Kaneka Co., Ltd, 5-1-1 Torikai-Nishi, Settsu, Osaka 566-0072 Japan
Hitoshi_Sashiwa@kn.kaneka.co.jp
Hitoshi Sashiwa was born in Osaka, Japan, in 1963. He received his Ph.D. degree from Hokkaido University (Japan) under the supervision of Professor S. Tokura in 1991. He worked at Tottori University (Japan) as Assistant Associated Professor from 1988 to 2000. He worked with Profesor R. Roy at the University of Ottawa (Canada) for 2 years (1998−2000). He worked at AIST Kansai (Japan) as a postdoctoral scholar during 2000−2004. He has been affiliated with Kaneka Co., Ltd. (Japan) since April 2004. His research interests include chemical modification of chitin and chitosan and their biomedical applications. He is a member of The Society of Polymer Science, Japan, and the Japanese Society for Chitin and Chitosan. He is the sole author of 70 publications and co-author of 30 publications.
Abstract: In the chitin bibliography, a major reference is the book written by Richards in 1951 âprimarily for entomologists and other invertebrate zoologistsâ but also, in the author's hope, for chemists: the perception of the need for more chemical information is manifest in the preface of the book.1 In fact, the chitin chemistry developed to that date was inadequate: for instance, color tests were not specific enough to provide a reliable picture of the distribution and location of chitin in living organisms. Specific and accurate techniques for chitin identification became accessible in 1963 with the improvement of the X-ray diffraction methods by Rudall2 and the enzymatic method of Jeuniaux.3 The book edited by Hepburn,4 starting with a biographical chapter honoring A. G. Richards followed by chapters on biochemical modifications of chitin by Rudall and Muzzarelli, remains a remarkable contribution. The books by Hepburn (1976)4 and Neville (1975)5 were immediately followed by the first book on chitin authored by Muzzarelli (1977)6 and, same year, by the 1st International Conference on Chitin and Chitosan (proceedings published by Muzzarelli and Pariser, 1978).7 Prior to these events, interest in chitin was cultivated mainly by zoologists, marine entomologists, and physiologists, but in the late 1970s, chemists all over the world devoted attention to chitin. In particular, it was immediately realized that chitin was an abundant source of chitosan, the unique cationic polysaccharide (as opposed to a variety of easily accessible anionic polysaccharides), and, as such, was superior to man-made cationic derivatives of cellulose and starch. The inherent biodegradability of chitin and chitosan was interpreted as an appealing characteristic property rather than a drawback (at a time when artificial polymers such as nylon were celebrated for their inertness). The development of chitin science in the last quarter of the century followed periods dominated by specific topics that can be roughly related to (i) technological advances (spinning, coloring, uptake of soluble species, cosmetic functional ingredients); (ii) biochemical significance (blood coagulation, wound healing, bone regeneration, immunoadjuvant activity); (iii) inhibition of biosynthesis (insecticides); (iv) chitin enzymology (isolation and characterization of chitinases, their molecular biology, biosynthesis, hydrolases with unspecific chitinolytic activity); (v) combinations of chitosan with natural and synthetic polymers (grafting, polyelectrolyte complexation; blends, coatings; (vi) use of chitosan as a dietary supplement and food preservative (anticholesterolemic dietary products, antimicrobial coatings for grains and exotic fruits). Each of these topics had a âhigh seasonâ that produced a burst of publications; as a whole, a deeper knowledge on chitosan was obtained, apart from fruitful integration of interdisciplinary interests. Today, drug delivery seems to be the topic of interest with a better understanding of the basics in chitin and chitosan chemistry, mainly chemical modifications, biodegradation, effects on various tissues, distribution to various body organs, mucoadhesion, association of chitosan with inorganic compounds, and advanced technological transformations. The key considerations that justify this interest are that chitosan is biocompatible and does not elicit adverse reactions when in contact with human cells. Chitosan can be degraded by ubiquitous enzymes in the human body, and oligomers can activate macrophages and stimulate synthesis of hyaluronan. Moreover, they provide building blocks for the reconstruction of extracellular matrix components. On the other hand, chitosan is recognized by tumor cells, and therefore, it can bring drugs to their target selectively. Chitosan is a safe and friendly substance for the human organism; therefore, medical and pharmaceutical applications can easily be worked out with joint efforts from specialists in various fields. The present review intends to provide interdisciplinary insight in the scientific knowledge immediately usable to realize the potential of chitosan in the pharmaceutical field.
