Atropos

As to most chiral atropisomeric ligand, resolution or asymmetric synthesis is requisite. Mikami developed a novel ligand-accelerated catalyst. The chirality of atropos, but achiral triphos ligand-Ru complex, can be controlled by chiral diamines. Using ( -dm-dabn as controller, the single diastereomeric triphos-Ru complex was achieved through isomerization of (i )-triphos-Ru complex in dichloroethane at 80 °G (Scheme l).44... 

In contrast to muscarine, atropine blocks these actions of acetylcholine and muscarine. Atropine is, therefore, an acetylcholine antagonist. It binds where acetylcholine binds and therefore prevents the binding of the latter but does not activate it. Two molecules cannot occupy the same binding site at the same time. Atropine is isolated from the plant Atropa belladonna. Extracts of this plant have been used for millennia for a variety of purposes. Although large doses are poisonous (Atropos is the name of the Fate who cuts the thread of life), small doses causes dilation of the pupils, a consequence of its action as an acetylcholine antagonist, and has been used for cosmetic purposes by women, hi Itahan, belladonna means beautiful woman. 

Asymmetric Activation of Chiraiiy Rigid (Atropos) Cataiysts... 

Asymmetric Activation/Deactivation of Chirally Rigid (Atropos) Catalysts... 

The effect of the tropos complex 31b with (S,.S)-DPEN can be observed in the hydrogenation of I -acetonaphthone 16 as compared with the results using ( )-10b/(S,S)-DPEN bearing racemic and atropos XylBlNAP (Table 8.10). ... 

The metal complexes even with tropos ligands can thus be used as asymmetric catalysts for carbon-carbon bond-forming reactions in the same manner as atropos catalysts. The single diastereomer (7 )-32/(/ )-DABN can be employed as an activated asymmetric catalyst for the Diels-Alder reaction at room temperature (Table 8.11). The high chemical yield and enantioselectivity (62%, 94% ee) in the Diels-Alder reaction of ethyl glyoxylate with 1,3-cyclohexadiene are obtained... 

The enantiopure complex 35 has since been employed as an atropos asymmetric catalyst for a variety of synthetic transformations (Scheme 8.33)." In addition, the hetero Diels-Alder reaction of glyoxylate could also be catalyzed by enantiopure... 

A) (23), was obtained in an improved yield using the modified literature procedure (28) starting from benzene diazonium chloride (1054) and hydroxymethylene-5-methylcyclohexanone (1055). A biomimetic coupling of l-hydroxy-3-methylcarba-zole (O-demethylmurrayafoline A) (23) by reaction with di-ferf-butyl peroxide l(t-BuO)2] afforded the dimer of O-demethylmurrayafoline A (204). Finally, oxidation of 204 with PCC afforded (+ )-bismurrayaquinone-A (215). The resolution of atropo-enantiomers was achieved by chiral HPLC using Chiracel OF. The assignment of the absolute configuration of the two enantiomers (S)-215 and (f )-215 was achieved by comparison of their theoretical and experimental circular dichroism (CD) spectra (166,167,661) (Scheme 5.164). 

When the aromatic substrates to be coupled do not contain any chiral information, stereodifferentiation may be achieved in those reactions that are mediated by chirally modified metal complexes. Thus, 2-naphthalenol is atropo-enantioselectively dimerized by oxidation with a chiral copper complex20,21. 

All parts of the belladonna plant contain the alkaloids. Linne named the species after one of the Fates, Atropos, who cut the thread of life. In Italy during the Middle Ages an extract of the plant was dropped onto the eyes in order to dilate the pupils (this practice gave rise to the name "belladonna" or beautiful lady since large dark pupils were considered a mark of beauty). Today atropine analogues, such as homatropine, are still used to dilate the pupils for opthalmalogical studies. Sympathomimetics can also be used for this purpose. See the Aside on Eye Openers . 

Morinville, A., D. Maysinger, and A. Shaver. 1998. From Vanadis to Atropos Vanadium compounds as pharmacological tools in cell death signalling. Trends Pharmacol. Sci. 19 452-60. 

Bach and co-workers developed the axially chiral N-arylthiazolium catalyst 41 bearing a menthol-derived backbone (Fig. 9.6) [45]. Using 20 mol% of this catalyst, they were able to isolate the Stetter product 30 (R = Me) in 75% yield with 50% ee. The low stereoselectivity was ascribed to an atropo-isomerization of the catalyst during the course of the reaction. 

Moritz, R.F. A., Kirchner, W.H. and Crewe, R. M. (1991). Chemical camouflage of the death s head hawkmoth (Acherontia atropos L.) in honeybee colonies. Naturwissenschaften, 78,179-182. 

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