Cyclodextrin alkyl esters

Veglia, A. V. and de Rossi, R. H., Beta-cyclodextrin effects on the photo-Fries rearrangement of aromatic alkyl esters, /. Org. Chem., 58,4941, 1993. 

Cyclodextrins, toroidal molecules composed of 6, 7 and 8 D-glucose units, are now commercially available at reasonable cost. They form inclusion compounds with a variety of molecules and often differentially include sulfoxide enantiomers29,30. This property has been used to partially resolve some benzyl alkyl, phenyl alkyl and p-tolyl alkyl sulfoxides. The enantiomeric purities after one inclusion process ranged from 1.1 % for t-butyl p-tolyl sulfoxide to 14.5% for benzyl r-butyl sulfoxide. Repeating the process on methyl p-tolyl sulfoxide (10) increased its enantiomeric purity from 8.1% to 11.4% four recrystallizations raised the value to 71.5%. The use of cyclodextrins in asymmetric oxidations is discussed in Section II.C.l and in the resolution of sulfmate esters in Section II.B.l. 

An attempt to directly resolve alkyl alkanesulfmates via 0-cyclodextrin inclusion complexes was only partly successful (35,106). In the majority of cases, the optical purity of the isolated esters was in the 5 to 10% range. In the case of isopropyl methanesulfinate, however, inclusion was highly stereospecific and afforded the ester with 68% optical purity. 

The stereospecific conversion of sulfinates into sulfoxides of known chirality has been applied as a general method for determining the absolute configuration of a wide range of optically active sulfinic esters. For example, the absolute configurations of a series of alkyl alkanesulfinates obtained by asymmetric synthesis (107) or resolution via 3-cyclodextrin inclusion complexes (106) were determined by this method. 

Stereoanalysis of 2-alkyl-branched acids, esters and alcohols in apple aroma concentrate Restriction capillary (25 m X 0.23 mm i.d.) coupled to a glass capillary column, (25 m X 0.32 mm i.d.) coated with a 18.8% solution of PS-255 and 1.5% dicumyl peroxide. Glass capillary column (38 m X 0.23 mm i.d.) coated with heptakis (2,3,6-tri-0-ethyl)-/3-cyclodextrin (33% in OV-1701-vinyl) 6... 

Octakis (2,3,6-tri-0-methyl-gamma-cyclodextrin) was used to separate enantiomers of methyl esters of deltametrinic acid and permetrinic acid the positional isomers of nitrotoluene were also separated on the same column [17,18]. Various alkyl- and dialkyl-benzenes have been separated on beta- and gamma-cyclodextrin [19]. A complete review of the use of cyclodextrins in chromatography has been published by Hinze [20]. Cyclo-dextrins have been analyzed by packed-column gas chromatography as their dimethylsilyl ethers [21]. 

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>. 

The poly(siloxane) polymers are usually prepared by the acid or base hydrolysis of appropriately substituted dichlorosilanes or dialkoxysilanes, or by the catalytic polymerization of small ring cyclic siloxanes [71-75]. The silanol-terminated polymers are suitable for use after fractionation or are thermally treated to increase molecular weight and in some cases endcapped by trimethylsilyl, alkoxy or acetyl groups [76,77]. Poly(siloxanes) synthesized in this way are limited to polymers that contain substituent groups that are able to survive the relatively harsh hydrolysis conditions, such as alkyl, phenyl, 3,3,3-trifluoropropyl groups. Hydrosilylation provides an alternative route to the synthesis of poly(siloxanes) with labile or complicated substituents (e.g. cyclodextrin, oligoethylene oxide, liquid crystal, amino acid ester, and alcohol) [78-81]. In this case... 

Cyclodextrins are the most used host compounds so far. Native cyclodextrins are effective inverse phase-transfer catalysts for the deoxygenation of allylic alcohols [3], epoxidation [4], oxidation [5], or hydrosilylation [6] of olefins, reduction of a,y9-unsaturated acids [7], a-keto ester [8], conjugated dienes [9] or aryl alkyl ketones [10]. Interestingly, chemically modified cyclodextrins like the partially O-methylated y0-cyclodextrin (RAME-y9-CD) show a better catalytic activity than native cyclodextrins in numerous reactions such as the Wacker oxidation [11], hydrogenation of... 

In application, the most important chemically modified CDs are the ether derivatives, such as hydroxypropyl-, methyl-, ethyl-CDs. These cyclodextrins etheric derivatives (CEDs) with the improved solubility, encapsulation ability and low toxicity have aheady been commercialized and widely used. The CEDs could be prepared in two ways. One way is that the CD reacts with the free hydroxyls such as dimethyl sulfate, diethyl sulfate, alkyl halides and epoxides. The other way is by sulfonic ester transformation. 

Under mildly alkaline conditions and in the presence of excess cyclo-heptaamylose the rate of degradation of penicillin is increased 2(U90-fold compared with the rate of alkaline hydrolysis (Tutt and Schwartz, 1971). Michaelis-Menten kinetics are observed which are indicative of complex formation. The apparent binding constant of 6-substituted penicillins varies little with the length of the alkyl side chain although it is increased about 10-fold for diphenylmethyl penicillin. The reaction is catalytic and hydrolysis proceeds by the formation of a penicilloyl- 3-cyclodextrin covalent intermediate, i.e. ester formation, by nucleophilic attack of a carbohydrate hydroxyl on the P-lactam. 

The internal hydrophobic cavity is the key structural feature of the cyclodex-trins it provides their ability to complex and hold a wide variety of inclusion molecules. Differences between the cyclomaltodextrins arise from differences in the diameters of their cavities. The organic inclusion molecules have alkyl, aromatic, alcohol, and ester groups. To bind with the cyclomaltodextrin, the inclusion molecule must have a size that fits, at least partially, into the cavity, creating the complex. The inclusion compound, however, does not have to be completely contained in the cavity. Complexes can be formed by the insertion of some specific functional group or part of the molecule to bind in the hydrophobic cavity. This partial insertion of the inclusion compound gives a cap or lid on the cavity. Sometimes more than one cyclodextrin will bind with a single inclusion molecule. 

F. derives de cyclodextrine Aim of derivatization is increased versatility by increasing the hydrophilic character of the outer surface area. This is accomplished with substituents such as sulfuric acid esters and alkyl, hydro-xyalkyl, carboxymethyl, aminoalkyl ethers formation of carboxyl groups by glycolic oxidation formation of branched c. with glucose or oligosaccharide side chains by pyrolytic reactions. Derivatization is mostly performed with P-cyclo-dextrin. Solubilities depend on DS as well as on the nature of the substituent groups levels up to 60% have been reached. In such cases, the viscos-... 

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