Abstract: Recent studies of the chemical modification of chitin and chitosan are discussed from the viewpoint of biomedical applications. Special emphasis is placed on the role of individual functional groups in applications of modified chitosan. The modifications discussed here include chitosan attached to sugars, dendrimers, cyclodextrins, crown ethers, and glass beads. Among these derivatives, sugar-modified chitosans are excellent candidates for drug delivery systems or cell culture owing to their specificity. Chitosanâdendrimer hybrids are interesting multifunctional macromolecules. Chitosan and its derivatives are useful as carriers in drug delivery systems, as antibacterial agents, and in other medical applications.
Abstract: -Acetyl- -glucosamine (GlcNAc) was produced from chitin by use of crude enzyme preparations. The efficient production of GlcNAc by cellulases derived from Trichoderma viride (T) and Acremonium cellulolyticus (A) was observed by HPLC analysis compared to lipase, hemicellulase, and pectinase. β-Chitin showed higher degradability than α-chitin when using cellulase T. The optimum pH of cellulase T was 4.0 on the hydrolysis of β-chitin. The yield of GlcNAc was enhanced by mixing of cellulase T and A.
Abstract: The Michael type reaction of chitosan with ethyl acrylate has been investigated. Although this reaction was quite slow in the case of chitosan, the reiteration of the reaction was an effective means for increasing the degree of substitution (DS) of ethyl ester. The N-carboxyethylchitosan ethyl ester as an intermediate was successfully substituted with various hydrophilic amines, although the simultaneous hydrolysis of the ester to carboxylic acid also occurred. Water-soluble chitosan derivatives were obtained by substitution with hydroxyalkylamines and diamines.
Abstract: A Michael reaction of chitosan was conducted in water containing acetic acid with various acryl reagents. The degree of substitution could be controlled by temperature, reaction time, and the amount of acryl reagents. Although the modified chitosan derivatives with acrylic acid esters showed water-solubility, that with poly(ethylene glycol) acrylate, however, turned to water-insoluble material by lyophilization. Good biodegradation was observed in modified chitosan derivatives by standard activated sludge.
Abstract: Chitosanâdendrimer hybrids having various functional groups such as carboxyl, ester, and poly(ethylene glycol) groups were prepared successfully using dendrimer acetal by reductive N-alkylation. The synthetic procedure could be accomplished by one-step reaction without organic solvent. The degree of substitution of dendrimer was 0.13â0.18 evaluated by 1H NMR. A perfectly or partially water-soluble chitosanâdendrimer hybrid could be obtained. By standard activated sludge, good biodegradation was observed in these hybrids.
