one nucleophile may fail or proceed inefficiently with another if the nucleophile is incompatible with substituents on the aromatic substrate. 

Hashimoto has shown that the the valine-derived catalyst Rh2(S-BPTV)4 (5) is effective in intermolecular tandem cyclization/intermolecular cycloaddition resulting in the formation of 46 in 92% ee (Eq. (26) [10]. More recent studies have broadened the range of substrates that can be used in the reaction although the enantioselectivity is variable [38,39],... 

The synthetically versatile benzotriazole moiety offers an effective and convenient leaving group that extends the range of substrates that participate in a type cd ring-closure. Racemic 3-amino-2,3-dihydrobenzo-l,4-diazepin-2-ones 88 were obtained in 59-77% yield when a-amidobenzotriazoles 87 were exposed to a saturated solution of NH3 in MeOH (Scheme 42) <1995JOC730, 2001M747, 2003JOC2844>. 

In addition, acyclic aliphatic N-allyl imines and cycloalkylimines were acceptable starting materials for the asymmetric hydrocyanation and enantioselectivity of up to 95% ee was obtained by use of 10a as catalyst [10]. Representative examples of the range of substrates are summarized in Scheme 5.6. It should be added that as an alternative to the N-allyl imines the analogous N-benzyl imines can be efficiently used as starting material [10]. An optimized procedure for preparation of the catalyst 10a has recently been reported by the Jacobsen group [11]. 

The substrate range scope and limitations Promising prospects for synthetic applications of the proline-catalyzed aldol reaction in the future were opened up by experimental studies of the range of substrates by the List [69, 70a, 73] and Barbas [71] groups. The reaction proceeds well when aromatic aldehydes are used as starting materials - enantioselectivity is 60 to 77% ee and yields are up to 94% (Scheme 6.19) [69, 70], The direct L-proline-catalyzed aldol reaction proceeds very efficiently when isobutyraldehyde is used as substrate - the product, (R)-38d, has been obtained in very good yield (97%) and with high enantioselectivity (96% ee). 

The range of substrates tolerated by this catalytic system is broad and includes other aromatic and aliphatic aldehydes (Scheme 6.97) [218, 219]. For all aromatic or a,/ -unsaturated aldehydes enantioselectivity is high (89-94% ee) and diastereoselectivity is excellent (d.r. (trans/cis) > 98 2). Yields were in the range 55-73% [219]. For aliphatic aldehydes yields were significantly lower, 32-35% (Scheme 6.97) [218, 219]. Diastereoselectivity also was somewhat lower and enantioselectivity varied from 68 to 90% ee [218, 219]. 

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