Chitin and chitosan, which are natural polysaccharides, have various chemical and biological functions. These functions strongly depend on the amino groups of chitin and chitosan. Therefore, chemical modification of the amino groups are expected to control the function of chitin and chitosan. Many reports on the chemical modifications of chitin and chitosan have been published and we have also studied the chemical modifications of chitosan from the standpoint of the control of chemical and biological functions of chitosan. In this article, we will introduce some studies on the control of functions of chitin and chitosan by chemical modification.
Current literature indicates that the reactivity of quinones towards chitosans is a topic of expanding interest, notwith-standing the analytical difficulties involved in the study of this class of reactions. The natural systems based on the tyrosinase-catalysed generation of quinones and their reactivity towards amines are taken as models in order to capture phenols, in food technology, to prepare biomaterials and to immobilise enzymes. Data obtained via combinatorial screening by coupling confirm that the selection of suitable compounds for reaction with chitosans can be made on the basis of the experimental evidence only, and no a priori theoretical consideration would be of help in predicting the behaviour of quinones towards chitosans: as an example, data concerning the efficient coupling of menadione and the scarce coupling of plumbagin are briefly presented.
The glycoconjugates existing at the cell surface and proteoglycan, an extracellular matrix, are synthesized by the sequential actions of multiple enzymes which hydrolyze or transfer specific glycosidic linkages. The specific inhibitors of such enzymes therefore are considered to play important roles in the functional investigation of oligosaccharides. Alkaloids and nucleotide analogs from natural sources are known to be inhibitors of these enzymes. Recent advances in the three dimensional analysis of glyco-related enzymes, especially the accumulated crystal structures of the glycosidases, have prompted chemists to design and synthesize inhibitors of glycoenzymes. A combined approach with combinatorial chemistry is also a current focus.