Ligands alkaloid

Scheme 42.6 Muscarinic receptor ligand alkaloids and synthetic derivatives...

Scheme 42.9 Nicotinic receptor ligand alkaloids and the synthetic anabaseine derivative...

Another important reaction associated with the name of Sharpless is the so-called Sharpless dihydroxylation i.e. the asymmetric dihydroxylation of alkenes upon treatment with osmium tetroxide in the presence of a cinchona alkaloid, such as dihydroquinine, dihydroquinidine or derivatives thereof, as the chiral ligand. This reaction is of wide applicability for the enantioselective dihydroxylation of alkenes, since it does not require additional functional groups in the substrate molecule ... 

The actual catalyst is a complex formed from osmium tetroxide and a chiral ligand, e.g. dihydroquinine (DHQ) 9, dihydroquinidine (DHQD), Zj -dihydroqui-nine-phthalazine 10 or the respective dihydroquinidine derivative. The expensive and toxic osmium tetroxide is employed in small amounts only, together with a less expensive co-oxidant, e.g. potassium hexacyanoferrate(lll), which is used in stoichiometric quantities. The chiral ligand is also required in small amounts only. For the bench chemist, the procedure for the asymmetric fihydroxylation has been simplified with commercially available mixtures of reagents, e.g. AD-mix-a or AD-mix-/3, ° containing the appropriate cinchona alkaloid derivative ... 

Appropriately designed biophysical studies can elucidate the mode(s), the binding affinities and the nature of the ligand-nucleic acid interaction that give rise to the observed selectivity and specificities. Thus, it is worthwhile to describe briefly the various physical techniques used to study alkaloid-DNA/RNA interactions. 

Usually non-cooperative and non-Unear binding isotherms were observed in alkaloid-B-DNA complexation and the data were fitted to a theoretical curve drawn according to the excluded site model [126] developed by McGhee and von Hippel [127] for a non-Unear non-cooperative ligand binding system using the following equation ... 

In order to synthesise the pyrrolidine alkaloid, (-l-)-197B, bis-(i ,i )-tri-fluoromethanesulfonamide ligand was employed in the enantioselective addition of Zn( -Bu)2 to an allene-aldehyde, alfording the corresponding (i )-alcohol in 70% yield and 94% ee (Scheme 3.52). ... 

Osmium tetroxide oxidations can be highly enantioselective in the presence of chiral ligands. The most highly developed ligands are derived from the cinchona alkaloids dihydroquinine (DHQ) and dihydroquinidine (DHQD).45 The most effective... 

Hartmann T, Ober D (2000) Biosynthesis and Metabolism of Pyrrolizidine Alkaloids in Plants and Specialized Insect Herbivores. 209 207-243 Haseley SR, Kamerling JP, Vliegenthart JFG (2002) Unravelling Carbohydrate Interactions with Biosensors Using Surface Plasmon Resonance (SPR) Detection. 218 93-114 Hassner A, see Namboothiri INN (2001) 216 1-49 Hauser A (2004) Ligand Field Theoretical Considerations. 233 49-58 Hauser A (2004) Light-Induced Spin Crossover and the High-Spin Low-Spin Relaxation. 234 155-198... 

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