Design, Synthesis of (±)-Millpuline A, and Biological Evaluation for the Lung Cell Protective Effects through SRC

In this study, a visible-light-induced intermolecular [2 + 2] photocycloaddition reaction based on flavonoids was constructed to address the problems of low yield, poor physicochemical properties, and lack of target definition in total synthesis of (perpendicular to)-millpuline A whose bioactivity remains unknown. As a result, 20 derivatives were synthesized for bioactivity evaluation. Consequently, lung cell protective effects of (+/-)-millpuline A and compound B13a were revealed for the first time and the crucial role of stereoconfiguration of the cyclobutane moiety in their protective effects against NNK in normal lung cells was demonstrated. Moreover, through target prediction and experimental verification in MLE-12 cells, SRC was determined to be the target of (+/-)-millpuline A regarding its protective effect in NNK-induced lung cell injury. Results from RT-Q-PCR and HTRF experiments verified that (+/-)-millpuline A could repress SRC activity through a transcriptional mechanism but not acting as an inhibitor to directly bind to and thereby inhibit SRC protein. The results in this paper are informative for the further development of visible lightcatalyzed cycloaddition of flavonoids and lay a scientific foundation for understanding the bioactivity and underlying mechanism of (+/-)-millpuline A and other structurally similar natural skeletons.

Automated summary

In this study, a visible-light-induced intermolecular [2 + 2] photocycloaddition reaction was used to synthesize 20 derivatives of (perpendicular to)-millpuline A for bioactivity evaluation. The protective effects of (+/-)-millpuline A and compound B13a against NNK-induced lung cell injury were revealed. The target of (+/-)-millpuline A was determined to be SRC protein, and its inhibitory effect on SRC activity was demonstrated through a transcriptional mechanism. These findings provide valuable insights for the further development of flavonoids and understanding the bioactivity and mechanism of (+/-)-millpuline A.