Chiral macrocycle

Enantiomeric recognition of amino compounds by chiral macrocyclic receptors including pyridine or triazole subunits 97CRV3313. 

Fig. 8-2. Schematic representation of the separation of enantiomers R and S using a supported chiral macrocyclic ligand host.

The analytical capability of these matrices has been demonstrated for chiral amines [12, 13]. The procedure is illustrated in Fig. 8-4 for the separation of NapEtNH " CIO . Concentrated methanol/dichloromethane solutions of the racemic mixture were placed on a column containing the chiral macrocycle host. The enantiomers of the ammonium salts were resolved chromatographically with mixtures of methanol and dichloromethane as the mobile phase. The amounts of R and S salts in each fraction were determined by polarimetry. Because the chiral supported macrocycle interacts more strongly with S salts, the R salt passes through the column first and the S salt last, as seen in Fig. 8-4. 

Zhang, X.X., Bradshaw, J.S. and Izatt, R.M. (1997) Enantiomeric recognition of amine compounds by chiral macrocyclic receptors. Chemical Reviews, 97, 3313-3361. 

Macrocyclic stereoisomeric phosphoramidates 80 and 81 containing oxadiazole segments were obtained starting from 2,5-(2 -hydroxyphenyl)-l,3,4-oxadiazole, phosphorus oxychloride, and other reagents <2001JST145>. Chiral macrocyclic phosphoramidates were also obtained <2001SC3197>. 

Scheme 1. Catalytic enantioselective aldehyde alkylation affords the chiral macrocyclic alcohol 3 in Oppolzer s total synthesis of muscone (1993).

In the preceding section it was shown that the stability of crown-ether complexes with alkylammonium salts depends on the relationship between the structures of the crown ethers and the ammonium ions. How critically this relationship determines the complex stability will become clear in this section, which deals with the discrimination between the two enantiomers of racemic salts by chiral macrocyclic ligands. 

With Secondaiy and Tertiary Amine Functions in Chiral Macrocyclic Polyether Rings. 264... 

With Fused Pyridino Rings in Chiral Macrocyclic Polyethers. 270... 

The chiral dimethyl derivatives RR)-M and (SS)-84 of tetraethylene glycol have been employed (126) in the preparation of chiral macrocyclic polyether diesters such as (JU )-85 and (SS)S6. The reactions of the chiral diols with the appropriate diacid chlorides generally proceed (Scheme S) in good yield in warm benzene under high dilution conditions. 

Nitrogen atoms have been incorporated into chiral macrocyclic polyethers in a variety of different ways. One of the most straightforward approaches is the... 

The pyridine subcycle unit has been introduced into a wide range of 18-crown-6 derivatives. For example, reaction of 2,6-pyridinedicarbonyl chloride with the dimethyl substituted tetraethylene glycol (SS)-84, derived from (S)-lactic acid, afforded (126) the chiral macrocyclic polyether diester (5S)-184. A similar preparative approach (127) gave (SS)-185, where the source of the chirality is (5)-mandelic acid. 

Finally, the chiral macrocyclic peracetylated polyhydroxy polyethers (+)-201 and (+)-202 have been prepared (194) recently by treatment of a- and 0-cyclodextrins, respectively, with diethylborane and 9-borabicyclo[3.3.1]nonan-9-yl methanesulfonate as catalyst. 

The magnitude becomes smaller because the chromophore is farther apart from the rim of the cavity of the chiral macrocyclic host. - (Adapted from Park et ah, 2002)... 

Chiral macrocyclic amino-ethers have been prepared recently (69). Ligands of type E are obtained by attaching a chain (or two chains, one at each Z center to the type D macrocycles (81). The synthesis of macro-cyclic peptides will not be discussed here. 

The structure of the ternary 1 1.5 3.5 complex with the chiral macrocyclic tetracarboxamide 12 can be regarded as a solid state model for a molecular channel. The macrocyclic units are organized in a polymolecular stack with the potassium ions located alternately inside and on top of successive macrocycles, Fig. 40. The in-plane potassium ions (0.25 A from mean plane) coordinate with all six ether oxygen atoms while the out-of-plane ions (1.13 A from mean plane) coordinate to only three oxygen atoms. 

Hence, in this work, we report the heterogeneization of this new chiral macrocycle onto micelle-templated silicate (MTS) surface by substitution of chlorine atom of previously grafted 3-chloropropyl chain. After A-alkylation of the tetraazamacrocycle with propylene oxide and metalation with Mn(lI)Cl2, the catalytic performance of the corresponding hybrid materials was evaluated in the heterogeneous enantioselective olefin epoxidation. 

A variety of macrocycles with asymmetric centers have been reported, examples of which are shown in (57) to (66). Chiral discrimination has been observed in the study of thiolysis of activated ester bonds with tetracysteinyl[18]crown-6 (67), e.g. Gly-L-Phe reacts up to 80 times faster than Gly-D-Phe with this ligand.231 The chiral macrocyclic ligand (66) is also capable of enantiomeric discrimination, by assisting in the selective reduction of carbonyl compounds with high optical yields.232,233... 

Given the observation of catalysis of alkene epoxidation by iron N-alkyl porphyrins, it is likely that these complexes may yield synthetically useful catalysts (32, 65). The possibility of chiral induction by using either a chiral N-alkyl group (66) or a chiral macrocycle such as N-Me etioporphyrin (67) is an area that should prove fruitful in the near future. 

The chirality of tartrates 60 and 61 are confirmed by circular dichroism (CD) spectroscopy <20060L1701>. Multiple bands in the CD spectra of 60 and 61 are due to tartrate dianions inducing CD in the anthracene rings. This is the first reported case of induced circular dichroism (ICD) observed in a chiral macrocycle. 

In more recent syntheses of chiral macrocycles containing pyridine units like 48, which are of interest in their reduced dihydropyridine-form as model compounds for the redox system NADH/NAD , the yield increasing effect of added cesium salts was also used [52]. The yield of 48 was doubled in the cyclization of bis-L-valine amide 47 with l,5-dibromoi ntane in DMF from 41 % (Na2C03) to 80% by application of CS2CO3. The results of cyclizations with several other alkali metal carbonates [52] are shown below. 

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