A novel chitin derivative having a pendant ester function, 2-N-(2-ethoxycarbonylethyl)chitin (2), was synthesized by a Michael-type nucleophilic addition of an amino group of partially deacetylated chitin (1) to ethyl acrylate in phosphate buffer/methanol (5 : 3, v/v) at 40°C. N-Selective monosubstitution occurred exclusively in the polymer reaction, which was supported by a reaction of methyl 2-amino-2-deoxy-D-glucopyranoside with ethyl acrylate to afford methyl 2-N-(2-ethoxycarbonylethyl)-2-amino-2-deoxy-D-glucopyranoside. The degrees of substitution (DSs) of 2 were determined by 1H NMR spectroscopy. T1 analysis of 2 was carried out in order to clarify differences of signal intensities of the pendant ester protons and the pyranose ring protons. The result of the T1 measurement suggested a relatively restricted molecular motion of the chitin backbone in comparison with the flexible pendant ethyl ester groups. Furthermore, 2-N-(2-carboxyethyl)chitin sodium salt (3) was synthesized from ethyl acrylate and 1 by the Michael addition followed by hydrolysis in 0.1 N NaOH aq. at 40°C. The DSs of 3 were varied from 0.26 to 0.88, which were almost controlled by the reaction period of the Michael reaction from 6 to 168 h. 3 showed good solubility in water. Viscosity measured on a cone-plate viscometer for the 1.0 wt.-% aqueous solution of 3 (DS, 0.26) was 0.074 Pas·sec.
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Aoi et al. (2000) studied this question.