Total Synthesis of Azulene Derivative, a Blue Pigment Isolated from Lactarius indigo, and Colorant Application of Its Aqueous Dispersion
- Kiyotaka Maruoka
- Ryuju Suzuki*
- Takaaki KamishimaTakaaki KamishimaEast Tokyo Laboratory, Genesis Research Institute, Inc., 717-86 Futamata, Ichikawa, Chiba 272-0001, JapanMore by Takaaki Kamishima
- Yoshitaka Koseki
- Anh Thi Ngoc DaoAnh Thi Ngoc DaoGraduate School of Engineering, Nagasaki University, 1-14 Bunkyo, Nagasaki, Nagasaki 852-8521, JapanMore by Anh Thi Ngoc Dao
- Toshihiro Murafuji
- , and
- Hitoshi Kasai*
Safety concerns in the food industry have increased the demand for natural food colorants. However, the application ranges of natural blue colorants are insufficient because they are scarce in nature, and the currently available natural blue dyes are limited to water-soluble products. In this study, we investigated a fat-soluble azulene derivative isolated from the mushroom Lactarius indigo as a potential candidate for a natural blue colorant. We developed its first total synthesis, where the azulene skeleton was constructed from a pyridine derivative and an ethynyl group was converted into an isopropenyl group using zirconium complexes. Moreover, nanoparticles of the azulene derivative were prepared via reprecipitation method, and their colorant ability was investigated in aqueous solutions. The new candidate food colorant exhibited a deep-blue color in an organic solvent and aqueous dispersion.
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