Nucleophilic substitution reactions components

The experiments presented above definitively established the fact the Lipson s HPD-forming procedure gives dimeric and trimeric porphyrin esters as the high-molecular weight component which is eminently better localized and retained in tumor cells and is responsible for most of the photodynamic activity associated with HPD. Mechanistically, the formation of ester linkage is not only understandable but expected as well. Under the alkaline condition employed in the synthesis of HPD, the nucleophilic substitution reaction illustrated in the following scheme is very similar to the... 

On the other hand, when 39 was heated with hydrogen bromide in acetic acid, 1,2-di-<9-acetyl-( 1,3/2,6)-3,4-dibromo-6-(bromomethyl)-l,2-cyclohexanediol (50) was obtained, which was converted into 1,2-di-0-acetyl-( 1,3/2)-3(bromomethyl)-5-cyclo-hexene-l,2-diol (51) by debromination with zinc dust in glacial acetic acid [21]. Hydro-xylation of 51 with osmium tetroxide, and successive acetylation yielded 1,2,3,4-tetra-C>-acetyl-6-bromo-6-deoxy-pseudo-a-DL-glucopyranose (52). Nucleophilic substitution reactions of 52 with sodium acetate gave pseudo-a-DL-glucopyranose pentaacetate (55), which gave pseudo-a-DL-glucopyranose (54) by usual hydrolysis [22]. Alternatively, the pentaacetate 55 was obtained as a minor component in a poor yield by nucleophilic substitutions of 2,3,4-tri-0-acetyl-l,6-dibromo-l,6-dideoxy-pseudo-... 

Bimolecular nucleophilic substitution reactions, SN2 reactions, are probably the reaction type that has been investigated the most in microemulsions. Such reactions often involve one lipophilic component that is insoluble in water and one very hydrophilic component, usually the anion of a salt with virtually no solubility in hydrocarbon. This means that the components meet and react at the interface. The area of the interface is obviously of importance. 

Surfactants in solutions show a broad variety of microstructures caused by molecular selforganisation. The observed structures depend essentially on the physical interactions of the involved components and the composition of the mixtures. For the selection of a suitable type of reaction medium the required composition of the reaction mixture is more important than the question of whether a micellar solution, a bicontinuous microemulsion, a w/o- or an o/w-microemulsion is formed. For synthetic purposes high concentrations of reactants are indispensable in order to avoid high-energy cost for work-up procedures. Therefore, a reaction system that allows high-reactant concentrations needs to be chosen. For stoichiometric reactions involving reactant incompatibility, like nucleophilic substitution reactions with an inorganic nucleophile, often an aqueous solution of this reactant has... 

A classical reaction leading to 1,4-difunctional compounds is the nucleophilic substitution of the bromine of cf-bromo carbonyl compounds (a -synthons) with enolate type anions (d -synthons). Regio- and stereoselectivities, which can be achieved by an appropiate choice of the enol component, are similar to those described in the previous section. Just one example of a highly functionalized product (W.L. Meyer, 1963) is given. 

Once formed, an acyl CoA is a substrate for further nucleophilic acyl substitution reactions. For example, iV-acetylglucosamine, a component of cartilage and other connective tissues, is synthesized by an aminolysis reaction between... 

In analogy, Ugi et al. reported on a lactam formation by running a one-pot three components reaction the condensation of L-lysine 7, isobutyraldehyde and methyl isocyanide led to the corresponding a-amino-c-caprolactam 9, but the yield was not given. The authors presumed either a nucleophilic substitution of the ester 8 as the primary Ugi product by the amino function of the side chain or, alternatively, the nucleophilic attack of the NH2-group on an intermediately formed 0-acylamide and a subsequent rearrangement (Scheme 1) [4]. 

The results of a thorough study of the kinetics, products and stereochemical course for the nucleophilic substitution and elimination reactions of ring-substituted 9-(l-Y-ethyl)fluorenes ([31]-Y, Y = Br, I, brosylate) have been reported (Scheme 19).121,122. The reactions of the halides [31]-Br and [31]-I were proposed to proceed exclusively by a solvent-promoted ElcB reaction or an E2 reaction with a large component of hydron transfer in the transition state .122... 

A coupling reaction is an electrophilic substitution of the diazonium compound with a nucleophilic partner (coupling component RH) ... 

The principal tumor-localizing component of Hematoporphyrin Derivative (HPD) has been demonstrated to be dimeric and trimeric hematoporphyrins (HP) interconnected with ester groups. Synthetic analogs as well as model compounds are used in our study to conclude that the reaction conditions employed in the traditional HPD preparation promote a nucleophilic substitution of the acetate group of one HP-acetate molecule by an propionate anion of another HP molecule. The effect of solvent on the stability and structural conformation of the diporphyrin esters have also been examined by spectroscopic methods. 

In contrast to the installation of the nucleobase via nucleophilic substitution of a suitable leaving group on the isoxazolidinyl cycloadduct, Colacino et al. (51) and Sindona and co-workers (52,53) prepared isoxazolidinyl nucleosides using vinyl nucleobases as the dipolarophile (Scheme 1.5). In Sindona s work, while a three-component reaction of hydroxylamine, formaldehyde, and 20 afforded a complex mixture of cycloadducts and byproducts, the known dipole 21 reacted with N-9-vinyladenine (20) in benzene at reflux to afford a racemic mixture of adduct 22 and its enantiomer (45%). The ester function was then used to effect a resolution by pig... 

According to eqn. (56) a nucleophilic substitution takes place, i.e. the component Y is attached to the a-carbon atom. Similarly in reaction (57) Ye attaches itself to the central atom of the X-group (such as the nitrogen atom in the nitro group). The last equation illustrates a typical oxidation process, producing an aldehyde or ketone with the removal of a hydrogen atom attached to the a-carbon atom. 

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