Cyclodextrin unsubstituted

Recently, two examples of the separation of enantiomers using CCC have been published (Fig. 1-2). The complete enantiomeric separation of commercial d,l-kynurenine (2) with bovine serum albumin (BSA) as a chiral selector in an aqueous-aqueous polymer phase system was achieved within 3.5 h [128]. Moreover, the chiral resolution of 100 mg of an estrogen receptor partial agonist (7-DMO, 3) was performed using a sulfated (3-cyclodextrin [129, 130], while previous attempts with unsubstituted cyclodextrin were not successful [124]. The same authors described the partial resolution of a glucose-6-phosphatase inhibitor (4) with a Whelk-0 derivative as chiral selector (5) [129]. 

The alkaline hydrolysis of p-nitrophenyl oxodecanoates [36] has been studied in the absence and presence of cyclodextrins (Cheng et al., 1985). These flexible keto-esters have either a 4-, 5- or 6-oxo substituent [36], and their rates of hydrolysis can be compared with unsubstituted ester [37]. The... 

Impulse response technique for measuring catalytic absorption, 19 243 Inactive additives and alloys, 32 190-191 Inclusion compounds, 32 418,420-426 cyclodextrin, 32 428-436, 462 unsubstituted compounds, 32 422-426... 

Unsubstituted cycloamyloses have been used to catalyze a number of reactions in addition to acyl group transfer. Brass and Bender (8) showed that cycloamyloses promoted phenol release from diphenyl and bis(p-nitro-phenyl) carbonates and from diphenyl and bis(m-nitrophenyl)methyl phos-phonates. Breslow and Campbell (10,11) showed that the reaction of anisole with HOCL in aqueous solution is catalyzed by cyclohexaamylose and cycloheptaamylose. Anisole is bound by the cyclodextrins and is chlorinated exclusively in the para position while bound. Cycloheptaamylose has been used to promote regiospecific alkylation followed by the highly selective oxidation shown in reaction (3) (95). In addition cycloheptaamylose effec-... 

We now can prepare, in principle, enzyme models by use of the concept of host design, where artificial enzymes are so designed as multiple recognition hosts schematically shown in Fig. 20. Although unsubstituted cyclodextrins are well known to catalyze some organic reactions such as ester hydrolysis, their catalytic activities are relatively small. Recent progress in cyclodextrin chemistry has shown that it is possible to enhance the catalytic... 

Tabushi I, Kuroda Y, Mizutani T (1986) J Am Chem Soc 108 4514. It should be noticed that unsubstituted a- and -cyclodextrin as well weakly bind tryptophan see therein and Lipkowitz KB, Raghothama S, Yang YA (1992) J Am Chem Soc 114 1554... 

Table VII (51). The relevant free dimensions are often similar for zeolite and nonzeolite. Urea (free diameter 5.2 A) is like Sieve A (free diameter of windows 4.3 A) in accommodating n- but not isoparaffins. Thiourea (6.1 A) and offretite (6.3 A) have channels with similar free diameters as do 0-cyclodextrin (7-8 A) and zeolite L (7.1 X 7.8 A). In thiourea the loose fit of n-paraffins in the tunnel appears to destabilize the adducts (85, 36). The same is true of disc-shaped molecules comprising only benzenoid rings. However, if suitably bulky saturated side chains are attached (cyclohexyl-benzene or fertf-butylbenzene), then adduction readily occurs. Heterocy-clics, like unsubstituted aromatics, do not readily form adducts. Thus flat molecules also exert a destabilizing effect upon the tunnels of a circular cross section. Such stability problems do not arise with the robust, permanent zeolite structures, and this constitutes an interesting distinction. Offretite, for example, readily sorbs benzene or heterocyclics with or without alkyl side chains, provided only that they are not too large to permeate the structure.

Better results for the enantioanalysis of S-perindopril were obtained when the carbon paste was impregnated with a-, /i- and y-cyclodextrins as chiral selectors [29]. There had been improvements in detection limits (lower with unsubstituted CDs as chiral selectors), enantioselec-tivity (higher especially when a-CD was used as chiral selector) and the values of the slope of the electrodes (higher especially when a-CD and y-CD were used as chiral selectors). 

EPMEs based on carbon paste impregnated with a-, />- and y-cyclo-dextrins are proposed for the assay of L-proline [31]. Response characteristics showed that the proposed electrodes could be reliably used in the assay of L-proline, with the best enantioselectivity and time-stability exhibited by a-cyclodextrin based EPME. The EPMEs based on the proposed unsubstituted cyclodextrins showed lower detection limits (10 10 magnitude order) than the one previously studied, based on /J-cyclodextrin derivative [30]. The widest linear concentration range is recorded for the y-cyclodextrin based EPME (10 8-10-3mol/L). The recovery tests performed for the assay of L-proline in the presence of d-proline (recoveries higher than 99.65%) proved that the proposed... 

It has been estimated that the internal cavity of 8-cyclodextrin is optimal for the inclusion of unsubstituted pyrene [42]. The axis of the included solute is located parallel to that of the cyclodextrin cavity. In the case of benzo(a)pyrene, no complex can be formed with either a- or 8-cyclodextrin [43]. However, a strong complex can be prepared using y-cyclodextrin, with the long axis of the included solute lying along the direction of the cavity axis. 

Several papers have dealt with electrophilic attack at the amide nitrogen of the unsubstituted benzisoselenazol-3(27T)-one. Alkylation using KOH and alkyl or allyl halide or halocarboxylic ester gave 2-substituted benzisoselenazol-3(27T)-ones <1991CZ135, 1989BSB395> and the reaction has synthetic value. 6-[Benzisoselenazol-3(27T)-one]-/3-cyclodextrin, designed as an artificial enzyme, was prepared by reaction of benzisoselenazol-3(2//)-one potassium salt with 6-iodo-/3-cyclodextrin (/3-CD-6-I) (Scheme 12) <2002CAR1309>. 

Surface tension 62 mN/m (62 dynes/cm) at 25°C Method of manufacture dimethyl-P-cyclodextrin is prepared from P-cyclodextrin by the selective methylation of all C2 secondary hydroxyl groups and all C6 primary hydroxyl groups (C3 secondary hydroxyl groups remain unsubstituted). 

Until recently, cyclodextrins (CD s) were used mostly for complexation of amino acids, with partially contradictive results. In some cases unsubstituted cyclodextrins were used fluorescence titrations with tyrosine containing pentapeptides showed with a-cyclodextrin even a lower association constant (around K=25 M" )... 

Since the Reimer-Tiemann reaction always yields a mixture of ortho- and para-substituted phenols whenever the two positions are unsubstituted (and sometimes even when the positions are substituted, see carboxy-substituted phenols), it is not surprising that attempts have been made to increase the regioselectivity. Earlier attempts (for details, see reviews) emphasized the nature of the cation, the solvent, or used phase-transfer catalysis. Recent studies have concentrated on the use of cyclodextrins as base-stable host compounds, permitting exclusive para substitution. Attaching the cyclodextrins to a solid support has also been attempted, a natural step in view of the high cost of the cyclodextrins and the need for cheap product i.e. p-hydroxybenzaldehyde). p-Hydroxybenzaldehyde has been prepared in 59-65% yield using P-cyclodextrin that has been immobilized with epichlorohydrin. TTie catalyst is easily recovered and can be reused without appreciable loss of activity. 

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