Abstract: In the field of electronic equipment such as computers, video equipment, and medical instruments, high-speed and high-density information processing is becoming increasingly common, and there is a danger that even low-intensity electromagnetic radiation may cause malfunctions. For example, the use of mobile telephones and computers is restricted in aircraft and hospitals. Hence, there is a need for high reliable electromagnetic radiation shielding materials. Chitosan 1 is a mucopolysaccharide composed of repeating d-glucosamine unit. Chitosan is biodegradable with the action of glycosidases such as chitosanase,2 chitinase,3 lysozyme,4 and cellulase.5 Moreover, chitosan can adsorb heavy metal ions. In conventional method of chemical plating, the body of the appliance made of plastic is etched in order to adsorb palladium (Pd) ion. After that, it is plated with layers of copper (Cu), to conduct electricity, and nickel (Ni), to prevent corrosion of Cu. Pd adsorbed can catalyze chemical plating of Cu on the surface. The plated Cu layer can shield electromagnetic radiation from lightweight electronic appliances, because Cu layer is electrically conductive. Etching with chromium, however, is not suitable for the Earth's environment owing to its toxicity. An alternative way is to utilize a binder, which possibly can adhere to plastic surfaces and adsorb the Pd ion. The purpose of this study is to prepare organosoluble chitosan derivatives as coating materials in order to give electromagnetic radiation shielding by chemical plating. Chitosan is the polymer of choice, because the amino group can adsorb the Pd ion.6 Moreover, it was reported that chemical plating on the hydrophilic glass surface was accomplished by coating with chitosan.7 Chitosan itself, however, is hydrophilic, while plastics used are hydrophobic. Therefore, chemical modification of chitosan is necessary to improve its adhesion to the plastics as well as its organosolubility so as to be sprayed on the surface of the plastics. On the other hand, biodegradability of chitosan derivatives as a binder is required for the environmental factor in the case of recycling of plastics. Introducing a hydrophobic moiety with an ester linkage into chitosan has two benefits (Scheme 1): (1) hydrophobic groups contribute organosolubility; (2) the ester linkage is hydrolyzed by enzyme like lipase, etc. Moreover, the glycoside linkage of chitosan derivatives is also degraded by glycosidases. Therefore, chitosan derivatives with O-acyl groups are designed as biodegradable coating materials. Although the selective O-acylation of chitosan in MeSO3H owing to the salt formation of primary amino group with MeSO3H was partly reported,8 the detailed chemical structure and the protecting effect of MeSO3H on amino group were not clear yet. The preparation of O,Oâ-didecanoylchitosan9 was also reported through protected N-phthaloylchitosan10 as an intermediate. This method, however, needs several steps for the protection and deprotection of N-phthaloyl groups.
Recently we have partly reported a one-pot synthesis for the O-acylation of chitosan in MeSO3H in a communication.1a Herein, we report the further study on the synthesis of organosoluble, palladium adsorbing, and biodegradable chitosan derivatives toward the chemical plating on plastics.
Abstract: N-carboxyethylchitosan methyl ester (degree of substitution (DS)=1.2 per repeating residue of chitosan), which was prepared from chitosan and methyl acrylate by the Michael reaction, was reacted with diamine and gave a water-soluble product. The DS value of the diamine moiety was 0.64â0.94. Acetal ending poly(amidoamine) (PAMAM) dendrimers were successfully attached to the ester and gave an N-carboxyethylchitosanâdendrimer hybrid without any crosslinking. The DS values of the hybrids were gradually decreased from 0.61 to 0.04 with the increasing generation of dendrimer.
Abstract: Chitin is a mucopolysaccharide composed of N-acetyl-d-glucosamine (GlcNAc) residue. Chitosan 1 is a N-deacetylated product of chitin mainly composed of d-glucosamine (GlcN) residue. Chitin and chitosan are attractive materials owing to their biological properties such as immunological activity2 or wound healing.3 Although chitin and chitosan are attractive biomacromolecules, these are water-insoluble materials because of their rigid crystalline structures. To obtain a water-soluble property is an important step toward the further application of chitin and chitosan as biomaterials. Some works have been reported to obtain water-soluble derivatives by N-acetylation of chitosan in aqueous medium, only around 50% DDA (degree of deacetylation) of the chitosan dissolved in water.4 In view of developing materials with advanced functions, many attempts have been made to modify the molecular structure of chitin and thereby to improve or control the properties such as carboxymethyl, dihydroxyethyl, sulfuryl, or phosphoryl groups, etc.5 In the case of cellulose chemistry, moreover, partial substitution of noncharged functional groups such as methyl or acetyl group to cellulose gives water-soluble properties. Despite the fact that chitin and chitosan are structurally similar to cellulose, there is no report about obtaining water-soluble derivatives by the substitution of methyl or acetyl groups. Herein we report the successful preparation of water-soluble chitosan derivatives by simple N,O-acetylation in MeSO3H as solvent. A noteworthy point is that both moderate substitution of N,O-acetyl groups and moderate molecular weight (MW) are important factors in obtaining water-soluble chitosan derivatives.
