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A convenient method is presented for the first time for the direct separation of enantiomers of a tris(2-phenylpyridine) iridium (III) and an analog substituted with long alkoxy chains on polysaccharide derivative-based chiral stationary phases by HPLC. Tris(2-phenylpyridine) iridium (III) was separated on the immobilized amylose 3,5-dimethylphenylcarbamate (Chiralpak IA) using hexane/CHCl₃/CH₂Cl₂ (75:20:5) as an eluent, and the analog could be separated on the coated cellulose 3,5-dimethylphenylcarbamate (Chiralcel OD) and cellulose 4-methylbenzoate (Chiralcel OJ) using hexane/2-propanol (96:4) as the eluent. CD spectra of the eluted HPLC fractions were also recorded, and the observed mirror image patterns confirm their enantioseparations.

The spherical beads consisting of cellulose 3,5-dimethylphenylcarbamate with partial hydroxyl groups were prepared to be used as chiral packing materials (CPMs) for HPLC. The beads were obtained without using macroporous silica gel, which is usually used as the support of the CPMs based on the polysaccharide derivatives. After the crosslinking in the bead with diisocyanates, such as 4,4′-diphenylmethane diisocyanate (MDI), 4,4′-dibenzyl diisocyanate (DBDI), tolylene-2,4-diisocyanate (TDI), and m-xylylene diisocyanate (XDI), the obtained beads were packed into an HPLC column. As the content of the hydroxyl groups of the cellulose derivatives decreased, the obtained CPM exhibited a higher chiral recognition ability. The beads possessed a higher loading capacity than the CPM prepared by coating the cellulose derivative on silica gel. The crosslinked beads could be used with the eluent containing chloroform. The amylose derivative beads were also prepared as a CPM for chiral HPLC.

Polysaccharide-based chiral packing materials (CPMs) for high-performance liquid chromatography have frequently been used not only to determine the enantiomeric excess of chiral compounds but also to preparatively resolve a wide range of racemates. However, these CPMs can be used with only a limited number of solvents as mobile phases because some organic solvents, such as tetrahydrofuran, chloroform, and so on, dissolve or swell the polysaccharide derivatives coated on a support, e.g., silica gel, and destroy their packed columns. The limitation of mobile phase selection is sometimes a serious problem for the efficient analytical and preparative resolution of enantiomers. This defect can be resolved by the immobilization of the polysaccharide derivatives onto silica gel. Efficient immobilizations have been attained through the radical copolymerization of the polysaccharide derivatives bearing small amounts of polymerizable residues and also through the polycondensation of the polysaccharide derivatives containing a few percent of 3-(triethoxysilyl)propyl residue. © 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 7: 91–103; 2007: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20107

N-(1-Phenyldibenzosuberyl)methacrylamide (PDBSMAM) and its derivative N-[(4-butylphenyl)dibenzosuberyl]methacrylamide (BuPDBSMAM) were synthesized and polymerized in the presence of (+)- and (−)-menthols at different temperatures. The tacticity of the polymers was estimated to be nearly 100% isotactic from the ¹H NMR spectra of polymethacrylamides derived in D₂SO₄. Poly(PDBSMAM) was not soluble in the common organic solvents, and its circular dichroism spectrum in the solid state was similar to that of the optically active poly(1-phenyldibenzosuberyl methacrylate) (poly(PDBSMA)) with a prevailing one-handed helicity, indicating that the poly(PDBSMAM) also has a similar helicity. Poly(BuPDBSMAM) was optically active and soluble in THF and chloroform. Its optical activity was much higher than that of the poly[N-(triphenylmethayl)methacrylamide], suggesting that one-handed helicity may be more efficiently induced on the poly(BuPDBSMAM). The copolymerization of BuPDBSMAM with a small amount of optically active N-[(R)-(+)-1-(1-naphthyl)ethyl]methacrylamide, particularly in the presence of (−)-menthol, produced a polymer with a high optical activity. The prevailing helicity may also be efficiently induced. The chiroptical properties of the obtained polymers were studied in detail. The chiral recognition by the polymers was also evaluated. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1304–1315, 2007

