ABSTRACT
In recent years, chitosan and its monomer glucosamine were subjected to various derivatizations to obtain new natural compounds with improved bioactivity than their predecessors (Fenton et al. 2000; Jiang et al. 2007; Prabaharan 2008). The main aim of the first derivatization was to produce the soluble forms of chitosan, which makes it more biofriendly and easily absorbed by the intestines for enhanced and rapid biological effects (Hai et al. 2003; Il’ina and Varlamov 2004; Kuroiwa et al. 2002; Mao et al. 2004). Since effectiveness of the compound is based on its absorption rate by the body, this kind of derivation opened up new angles for chitosan derivation toward novel bioactive compounds. In this respect, enzymatic hydrolysis of chitosan to obtain oligomers with higher water solubility is of great interest recently (Jeon and Kim 2000). Expectedly, this interest promoted a new derivative with much improved solubility and promising bioactivities compared to that of chitosan itself. In this manner, the obtained oligosaccharide (COS) is the hydrolyzed derivative of chitosan composed of β-(1 → 4) d-glucosamine units. It has been reported to possess better properties such as relatively smaller molecular size in comparison to chitosan and high solubility in aqueous solutions. Moreover, the research conducted also suggested that chitosan oligosaccharides (COS) is effective agents for lowering blood cholesterol and pressure, controlling arthritis, and enhancing antitumor properties (Kim and Rajapakse 2005). Besides oligomerization, another main derivation for chitosan and its monomer glucosamine is adding negative and/or positively charged side chains. In this manner, glucosamine, chitin, chitosan, and COS were reformed under chemical conditions to give sulfated-, phosphorylated-, carboxymethyl-, deoxymethyl-derivatives, and so on (Cho et al. 2011; Huang et al. 2005; Je and Kim 2006; Kim et al. 2005, 2010). Since oligosaccharides and many other derivatives are biodegradable, water-soluble, and nontoxic compounds (Qin et al. 2006), they might be beneficial biomaterials for diseases such as diabetes and obesity with increasing morbidity and mortality rates.