Abstract: The selective and efficient production of N-acetyl- -glucosamine (GlcNAc) was achieved from flake type of α-chitin by using crude enzymes derived from Aeromonas hydrophila H-2330. Efficient (yield=77%) production of GlcNAc was achieved from flake type of α-chitin by crude enzyme.
Abstract: Polyamidoamine (PAMAM) dendrimers of various generations (G=0.5â5) were prepared from commercial aminoacetaldehyde diethyl acetal. After transforming acetal to aldehyde, chitosanâdendrimer hybrids were prepared by reductive N-alkylation. The reactivity of dendrimer to primary amino group of chitosan was decreased at G=3.5 or above MW>6305. Chitosanâsialodendrimer hybrid (G=3) was also prepared under the same conditions.
Abstract: Tetraethylene glycol was modified by two different approaches to synthesize the scaffold of dendrimer. Poly(amido amine) (PAMAM) dendrimers (G=1â3) having tetraethylene glycol spacer were prepared and attached to chitosan by reductive N-alkylation. On chitosan molecules, the degree of substitution of dendrimers was 0.03â0.18. Sialic acid residue bound PAMAM dendrimers of each generation were successfully attached to chitosan.
Abstract: Surface bound chitosanâsialodendrimers with a high degree of substitution were successfully prepared using a doubly convergent approach. Poly(amidoamine) (PAMAM) dendrimers (G = 1â5) having a 1,4-diaminobutane core were amidated to N-carboxyethylchitosan methyl ester under conditions that prevented cross-linking. The extent of attachment (DS) to the polysaccharide backbone decreased from 0.53 to 0.11 with increasing dendrimer generation. Peracetylated p-formylphenyl α-sialoside was then successfully attached to the primary amine end groups of the dendrimerized chitosan hybrid with degree of substitution (DS) ranging from 0.7 to 1.4 using reductive amination. Water-soluble chitosanâsialodendrimer hybrids were finally obtained after protecting group hydrolysis and chitosan N-succinylation.
Abstract: Sialic acid dendrons bearing a focal aldehyde end group were synthesized by a reiterative amide bond strategy. Polyamine-ending trivalent (G = 1) and nonavalent (G = 2) dendrons having gallic acid as branching unit and tri(ethylene glycol) as spacer arm were prepared and initially attached to a sialic acid p-phenylisothiocyanate derivative. The focal aldehyde sialodendrons were then convergently grafted onto the polysaccharide chitosan backbone by reductive amination in 76â80% yields. The degrees of substitution (DS) of the sialodendrimer in the hybrids were 0.13 (G = 1) and 0.06 (G = 2), which indicates that 87% and 40% of the sialodendrons were attached to the primary amino groups of chitosan. The water solubility of these novel hybrids was further improved by N-succinylation of the remaining amine functionality.
Abstract: Water-soluble α-galactosyl-chitosan conjugates were prepared by reductive amination of p-formylphenyl β-melibioside on chitosan in good yield. Strong binding with phytohemagglutinin was demonstrated using Griffonia simplicifolia
Abstract: Chitosan is a polysaccharide composed mainly of β-(1â4)-2-amino-2-deoxy-d-glucopyranose repeating units. Chitosan shows interesting biological properties such as immunological,1 antibacterial,2,3 and wound healing activity.4 Moreover, it is a nontoxic3 and biodegradable polymer,5 and the free amino groups of chitosan offer great potential for further derivatization. Alternatively, dendrimers also offer several possibilities in molecular design owing to their multifunctional attachment sites. They have been used to scaffold neoglycoconjugates,6 probes, catalysts, and so on.7 Herein we report the preparation of sialic acid bound dendronized8 chitosanâdendrimer hybrids. These molecules may have the potential to inhibit the hemagglutination of human erythrocytes by influenza virus hemagglutinin as recently observed with straight polymers and hyperbranched polymers.6 As polymer backbones used so far are highly toxic, it is expected that scaffolding poly(amidoamine) (PAMAM) dendrimer onto nontoxic chitosan core would present biopharmaceutical advantage.
