Facile synthesis of acyl chitosan isothiocyanates and their application to porphyrin-appended chitosan derivative

Chitosan (1) was reacted with phenylisothiocyanate in 5% AcOH/H2O to give N-phenylthiocarbamoyl chitosan (2) with a degree of substitution (DS) of N-phenylthiocarbamoyl groups of 0.86 in 87.1% yield. The following acylation of compound 2 with hexanoyl chloride in the presence of pyridine afforded 3,6-di-O-2,3-hexanoyl chitosan isothiocyanate (4a) with a DS of the isothiocyanate groups of 0.70 in high yield, unexpectedly. Compound 4a exhibited high levels of reactivity toward various amines to give the corresponding N-thiocarbamoyl chitosan derivatives in high yields. Other acyl (decanoyl (4b), myristroyl (4c), stearoyl (4d), benzoyl (4e)) chitosan isothiocyanates were also prepared from chitosan (1) in high yields. To evaluate the potential applications of acyl chitosan isothiocyanates, N-(triphenylporphynyl)thiocarbamoyl chitosan derivative 6 with a DS of the triphenylporphynyl groups of 0.46 was prepared from compound 4b. The Langmuir–Blodgett monolayer film of compound 6 gave a good photon-to-electron conversion performance.