Epoxidation of barrelene (3) with a neutralized solution of Oxone^® gave the barrelene trisepoxide 6 in 82 % isolated yield, while lead tetraacetate promoted aziridination of 3 with two equiv. of N-aminophthalimide gave a mixture of mono-7 and bis(aziridine) endo,exo-8, which were isolated in 67 and 8 % yield, respectively. Fourfold repetition of this aziridination gave the bis(aziridines) exo,exo- and endo,exo-8 along with the trisaziridine 9 in 21, 8 and 19 % yield, respectively. Epoxidation of 7 and endo,exo-8 with buffered m-chloroperbenzoic acid furnished the dioxaazatrishomobarrelene 10 and oxadiazatrishomobarrelene 11 in 36 and 62 % yield, respectively. The structures of triheteratrishomobarrelenes 6 and 9 were established by X-ray crystallography. Upon treatment with BF₃·Et₂O at –20 °C (for 6) or with the strongly acidic ion exchange resin Amberlyst 15 at ambient or elevated temperatures (for 9–11), these triheteratrishomobarrelenes rearrange to give the triheteratrishomocubanes rac-12 to rac-15, as proved by X-ray crystal structure analysis of rac-13, in 75–100 % yield. The enantiomeric pairs of trioxa- 12 and triazatrishomocubane 13 were separated by preparative HPLC on a chiral column. 12 exhibited specific rotationsof [α]_D²⁵ = +196 and [α]₃₆₅²⁵ = +652 (c = 0.497, CHCl₃) for the firstly eluted and [α]_D²⁵ = –173 and [α]₃₆₅²⁵ = –608 (c = 0.503, CHCl₃) for the secondly eluted enantiomer; 13 had [α]_D²⁵ = +30 and [α]₄₃₅²⁵ = +501 (c = 0.490, CHCl₃) for the firstly as well as [α]_D²⁵ = –28 and [α]₄₃₅²⁵ = –475 (c = 0.501, CHCl₃) for the secondly eluted enantiomer. The geometry of rac-13 and the absolute configurations of (–)-12 and (+)-13 were determined by X-ray crystal structure analyses. According to this, (–)-12 and (+)-13 possess the same (1R,3R,5R,6R,8R,10R)-configuration. Theabsolute configuration of the former was also confirmed byDFT computations at the TD-B3LYP/6-31+G(d,p)//B3LYP/6-31+G(d) level of theory; the computed specific rotation for (–)-12 was –178. Computations for the elusive (all-R)-triazatrishomocubane (all-R)-13-H without phthalimidyl substituents on the nitrogen atoms disclosed that the sign of rotation is the same for the parent (all-R)-13-H and (all-R)-trioxatrishomocubane (all-R)-12 with the same absolute configuration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Cellulose and amylose phenylcarbamates having one or two alkoxy groups on a phenyl ring were synthesized, and their chiral recognition abilities as chiral stationary phases for HPLC were evaluated. Compared to the 4-methoxyphenylcarbamates of cellulose and amylose, which are known to show a poor chiral recognition, the 3-methoxyphenylcarbamates exhibited much higher chiral recognitions. For cellulose derivatives, as the bulkiness of the 3-alkoxy group increased, the chiral recognition ability increased. On the other hand, for the amylose derivatives, a clear relation between the chiral recognition and the bulkiness of the alkoxy group was not observed, and the 3-methoxy, ethoxy, and isopropoxyphenylcarbamates showed relatively high chiral recognitions. The introduction of two methoxy groups to the meta-positions decreased the chiral recognition ability. In order to discuss the relationship between the structure and chiral recognition ability of the alkoxyphenylcarbamates, their molecular models were constructed.

Different kinds of vinyl groups were randomly introduced onto the glucose units of cellulose 3,5-dimethylphenylcarbamates by a one-pot method using the bifunctional reagents dec-1-ene-10-isocyanate, 2-isocyanatoethyl methacrylate, and methacryloyl chloride. The chiral recognition properties of the prepared derivatives were then evaluated by coating and immobilizing them on silica gel as HPLC packing material. Immobilization was carried out by radical copolymerization with a vinyl comonomer, 1,5-hexadiene, in toluene at 80°C. The effects of the structures and content of the vinyl groups on the immobilization and on enantioseparations were investigated. This one-pot method was also extended to the synthesis of amylose 3,5-dimethylphenylcarbamates having a random vinyl group. Comparisons of the chiral resolution powers of our laboratory-made packing materials and the newly commercialized Chiralpak IA with immobilized amylose 3,5-dimethylphenylcarbamate and Chiralpak IB with immobilized cellulose 3,5-dimethylphenylcarbamate are discussed.

