Amylose ester derivatives

Ester derivatives of cellulose, chitin, dextran, amylose, and amylopectin were prepared utilizing the acid chloride derivatives described in Part B of the Experimental Section. 

Table I lists physical data for a number of the carbamate and ester derivatives of cellulose, chitin, amylose, amylopectin, and dextran synthesized as described in the Experimental Section. The solubility of the polysaccharide starting materials as well as that of the produced derivatives allows for macromolecular characterization through techniques including UV, NMR, IR, high pressure liquid chromatography, etc.

To address development of chiral separations by SFC, Villeneuve and Anderegg have developed an SFC system using automated modifier and column selection valves. Columns (250 x 4.6 mm i.d., 10 pm) packed with Chiralpak AD, Chiralpak AS amylose derivative, Chiralcel OD cellulose carbamate derivative, and Chiralcel OJ cellulose ester derivative (Chiral Techologies, Exton, PA) were connected to a column-switching valve. Candidate samples were run successively on each column using fixed isocratic, isobaric, and isothermal conditions of 2 ml/min, 205 atm pressure, and 40 °C with the vari-... 

The ester and carbamate derivatives of cellulose and amylose are among the most successful and versatile chiral stationary phases for liquid and supercritical fluid chromatography [1,4,28,107-109]. These phases are prepared by reaction of the poly(saccharide) with an acid chloride (ester derivative) or phenylisocyanate (carbamate... 

The stereospecificity of the interactions of several spin-labelled substrates with cyclohexa- and cyclohepta-amyloses, as models for chymotrypsin, has been studied. Complexes of the cycloamyloses with 2,2,6,6-tetramethyl-4-oxy-pyridyl-1-oxide in aqueous solution were examined by e.s.r. spectroscopy the nitroxide function moved to a relatively hydrophobic environment on binding to cyclohepta-amylose, and lost some freedom of rotation on binding to both cycloamyloses. The dissociation constant for the cyclohexa-amylose complex of the nitroxide is greater than that for the cyclohepta-amylose complex, consistent with measurements made on molecular models. In the hydrolysis of the asymmetric compound 3-carboxy-2,2,5,5-tetramethylpyrrolidyl-l-oxide 3-nitro-phenyl ester, catalysed by cyclohexa-amylose, enantiomeric specificity was observed in the acylation step but not in formation of the Michaelis complex , or on hydrolysis of the acylated cycloamylose intermediate. No differences were found in the e.s.r. spectra of solutions of the trapped acylcyclohexa-amylose intermediates derived from ( + )- and ( )-forms of the asymmetric nitroxide. The nitroxide function is less free to rotate in the acylcycloamylose intermediate than in the Michaelis complex and is not included in the cycloamylose cavity. 

Among optically active polymers, polysaccharide derivatives are particularly valuable. Polysaccharides such as cellulose and amylose are the most readily available optically active polymers and have stereoregular sequences. Although the chiral recognition abilities of native polysaccharides are not remarkable, they can be readily converted to the esters and carbamates with high chiral recognition abilities. The chiral recognition mechanism of these derivatives has been clarified to some extent. 

Starch (amylose and amylopectin) hydrolysis along with ester-fication, etherification or oxidation have been previously discussed as available methods for producing starch derivatives with improved water dispersibilities and reduced retrogradation potential (, ). Since oxidative and hydrolytic reactions are simple, easily controlled chemical modifications, starch-derived polymers made by hydrolysis alone or oxidative and hydrolytic processes were developed and tested. 

Natural polymers like cellulose and amylose comprise the Type IIIA CSPs, but the mechanical stability of these packings is not sufficiently adequate to be used as a chromatographic sorbent. More satisfactory sorbents have been obtained by chemically modifying them as ester or carbamate derivatives and then coating them onto large-pore silica (300 A) [276]. These CSPs are marketed under the trade names ChiralCel (cellulose) and ChiralPak (amylose). These packings have a wide scope of applications, good stability, and use on a preparative scale. 

One important type of chiral packing material is derivatized polysaccharides, which provide a chiral lattice, but separation is improved by the addition of structural features that enhance selectivity. One group of compounds includes aroyl esters and carbamates, which are called Chiralcels (also spelled Chiracel) two of the most important examples are the 4-methylbenzoyl ester, called Chiralcel OJ, and the 3,5-dimethylphenyl carbamate, called Chiralcel OD. There is a related series of materials derived from amylose rather than cellulose, which have the trade name Chiralpak. 

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