Synthesis and Some Properties of Nonnatural Amino Polysaccharides:  Branched Chitin and Chitosan

Abstract

Regioselective introduction of N-acetyl-d-glucosamine and d-glucosamine branches at C-6 of chitin and chitosan has been accomplished. N-Phthaloylchitosan was used as an organosoluble key intermediate for a series of controlled modification reactions, and the derived 3-O-acetyl-2-N-phthaloylchitosan and 3-O-acetyl-2-N-phthaloyl-6-O-trimethylsilylchitosan proved to be suitable acceptors for glycosylation with an oxazoline from glucosamine. The resulting branched product had a substitution degree up to 0.63. It was deprotected to give branched chitosan, which was subsequently N-acetylated to afford branched chitin. The introduction of such branches markedly improved the affinity for solvents, and the product with protecting groups was soluble in common organic solvents in sharp contrast to the insoluble chitin and chitosan. Furthermore, both the branched chitin and chitosan were readily soluble in neutral water and showed high moisture absorption and retention. The branched chitin was degraded with lysozyme, and the susceptibility decreased with increasing extent of branching. The branched chitosan was characterized by marked antimicrobial activity and aggregation ability for bovine serum albumin.

N-Phthaloylated Chitosan as an Essential Precursor for Controlled Chemical Modifications of Chitosan: Synthesis and Evaluation

“…Conversion of N,O-Phthaloylated Chitosan 1 to N-Phthaloyl-chitosan 2: a) Tritylation Followed by Detritylation O-Phthaloyl groups of 1 could be removed by transesterification with methoxide/methanol to give Nphthaloyl-chitosan (2) (Scheme 2), and the structure was confirmed by 1 H NMR, IR, and elemental analysis as reported previously. 11 However, it was necessary to conduct the reaction for a long time, around 4 d, or to repeat the reaction two or three times for complete removal owing to the reaction under heterogeneous suspension conditions. Moreover, the N-phthaloyl group was not stable under alkaline conditions and tended to decompose to some extent especially in the presence of a small amount of contaminated water.…”

“…However, phthaloylated chitosan thus far used actually has O-phthaloyl groups, since treatment of chitosan with phthalic anhydride results in partial Ophthaloylation in addition to the N-substitution. 10,11 Furthermore, the reaction is sensitive to various factors including reaction conditions and the state of chitosan, which often fails to give reproducible results. Though N,O-phthaloylated product is suitable for y To whom correspondence should be addressed (Tel: +81-422-37-3745, Fax: +81-422-37-3871, E-mail: kurita@st.seikei.ac.jp).…”

Quantitative protection of chitin by one-step tritylation and benzylation to synthesize precursors for chemical modifications

“…As protective and solubilizing groups, trimethylsilyl [11][12][13] and phthaloyl [14][15][16][17][18][19][20][21][22] are especially practical for chitin and chitosan to give derivatives with required molecular structures. For instance, sugar branches could be incorporated into chitin and chitosan through a series of site-specific reactions starting from 2-N-phthaloylchitosan; the resulting nonnatural branched chitins and chitosans were water-soluble and exhibited significant medicinal functions such as antimicrobial [16,17,19] and antitumor activities [22].…”

Synthesis and characterization of branched polysaccharides by reaction of cellulose with 2,3,4,6-tetraacetyl-1-bromo-α-D-glucopyranoside

“…14,15 Kurita et al have found that some properties of chitin and chitosan (antimicrobial activity, aggregation ability for bovine serum albumin) are improved after glycosylation reaction with a glucosamino derivative. 16 In the course of our ongoing work on water-soluble cellulose derivatives, we have reported results on oxidized cellulose derivatives 17 , cellulosics bearing cationically charged moieties, 18 cellulosics bearing oxocarbonic acid esters of high DS, 19 carboxymethyl cellulose 20 , and cellulose polyelectrolytes prepared via click-reaction. 21 For homogeneous chemical modification of cellulose, DMA/LiCl developed by McCormick, is a very versatile reaction medium.…”