Monolithic capillary columns containing native silica gel were covalently modified with 3,5-disubstituted phenylcarbamate derivatives of cellulose and amylose and applied for enantioseparations in capillary LC. The method previously used for covalent immobilization of polysaccharide phenylcarbamate derivatives onto the surface of microparticulate silica gel was successfully adapted for in situ modification of monolithic fused-silica capillary columns. The effects of the nature of polysaccharide and the substituents, as well as of multiple covalent immobilization of polysaccharide derivative on chromatographic performance of capillary columns were studied. The capillary columns obtained using this technique are stable in all solvents commonly used in LC and exhibit promising enantiomer resolving ability.

We investigated the separation of chrysanthemate isomers (1), particularly the (1R)-trans form, by high-performance liquid chromatography (HPLC) using polysaccharide derivatives, such as the phenylcarbamates and benzoates of cellulose and amylose, as the chiral stationary phases (CSPs). The chiral packing materials (CPMs) having a high chiral recognition for the chrysanthemic acid ethyl ester (1a) were prepared by coating cellulose tris(4-methylbenzoate) (2a) dissolved in solvents containing methyl benzoate or acetophenone as an additive on silica gel. The separation factor for 1a significantly depended on the preparation conditions of CPM 2a, such as the coating amount of 2a and the type and amount of additives. The chiral recognition ability created by imprinting the additives was lost when the CPM was heated at a high temperature, and was recovered by contacting it with the additive in a packed column. The structural change in 2a during these treatments was not clearly detected by spectroscopic methods. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5087–5097, 2006

Phenylcarbonate, benzoylformate, and p-toluenesulfonylcarbamate of cellulose and five new benzoylcarbamate derivatives of both cellulose and amylose were synthesized and their chiral recognition abilities were evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC). Cellulose benzoylcarbamate has a higher chiral recognition ability compared to phenylcarbonate, p-toluenesulfonylcarbamate, and benzoylformate of cellulose. The benzoylcarbamate derivatives exhibited a characteristic chiral recognition for the racemates, which bear a hydrogen atom capable of hydrogen bonding to the carbonyl group of the benzoylcarbamates. The structures of the benzoylcarbamates were investigated by CD spectroscopy. Chirality 17:299–304, 2005. © 2005 Wiley-Liss, Inc.

Monolithic capillary columns containing native silica gel were modified with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) and used for enantioseparations in capillary liquid chromatography. The method adopted for in situ enantioselective modification of monolithic fused silica capillary columns by coating with CDPMC appears to be fairly simple and fast. High efficiency enantioseparations of test racemic compounds and several chiral drugs were achieved in a short time. It was possible to increase the amount of chiral selector present by multiple coating of monoliths with CDMPC. The baseline enantioseparation of 2,2,2-trifluoro-1-(9-anthryl)ethanol was achieved in an analysis time less than 30 s with this capillary column. In addition, reproducible enantioseparations were obtained when the chiral selector was removed from the monolithic column by flushing it with appropriate solvent and the column recoated.

Selectively functionalized molecular knots (knotanes) of the amide-type have been used as building blocks in syntheses of higher covalent assemblies composed of up to four knotane units. Preparation of linear and branched tetraknotanes consisted of the consecutive selective removal of allyl groups followed by linking of the intermediate hydroxyknotanes with biphenyl-4,4′-disulfonyl chloride. Macrocyclic knotane oligomers involving two, three, and four knotane moieties were obtained by high-dilution cyclization of dihydroxyknotane and biphenyl-4,4′-disulfonyl chloride. Due to their relation with cyclophanes, the latter class of oligomeric knotanes was termed “knotanophanes“. Chiral resolution analysis of new oligoknotanes has been attempted on chemically bonded Chiralpak AD stationary phases, however met severe difficulties due to their complex isomeric compositions, and in most cases a significant overlap of the isomer fractions was observed. In spite of the limits of presently available chiral stationary phases that allowed only partial resolution of the synthesized topologies, oligoknotanes have been shown to be of high fundamental interest due to their unprecedented chirality. The chirality descriptions of topologically chiral unsymmetrical dumbbell 4, and the linear tetraknotane 5 are analogous to the Fischer projections of erythrose/threose and hexaric acid, respectively, while the isomeric composition of the branched tetraknotane 8 is completely unique. Moreover, the linear and branched tetraknotanes are constitutional isomers. Chirality of knotanophanes represents, in turn, analogies to known cyclic forms of peptides or sugars with multiple stereogenic centers.

