Acceptor substrate

Iminocarbene complexes of chromium and tungsten are useful isolable synthetic equivalents to nitrile ylides having the advantage that the range of 1,3-dipo-larophiles is not limited to electron-acceptor substrates and can be extended to electronically neutral as well as to electron-rich systems [56] (Scheme 18). 

Unlike the late metal chemistry reviewed above, these reactions did not require Michael acceptor substrates, but the reactions were rather slow (turnover frequencies range from 2 to 13 h at 22°C). For phosphino-alkenes (Scheme 5-15, Eqs. 1-3), a competing uncatalyzed reaction gave six-membered phosphorinane rings (Scheme 5-15, Eq. 6) this could be minimized by avoiding light and increased temperature. For phosphino-alkynes (Scheme 5-15, Eqs. 4 and 5), the products were unstable and could not be isolated [14]. 

Figure 6.9 Broad acceptor substrate tolerance of sialic acid aldolase in synthesis of nonnatural disaccharides...

Fig. 3. Product spectra of the wild-type (WT) GTFR and mutant S628D enzymes (200 U/L) incubated (7 days at 30 °C) with sucrose (146 mM) and different acceptor substrates (292 mM, Glc glucose Fru fructose). Yields are given in percentage (mol/mol Glc). Yields of higher oligosaccharides (DP >5) and...

Fig. 5. Acceptor-substrate-directed synthesis by GTFR and GTFA enzymes.73...

A general method to investigate the presence of solute/solute interactions is based on the spectroscopic differences of the mixtures (i.e. of amines and of potential acceptors) from the solutions of the separate substances. When appropriate solutions of amines are mixed with solutions of electron acceptor substrates, an instantaneous colour development may be observed even if no reaction products are formed. 

Complexation of electron acceptor substrates with aromatic solvents by electron donor-acceptor complexes is an important way of understanding solvation and reactivity behaviours. 

The reactions 33 between tetrachloro-A-n-butylphthalimide (113) and n-butylamine275 in aprotic and apolar media (cyclohexane, benzene, toluene, xylenes) show a third experimental reaction order in the amines explained by the formation of a complex (n-jr-like) between the electron acceptor substrate (the derivative of the phthalimide) and the electron donor nucleophile (the amine). In mixed solvents (such as the mixtures cyclohexane/aromatic solvents) the kinetic investigation reveals the presence of a competition between the electron donor solvent and the amine in complexing the substrate. 

Scheme 1.57). Although the natural donor aldehyde is D-2-deoxyribose-5-phosphate, non-phosphorylated donor aldehydes are also tolerated and the enzyme displays some flexibility towards both donor and acceptor. Importantly, as both donor and acceptor substrates are aldehydes, the enzyme can perform sequential aldol reactions allowing the preparation of a key lactol intermediate to the atorvastatin side chain in a single step. Following substantial modification, this approach is now operated on an industrial scale to... 

Another set of unusual C domains include those that catalyze the formation of more than one amide bond on an acceptor substrate containing multiple amine moieties. For example, the C domain of the NRPS module FscI in fuscachelin biosynthesis likely catalyzes amide bond formation at both the a- and -amines of a PCP-bound L-hOrn intermediate. Other domains displaying similar activity include the condensation domain of MxcG, the third C domain of CchH, and the second C domain of VibF from the biosynthetic pathways for myxochelin, coelichelin, and vibriobactin, respectively. 

Acetogens can also use a diverse number of terminal electron acceptors substrates (Drake 1994 Drake et al. 1997) these acceptors and the resulting reduced end products include ... 

Nandi DL, Westley J. 1998. Reduced thioredoxin as a sulfur-acceptor substrate for rhodanese. Int J Biochem Cell Biol 30 973-7. 

It should be emphasized that reactions conducted in traditional ways under inert gaseous atmosphere may sometimes fail. Oxygen accelerates the reactions involving strong acceptor substrates. This is similar to a promoting effect of active organic oxidizers of the dinitrobenzene type. The first example of such catalytic reactions was described almost half a century ago (Russell 1954). A carb-anion (R ) reacts with O2 according to the mechanism of catalysis with a one-electron transfer ... 

This enzyme [EC 2.S.2.9] catalyzes the reaction of agaritine with an acceptor substrate to generate 4-hydroxy-methylphenylhydrazine and the y-glutamyl-acceptor. Examples of substrate acceptors include 4-hydroxyani-line, cyclohexylamine, 1-naphthylhydrazine, and similar compounds. The enzyme will also be the catalyst in the hydrolysis of agaritine. See also y-Glutamyl Transpeptidase... 

This enzyme [EC 1.2.99.2], also known as acetyl-CoA synthase, catalyzes the reaction of carbon monoxide with water and an acceptor to produce carbon dioxide and the reduced acceptor. The cofactors of this enzyme include nickel and zinc ions as well as non-heme iron. Methyl viologen can act as the acceptor substrate. The enzyme is isolated from Clostridium sp. Interestingly, it also catalyzes an exchange reaction of carbon between Cl of acetyl-CoA and carbon monoxide. The protein participates in the synthesis of acetyl-CoA from carbon dioxide and hydrogen in the organisms. 

This enzyme [EC 1.3.99.11] catalyzes the reaction of (S)-dihydroorotate with an acceptor substrate to produce orotate and the reduced acceptor. Both iron and zinc ions are needed as cofactors. Acceptor substrates include 2,6-dichloroindophenol, 1,10-phenanthroline, and dioxygen (although dioxygen isn t as effective as the first two). 

Galactoside 2-L-fucosyltransferase [EC 2.4.1.69], also known as blood group H a-2-fucosyltransferase, catalyzes the reaction of GDP-L-fucose with /8-D-galacto-syl-R to produce GDP and a-L-fucosyl-l,2-/3-D-galac-tosyl-R. Lactose can also act as the acceptor substrate. 

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