Foreword

Cyclodextrins were first isolated in 1891 as degradation products of starch and were characterized as cyclic oligosaccharides. The α-, β-, and γ-cyclodextrins are the most common natural forms, consisting of six, seven, and eight glucose units, respectively. Recently, various kinds of cyclodextrin derivatives have been developed to extend the physicochemical properties and inclusion capacity of natural cyclodextrins. The inclusion phenomenon of cyclodextrins has been widely used in various fields and is currently applied to household commodities, food, cosmetics, supplements, pharmaceuticals, biotechnology, paints, etc. A continuously increasing number of publications demonstrates the existing interest in cyclodextrin research and development. According to Cyclodextrin News, the number of cyclodextrin-related publications (papers, patents, and conference presentations) has increased in recent 5-year periods, e.g., to 10450, 13404, and 18430 in 2001–2005, 2005–2010, and 2011–2015, respectively. The leading application is still pharmaceutical. In particular, Sugammadex, a γ-cyclodextrin derivative, is the first clinical representative of a new class of drugs called selective relaxant-binding agents. Analytical applications and those in the chemical and biotechnology industry are almost equal in second place. Additionally, cyclodextrin chemistry, theoretical studies on inclusion complex formation, cyclodextrin cell biology, and cyclodextrin applications in food, cosmetics, and agriculture have been extensively studied.

Much to our delight, the Royal Swedish Academy of Sciences decided to award Prof. Jean-Pierre Sauvage, Prof. Sir J. Fraser Stoddart, and Prof. Bernard L. Feringa the Nobel Prize in Chemistry 2016 for the design and synthesis of molecular machines. This is highly appreciated in the field of supramolecular chemistry utilizing building blocks of host–guest complexes including cyclodextrin complexes. Cyclodextrins have been used as a cyclic component in the construction of supramolecular architectures, e.g., rotaxanes, polypseudorotaxanes, and catenanes. As a result, cyclodextrins have been applied as a component of molecular shuttles, motors, and machines.

The Current Topics section in this issue of the Chemical and Pharmaceutical Bulletin is composed of six reviews. The first review by Prof. Hatsuo Yamamura demonstrates the microwave-assisted click reaction for the polymodification of cyclodextrin and amylose molecules and its application to the synthetic study of membrane-active antibacterial derivatives.

In the second review, Prof. Takashi Hayashita and colleagues clarify the unique saccharide-recognition functions of cyclodextrin, chemically modified cyclodextrin, and cyclodextrin gel complexes based on a synergistic function, thereby confirming their use as supramolecular saccharide sensors.

Prof. Kohzo Ito introduces the synthesized slide-ring materials using cyclodextrin by cross-linking polyrotaxanes, typical supramolecules, in the third review paper. The slide-ring materials show remarkable scratch-proof properties, making them suitable for coating automobiles, cell phones, mobile computers, etc.

In the fourth review, Prof. Akira Harada and colleagues described the recent development of cyclodextrin-based supramolecular polymeric materials: polymers carrying host and guest residues exhibit unique properties, and this is an important new frontier between materials science and life science.

The potential use of the hemoCD complex, which is composed of meso-tetrakis(4-sulfonatophenyl)porphinatoiron(II) and a per-O-methylated β-cyclodextrin dimer linked by a pyridine linker, as a biological carbon monoxide-depleting agent is explained by Prof. Hiroaki Kitagishi and Ms. Saika Minegishi in the fifth review.

The last review by Prof. Hidetoshi Arima and colleagues demonstrates that cyclodextrins have significant potential as promising drug carriers for low molecular-weight agents, proteins, antibodies, small interfering RNA (siRNA), decoy DNA, and genes as well as active pharmaceutical ingredients against various diseases such as lysosomal storage diseases, leukemia, and solid tumors.

This year marks the 126th anniversary of the discovery of cyclodextrins. Therefore, some may think of them as “unmasked” compounds on which research has been completed. However, the reviews contained here show that would be a mistake. Basic research on cyclodextrins including inclusion complexes and supramolecular complexes will develop further in future and consequently contribute to happiness and well-being through applications in various products.