Synthesis and HPLC chiral recognition of regioselectively carbamoylated cellulose derivatives

Four regioselective-carbamoylated cellulose derivatives having two different substituents at 2-, 3-, and 6-position were prepared and evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography. Investigations showed that the nature and arrangement of the substituents significantly influenced the chiral recognition abilities of the heterosubstituted cellulose derivatives and each derivative exhibited characteristic enantioseparation. Some racemates were better resolved on these derivatives than the corresponding homogeneously substituted cellulose derivatives including a commercial CSP, Chiralcel OD. Racemic compounds shown in this study were most effectively discriminated on cellulose 2,3-(3-chloro-4-methylphenylcarbamate)-6-(3,5-dimethylphenylcarbamate) and 2,3-(3,5-dimethylphenylcarbamate)-6-(3-chloro-4-methylphenylcarbamate).     

Synthesis and structural characterization of 3-O-ethylene glycol functionalized cellulose derivatives

The synthesis of 3-O-ethylene glycol cellulosics via 2,6-di-O-thexyldimethylsilyl cellulose was studied. Reaction yield and degree of substitution were dependent on reaction conditions and size of the ethylene glycol group. The presence of tetra-n-butylammonium iodide in catalytic amounts and prolonged reaction times significantly increased the degree of substitution of the ethylene glycol substituents. However, the longer reaction times lead to significant degradation of the cellulosic polymer chain. The structure of the 3-O-ethylene glycol 2,6-di-O-thexyldimethylsilyl cellulose intermediates and the 3-O-ethylene glycol 2,6-di-O-acetyl celluloses were confirmed by means of one- and two-dimensional NMR spectroscopy. The degree of 3-O-ethylene glycol substitution was confirmed by quantitative ¹³C NMR ratified by T1 experiments.     

Synthesis of regioselectively substituted cellulose derivatives and applications in chiral chromatography

Various cellulose-2,3-bis-arylcarbamate-6-O-arylesters and cellulose-2,3-bis-arylester-6-O-arylcarbamates, designed to test the possible combined effects of the known tris-arylcarbamate and tris-arylester classes, were synthesized with high regioselectivity at O-C(6), and their use as CSP s in liquid chromatography for enantiomeric separations was investigated. The separations obtained with the synthesized CSP s were compared to the separations achieved on a self-packed reference column, consisting of cellulose-tris-(3,5-dimethylphenyl-carbamate) as CSP standard. Among the synthesized, regioselectively substituted cellulose derivatives, 2,3-bis-O-(3,5-dimethylphenylcarbamate)-6-O-benzoate-cellulose and 2,3-bis-O-(benzoate)-6-O-(3,5-dichlorophenylcarbamate)-cellulose gave the best CSP s for the separation of the test racemates. CSP s from regioselectively substituted cellulose derivatives seem to exhibit higher selectivities than cellulose-tris-(3,5-dimethylphenylcarbamate) for certain classes of racemic compounds. Chirality 10:294–306, 1998. © 1998 Wiley-Liss, Inc.     

Synthesis, characterization, and mesophase formation of phenylacetoxy cellulose and its halogenated derivatives

A series of phenylacetoxy cellulosics with degrees of substitution (DS) between 1.4 and 3.0 and different halogenation (2-chloro, 3-chloro, 4-chloro, 2,4-dichloro, 3,4-dichloro, and 4-bromo) were synthesized. All the prepared phenylacetoxy cellulosics were soluble in dimethylformamide (DMF) and DMAc. The solubility increased with increasing DS. Mesophases were observed for all of the phenylacetoxy cellulosics with low to medium DS (DS < 2.5) in DMF and DMAc. Non- or mono-halogeneated phenylacetoxy cellulosics with high DS (DS > 1.9) were soluble in methylene chloride (CH2Cl2), whereas those with very low DS or di-halogenation on the phenyl ring were only slightly swollen or partially soluble in CH2Cl2. Non- and mono-halogenated phenylacetoxy cellulosics were soluble in DMSO and formed liquid crystals regardless of the DS, in contrast to CH2Cl2 solutions which display liquid crystalline behavior at medium to high DS (DS > 1.9) only. The solubility of the di-halogenated phenylacetoxy cellulosics in DMSO was limited to approximately 40 wt %.     

New cellulose sulfate derivatives and applications

The preparation of water-soluble cellulose sulfates having a degree of substitution (d.s.) of 0.3–2.0 by a homogeneous method is reported. Instead of sulfating cellulose directly, a reactive intermediate, namely, cellulose nitrite, was used, thereby permitting sulfation to proceed under homogeneous conditions. Products obtainable via the homogeneous method differ substantially from those prepared via the heterogeneous method used at present for the production of water-soluble cellulose derivatives. Principal chemical differences are the uniform distribution of the substituents, the exceptionally high molecular weight of the sulfate esters, and in the location of the substituents on the glucosyl residues. The differences result in a number of chemical and physical properties that are unique and not exhibited by other cellulose derivatives. Performance in application areas, such as oil recovery, paints, paper, textiles, cosmetics, and the like, is indicated by these properties.     

