Foreword

Improvements in physicochemical and separation methods have contributed to the identification of many unique bioactive substances from natural medicinal resources. Optimization of chemical modifications of natural products has led to the development of effective medicines including intractable diseases such as cancer. Actually, approximately 65% of anticancer drugs are structurally based on natural products. The search for novel bioactive substances from natural products is essential for drug discovery and is one of the cornerstones of research in the field of natural product chemistry. In addition, the accumulated knowledge of natural products can lead to new insight for the development of medicines for intractable diseases by using new computational sciences and technology. This Current topics of Chemical and Pharmaceutical Bulletin contains one review and four regular articles describing the latest research on natural product chemistry that have been contributed by young researchers. Topics include computer science technology in natural products research, isolation of biological constituents from medicinal plants, evaluation of the biological activity of natural products, and synthesis of biological constituents from medicinal plants.

The first review entitled “Computer Science Technology in Natural Products Research: A Review of Its Applications and Implications” is reported by Dr. Ogawa et al. This review outlined artificial intelligence (AI) approaches to natural product-based drug development. In detail, natural product research that utilizes machine learning is described in terms of the exploration of active compounds, automatic compound design, and application to spectral data. In addition, this review aims to promote progress in natural product research by presenting the current state of computational science and chemoinformatics approaches in terms of its applications, strengths, limitations, and implications for the field.

The first regular article entitled “Chemical Structures and Anti-proliferative Effects of Valeriana fauriei Constituents on Cancer Stem Cells” is reported by Dr. Matsumoto et al. The authors isolated new sesquiterpenes and lignans from the extracts of the rhizomes and roots of Valeriana fauriei and elucidated their structures based on chemical and spectroscopic findings. Among the isolated compounds, valerianalignans I and II exerted antiproliferative activity against human astrocytoma cells (U-251 MG) and their cancer stem cells (U-251 MG CSCs). Valerianalignans I and II notably exerted anti-proliferative activities at lower concentrations against CSCs than non-CSCs.

The second regular article entitled “Antiproliferative Activities of Diterpenes from Leaves of Isodon trichocarpus against Cancer Stem Cells” is reported by Nakamura et al. New diterpenes were isolated from the extract from the leaves of Isodon trichocarpus together with 19 known diterpenes. Among the isolated compounds, oridonin, effusanin A, and lasiokaurin, exerted antiproliferative activity against breast cancer cells (MDA-MB-231), U-251 MG cells, and their cancer stem cells (MDA-MB-231 CSCs and U-251 MG CSCs). Effusanin A exerted anti-proliferative activities at lower concentrations against MDA-MB-231 CSCs than against MDA-MB-231 non-CSCs.

The third regular article entitled “Angiotensin I-Converting Enzyme-Inhibitory Activity and Phytochemical Profile of Constituents of the Leaves of Rehmannia glutinosa f. hueichingensis” is reported by Dr. Ohta et al. The authors performed bioassay-guided fractionation of R. glutinosa leaf extract, which led to the isolation of eight compounds. The ACE-inhibitory activities of the isolated compounds and compounds reportedly present in R. glutinosa leaves and roots were examined to determine their efficacy. Finally, a simultaneous analytical method was established to compare the concentration of these compounds in R. glutinosa leaves and roots. The findings suggest that R. glutinosa leaves could be used as a medicinal resource exhibiting ACE-inhibitory activity.

The fourth regular article entitled “Regioselective SmI₂-Mediated Radical ipso-Substitution Cyclization for the Construction of Pyrrolophenanthridinone Skeletons: The Synthesis of Amaryllidaceae Alkaloids” is reported by Dr. Iwasaki et al. The authors developed a regioselective SmI₂-mediated ipso-substitution cyclization. In this reaction, a methoxy group functions as the leaving group. While it was found that the electron density of the benzene ring on the radical acceptor affects the yield of this reaction, high regioselectivity could be achieved by adjusting the additives and reaction temperature. Furthermore, the present reaction was applied to the synthesis of Amaryllidaceae alkaloids. The author’s methodology could contribute to the synthesis of natural products by suppressing the formation of regioisomers that are difficult to purify by conventional column chromatography.

The organizer believes that the research articles in this Current Topics provide useful information for researchers in natural product chemistry. I would like to extend my gratitude to all of the authors for their great contribution to this Current topics.