Reactivity characteristics of squid β‐chitin as compared with those of shrimp chitin: High potentials of squid chitin as a starting material for facile chemical modifications

Chemical reactivity of β‐chitin isolated from squid pens has been examined in various reactions to elucidate the possibility of facile modifications in simple manners leading to the preparation of derivatives with well‐defined structures. β‐Chitin swelled in common solvents such as methanol and pyridine unlike the ordinary α‐chitin and exhibited much higher reactivity than β‐chitin. Free amino groups present in β‐chitin were easily and selectively acetylated with acetic anhydride in methanol to give chitin with a uniform structure, poly(N‐acetyl‐D‐glucosamine). When acetylation reaction was carried out in pyridine, O‐acetylation proceeded smoothly besides N‐acetylation. In the presence of 4‐dimethylaminopyridine as the catalyst, even full acetylation was achieved under mild conditions. Tosylation was also quite efficient in pyridine without side reactions such as N‐deacetylation which is unavoidable in the tosylation of α‐chitin. β‐Chitin also enabled direct tritylation in pyridine in the presence of 4‐dimethylaminopyridine. All these reactions were quite sluggish with β‐chitin, and no reactions or only very low extents of substitution were observed, indicating the high potential of β‐chitin as a versatile starting material for facile modification reactions.