ONFIGURATIONS

Memantine is achiral. The molecule has a plane of symmetry in which the enantiomorphic halves of the molecule are reflections of each other. Both the carbon atom attached to the amino group and the tertiary carbon atom are pseudo chirality centres and both are r-c onfigured. Note that the configuration of the pseudo chirality centres remains unaltered on mirror reflection. Although there are four stereogenic centres in the molecule, it is unnecessary to use any stereodescriptor to describe the configuration of the molecule since there are no stereoisomers. 

FruA is stereoselective and stereocenter 2 is created with the SNuclear Overhauser Effects (NOEs) observed, and the coupling constants measured, the configurations found for compound 11 were IS, 2S, 3R, and 6R. AH the substituents are equatorially positioned on the cyclohexane ring. The (2S,3R)-configurations are consistent with the usually observed diastereoselectivity of FruA In a second exploration [20], the racemic aldehyde 10 was condensed with DHAP after ketal hydrolysis of rac-14 under acidic conditions. In this case, two major isomers 12 and 13 were isolated in 35 and 29% yields after flash chromatography purification. 

Alkenyl allyl ethers. A silyl enol ether, an allylic alcohol, and NIS react to form mixed acetal of iodoacetaldehyde. The elimination of an iodine atom and the siloxy group with BuLi furnishes the alkenyl allyl ether with a defined (Z)- or ( )K onfiguration. An important factor is that the elimination pattern in DME is strictly anti, while in hexane it is syn. 

With the anthelmintic tetramisole (124) some mood elevating activity in depressed schizophrenics was observed during a double-blind crossover study [306,307]. The (+)-enantiomer of (124), dexamisole, showed effects in depression in small preliminary clinical trials [308].The(—)-antipode,levamisole,was the active anthelmintic in the racemate [309-311], but of its central activity nothing is mentioned. The [Pg.295]

Whereas cyclic allyhc alcohols of normal size can only yield (Z)acyclic allylic alcohols preferentially give ( )-isomers. Indeed, the Meerwein-Eschenmoser-Claisen rearrangement is an excellent method for the stereoselective formation of di- and trisubstituted (E)-double bonds in acyclic systems. The high diastereoselectivities observed (dr >95 5) can be explained by invoking a chair shaped transition state 35a or 36a (Scheme 7.15). This minimizes... 

The intermediate alkenylmagnesium intermediate 257 can be trapped with a variety of electrophiles to generate functionalized singlewith benzaldehyde provide the aUylic alcohols as single alkene isomers in good yields (Scheme 10.89) [72]. 

During the past decades, iridium-catalyzed allylation chemistry developed dramatically, and the improvements made have been summarized in several reviews [143]. In contrast to the paUadiumallyl complex derived from a branched or linear ( )linear products with conserved double-bond geometry are formed, indicating a slow anti-syn isomerization (Scheme 12.63) [144]. 

In several antidepressant tests, (46) is very active the oral EDso in reserpine and tetrabenazine tests is 03-1 mg kg" [133,134]. Compound (46), and also its meta-MeO analogue, with 5biogenic amine uptake mechanisms in mouse and rat heart were half as potent as, and of shorter duration than, those of imipramine (I). Uptake of NA in rat medulla or hypothalamus was not inhibited by (46), but alteration of the NA-metabolite pattern was similar to that associated with (I) [136]. Ginically a rapid onset of action of (46) in depressed patients was claimed [ 137], but in subsequent trials only a minority adhered to this view in general no difference from imipramine was demonstrated in various double-blind trials [132]. It appeared to have less peripheral anticholinergic and possibly a lower intrinsic activity in blocking the monoamine uptake process than (1). In depressed patients with clear anxiety components, (46) showed also favourable results [138]. 

Based on these results the following reaction pathway can be assumed. Iminium catalysis is reahzed by the use of chiral imidazolidinones. The subsequent enamine catalysis (HOMO achvation) is realized by deployment of proline. The anti-configured products were detected by application of L-proline, whereas the use of D-proline determines the syn[Pg.90]

To rationalize these results, a conformational study of these peptidomimetics was undertaken. DKP scaffolds can induce a well-defined tridimensional stracture and the importance of this characteristic was proven in several studies [20]. In fact, as a consequence of the absolute configuration of the two a-amino acids forming the cyclic dipeptide unit, the two reachve functionalities (amino and carboxylic acid) are locked in a cis- (catalysts 7 and 8) or trans[Pg.104]

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