Three novel cycloalkylcarboxylates, cyclopentyl, cyclohexyl, and 1-adamantylcarboxylates of cellulose and amylose were prepared and their chiral recognition abilities as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) were evaluated using a methanol–water mobile phase. Among these esters, cellulose tris(cyclohexylcarboxylate) showed a relatively high chiral recognition ability. The 1-adamantylcarboxylates of cellulose and amylose showed dissimilar chiral recognition abilities from the other two, probably due to the low degree of substitution and the high hydrophobicity of this group. Chirality 16:309–313, 2004. © 2004 Wiley-Liss, Inc.

A chiral diamine alkaloid, (−)-sparteine (Sp), has been found to be very effective as a ligand for Grignard reagents when used for the enantiomer-selective polymerization of racemic RS-1-phenylethyl methacrylate. The enantiomeric excess of the initially polymerized monomer is 93%, and at about a 60% conversion, nearly optically pure R-monomer is recovered. This enantiomer selectivity is today the highest in polymer chemistry. Triphenylmethyl methacrylate (TrMA) is a unique monomer that gives a highly isotactic polymer even during radical polymerization. When TrMA is polymerized with the Sp complex with n-butyllithium in toluene at −78 °C, an optically active, isotactic polymer [poly(triphenylmethyl methacrylate) (PTrMA)] with a one-handed helical conformation is obtained. The helical structure is maintained even at room temperature in solution. Analogous helical polymethacrylates that show various conformational changes have also been found. One-handed helical PTrMA exhibits high chiral recognition to a variety of racemates as a chiral stationary phase (CSP) for high-performance liquid chromatography. This finding has led to the development of very powerful CSPs based on polysaccharides, such as cellulose and amylose. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4480–4491, 2004

The radical polymerization of an optically active methacrylamide, N-[(R)-α-methoxycarbonylbenzyl]methacrylamide, was carried out in the absence and presence of Lewis acids such as yittribium trifluoromethanesulfonate [Yb(OTf)₃] and scandium trifluoromethanesulfonate [Sc(OTf)₃]. Catalytic amounts of the Lewis acids significantly affected the stereoregularity of the obtained polymers. The polymerization with Yb(OTf)₃ in tetrahydrofuran afforded isotactic polymers (up to mm = 87%), whereas the conventional radical method without the Lewis acid produced polymers rich in syndiotacticity (up to rr = 88%). The radical polymerization in the presence of MgBr₂ proceeded in a heterotactic-selective manner (mr = 63%). Thus, the isotactic, syndiotactic, and heterotactic poly(methacrylamide)s were synthesized by the radical processes. The chiral recognition abilities of the obtained optically active poly(methacrylamide)s were affected by the stereoregularity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3354–3360, 2003

The effects of Lewis acids, that is, rare earth metal trifluoromethanesulfonates, on the free-radical polymerization of N-methylmethacrylamide (MMAM), N-isopropylmethacrylamide (IPMAM), N-tert-butylmethacrylamide (tBMAM), N-phenylmethacrylamide (PMAM), and methacrylamide were examined under various conditions. A catalytic amount of Yb(OSO₂CF₃)₃ significantly affected the stereochemistry during the radical polymerization. Polymerization solvents strongly influenced the effect of the Lewis acids. Methanol was the best solvent for increasing the isotactic specificity during the polymerization of MMAM and IPMAM, whereas tetrahydrofuran was more effective for the tBMAM and PMAM polymerizations. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1027–1033, 2003

The immobilization of cellulose 3,5-dimethylphenylcarbamate derivatives having a polymerizable vinyl group, i.e., 4-vinylphenylcarbamate or 2-methacyloyloxyethylcarbamate, on silica gel was examined under various conditions. The immobilization was basically conducted through the radical copolymerization of the derivatives with a vinyl monomer. Several factors, such as the vinyl monomer content and the type and amount of the vinyl group of cellulose derivatives, were varied. The introduction of a vinyl group onto the silica surface resulted in a more efficient immobilization of the cellulose phenylcarbamate derivatives on the silica gel. As the content of the vinyl group on the cellulose derivatives was reduced, the immobilization became more difficult, although the obtained phase exhibited higher chiral recognition abilities. These immobilized CSPs could be stably used with the eluent containing 10% chloroform, which cannot be used for the phase prepared by coating the derivatives on silica gel. Some racemates were better resolved on the immobilized CSP by using chloroform as a component of the eluent. Chirality 15:77–82, 2003. © 2002 Wiley-Liss, Inc.

