CD ester derivatives

Figure 6 Enantiomer separation and proof of enantiomeric purity of DOPA (tri-fluoroacetyl/methyl ester derivative). 25-m Fused silica capillary with per-pe-a-CD at 150 C.

So far, cyclodextrin (CD 4) derivatives have been the most successful artificial enzymes based on small synthetic host molecules. Since CD derivatives form inclusion complexes with various hydrophobic molecules, they have been utilized as binding pockets." " Examples are illustrated by 5 and 6. The CD derivative indicated in 5 is a mimic of ribonuclease in which the two histidyl imidazoles of the active site are believed to act as a general acid and a general base catalyst. The CD dimer indicated in acts as an artificial metalloesterase manifesting selectivity toward esters with two hydrophobic groups. 

A CD-PEI derivative containing macrocyclic metal centers have been prepared by random functionalization (34), Here, the secondary and the tertiary amino groups were blocked by acetylation. Hydrolysis of a nitrophenyl carboxylate ester... 

Particles of the enzymatically synthesized phenolic polymers were also formed by reverse micellar polymerization. A thiol-containing polymer was synthesized by peroxidase-catalyzed copolymerization of p-hydroxythiophenol and p-ethylphenol in reverse micelles [70], CdS nanoparticles were attached to the copolymer to give polymer-CdS nanocomposites. The reverse micellar system was also effective for the enzymatic synthesis of poly(2-naphthol) consisting of qui-nonoid structure [71], which showed a fluorescence characteristic of the naphthol chromophore. Amphiphilic higher alkyl ester derivatives were enzymatically polymerized in a micellar solution to give surface-active polymers at the air-water interface [72, 73]. 

Bicyclic diacid template (Fig. 29.20) has also been designed and synthesized to stabilize the hydrogen-bonding pattern of a conjugated peptide in an a-helix conformation. A hexapeptide EALAKA-NH2 was attached to either the bicyclic amide or ester derivatives, and the influence of the template on the peptide conformation was evaluated in aqueous solution by using both CD and NMR. The ester-linked template enhanced the helicity of the peptide to 49% at 0°C compared with the reference hexapeptide value of 8%, while the amide-linked template was only slightly effective. 

The benzoyl acid ester CD is an important intermediate in CD modification. Selecting the appropriate nucleophile (iodide, azide, thio-amyl acetate and hydroxylamine, alkyl amines) to attack the carbon atoms which connect with tosyl, can trigger nucleophilic substitution reaction. Then, series of functional CD sulfonate derivatives can be obtained. 

In alkaline medium, the aromatic amino acid derivatives show a negative Cotton effect at about 273-268 nm. However, the CD spectra of both aliphatic and aromatic series are similar in a group of organic solvents with negative Cotton effects at 285-275 and 250-245 nm and a positive one at 217-214 nm. The CD spectra of the aliphatic ester derivatives show minor differences from those of the acid derivatives. 

The CD spectra of aliphatic N-(3-methyl-2-quinoxaloyl)-L-a-amino acid and ester 1,4-dioxides are similar to those of aromatic L-a-amino acid and ester derivatives a weak negative band at 370 nm, a weak positive one at 325 nm, and strong positive bands at about 268 and 230 nm (in acetonitrile). A number of these compounds also have a weak positive Cotton effect in their CD spectrum at about 395 nm. On the other hand, the CD spectra of the quinoxaline derivatives of aliphatic-L-a-amino acids and esters are... 

These CD-based polymers were engaged in hydrolysis reaction of various p-nitrophenol esters derivatives. The reaction was monitored by UV at 400 mn. Among the CD-based polymers, only poly- 3-CD-A showed a high hydrolysis activity. The pseudo first-order rate constant k measured for the ester hydrolysis catalyzed by poly- 3-CD-A is compared to the rate constant measured using the native 3-CD. The rate enhancements resulting from the use of poly- 3-CD-A are presented in Table 2.1. 

Supramolecular catalysts using synthetic host molecules have been well researched. Early studies realized a hydrolysis reaction for ester derivatives using modified cyclodextrins (CDs). CDs are suitable for the study of two-substrate supramolecular catalysis and for the synthesis of artificial enzymes. 2-Benzyimidazoleacetic acid-modified a-cyclodextrin hydrolyzes m-tert-butylphenyl acetate at an accelerated rate. The imidazole has a benzoate group in a position that imitates the function of the aspartate ion with the catalytic triad characteristics of serine proteases such as chymotrypsin (Figure 12.1). ... 

A calix[4]arene substituted at the upper-rim VIg was synthesized from calix[4]arene-0-tetra pentyloxy derivative conformationally fixed at the low rim by alkyl chains and substituted with two nitro groups and two phenolic hydroxyls at the wide rim in the opposite positions at the platform. After 0-alkylation with two equivalents of the CD-dioxane derivative and on reduction of the nitro fnnctions to the ammonium group, two CMPO functions were introduced by reaction with the active ester ae-1 (see Figure 19.3, VIg) (Griiner et al, unpublished results). However, in contrast to organic upper-rim CMPO calix[4]arenes (Schmidt, 2003), a lower separation efficiency was observed for this compound with respect to the low-rim series. This can be possibly explained by a different complexation mode. No An +/Ln2+ selectivity was observed, similarly as for the low-rim series. 

Further developments of ferrocene based esters led to even faster acyl transfers to /3-CD (Trainor and Breslow, 1981 Breslow et al., 1983), the most spectacular rate accelerations, up to 6 million, being with the derivatives [17] and [18] in which an acrylate moiety is conformationally... 

In an effort to obtain a salvinorin derivative possessing an oe-diol system which can be transformed into the dibenzoate ester required for the exciton chirality CD method, salvinorin A (1) or B (2) was treated with sodium borohydride in various protic solvents. The products having the la,2a-diol group were obtained in high yield. However, this reduction was accompanied by extensive isomerization at C-8. While mechanistic details for this unexpected observation remain to be established at this time, the isomerization at C-8 appears to be the result of the base-promoted clevage of the C-8/9 bond under the reaction conditions followed by the reclosure to provide the 8-epimer prior to the reduction of the 1-ketone. Furthermore, attempts to obtain the 1,2-dibenzoate derivative of the major reduction product 3 under various benzoylating conditions invariably produced only the 2-monobenzoate. 

Without postulating the formation of dichloronaphthalide 368, one may explain using Scheme 7 the reaction of naphthaloyl dichloride 367 with two molecules of sodium malonic ester, which does not result in the expected 1,8-dimalonylnaphthyl diketone 372, but leads to a 2-malonylydene derivative of naphtho[cd]pyran-9-one 373 (36MI3). However, we do not insist on the suggested mechanisms for the reactions of naphthaloyldichloride 367 with aromatic compounds or sodium malonic ester one can assume the alternative course via dichloronaphthalide 368. Moreover, hemo-... 

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