Rapid access to icetexane diterpenes: Their protective effects against lipopolysaccharides-induced acute lung injury via PI3K/AKT/NF-κB axis in macrophages

Acute lung injury (ALI) is a life-threatening disease with limited therapeutic options available in clinic. Development of novel strategies and drugs for anti-ALI therapy are urgently needed. In this study, a facile synthesis of 21 icetexane diterpenes and derivatives with widely-varied oxidation states, particularly the taxamairins that are otherwise challenging to access, were developed from the readily available carnosic acid. Further explorations of their biological implications led to the identification of taxamairin B (6) as a potent anti-inflammatory agent by decreasing the gene expressions of proinflammatory cytokines (TNF-α, IL-1β and IL-6), as well as mitigating NO and ROS production, within LPS-induced RAW264.7 cells. Taxamairin B (6, 25 mg/kg) also exerted significant protective effects against in LPS-induced ALI in mice. Mechanistic insights drawn from the transcriptomic analysis revealed that taxamairin B (6) down-regulated the PI3K-AKT pathway, along with the suppression of the nuclear translocation of NF-κB. This study not only paves a new pathway to taxamairins, but also provides novel drug leads for the development of anti-inflammatory agents with unique mode of actions.