Alpha selectivity

The nitration route shows insufficient alpha-selectivity in addition to producing considerable dinitro product. Although a large amount of work has been done to maximize the yield of 1-nitro compound, the best result is less than 80%. Several methods have been developed to remove 2-nitroanthraquinone and dinitroanthraquinones from cmde 1-nitroanthraquinone. Purification is carried out, for example, by recrystaUization from nitric acid, or from organic solvents (15). 

Efforts to raise the alpha-selectivity have been made. Thus nitration of anthraquinone using nitrogen dioxide and ozone has been reported (17). l-Amino-4-bromoanthraquinone-2-sulfonic acid (bromamine acid) [116-81 -4] (8) is the most important intermediate for manufacturing reactive and acid dyes. Bromamine acid is manufactured from l-aminoanthraquinone-2-sulfonic acid [83-62-5] (19) by bromination in aqueous medium (18—20), or in concentrated sulfuric acid (21). l-Aminoanthraquinone-2-sulfonic acid is prepared from l-aminoanthraquinone by sulfonation in an inert, high boiling point organic solvent (22), or in oleum with sodium sulfate (23). 

Stauffer SR, Coletta CJ, Tedesco R, Nishiguchi G, Carlson K, Sim J, Katzenellenbogen BS, Katzenellenbogen JA (2000) Pyrazole ligands structure-affinity/activity relationships and receptor-alpha-selective agonists. J Med Chem 43 4934-4947... 

The Alpha Select process based on metallocene catalysis... 

The last, the Alpha Select process, was introduced to satisfy the demand for plasticizer olefins, which was growing faster than the detergent olefins. 

What is the main difference in results between the Ziegler process and the Alpha Select process ... 

The Ziegler process produces the full range of alpha olefins, from C4 to C2o The Alpha Select process produces C4 through Cio-... 

Description Polymer-grade ethylene is oligomerized in the liquid-phase reactor (1) with a catalyst/solvent system designed for high activity and selectivity. Liquid effluent and spent catalyst are then separated (2) the liquid is distilled (3) for recycling unreacted ethylene to the reactor, then fractionated (4) into high-purity alpha-olefins. Spent catalyst is treated to remove volatile hydrocarbons and recovered. The table below illustrates the superior purities attainable (wt%) with the Alpha-Select process ... 

Table I. Influence of Alcohol and Halide-Ion Concentration on Alpha Selectivity in Glycosidations...

Table III. Influence of Substituents and Solvents on Alpha Selectivity In Glycosidationsa...

Law SF, Yasuda K, Bell GI, Reisine T (1993) Gj alpha 3 and G(o) alpha selectively associate with the cloned somatostatin receptor subtype SSTR2. J Biol Chem 268 10721-10727... 

E. Adrenoceptor Blockers Alpha -selective agents (eg, prazosin) and beta-blockers (eg, propranolol) are effective antihypertensive drugs. Alpha-blockers reduce vascular resistance and venous return. The nonselective alpha-blockers (phentolamine, phenoxybenzamine) are of no value in chronic hypertension because of excessive compensatory responses, especially tachycardia. Alpha,-selective adrenoceptor blockers are relatively free of the severe adverse effects of the nonselective alpha-blockers and postganglionic nerve terminal sympathoplegic agents. 

Alpha -selective blocker prototype used in HTN and benign prostatic hyperplasia. Tox first-dose orthostatic hypotension. Other osins terazosin, doxazosin. 

Spada, C.S., Woodward, D.E, Krauss, A.H-P, Neives, A.L., Wheeler, LA., Scott, D., and Sachs, G. (2002). Bimatoprost and PGF2-alpha selectively stimulate calcium signals in different cat iris sphincter cells. Ebcp. Eye Res., 12, Suppl. 2, 78. 

Hairston, N. G., 1983, Alpha selection in competing salamanders Experimental verification of an a priori hypothesis, Nat., 122 105. 

More importantly, the phosphate dmior can also be applied to the convergent block symthetic strategy to synthesize the various lengths of a 2,9-linked oligosialic acid up to dodecamer in good yield and alpha selectivity (Scheme 2) [72]. 

The ribofuranosylation of alcohols has been achieved using a base/triphenylphosphine promoted addition of ribofuranosyl iodide to alkyl iodides (Scheme 2.12) [17]. The chemistry was carried out under mild conditions (0 °C) and was highly alpha-selective. Triphenylphosphine was a critical component of the chemistry, and although the precise role of this additive was not fully elucidated, its presence nearly completely suppressed the formation of products resulting from beta-addition. A range of alcohols were successfully functionalized using this approach with excellent selectivity. 

Sodium iodide is believed to further enhance the alpha selective addition of nucleophiles under these conditions [32], Addition of sodium iodide to the CAN/acetonitrile/thiophenol reaction mixture with the anhydroglycal 7 gave a diminished amount of glycoside 10a,b (35%, a p, 2 1) and increased amounts of Perrier product (65%). Only the a-Ferrier product 11a was isolated. 

Olivier-Bourbigou Lecocq, 2003) Chloroaluminate ILs and Ni(COD)(2) with a Bronsted acid ILs Biphasic ethylene oligomerization or butene and higher olefins dimerization (Difasol process). These solvents stabilize and activate nickel catalysts, even without ligand, and greatly enhance the reaction activity. The presence of a diimine ligand allows the production of C4-C6 linear olefins with improved alpha-selectivities. 

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