Cascade reactions activation

Remaining in the field of hetero-Michael reaction, Gong et al. disclosed a four-component quadruple cascade reaction activation initiated by oxa-Michael addition of alcohol to acroleins providing an easy and direct access to highly functionalized chiral trisubstituted cyclohexene derivatives 170 (Scheme 2.54) [81]. 

The operational model allows simulation of cellular response from receptor activation. In some cases, there may be cooperative effects in the stimulus-response cascades translating activation of receptor to tissue response. This can cause the resulting concentration-response curve to have a Hill coefficient different from unity. In general, there is a standard method for doing this namely, reexpressing the receptor occupancy and/or activation expression (defined by the particular molecular model of receptor function) in terms of the operational model with Hill coefficient not equal to unity. The operational model utilizes the concentration of response-producing receptor as the substrate for a Michaelis-Menten type of reaction, given as... 

For the purpose of discussion, crossbridge regulation can be split into three overlapping sets of reactions (a) the Ca-calmodulin cascade (MLCK activation), (b) the phosphorylation-dephosphorylation cycle (the Four State Model), and (c) actin-myosin cycle (chemomechanical transduction). 

Dihydronaphthalenes are remarkable substrates for the combined C-H activation/Cope rearrangement, but under certain circumstances, further cascade reactions can occur. This was seen in the Rh -DOSP -catalyzed reaction of vinyldiazoacetate 26 with dihydronaphthalene 25 (Equation (35)).96 In this case, the isolated product was the formal C-H insertion product. The reaction proceeded through a combined C-H activation/Cope rearrangement to form 27, followed by the reverse Cope rearrangement. As both steps were highly stereoselective, the formal C-H insertion product 28 was produced with very high stereoselectivity (>98% de, 99.6% ee).96... 

Cascade Addition-Cyclization Reactions Given the importance of cascade reactions in modem chemical synthesis, the MacMillan group has proposed expansion of the realm of iminium catalysis to include the activation of tandem bond-forming processes, with a view toward the rapid constraction of natural products. In this context, the addition-cyclization of tryptamines with a,p-unsaturated aldehydes in the presence of imidazolidinone catalysts 11 or 15 has been accomplished to provide pyrroloindoline adducts in high yields and with excellent enantioselectivities (Scheme 11.3a). This transformation is successful... 

Chain growth polymerizations (also called addition polymerizations) are characterized by the occurrence of activated species (initiators)/active centers. They add one monomer molecule after the other in a way that at the terminus of each new species formed by a monomer addition step an activated center is created which again is able to add the next monomer molecule. Such species are formed from compounds which create radicals via homolytic bond scission, from metal complexes, or from ionic (or at least highly polarized) molecules in the initiating steps (2.1) and (2.2). From there the chain growth can start as a cascade reaction (propagation 2.3) upon manifold repetition of the monomer addition and reestablishment of the active center at the end of the respective new product ... 

In step growth reactions, on the other hand, neither are specific activated centers present to force the connection of the monomers, nor does the process occur as a cascade reaction. Instead, the monomers are tied together in discreet, independent steps via conventional organic reactions such as ester-, ether-, amide-, or urethane formation. Depending on whether small molecules are set free in the connection step, one distinguishes between polycondensations (2.9) and polyadditions (2.10) ... 

Chiral l,3-dioxin-4-ones photochemically react intermolecular with (cyclic) ethers, acetals, and secondary alcohols to give the addition products in reasonable yields. The radical addition was completely stereoselective at C-6 of the heterocycle <1999EJO1057>. The exocyclic diastereoselectivity, where relevant, was about 2 1 (Equation 30). In analogy, an intramolecular cascade reaction of a 1,3-dioxin -one derived from menthone was used to get a terpenoid or a steroid framework in optically active form <1997JA1129, 1999JA4894>. 