„Picoröhren“: In einer überraschend glatten Reaktion wurde durch Friedel-Crafts-Alkylierung einer vollständig konjugierten röhrenförmigen Struktur eine chirale Röhre gebildet (siehe Bild). Im Unterschied zu den Kohlenstoff-Nanoröhren, die bei hohen Temperaturen synthetisiert werden, ist diese chemisch modifizierte „Picoröhre“ chiral durch Substitution. Die beiden Enantiomere wurden durch Chromatographie an einer chiralen Phase getrennt.

“Picotubes”: A chiral tube is formed in the surprisingly clean Friedel–Crafts alkylation of a fully conjugated tubelike structure. Unlike helical carbon nanotubes synthesized at high temperatures, this chemically modified picotube is chiral by substitution. The two enantiomers were separated by chromatography on a chiral stationary phase.

Polysaccharide-immobilized chiral stationary phases (CSPs) were prepared by the polymerization of cellulose 3,5-dimethylphenylcarbamate, having a polymerizable vinyl group, such as 4-vinylphenylcarbamate or 2-methacryloyloxyethylcarbamate, at the 6-position, with a vinyl monomer, such as styrene, isoprene, t-butyl acrylate, or t-butyl methacrylate, on silica gel under various conditions. Their chiral recognition abilities were then evaluated with high-performance liquid chromatography. The immobilized cellulose 3,5-dimethylphenylcarbamate remained on the silica gel even if washed with tetrahydrofuran, which could dissolve the cellulose derivative. The chiral recognition abilities of the immobilized CSPs were similar to those of the coated CSPs when the vinyl monomer content was low. The chiral recognition abilities of the obtained immobilized CSPs slightly depended on the vinyl monomers. The immobilization of the cellulose derivatives was more efficiently attained on the silica gel modified with a vinyl compound. The cellulose derivatives, randomly having a vinyl group at the 2-, 3-, or 6-position of the glucose unit, were prepared by a one-pot reaction. The immobilization efficiency of these derivatives was slightly lower than that of the derivative with the vinyl group at the 6-position. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3703–3712, 2003

In this study the potential of amylose tris(3,5-Dimethylphenylcarbamate) (ADMPC) was evaluated for enantioseparations in capillary liquid chromatography (CLC) and capillary electrochromatography (CEC). This material was previously used for enantioseparations in CEC with nonaqueous alcohols and the first study in aqueous-organic mobile phase indicates its potential for CEC enantioseparations. The effect of various experimental parameters on the separation characteristics was investigated in both CLC and CEC mode. Under optimized conditions the plate numbers in CEC mode reached 500 000 plates/m for thiourea and exceeded 240 000 plates/m for the enantiomers of some chiral compounds investigated. Comparative enantioseparations performed in CLC and CEC mode revealed significant advantages of CEC.

For the first time, knot molecules (of the amide type) are synthesized, which bear one to three dendritic units of various generations at their periphery. They were obtained through two different routes: i) attachment of dendritic wedges to new mono-, di- and trihydroxy functionalized dodecaamide knots that have been obtained by selective debenzylation of oligobenzyloxy substituted knots, or ii) cyclization of already dendron substituted pyridine-2,6-dicarbonyl dichlorides with an “extended diamine” to directly yield the “tri-dendroknots”. The derivatization of knot molecules by functional substituents and even large dendritic units is an important advance in the synthesis and property variation of molecular knots. This holds true in particular for substitution of the pyridine units of the knots, whereas the isophthalic acid units seem not to tolerate larger substitutents, as reflected in lower knot yields. These syntheses also demonstrate knots to be accessible indirectly by substitution of the corresponding mono-, di- and tri-functionalized knot skeleton. An advantage of dendritic “decoration” is the control of solubility and chromatographic behaviour of the molecular knots (knotanes). Suggestions are made about the threading mechanism by supramolecular template effects leading to the formation of amide-based molecular knots. The topological chirality of the new “dendroknots” is shown by efficient enantioseparations (separation factor α between 1.22 and 1.48). For this purpose (commercially unavailable) chiral column material of the Chiralpak type was used, in which the chiral component is covalently bonded to the silica gel support. The racemate splittings provide additional evidence for the knotted structure, as all other conceivable isomers such as macromonocyclic or catenated dodecaamides would not be chiral. The pure enantiomers obtained exhibit pronounced Cotton effects in their circular dichroism spectra. By comparison with the unsubstituted knot, the absolute configuration (Λ, Δ) of all new knots is derived.

