Polysaccharides carbamates

Preweighed 1.0 mg samples of each polysaccharide carbamate derivative were submerged in aqueous solutions at three pH values 3.1 7.0 and 11.3. Three milliliter aliquots were withdrawn at periodic intervals and analyzed by ultraviolet spectroscopy. Typical results are shown in Figures 3 and 4 for pendant hydrolysis rates of carbamate derivatives of cellulose and chitin respectively as a function of pH. 

Cellulose, Amylose and Other Polysaccharide Carbamate Derivatives... 

Okamoto, Y. and Hatada, K., Separation Agent Comprising Polysaccharide Carbamate, EU Patent 157365, 1985. 

Okamoto, Y. Kaida, Y. Resolution by high-performance liquid chromatography using polysaccharide carbamates and benzoates as chiral stationary phases. J. Chromatogr. 1994, 666,403. 

Okamoto Y, Kaida Y (1994) Resolution by high-perfOTmance liquid chromatography using polysaccharide carbamates and btmzoates as chiral statimiary phases. J Chromatogr A 666 403 19... 

Chemical stabilizers have been used to reduce the rate of oxygen-promoted degradation of polysaccharides at T>225°F. Methanol and sodium thiosulfate are the most commonly used (86). Sodium dithio-carbamate, alkanolamines, and thiol derivatives of imidazolines, thiazolines, and other heterocyclic compounds have also been tested for this application. Calcined dolomite (B7) and Cu(l) and Cu(ll) salts (88) have been reported to increase the thermal stability of HEC. 

As previously mentioned above, the chiral recognition abilities of the phenyl-carbamates of polysaccharides are greatly influenced by the substituents on the phenyl groups. In order to evaluate the effect of the substituents on the interaction between CSPs and solutes, the retention times of acetone and the first-eluted isomer of l-(9-anthryl)-2,2,2-trifluoroethanol (39) on 3- and 4-substituted CSPs are plotted against the Hammett parameter a of the substituents (Figure 3.33).130 The retention times of acetone tend to increase as the electron-withdrawing power of the substituents increases, whereas those of the first-eluted isomer of 39 tend to decrease. These results indicate that... 

The phenylcarbamates of polysaccharides also separate several nonpolar aromatic compounds,141 which cannot interact with the carbamate group through polar interaction. This indicates that, besides the polar interactions,... 

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. 

Lithium salts in organic solvents with high solubility parameters have been previously used to dissolve strongly hydrogen-bonded polyamidesfciy and polysaccharides /for viscosity studies and for preparation of films or fibers. We are not aware of any previous attempts to utilize these solvent systems to prepare ester or carbamate polysaccharide derivatives... 

In a typical experiment the isocyanate (0.006 moles) was reacted with 1.5 g of the polysaccharide in 150 ml of a 5% LiCl/ N,N-dimethylacetamide solution at 90°C under nitrogen for two hours. The appearance of a strong infrared absorbance at 1705 cm l was an indication of carbamate formation. The derivatized polymer was isolated as a white powder by precipitation of the reaction solution into a nonsolvent such as methanol. Alternatively thin films were cast directly from solution the lithium salt could be removed by rinsing with acetone. Figure 1 illustrates the reaction of cellulose with phenyl isocyanate. 

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.

Derivatives (Table I) formed by the reaction of the chosen polysaccharide with an isocyanate or acid chloride are carbamates and esters respectively. However, chitin or poly[(1+4)(N-acetyl-2-amino-2-deoxy-f3-glucopyranose)] actually used in this experiment contains approximately 16% free amine groups which can form urea and amide derivatives with the above reagents. 

More recent developments in the field of the Pirkle-type CSPs are the mixed r-donor/ r-acceptor phases such as the Whelk-Of and the Whelk-02 phases.The Whelk-Of is useful for the separation of underiva-tized enantiomers from a number of families, including amides, epoxides, esters, ureas, carbamates, ethers, aziridines, phosphonates, aldehydes, ketones, carboxylic acids, alcohols and non-steroidal anti-inflammatory drugs.It has been used for the separation of warfarin, aryl-amides,aryl-epoxides and aryl-sulphoxides. The phase has broader applicability than the original Pirkle phases. The broad versatility observed on this phase compares with the polysaccharide-derived CSPs... 

Figure 3. Structure of cellulose carbamates used as CSPs. Similar are the amylose carbamates, but with a different configuration and conformation of the basic polysaccharide (see also Figure 2).

More often, carbamates of dextran are prepared by one-step conversion of the polysaccharide with isocyanates or isothiocyanates. This path is especially useful for the conjugation of fluorescent dyes. Fluorescent-marked dextrans are commercial products today. Fluorescent dextran derivatives with different molecular weights and substituents are available as invaluable tracers for studies on microcirculation and vascular permeability in health and disease [8]. Fluorescein isothiocyanate (FITC) dextran (actually the thiocarba-mate) has been well established in this area of research since the 1970s [358]. The isothiocyanate of fluorescein is covalently bound to dextran leading to... 

Polysaccharides containing grafted 9H-fluorenyl- or 5-indanyl-carbamates have been prepared that are effective in the separation of aromatic racemic mixtures when used as fdler in gas chromatography column. 

TABLE 1. Elemental analysis of polysaccharides functionalized with 9H-fluorenyl- and 5-indanyl carbamates. 

TABLE 2. Effectiveness of enantiomeric separations for racemates (a)-(f) using carbamate-functionalized polysaccharides entries lA, IB, and IIB described in Table 1 with hexane/2-propanol, 90 10, v/v, as the mobile phase at a flow rate of 0.5 ml/min at 25 C. 

---