Inflammation is a defense reaction of an organism against harmful stimuli such as tissue injury or infectious agents. Upon microbial invasion, an effective immuno-regulatory cascade is activated to protect the body against the intruders. The defense mechanisms that protect an organism against infections can be divided into... 

Oxidatively generated oxocarbenium ions have been used for intramolecular epoxide activation. Cascade reactions to form oligotetrahydrofuran products that demonstrated a strong preference for the exo-cyclization pathway were achieved in good yields when disubstituted epoxides were used as substrates. High stereoselectivity was observed in these reactions, with complementary diastereomers being formed from diastereomeric (g) epoxides.257... 

It is very well known that jr-allyl palladium complex 1, which is a key intermediate for the Tsuji-Trost type allylation, has an electrophilic character and reacts with nucleophiles to afford the corresponding allylation products. We discovered that bis 7r-allyl palladium complex 2 is nucleophilic and reacts with electophiles such as aldehydes [27] and imines [28-32] (Scheme 2, Structure 2). We have also shown that bis 7r-allyl palladium complex 2 can act as an amphiphilic catalytic allylating agent it reacts with both nucleophilic and electrophilic carbons at once to produce double allylation products [33]. These complexes incorporate two allyl moieties that can bind with different hapticity to palladium (Scheme 3). The different complexes may interconvert by ligand coordination. The complexes 2a, 2b and 2c are called as r]3,r]3-bisallypalladium complex (also called bis-jr-allylpalladium complex), r)l,r)3-bis(allyl)palladium complex, -bis(allyl)palladium complex, respectively. Bis zr-allyl palladium complex 2 can easily be generated by reaction of mono-allylpalladium complex 1 and allylmetal species 3 (Scheme 4) [33-36]. Because of the unique catalytic activities of the bis zr-allyl palladium complex 2, a number of interesting cascade reactions appeared in the literature. The subject of the present chapter is to review some recent synthetic and mechanistic aspects of the interesting palladium catalyzed cascade reactions which in-... 

This was performed for each enzyme independently, feeding the reactor with the appropriate substrate (nitrile for the cascade reaction, amide for the sole amidase). The activation energies of both catalysed reactions were evaluated together with those of the inactivation process that inevitably takes place even under the most suitable operational conditions. In the nitrile hydratase/amidase cascade system nitrile hydratase is the more labile enzyme that imposes process temperature choice. These findings make accessible the complete kinetic expression of the dependence from temperature of reaction rate, allowing accurate prediction on reactor performances for process scale-up. 

Liu et al. [16] synthesized twenty novel 2,4,5-trisubstituted oxazole derivatives (iv) containing heterocycle moiety and evaluated them for their antiproliferative activity. They showed that the microwave irradiation promoted the rapid 0,N-acylation-cyclodehydration cascade reaction of oximes and acid chlorides. 

Fig. 25.3. Detection of a two-step cascade reaction by observing single hypobromite reaction events, (a) Reaction mechanism. The haloperoxidase enzyme produces hypobromite. These reactive oxygen species react with aminophenyl fluorescein (APF) in a secondary reaction to yield the highly fluorescent dye fluorescein, (b) Representative part of a fluorescence intensity time trace. Every intensity burst corresponds to one reaction event between hypobromite and APF. (c) Histogram of the time-averaged activities of approximately 100 individual enzymes, obtained by measuring the secondary reaction between hypobromite and APF. (d) Frequency of observing individual reaction events as a function of distance from the enzyme. At distances farther than the diffraction limit, a considerable number of reaction events occurs indicating that the secondary reaction takes place in solution following the release of most of the hypobromite from the enzyme...

The incidence of transfusion-related acute lung injury is 0.16-0.24% per transfusion of blood products and is the cause of 15% of all fatal complications of blood transfusion (11). Specific antigen-antibody reactions involving donor antibodies specific for leukocyte antigens of the recipients cause activation of neutrophils and aggregation in small pulmonary vessels (11). The complement and cytokine cascade is activated, leading to capillary leakage. 

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