Amines linkage isomers

Tracer studies have shown that the isomerization of /ra/zj-[Co(en)2(NH3)-(SCN)] to the A-thiocyanato-linkage isomer in basic aqueous solution is intramolecular. The detailed mechanism may involve an intimate ion pair which does not exchange its thiocyanate with the thiocyanate in solution, a species in which the thiocyanate is Ji-bonded to the cobalt, or intramolecular attack of a deprotonated amine nitrogen at the thiocyanate carbon (Scheme 5). Aquation of [Co(NH3)5(sulphamate)] - is preceded by isomerization of the starting complex to an equilibrium mixture of N- and 0-bonded isomers. The specific rate constant for approach to equilibrium is l.lxlO s at 25 °C composite activation parameters are AH = 24.7 kcal mol and AS = 10.9 cal deg mol . Inability to estimate the equilibrium constant satisfactorily precludes the separation of these kinetic parameters into their forward and backward components. ... 

The ammonioacetonitrile complex (206) reacts with NH3 to produce the amidine-bonded aminoacetamidine (207) complex, whereas in aqueous base it hydrolyzes to the amid o-A -bo ruled glycinamide complex (208).908 Acid-catalyzed linkage isomerization to first the O-bound form (209) precedes formation ultimately of the amino-bonded isomer (210) as the stable product upon deprotonation of the free amine above pH 6. 

The best known of the muscarinic blocking drugs are the belladonna alkaloids, atropine (Atropine) and scopolamine (Scopolamine). They are tertiary amines that contain an ester linkage. Atropine is a racemic mixture of DL-hyoscyamine, of which only the levorotatory isomer is pharmacologically active. Atropine and scopolamine are parent compounds for several semisynthetic derivatives, and some synthetic compounds with little structural similarity to the belladonna alkaloids are also in use. All of the antimuscarinic compounds are amino alcohol esters with a tertiary amine or quaternary ammonium group. 

The low quantum yields plus the interference of photoredox limits the synthetic applications of photochemistry among the Co(lll) amines. However, several applications involve linkage isomerization of ambidentate ligands, e.g., the photolysis of nitro complexes leads to nitrito isomers, presumably via a charge-transfer excitation. In H O both photoreduction to Co and linkage isomerization are noted ... 

To achieve a high-level of control over polymerizations, and resulting polymer microstructures, the preparation of pure exo isomers of the monomers were targeted. Exo-endo mixtures that were obtained as the cycloaddition adducts were not always separable by selective reciystallizations. Compounds 5, 6, 8, and 9 were separated from their endo isomers through selective recrystallization to give white crystalline solids. Cobalt-catalyzed transformation of the anhydride into a substituted imide linkage resulted in the protected amine functionalized monomer structure in excellent yield. For monomers 6, 8 and 9, pure exo isomer was isolated by successive recrystallizations from cold ether overall yields were 40 to 56%. 

More recently, several reports have appeared which describe the preparation of HPLC columns which contain CD chemically bonded to silica gel [15-18]. Of these, there are presently two types. The first consists of CD bonded to the silica via amide or amine bonds [15,16] while the second contains no nitrogen linkages [17,18]. This review article summarizes our chromatographic work to date with the latter type of CD bonded phases. In particular, we demonstrate the successful HPLC separation of enantiomers, epimers, cis-trans and other structural isomers as well as important classes of routine compounds by use of a P- or y-CD bonded phase. The obtained chromatographic separations are compared to those obtained on the more conventional normal or reversed phase packings. Additionally, the effect of changes of the pertinent chromatographic variables (such as flow rate, temperature, and solvent composition of the mobile phase) upon the separations are described. Lastly, a brief prospectus on the future of CD bonded phases in HPLC is presented. 

The terminal AT-acetylneuraminic acid was cleaved off with neuraminidase to yield neutral carbohydrate compounds. The structures shown above only differ in the labeled -1,3- and 4-linkage between galactose and AT-acetylglucos-amine in the lactosamine residue of this triantennary oligosaccharide [269]. Neither isomer can be separated with conventional RPLC techniques. 

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