The radical polymerization of N-methylmethacrylamide (MMAM) and N-isopropylmethacrylamide (IPMAM) was carried out in the presence of various Lewis acids. The isotacticity (mm) of the polymers obtained from the polymerization of MMAM and IPMAM in the presence of Yb(OTf)₃ reached 59 and 67%, respectively, although the radical polymerization in the absence of Lewis acids gave syndiotactic polymers. The phase-transition temperature of poly(N-isopropyl- methacrylamide) depended on the tacticity.

Cyclopentyl and (±)-exo-2-norbornylcarbamates of cellulose and amylose were prepared and their chiral recognition abilities as chiral stationary phases for high-performance liquid chromatography (HPLC) were evaluated. Among these carbamates, cellulose tris(cyclopentylcarbamate) and amylose tris((±)-exo-2-norbornylcarbamate) showed particularly high chiral recognition, which is comparable to that of several well-known phenylcarbamate derivatives. The chiral recognition mechanism of cellulose tris(cyclohexylcarbamate), which was previously found to be an effective chiral stationary phase for HPLC, was investigated using NMR spectroscopy. The derivative dissolved in chloroform exhibited the chiral discrimination of several enantiomers in NMR as well as in HPLC. For example, the 1,1′-bi-2-naphthol enantiomers were distinctly discriminated in the ¹H, ¹³C, and 2D-NOESY spectra. Chirality 14:372–376, 2002. © 2002 Wiley-Liss, Inc.

Durch Vergleich der experimentellen mit der theoretischen Circulardichroismus-Kurve konnten die absoluten Konfigurationen der chromatographisch basisliniengetrennten Enantiomere einiger neuer Kleeblatt-Amid-Knoten (siehe schematische Darstellung) bestimmt werden. Aus den Ergebnissen der Synthese mit unterschiedlich substituierten Ausgangsverbindungen konnten Rückschlüsse auf den Verknotungsmechanismus gezogen werden.

The stereospecific radical polymerization of vinyl esters, methacrylates, and α-substituted acrylates was studied. Fluoroalcohols, as a solvent, have remarkable effects on the stereoregularity of the radical polymerizations of vinyl acetate, vinyl pivalate, and vinyl benzoate, affording polymers rich in syndiotacticity, heterotacticity, and isotacticity, respectively. This method was successfully applied to the polymerization of methacrylates to give syndiotactic polymers. The steric repulsion between the entering monomer and the chain-end monomeric unit bound by the solvent through hydrogen bonding is important for the stereochemical control in these systems. Lewis acid catalysts, such as lanthanide trifluoromethanesulfonates and zinc salts, were also effective for the stereocontrol during the radical polymerization of methyl methacrylate, to reduce the syndiotacticity and α-(alkoxymethyl)acrylates to synthesize isotactic and syndiotactic polymers. Radical polymerization of the methacrylates bearing a bulky ester group, such as the triphenylmethyl methacrylate derivatives, gave highly isotactic polymers, as in the case of anionic polymerization. In addition, the control of one-handed helical conformation was attained in the radical polymerization of 1-phenyldibenzosuberyl methacrylate using chiral neomenthanethiol or cobalt(II) complexes as an additive. © 2000 John Wiley & Sons, Inc. and The Japan Chemical Journal Forum Chem Rec 1:46–52, 2001

(1-Methylpiperidin-4-yl)diphenylmethyl methacrylate produced an optically active, helical polymer with a highly isotactic configuration by asymmetric anionic polymerization. The optical activity of the polymer was based on the excess helical sense of the main chain. The monomer also afforded an optically active, helical polymer by the radical polymerization of (−)-menthol as a chiral additive.

The free-radical polymerizations of methyl methacrylate (MMA), ethyl methacrylate, isopropyl methacrylate, and 2-methoxyethyl methacrylate were carried out in the presence of various Lewis acids. The MMA polymerization in the presence of scandium trifluoromethanesulfonate [Sc(OTf)₃] in toluene or CHCl₃ produced a polymer with a higher isotacticity and heterotacticity than that produced in the absence of Sc(OTf)₃. Similar effects were observed during the polymerization of the other monomers. ScCl₃, Yb(OTf)₃, Er(OTf)₃, HfCl₄, HfBr₄, and In(OTf)₃ also increased the isotacticity and heterotacticity of the polymers. The effects of the Lewis acids were greater in a solvent with a lower polarity and were negligible in tetrahydrofuran and N,N-dimethylformamide. Sc(OTf)₃ was also found to accelerate the polymerization of MMA. On the basis of an NMR analysis of a mixture of Sc(OTf)₃, MMA, and poly(methyl methacrylate), the monomer–Sc(OTf)₃ interaction seems to be involved in the stereochemical mechanism of the polymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1463–1471, 2001

