Structure-activity relationships of natural and synthetic lathyrane-based diterpenoids for suppression of NLRP3-driven inflammation and gouty arthritis.

Lathyrane-based diterpenoid is one of the critical bioactive elements of Euphorbia lathyris L., a widely used traditional Chinese medicine for the treatment of inflammation and infection. In this study, we introduced and evaluated seven synthetic or natural lathyrane-based diterpenoids with the same core structure but notable structural variations at specific positions, for their anti-inflammatory and gout-alleviating properties. There was no significant cytotoxicity below 10 µM among the initial test of the cell counting kit 8 of the seven candidate derivatives (compounds 13 to 19) in this work. Furthermore, maintaining the acyloxy group at 15-C position and the strongly hydrophobic aryl structure at 3-C and 5-C positions, compounds 15 (Euphorbia factor L3, EFL3) and 17 strikingly inhibited the production of IL-1ß related to the actuation of the inflammasome in our study. The ELISA assay indicated that the anti-inflammatory effects of EFL3 were better associated with MSU stimulation than other second-line pathways triggered by inflammasome. Further examinations on the acute paw gout model in C57BL/6 mice showed that EFL3 had a significantly inflammatory retarding effect by intraperitoneal injection. It decreased swelling volume as well as the cleavage and activation of local IL-1ß and casepas-1 in the paw. To conclude, our findings reveal several potential key structure-activity relationships that govern the anti-inflammatory effects of lathyrane-type diterpenoids, the dispensable acyl group at the 15-C position, the importance of maintaining the spatial structure of the B-ring, and the potential importance of hydrophobic substituents at the 3-C position. These insights may provide guidance for the structural design of lathyrane-type agents in the future; furthermore, we found that the lathyrane-based diterpenoid EFL3 is a potential agent for gout that is expected to provide a novel therapeutic strategy for inflammation intervention.

Oxidative aromatization mechanism of ligustilide.

The aromatization mechanisms of ligustilide (1), a versatile monomeric phthalide, were investigated. DFT calculations combined with control experiments prove that the aromatization could result from direct oxidation by triplet oxygen in mild conditions with no catalyst, which is generally thought to be difficult. Moreover, it is predicted that the aromatization could rapidly clear away the harmful-to-organism singlet oxygen, which may be relevant to the general antioxidation activity of phthalides, providing a new point of view to understand the bioactivity from chemical reaction.