C Coupling Pathways

FIG. 9. Four-quadrant plots of DFT results for an ethyl /J-D-glucopyranoside mimic of a disaccharide, showing phase shifting of 3/Ccoc Karplus curves for C-C-O-C coupling pathways bearing an internal electronegative substituent. The mimic has deoxy functions at C-3, C-4, and C-6. 

The N-3 resonance is always 20-30 ppm more shielded in N -substituted compounds than in the comparable N -isomers. This feature has been used together with the characteristic three-bond H- C coupling pathways to study the structures of various N-substituted purine derivatives. Very recently, an identical approach has been used to determine the position of alkylation for several purine derivatives reacted with... 

V(H,H) couplings through the H—C—S—C—coupling pathway in 2-phenyl-l,3-dithiane were found to be positive by Schaefer et al RPA AMI... 

An example of C.O-coupling of a-ketoalkyl radicals with reversible formation of an enol ether has also been reported for a system where C,C-coupling is very hindered (Scheme 1.10).154 However, this pathway is not observed for simpler species (Section 5.2.2.1.2). 

Second, apart from a different mode of activation, different modes of reactivity are observed. Hence, for FeCls reactions like oxidative C-C but also nonoxidative C-C couplings are as well observed as bond formation via Lewis-acid activation (Scheme 2) [11-16]. Depending on the reaction type, one or more mechanistic pathways are accessible at the same time, which makes it difficult to shed light into mechanistic details. 

Correlations between the Jc,c couplings and the aldopyranosyl ring configuration and conformation have also been deduced.4 Previous correlations involving Cl and C6 were confirmed, extended and/or modified, and new structural correlations involving C1-C5, through single and dual pathways, specifically for 3/c3,cs, 3 + 3 ci,c4, 3./< 2.< s were proposed. 

The coupling of superantigen—major histocompatibility complex class II to T-cell receptor swifdy results in cell-signaling cascades. ° These staphylococcal toxins can increase levels of phosphatidyl inositol from quiescent T cells, such as other mitogens, as well as elicit intracellular Ca movement that activates the protein kinase C (PKC) pathway important for interleukin-2 (IL-2) expression. " IL-2 is intimately linked to T-cell proliferation. In addition to the PKC pathway, the protein tyrosine kinase (PTK) pathway is also activated by superantigens, leading to elevated expression of various proinflammatory cytokines. Staphylococcal superantigens also potently activate transcriptional factors NF-/IB (nuclear factor kappa B) and AP-1 (activator protein-1), which subsequently elicit the synthesis of proinflammatory cytokines. " " ... 

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