Rheological properties of sulfoacetate derivatives of cellulose

Water-soluble cellulose acetate sulfate derivatives (CAS) have been prepared through chemical reaction involving sulfuric acid as a catalyst. These CAS have been obtained from cellulosic materials of different origins (pure cellulose, wheat bran, maize bran) and their rheological behavior in salt-free aqueous solution has been estimated in dilute and semi-dilute regime using dynamic viscoelastic and viscosity measurements. Influence of concentration, temperature of solubilization and temperature of measurement has been investigated. Weak gel-like properties were exhibited at elevated concentration (typically above 7-8 g/L). These systems also exhibited thixotropic properties: the structure was partly broken down upon shearing and recovered at rest. They also displayed thermoreversibility with large hysteresis, the melting temperature being approximately 15 degrees C higher than the temperature at which gelation took place. These overall observations clearly indicate that these distinctive properties arise from intermolecular association of the macromolecular chains of the cellulose derivative.     

酵母表面展示脂肪酶合成己二酸二异辛酯

展示酶的酵母细胞既具有固定化酶的优点,又有制备简单、成本较低的特点.采用表面展示南极假丝酵母脂肪酶B (Candida antarctica lipase B,CALB)的毕赤酵母细胞催化合成己二酸二异辛酯(Diisooctyl adipate,DIOA),对该反应体系进行优化,并实现了初步工艺放大制备.经条件优化后,在10mL反应体系中,DIOA的产率可达85.0％.该工艺放大到200mL反应体系时,DIOA产率可达97.8％.经减压蒸馏,DIOA纯度可达到98.2％.该酵母表面展示脂肪酶在合成绿色润滑油己二酸二异辛酯中具有良好应用前景.     

Alteration of in vivo cellulose ribbon assembly by carboxymethylcellulose and other cellulose derivatives

In vivo cellulose ribbon assembly by the Gram-negative bacterium Acetobacter xylinum can be altered by incubation in carboxymethylcellulose (CMC), a negatively charged water-soluble cellulose derivative, and also by incubation in a variety of neutral, water-soluble cellulose derivatives. In the presence of all of these substituted celluloses, normal fasciation of microfibril bundles to form the typical twisting ribbon is prevented. Alteration of ribbon assembly is most extensive in the presence of CMC, which often induces synthesis of separate, intertwining bundles of microfibrils. Freeze- etch preparations of the bacterial outer membrane suggest that particles that are thought to be associated with cellulose synthesis or extrusion may be specifically organized to mediate synthesis of microfibril bundles. These data support the previous hypothesis that the cellulose ribbon of A. xylinum is formed by a hierarchical, cell- directed, self-assembly process. The relationship of these results to the regulation of cellulose microfibril size and wall extensibility in plant cell walls is discussed.     

Location of sulfate groups on sulfoacetate derivatives of cellulose

A water-soluble cellulose acetate sulfate (CAS) with a degree of acetylation (DS(Ac)) 2.4 and a degree of sulfation (DS(Sulf)) of 0.3 was obtained by direct acetylation of cellulose using sulfuric acid as catalyst. Using methylation analysis, IR and NMR spectroscopy, sulfate groups have been located on primary alcohol function of glucose residues. The distribution of the sulfate groups along the cellulose chain has been investigated using enzymatic hydrolysis. CAS was first de-acetylated under mild hydrolysis conditions (NaOH 0.25 mol/L at room temperature), and then cellulose sulfate was hydrolyzed by a cellulolytic complex (Celluclast 1.5L). Reaction products were separated by ion exchange chromatography on a DEAE Sepharose CL6B column into five fractions F(1), F(2), F(3), F(4) and F(5), which were analyzed for their chemical composition. F(1) was glucose and represented the main product of reaction (approximately 50% of the initial glucose), F(2) was a dimer (approximately 30%) with a ratio Sulfates-Glucose of 0.41 (about one sulfate group for two glucose units), F(3) a trimer (approximately 10%) with a ratio Sulfates-Glucose of 0.62 (about two sulfate groups for three glucose units), and F(4) a tetramer (approximately 5%) with a ratio Sulfates-Glucose of 0.69. The structure of the oligomers was established using 1H and 13C NMR. The observed proportion of the different blocks of sulfate groups was in good agreement with computed random distribution.     

Preparation of sulfoacetate derivatives of cellulose by direct esterification

A new and efficient method for the preparation in one step of water-soluble cellulose acetate sulfate derivatives (CAS) is reported. Acetylation and sulfation were carried out simultaneously, using a mixture of acetic anhydride and sulfuric acid in glacial acetic acid. The reaction time and the amount of acetic anhydride were optimized and the method provided water-soluble esters, with a degree of acetylation in the range 1.6 and 2.4 and a degree of sulfation of 0.3. This method has been successfully applied to pure cellulose and to cellulose-enriched materials obtained from agricultural by-products. The product exhibited a high viscosity in aqueous solution suggesting interesting rheological properties.     

