Reagent natural ligand modifying

Co-extraction of Mo and Cu is potentially a problem with certain feed solutions,14 and again selectivities are very dependent on the nature of modifiers present in formulated reagents.142 The Mo species extracted have not been fully characterized, but may include a neutral dioxo complex, [Mo02L2], which can be assumed to have an N2022 donor set similar to that in the Cu11 complex, and molybdate complexes solvated by neutral phenolic oxime ligands such as [M0O4112 LI l].143 Formation of solvated forms of molybdic acid is supported by evidence that extraction is favorable at very low pH values and that the complexes are readily stripped by aqueous ammonia to produce ammonium molybdate,144... 

Fig. 3.26. The interaction of macromolecular photoaffinity reagents with a receptor, a The natural ligand binds tightly to a receptor on a membrane (or in solution), b A ligand modified with a bifunctional reagent close to its site of interaction with the receptor may not bind well. c If the ligand is modified with a short-armed reagent at an alternative site it may not label the receptor but, d if a long-armed reagent is used neighboring or irrelevant polypeptides may...

If an achiral ferrocene derivative is converted to a chiral one by chiral reagents or catalysts, this may be called an asymmetric synthesis. All asymmetric syntheses of ferrocene derivatives known so far are reductions of ferrocenyl ketones or aldehydes to chiral secondary alcohols. Early attempts to reduce benzoylferrocene by the Clemmensen procedure in (5)-l-methoxy-2-methylbutane as chiral solvent led to complex mixtures of products with low enantiomeric excess [65]. With (25, 3R)-4-dimethylamino-l,2-diphenyl-3-methyl-2-butanol as chiral modifier for the LiAlH4 reducing agent, the desired alcohol was formed with 53% ee (Fig. 4-9 a) [66]. An even better chiral ligand for LiAlH4 is natural quinine, which allows enantioselective reduction of several ferrocenyl ketones with up to 80% ee [67]. Inclusion complexes of ferrocenyl ketones with cyclodextrins can be reduced by NaBH4 with up to 84% enantioselectivity (Fig. 4-9 b) [68 — 70]. 

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