Multifunctional complexes

The heterobimetallic multifunctional complexes LnSB developed by Shibasaki and Sasai described above are excellent catalysts for the Michael addition of thiols [40]. Thus, phenyl-methanethiol reacted with cycloalkenones in the presence of (R)-LSB (LaNa3tris(binaphthox-ide)) (10 mol %) in toluene-THF (60 1) at -40°C, to give the adduct with up to 90% ee. A proposed catalytic cycle for this reaction is shown in Figure 8D.9. Because the multifunctional catalyst still has the internal naphthol proton after deprotonation of the thiol (bold-H in I and II), this acidic proton in the chiral environment can serve as the source of asymmetric protonation of the intermediary enolate, which is coordinated to the catalyst II. In fact, the Michael addition of 4-/en-butylbenzcnethiol to ethyl thiomethacrylate afforded the product with up to 93% ee using (R)-SmSB as catalyst. The catalyst loading could be reduced to 2 mol % without affecting enantioselectivity of the reaction. 

Some enzymes exist as multienzyme or multifunctional complexes (Bisswanger and Schmincke-Ott, 1980 Perham, 2000 Reed, 1974 Srere, 1987). 

Sanderson IR, Walker WA (1993) Uptake and transport of macromolecules by the intestine possible role in clinical disorder (An update). Gastroenterol 104 622-629 Schneeberger EE, Lynch RD (2004) The tight junction a multifunctional complex. Am J Physiol Cell Physiol 286 1213-1228... 

Another species that qualifies as an alkoxy derivatized phenol is morphine. Because of the multifunctional complexity and solid phase of the compound, as well as the dates of the literature citations (1899, 1900) the result is essentially without use in our thermochemical context. 

Malonyl-CoA is then used for fatty acid synthesis. This process requires Fatty Acid Synthase (FAS) (Chirala and Wakil, 2004) that uses acetyl-CoA as a primer, malonyl-CoA as a two-carbon donor, and NADPH as a reducing equivalent (Fig. 1.1). The predominant fatty acid produced by FAS is palmitic acid (Cl 6 0). The structure of FAS has been extensively studied (Asturias et al., 2005 Maier et ah, 2006). FAS is a multifunctional complex consisting of two identical monomers. However, only the dimeric form is active (Chirala et al.,... 

The clustering of two or more enzymes (active sites) in a single polypeptide chain ensures that their synthesis is coordinated and helps assure that they will assemble into a coherent complex. Also, the proximity of the active sites means that side reactions are minimized as substrates are channeled from one active site to another. Finally, a multifunctional complex with covalently linked active sites is likely to be more stable than a complex formed by noncovalent interactions. 

The unique combination of binding sites for both cations and anions in a neutral receptor molecule leads to hosts with multifunctional complexation properties, eg. for the complexation of both constituents of a salts. 

The remaining series of reactions of fatty acid synthesis in eukaryotes is catalyzed by fatty acid synthase (FAS) is a homodimeric and multifunctional complex of 250 kDa and contains seven different enzymatic activities plus a domain that covalently binds a molecule of 4 -phosphopantetheine, of the acyl carrier protein (ACP) [105,106]. PA, the most abundant acid, is synthesized de novo firrm acetyl-CoA as a primer, malonyl-CoA as a carbon donor, and NADPH as a reducing equivalent according to the following reaction [104, 105, 107]. 

Schneeberger, E. E., and Lynch, R. D. (2004). The tight junction A multifunctional complex. Am. J. Physiol. Cell Physiol 286, C1213-C1228. 

There are two main types of FAS Type I FAS occurring in animals, fimgi, protozoa and some bacteria, and type II characteristic of bacteria and green plants including algae. Type I FAS are stable, high molecular weight (410,000 to 2 x 10 daltons) multifunctional complexes. The enzyme from mammals and birds consists of two subunits, each of which can catalyze all steps in fatty acid synthesis except for condensation (P-keto-acyl synthetase). Dimerization restores this activity. 

Chem. Descrip. Ashless multifunctional complex long chain aliphatic phosphate ester... 

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