New chiral dendrimers with planar-chiral, cycloenantiomeric and topologically chiral cores were prepared in yields of up to 90% starting from a racemic 4-hydroxy[2.2]paracyclophane, a [2]rotaxane with sulfonamide groups in the wheel and axle positions and [2]catenane with a sulfonamide group in both of its macrocycles. The separation of the racemic mixture of these dendrimers was possible by HPLC on chiral stationary phases. The CD spectra of the dendro[2.2]phanes showed a hitherto unknown influence of the dendritic part on the intensities of the Cotton effects. The chirality of these dendrimers is dependent not only on its chiral elements but also on its dendritic wedges and their generation.

Novel optically active phenyl isocyanate derivatives (1–6) bearing an (R)-sec-butoxy, (S)-2-methylbutoxy or (S)-3,7-dimethyloctyloxy group at the meta or para position on the phenyl ring were prepared and polymerized with an anionic initiator in tetrahydrofuran (THF). The resulting polymers from 1, 2, 4 and 6 showed much greater specific rotation than that of the corresponding monomers and an intense circular dichroism (CD) band in the main-chain absorption region, indicating that these polymers have a predominantly one-handed helical conformation in solution. On the other hand, the polymers obtained from 3 and 5 showed a much smaller specific rotation than that of the above polymers at room temperature. The polymers from 2 and 5 showed a remarkable change in optical activity with change in temperature, and the specific rotation of the polymers changed from a positive to a negative value with decrease in temperature. The CD band of the polymers in the absorption region due to the main chain changed from a positive to a negative peak with a change in specific rotation. These results indicate that poly-2 and poly-5 undergo a thermally induced helix–helix transition in THF. The temperature for the helix–helix transition of poly-2 was independent of the degree of polymerization. Poly-2 exhibited a reversible helix–helix transition in chloroform and diethyl ether and also in THF, whereas in toluene and dichloromethane such a transition was not observed. Copyright © 2000 John Wiley & Sons, Ltd.

The free-radical polymerization of 2,2,2-trifluoroethyl acrylate (TFEA), 1,1,1,3,3,3-hexafluoro-2-propyl acrylate (HFiPA) and perfluoro-tert-butyl acrylate (PFtBA) was carried out under various conditions and the stereostructure of the obtained polymers was investigated. Most polymerizations of the three monomers afforded polymers rich in diad syndiotacticity (r) in bulk or in solution; the r-specificity was higher in the HFiPA and PFtBA polymerization than in the TFEA polymerization. Although the tacticity was nearly independent of reaction temperature during the polymerization of TFEA, the r-specificity increased by lowering the reaction temperature during the polymerization of the other two monomers. The polymerization stereochemistry was also affected by the reaction solvents including toluene, tetrahydrofuran, and fluoroalcohols. It was noted that the stereochemistry of the polymerization of HFiPA and PFtBA also depended on the monomer concentration, and a lower monomer concentration led to a higher r-specificity. By optimizing the aforementioned reaction conditions, the poly(HFiPA) having r = 81% (polymerization in tetrahydrofuran at −98 °C at [M]_o = 0.2M) and the poly(PFtBA) having r = 77% (polymerization in toluene at −78 °C at [M]_o = 0.2M) were obtained. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1024–1032, 2000

Ortho-substituted styrenes, such as 2-(N,N-dimethylaminomethyl)styrene (1), 2-(1-pyrrolidinylmethyl)styrene (2), and 2-[(S)-2-(1-pyrrolidinylmethyl)-1-pyrrolidinylmethyl]styrene (3), were synthesized, and the effects of the ortho-substituents on the polymerizability and stereoregularity of the obtained polymers using the anionic method were examined. The bulkiness and coordination of the ortho-substituted amino groups to the counter cation significantly affected the polymerizability and stereochemistry of the obtained polymers. The anionic and radical polymerizations of 2 with a less hindered ortho-substituent afforded polymers in good yields, whereas those of 1 and 3 resulted in lower yields. The anionic polymerization of 3 bearing an optically active diamine derivative at the ortho-position with n-butyllithium in toluene at 0 °C gave a polymer with a high stereoregularity and stable regular conformation based on the stereoregular backbone structure. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4088–4094, 2000