Abstract: Derivatives of partially N-deacetylated chitin (DAC) were prepared via ring-opening reactions with various cyclic acid anhydrides in lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) system. Some cyclic acid anhydrides such as succinic, maleic, glutaric, and phthalic anhydrides gave successfully water-soluble DAC derivatives. From the enzymatic studies, the glycosyl bond of succinyl and maleoyl DAC-20 (20% DAC) was rapidly degraded by lysozyme or chitinase, though that of phthaloyl DAC-20 was not. The ester linkage of succinyl DAC-20 was stable against lipase for five days at room temperature.
Abstract: N-Acylated partially deacetylated chitin (DAC-88) derivatives were prepared via ring-opening reactions with various cyclic acid anhydrides in aqueous MeOH system. N-Alkylation of DAC-88 were also performed in aqueous MeOH with various aldehydes, monosaccharides, and disaccharides. The water solubility of N-acylated and N-alkylated chitosan derivatives at various pHs were studied.
Abstract: The enzymatic (lysozyme, chitinase etc.) digestibility of chitins obtained from squid pen and shrimp shell, and of partially deacetylated chitins (DA-chitins) was investigated. The digestibility of various chitins by the chitinase from Bacillus sp. PI-7S was much higher than that by lysozyme, and β-chitin was digested more smoothly than α-chitin. DA-chitin deacetylated under homogeneous conditions ( ) was hydrolysed by lysozyme more rapidly than that deacetylated under heterogeneous conditions (DAC). DACs from shrimp shell and squid pen showed the same degree of digestibility by lysozyme in spite of a difference in the crystal structure of the original chitins. The crystal structure of chitin and the degree of N-acetyl group aggregation among DA-chitin molecules affect the enzymatic digestibility of chitin and DA-chitin, respectively.
Abstract: The distribution of N-acetyl group in partially deacetylated chitin (DA-chitin) was investigated by nitrous acid deamination. Most deamination products of various DA-chitins (over 50% of deacetylation), prepared under homogeneous conditions, were oligomers of less than six units. These results would suggest a random distribution of N-acetyl groups in the DA-chitin molecule.
Abstract: Copolymers containing cellulose triacetate were prepared under various conditions. A bacteriological plastic dish was coated with the copolymer (HCTA-MDI copolymer) composed of hydrolysed cellulose triacetate (HCTA) and diphenylmethane diisocyanate (MDI). The deacetylated copolymer (DA-copolymer) was prepared by the deacetylation of HCTA-MDI copolymer. The behaviour of animal cells such as a mouse macrophage cell line (A640-BB-2 cells) and a mouse fibroblast (3T6 cells) on prepared dishes was investigated morphologically. A640-BB-2 cells showed good adhesion and smooth spreading, and 3T6 cells also showed good adhesion and sufficient cell growth on the dish coated with HCTA-MDI copolymer. These results suggest that these copolymers are useful for biomedical materials.
Abstract: The distribution of the acetamide group in partially deacetylated chitins (DAC) was investigated by nitrous acid deamination. Deamination products of various DAC (DAC-66, DAC-77, DAC-84 and DAC-91) were mainly trisaccharide, disaccharide, and monosaccharide. These results would suggest random distribution of the acetamide group in the DAC molecule prepared by heterogeneous deacetylation.
Abstract: Lysozyme susceptibility of partially deacetylated chitins (DACs) was investigated by viscometric and gel permeation chromatographic procedures. The highest lysozyme susceptibility was shown by the DAC of around 70% deacetylation which have already been reported to have the highest immunoadjuvant activity through mouse peritoneal macrophage activation.