Synthesis of novel water-soluble sulfonated cellulose

Water-soluble sulfonated cellulose (SC) samples were synthesized by oxidizing hardwood kraft pulp with sodium periodate followed by the sulfonation reaction with sodium bisulfite. Six levels of oxidation/sulfonation were obtained by using different mmols (0.93-4.67) of periodate per gram of pulp. The aldehyde and sulfonic acid contents, surface morphology, and water solubility property of these treated fibers were characterized. It was found that carbonyl group content increased with the periodate charge and so did the sulfonic acid content in subsequent sulfonation step. Scanning electron microscopy images showed a significant change in surface morphology of the sulfonated samples. Solubility of sulfonated cellulose in water was determined from ¹H NMR spectra and a solubility of 28.57 g/L was found when cellulose was oxidized with 4.67 mmol periodate per gram cellulose followed by the sulfonation reaction.     

Products of enzymatic hydrolysis of cellulose and its derivatives

Cellobiose and glucose were determined in a mixture of the two carbohydrates by methods involving the use of glucose oxidase and of β-glucosidase.Paper-partition chromatography is used as a confirmatory method in the identification of the hydrolysis products and in the detection of the various constituents.The cellulolytic organisms studied produce large amounts of the enzyme Cx, which diffuses into the medium. Only small amounts of β-glucosidase are found outside the cell. Cellobiose resulting from Cx activity can enter the cells as rapidly as can glucose.The role of cellobiose as a principal product in the hydrolysis of cellulose is confirmed. It is hypothesized that the principal final product of Cx activity is cellobiose, and that the presence of cellobiase in the medium is not a prerequisite to utilization of cellobiose by the organism. This is a correction of the hypothesis previously published stating that glucose appeared to be the final product of Cx activity.     

Chromatographic enantioseparation by cycloalkylcarbamate derivatives of cellulose and amylose

Cyclopentyl and (+/-)-exo-2-norbornylcarbamates of cellulose and amylose were prepared and their chiral recognition abilities as chiral stationary phases for high-performance liquid chromatography (HPLC) were evaluated. Among these carbamates, cellulose tris(cyclopentylcarbamate) and amylose tris((+/-)-exo-2-norbornylcarbamate) showed particularly high chiral recognition, which is comparable to that of several well-known phenylcarbamate derivatives. The chiral recognition mechanism of cellulose tris(cyclohexylcarbamate), which was previously found to be an effective chiral stationary phase for HPLC, was investigated using NMR spectroscopy. The derivative dissolved in chloroform exhibited the chiral discrimination of several enantiomers in NMR as well as in HPLC. For example, the 1,1'-bi-2-naphthol enantiomers were distinctly discriminated in the (1)H, (13)C, and 2D-NOESY spectra.     

Enantioselective retardation of rac-propranolol from matrices containing cellulose derivatives

The dissolution characteristics of propranolol enantiomers from tablet formulations containing cellulose, or one of eight cellulose derivatives, were determined under a range of conditions. The derivatives examined were: cellulose tris(phenylcarbamate) (1), cellulose tris(2,3-dichlorophenylcarbamate) (2), cellulose tris 2,4-dichlorophenylcarbamate (3), cellulose tris(2,6-dichlorophenylcarbamate) (4), cellulose tris(2,3-dimethylphenylcarbamate) (5), cellulose tris(3,4-dichlorophenylcarbamate) (6), cellulose tris (3,5-dichlorophenylcarbamate) (7), cellulose tris(3,5-dimethylphenylcarbamate) (8). In water at 25°C, the release rates of (-)R-propranolol were generally greater than those of (-)-S-propranolol, although these differences were not always statistically significant; only compounds 5 and 8 demonstrated significant enantioselectivity. Using compound 8 in further experiments, statistically significant stereoselective dissolution of propranolol HCl was observed in buffer pH 7.4 at 25°C (intrinsic dissolution rates: 0.41 ± 0.01 mgcm²min⁻¹ for R-propranolol and 0.30 ± 0.02 mgcm²min⁻¹ for S-propranolol; P = 0.003). The cumulative amounts of enantiomers released at every time point were also found to be statistically significant (mean ratio R:S 1.25 ± 0.05). The observed low stereoselectivity of 8 with propranolol base was probably attributable to low solubility in pH 7.4 buffer, although stereoselective release did increase with time. This suggested that there is a relationship between stereoselectivity and contact time in an aqueous environment. Results also suggested that increased temperature may affect the release process as well as stereoselective interactions of 8 with individual enantiomers. To conclude, differential release of rac-propranolol from cellulose derivative matrices has been demonstrated, which supports the principle of stereoselective retardation as a potential means of stereoselective drug delivery for solid dosage forms. Chirality 9:307–312, 1997. © 1997 Wiley-Liss, Inc.