The free-radical polymerization of methyl methacrylate (MMA), ethyl methacrylate (EMA), isopropyl methacrylate (IPMA), and tert-butyl methacrylate (t-BuMA) was carried out under various conditions to achieve stereoregulation. In the MMA polymerization, syndiotactic specificity was enhanced by the use of fluoroalcohols, including (CF₃)₃COH as a solvent or an additive. The polymerization of MMA in (CF₃)₃COH at −98 °C achieved the highest syndiotacticity (rr = 93%) for the radical polymerization of methacrylates. Similar effects of fluoroalcohols enhancing syndiotactic specificity were also observed in the polymerization of EMA, whereas the effect was negligible in the IPMA polymerization. In contrast to the polymerizations of MMA and EMA, syndiotactic specificity was decreased by the use of (CF₃)₃COH in the t-BuMA polymerization. The stereoeffects of fluoroalcohols seemed to be due to the hydrogen-bonding interaction of the alcohols with monomers and growing species. The interaction was confirmed by NMR measurements. In addition, in the bulk polymerization of MMA at −78 °C, syndiotactic specificity and polymer yield increased even in the presence of a small amount {[(CF₃)₃COH]/[MMA]_o < 1} of (CF₃)₃COH. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4693–4703, 2000

Three fungicidal triazolyl alcohols (triadimenol, hexaconazole, and cis/trans-1-4-chlorophenyl-2-1H-1,2,4-triazol-1-yl-cycloheptanol) were completely separated into enantiomers by chiral HPLC using polysaccharide-based chiral stationary phases. A better separation was achieved on cellulose and amylose carbamate phases compared with a cellulose ester phase. Peak shapes were almost symmetrical except for two cases, where tailing of the first eluted enantiomer and unusual symmetric peak broadening were observed. The effect of eluents on enantioseparation was also investigated. Chirality 11:195–200, 1999. © 1999 Wiley-Liss, Inc.

Trennung und Anreicherung von Enantiomeren lassen sich bei der HPLC an chiralen stationären Phasen kombineren. Voraussetzung für das Gelingen der Methode ist, daß sich die Komponenten des Racemats wie bei 1 z. B. thermisch ineinander umwandeln lassen. Im unten schematisch dargestellten Zweisäulensystem werden in der ersten Säule die Enantiomere bei niedriger Temperatur partiell getrennt. Die Chromatographie wird dann unterbrochen, um die zuerst eluierte Fraktion A auf der zweiten Säule äquilibrieren zu lassen.

The first resolution of enantiomers was performed 150 years ago–mechanically. Today a powerful method for carrying out this task is HPLC on polysaccharide derivatives as chiral stationary phases. Most racemates, from an analytical to a preparative scale, now appear to be resolved by this technique. As an example, the chromatogram for the enantiomeric resolution of a fullerene derivative is shown on the right.

The separation and enrichment of enantiomers can be combined by HPLC on chiral stationary phases. One requirement for success is that the components of the racemate—as, for example, with 1—undergo thermal interconversion. In the two-column system shown below the enantiomers are partially separated in the first column at low temperature. The chromatographic flow is then stopped to allow the first fraction eluted (A) to equilibrate on the second column.

Vor 150 Jahren wurde die erste Racematspaltung durchgeführt – und zwar mechanisch. Heute ist dies effizient möglich durch HPLC an Polysacchariden als chiralen stationären Phasen. Sowohl im analytischen als auch im präparativen Maßstab werden heute die meisten Enantiomerengemische mit dieser Methode getrennt. Exemplarisch ist rechts das Chromatogramm für die Trennung der Enantiomere eines Fullerenderivats abgebildet.

Twelve different disaccharides and a series of noncyclic malto- and cello-oligosaccharides were used as chiral selectors in capillary electrophoresis (CE). Most saccharides resolved the enantiomers of atropisomeric 1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (BDHP) depending on the type (α or β) and position of the linkage between monosaccharides. The effect of chain length of malto- and cello-oligosaccharides on enantioseparation of BDHP was also investigated. The nature of cations in background electrolytes affected significantly the separation of BDHP enantiomers. Chirality 10:134–139, 1998. © 1998 Wiley-Liss,Inc.