Rotaxanes chirality

Template synthesis and chirality of catenanes, rotaxanes, and pretzelanes including N-macroheterocyclic lactams and related compounds as structure components 99PAC247. 

This molecule has no chiral carbons, nor does it have a rigid shape, but it too has neither a plane nor an alternating axis of symmetry. Compound 32 has been synthesized and has, in fact, been shown to be chiral. Rings containing 50 or more members should be able to exist as knots (33, and see 37 on p. 114 in Chapter 3). Such a knot would be nonsuperimposable on its mirror image. Calixarenes, ° crown ethers, catenanes, and rotaxanes (see p. 113) can also be chiral if suitably substituted. For example, A and B are nonsuperimposable mirror images. 

Other supramolecular structures such as catenanes and rotaxanes can be formed using zinc as a template ion for example, a benzylic imine catenate formed by Leigh et a/.288 The reversible five-component assembly of a [2]catenane from a chiral metallomacrocycle and a dinaphtho-crown ether has been achieved. Zinc is used as the metal component and drives assembly via the coordination to a bipyridyl unit 7r interactions between the aromatic components are also... 

Kameta N, Hiratani K, Nagawa Y (2004) A novel synthesis of chiral rotaxanes via covalent bond formation. Chem Commun 4 466 -67... 

Out of many exciting recently obtained topologically distinct structures combined rotaxanes 41,400 [23], pretzel-molecule 35 [24a] and bis(pretzelane) 401 [24b], a topologically chiral [2]catenane [25] and an interestiig catenated... 

Figure 49. The first cycloenantiomeric [2]rotaxane - the different atom sequence of wheel with respect to the unsymmetric axle creates this rare case of chirality.

Amide-linked catenanes and rotaxanes can play a major role in the study of rare forms of chirality, e.g. topological chirality and cycloenantiomerism [60]. Resolution of enantiomeric catenanes, rotaxanes, and pretzelanes has been achieved by HPLC on chiral column materials, but further work must be performed to determine absolute configurations and to realize new chiral skeletons composed of achiral building blocks. Topological asymmetric synthesis still belongs to dreams of the future yet should be kept in mind. 

The latest findings of amide-based rotaxanes focus on their chemistry and stereochemistry. The optical properties of an axle bearing chiral glucose stoppers are significantly influenced by rotaxanation - Cotton effects are amplified and the maxima of the CD spectra are shifted bathochromically [71]. 

ARROWS PIDICATF AN ATOM SEQUENCE INTRODUCING A WRFmONALITY INTO THE CDMJWfiNl S OR OK CATENAS AND ROTAXANE. Tilt KNOT IS INlIRKENTLr CHIRAL AND POES NOT NEED ANY SUCH ELEMENT OF... 

In addition, chiral dendrimers (see Section 4.2) can be resolved with the aid of HPLC into their enantiomers, if the silica gel material used as stationary phase has optically active substances bound to its surface [9]. Since the chiral stationary phase (CSP) [10] undergoes different intensities of interaction with the enantiomeric dendrimers, they are retained to different degrees, and in the ideal case two completely separated (baseline separated) peaks are obtained. This separation technique was successfully applied inter alia to racemic mixtures of planar-chiral dendro[2.2]paracyclophanes, cycloenantiomeric dendro[2] rotaxanes, topologically chiral dendro[2]catenanes [11] as well as topologically chiral, dendritically substituted molecular knots (knotanes) [12] (Section 4.2.3). 

Fritz Vogtle Barcelona, Spain Rotaxanes, Catenanes. Pretzelanes- Template Synthesis and Chirality... 

Schalley, C.A., Beizai, K. and Voegtle, F. (2001) On the way to rotaxane-based molecular motors studies in molecular mobility and topological chirality, Acc. Chem. Res. 34, 465-476. 

As shown in Figure 8, sulfonamide centers render catenanes such as 13 and rotaxanes such as 14 chiral, because these groups introduce the directionality into both constituent parts. 

In addition, sulfonamides bear more acidic, compared to carboxamides, protons that can be selectively A-alkylatcd or V-acylatcd. Thus, alkylation of sulfonamide catenane and rotaxane with Frechet-dendrons of 2nd generation led to the first representatives of the dendrocatenane 15 and dendrorotaxane 16 [46], respectively. These compounds were of especial interest, since they allowed for the first time to study chiral induction of topologically chiral cores on appended dendrons and to compare to the analogous centrochiral dendrimers for which phenomenon of the crypto-optical activity was postulated [47],... 

Our vision is to use the knotanophanes and the linear oligomeric knotanes as chiral wheel and axle components, respectively, in future giant rotaxanes which would mimic naturally occurring enzyme complexes [60],... 

Yamamoto, C., Okamoto, Y., Schmidt. T., Jager, R., Vogtle, F. Enantiomeric resolution of cycloenantiomeric rotaxane, topologically chiral catenane, and pretzel-shaped molecules observation of pronounced circular dichroism, J. Am. Chem. Soc. 119 (1997), 10547-10548. 

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