Toshio Fujita was born on January 26, 1929 in Kyoto, Japan. He graduated from the Department of Agricultural Bioorganic Chemistry at Kyoto University in 1951, later earning his Ph.D. in that same department (1962). He completed his postdoctoral studies at the Department of Chemistry, Pomona College, California, where he worked with Corwin Hansch, 1961–1963 [1, 2].

Hansch and Fujita are widely considered as the pioneers of the QSAR (Quantitative Structure–Activity Relationship) method [3], which provided timeless guidelines as to how to translate differences in chemical structures into those properties that relate to how to differences in their biological properties.

figure a

They 1964 papers, “A New Substituent Constant, π, Derived from Partition Coefficients” [4] and “ρ–σ–π Analysis. A Method for the Correlation of Biological Activity and Chemical Structure” [5] have been cited more than 1200 times each, and listed as the 39th and 44th “the most-cited JACS Publications” in 2003 [6]. These two papers are now identified as “citation classics”: According to Google Scholar, the first paper was cited nearly 2800 times, whereas their insights into the calculation of log P, nearly 1700 times (search date: October 11, 2017).

https://scholar.google.com/scholar?hl=en&q=author%3Ahansch+author%3Afujita&as_sdt=1%2C21&as_sdtp=&oq=au.

Their formulation of QSAR in 1964 provided six key insights that remain relevant to this day:

  1. 1.

    Usually differences in more than one molecular property are required to understand the basis of differences in the biological activities of molecules.

  2. 2.

    The logarithm of the 1-octanol/water partition coefficient (log P) used as a hydrophobicity index is a key to understanding structure–activity relationships.

  3. 3.

    There is frequently an optimum log P associated with a particular biological response.

  4. 4.

    It is possible to estimate log P from a chemical structure, as first demonstrated by Albert J. Leo and David Weininger [7].

  5. 5.

    Mathematical models such as multiple regression analyses can be used to identify linear-free-energy relationships between molecular properties and biological activities.

  6. 6.

    A digital computer is necessary to explore the possible relationships.

In many ways, their work paved the way to computer-aided drug discovery, the use of machine learning in chemistry and biology, which is the precursor of using AI in drug discovery [8].

Professor Fujita returned to Kyoto University after completing another postdoctoral fellowship at the Department of Chemistry and Chemical Engineering, University of Illinois in 1964. Prof. Fujita instructed and lectured at Kyoto University between 1951 and 1966. He was an Associate Professor in the Department of Agricultural Chemistry until 1981. The following year, he became Professor at the Pesticide Chemistry Laboratory, which was renamed as the Bioregulation Chemistry Laboratory in 1990. Since 1992 to the present, he has served as Professor Emeritus at Kyoto University. Between 1992 and 1998, Prof. Fujita worked as a consultant at the Fujitsu Kansai Systems Laboratory. He continued to pursue QSAR, publishing approximately 300 original papers and review articles and editing four books [9]. One of his most recent papers, with David Winkler, discussed the role of the “two QSARs” (explanation vs. prediction) [10]. He was the inventor and chief developer of EMIL (Example-Mediated Innovation for Lead Evolution) software that contains a database of bioisosteric transformations, i.e., structural transformations of drugs and pesticides that retain the biological properties of the original molecule [11].

Professor Fujita’s scholar activities include Vice president and President of the Pesticide Science Society of Japan (1984–1986) and Chairman of the Kansai Regional Section of the Japan Society for Bioscience, Biotechnology and Agrochemistry (1989–1990). His work on QSAR was recognized by the Award for Research Achievement from the Pesticide Science Society of Japan, March 1979; the Award for Research Achievement from the Agricultural Chemical Society of Japan, March 1989; Recognition for Research Performance from the Division of Agrochemicals of the American Chemical Society, August 1992; and the International Award in Pesticide Chemistry from the American Chemical Society, August 1994. He received the Pharmaceutical Society of Japan Award for Distinguished Service in 2017, and was scheduled to give a special lecture at the Annual Symposium of Structure–Activity Relationships in Japan, November 2017. Professor Fujita passed away on August 22, 2017, at the age of 88, in Kyoto, Japan, after a bout of pneumonia.

To honor his impact of his contributions in the field of computer-aided drug discover and QSAR, the Hansch Fujita Foundation bestows the Fujita Award. Its first recipient was Prof. Jurgen Bajorath (2016). Toshio Fujita never took a break from his research, and was an outstanding mentor and advisor.