Catalysis site-selectivity

Catalytic Properties. In zeoHtes, catalysis takes place preferentially within the intracrystaUine voids. Catalytic reactions are affected by aperture size and type of channel system, through which reactants and products must diffuse. Modification techniques include ion exchange, variation of Si/A1 ratio, hydrothermal dealumination or stabilization, which produces Lewis acidity, introduction of acidic groups such as bridging Si(OH)Al, which impart Briimsted acidity, and introducing dispersed metal phases such as noble metals. In addition, the zeoHte framework stmcture determines shape-selective effects. Several types have been demonstrated including reactant selectivity, product selectivity, and restricted transition-state selectivity (28). Nonshape-selective surface activity is observed on very small crystals, and it may be desirable to poison these sites selectively, eg, with bulky heterocycHc compounds unable to penetrate the channel apertures, or by surface sdation. 

The functionalization of folded motifs is based on an understanding of secondary and tertiary structures (Fig. 2) and must take into account the relative positions of the residues, their rotamer populations and possible interactions with residues that do not form part of the site. For example, glutamic acid in position i has a strong propensity for salt-bridge formation, and thus reduced reactivity, if there is a Lys residue available i-4 in the sequence, but the probabihty is much less if the base is i-3 [60]. Fortunately, there is a wealth of structural information on the structural properties of the common amino acids from studies of natural proteins that provides considerable support for the design of new proteins. The naturally occurring amino acids have so far been used to construct reactive sites for catalysis [11-13], metal- and heme-binding sites [14,15,19,21,22] and for the site-selective functionalization of folded proteins [24,25]. 

Miller also explored the ASD of glycerol derivatives through an enantioselective acylation process which relies on the use of a pentapeptide-catalyst which incorporates an A-terminal nucleophilic 3-(l-imidazolyl)-(5)-alanine residue [171], Most recently, Miller has probed in detail the role of dihedral angle restriction within a peptide-based catalyst for ferf-alcohol KR [172], site selective acylation of erythromycin A [173], and site selective catalysis of phenyl thionoformate transfer in polyols to allow regioselective Barton-McCombie deoxygenation [174],... 

Stahley MR, Strobel SA. RNA splicing group I intron crystal structures reveal the basis of splice site selection and metal ion catalysis. Curr. Opin. Struct. Biol. 2006 16 319-326. 

Formaldehyde, 2,2-dimethoxypropane, or cyclohexanone reacts with ( S)-malic acid under acidic catalysis to form dioxolanones of type 173. These are primarily used for C-4 site-selective reactions on the malic acid framework, and are discussed in Section 3.2.4. 

Starting material and the product (Scheme 1.58, middle). Furthermore, the catalyst control of site selectivity was achieved by changing the catalyst to the CFa-modified complex C22. Artemisinin 151 was transformed to ClO-oxi-dized hydroxyl artemisinin 152 under the catalysis of C21. However, when C22 was used, C9-oxidized 9-oxo-artemisinin 153 was obtained as the main product. Furthermore, the development of quantitative structure-based catalyst reactivity models could predict the ratio of the site selectivity (Scheme 1.58, bottom). This discovery should inspire and guide future catalyst design. 

Pd-catalyzed site-selective cross-coupling reactions demonstrate the influential role of ligands in transition metal catalysis. The reactions described in this review discuss efficient approaches to introduce various substituents at specific halo-substituted posititMis (Ml (hetero)aromatic compounds. The commercial availability of a variety of dihalo-substituted starting materials makes site-selective crosscoupling reactions practical for the rapid production of diverse (hetero)arenes with multiple substituents. In all examples described here, the reactions proceeded successfully only on substrates containing hetero atoms, and this field of chemistry aims to include substrates without hetero atoms in the substrate scope. 

Han S, Miller SJ (2013) Asymmetric catalysis at a distance catalytic, site-selective phosphorylation of teicoplanin. J Am Chem Soc 135 12414-12421... 

By virtue of its structural complexity and potent antibiotic activity, the glyco-peptide natural product teicoplanin is a substrate of great interest for site-selective catalysis. Miller and co-workers approach to discovering catalysts for selective... 

Sanchez-Rosello M, Puchlopek ALA, Morgan AJ, Miller SJ (2008) Site-selective catalysis of phenyl thionoformate transfer as a tool for regioselective deoxygenation of polyols. J Org Chem 73 1774... 

Chen 1-H, Kou KGM, Le DN, Rathbum CM, Dong V (2014) Recognition and site-selective transformation of monosaccharides by using copper(II) catalysis. Chem Eur J 20 5013... 

Introdijction The Barrier Challenge of Site-Selective Catalysis. 158... 

A CoimectiOTi Between Site-Selective Catalysis in Natural Products and Remote... 

The combination of both asymmetric catalysis and differential innate functional group reactivity also allowed preparation of a number of inositol polyphosphates (Scheme 3c) [35]. Key to this last strategy was the site-selective phosphitylation of the 4-hydroxyl over the 6-hydroxyl of intermediate 21 to yield 22 the latter hydroxyl was sterically encumbered by a bulky TBS protecting group on the 1-hydroxyl. This hypothesis regarding steric differentiation was supported by the selective phosphitylation of 23 to yield 24, which, using the smaller BOM... 

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