Research group of Rao Yijian, Jiangnan University: new progress in cercosporin mediated photocatalytic selective oxidation

The selective oxidation of organic compounds is one of the most basic reactions in organic synthesis, and also one of the most critical challenges in the chemical industry Traditionally, these chemical transformations are realized by stoichiometric metal reagents or oxidants, such as metal oxides or peroxides In recent years, because people pay more and more attention to environmental problems, chemists have invested a lot of energy to develop cleaner synthesis strategies, using molecular oxygen as the most economical and environmentally friendly terminal oxidant However, triplet ground state oxygen molecules have low reactivity and are difficult to activate In order to overcome these shortcomings of ground state oxygen molecules, chemists usually use expensive noble metal catalysts or porous graphene / carbon nitride composites to realize oxidation reaction in high temperature and high pressure oxygen atmosphere At present, due to the continuous development of photocatalysis and its wide application in many fields, chemists have developed many metal photocatalysis systems for the oxidation of organic compounds, but the use of precious metals obviously limits their practical application Therefore, it is of great significance to use non-metallic photocatalysts for the selective photocatalytic oxidation of organic compounds under mild conditions Recently, the research group of Professor Rao Yijian from the school of bioengineering of Jiangnan University has successfully realized a series of selective oxidation reactions of organic compounds by using the natural product cercosporin obtained by fermentation engineering as a new non-metallic photocatalyst Relevant results were published online in greenchemistry (2019, DOI: 10.1039 / c9gc02270h) Prof Rao Yijian: since its establishment in 2016, the research group has focused on the analysis of biosynthesis pathway and application development of complex natural products (drugs) by combining synthetic biology, structural biochemistry, fermentation engineering and organic synthesis, and has made a series of progress in NAT Commun., PNAs, J am Chem SOC., green A series of original research results have been published in international first-class journals such as chem., PLoS Biology, J catalysis, etc The research group now has 1 associate professor, 1 assistant researcher, 1 research assistant, 1 postdoctoral, and more than 10 postgraduates Prof Rao Yijian, Professor of School of bioengineering, Jiangnan University, doctoral supervisor, project leader Graduated from Wuhan University of Engineering in 2003 From 2003 to 2006, he studied for master's degree in Fujian Institute of material structure, Chinese Academy of Sciences In 2007, he entered Berlin Free University, Germany, and studied for a doctor's degree In 2011, he joined Max Planck Institute of biochemistry in Germany and engaged in postdoctoral research In 2016, he was employed as a professor by Jiangnan University and incorporated into the youth thousand talents plan of the selected group Department, the distinguished professor of Jiangsu Province and the entrepreneurship and innovation talents plan of Jiangsu Province Advanced scientific research achievements: the photocatalytic selective oxidation of oxygen mediated by cercosporin can be converted into highly reactive substances under the action of light, commonly known as ROS, including singlet oxygen (1O2), peroxide (O2 -), superoxide (• O2 -) and hydroxyl radical (Ho ·) These ROS can be active substances in many organic transformations, so the key step of selective oxidation of organic compounds is to find or design non-metallic photocatalysts to produce ROS In fact, nature has evolved into various oxygen utilization systems, which convert oxygen molecules into active oxygen through free radical reactions, and can spontaneously react with many organic compounds at or below room temperature (biologically called autoxidation) For example, cercosporin (CP) (Figure 1), a natural perylene quinone pigment (PQP) produced by the plant pathogenic fungus Cercospora species, reacts with molecular oxygen after absorbing sunlight to generate reactive oxygen species (ROS) As a "weapon" to infect and destroy plant cells, it can obtain the nutrition needed for its own growth and reproduction Therefore, using the concept of bionics, the research group tried whether cercosporin can be used as an effective "non-metallic" organic photocatalyst to activate oxygen to obtain active oxygen Under mild conditions, the classical reactions such as selective oxidation of benzyl SP 3 C-H bond to carbonyl, selective oxidation of benzylamine to aldehyde and selective oxidation of thioether to sulfoxide were realized Fig 1 Introduction of organic photocatalyst cercosporin (a) The process of producing living oxygen by caudosporin stimulated by visible light; (b) photocatalytic selective oxidation mediated by caudosporin (source: greenchem.) After optimization of fermentation conditions, the conditions of high cercosporin (128.2 mg / L) were obtained After that, three kinds of reactions were optimized with phenylethane, benzylamine and phenylbenzylthioether as template substrates It was found that the three kinds of reactions had the highest activity and selectivity in methanol solvent under the conditions of oxygen atmosphere, room temperature and light, but the oxidation of benzyl sp 3c-h needed to be activated by adding additional KBr Under the optimal conditions, the C-H bond of benzyl SP 3 was selectively oxidized to carbonyl, benzylamine to aldehyde and thioether to sulfoxide In order to investigate the applicability of this method, three types of substrates were examined (Fig 2-4) It is found that these three kinds of reactions can be compatible with a series of electron absorbing or electron donating groups, and the halogen atoms can also be well preserved in the reaction process, which shows that the reaction has good functional group compatibility Fig 2 Study on the selective oxidation of SP 3 C-H bond to carbonyl by cercosporin photocatalysis (source: greenchem.) (source: greenchem.) (source: greenchem.) finally, in order to further clarify the mechanism of the reaction, the author designed a number of control experiments On the one hand, according to the experiments of free radicals and singlet oxygen capture, the author speculates that the oxidation of benzyl sp 3c-h and benzylamine undergoes the intermediate process of free radicals, i.e oxygen anion, while the oxidation of thioether undergoes the process of both free radicals and singlet oxygen The redox potential of the single electron transfer pathway measured by electrochemistry can also be confirmed 18 O isotope labeling experiments show that oxygen is indeed involved in the reaction Based on the above conclusions, the author speculates that the reaction mechanism is shown in Figure 5: Figure 5 Reaction mechanism (source: greenchem.) to sum up, the author used microbial fermentation technology to prepare cercosporin in a green and efficient way, and developed a new organic photocatalyst, which was successfully applied to the selective oxidation of SP 3c-h, benzylamine and thioether The reaction conditions are mild, selectivity is high, efficiency is high, and it provides a new green, environmental protection and economic method for photocatalytic oxidation of organic compounds The chemistry part of the research work was completed by postdoctoral Li Jia, the biosynthesis part of cercosporin was completed by postdoctoral Bao Wenhao, Tang Zhaocheng and doctoral Guo Baodang, Associate Professor Zhang Yan and Professor Rao Yijian of Jiangnan University As the co-author of this study, the research work has been supported by national key research and development plan, the youth thousand talents project of the Central Organization Department, Jiangsu Province distinguished professor and other projects Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information website, chembeangoapp, chembeango official micro blog, CBG information wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the representative research groups in China, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.