Generation of the Icetexane Core by Use of a Heck Strategy: Total Synthesis of Taxamairin B

Total Synthesis of Brevitaxin

Brevitaxin was prepared in nine steps from commercially available carnosic acid. The construction of the 1,4-benzodioxin moiety involved an unique stepwise ortho-quinone-engaged [4+2] cycloaddition. Two strategic stages were employed to prepare the highly unsaturated cycloaddition precursor 3: (1) synthesizing the diene moiety (C1-C2 and C10-C20 double bonds) by regioselective ortho-quinone tautomerization, and (2) installing four sp2-hybridized carbon atoms (C3, C5, C6 and C7) in one step using a SeO2-promoted chemo- and regioselective oxidation reaction.

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.

Recent Developments with Icetexane Natural Products

Icetexane diterpenoids are a diverse family of natural products sourced from several species of terrestrial plants. Icetexanes exhibit a broad array of biological activities and together with their complex 6-7-6 tricyclic scaffolds, they have piqued the interest of synthetic organic chemists, natural products chemists, and biological investigators over the past four decades and were reviewed 13 years ago. This review summarizes icetexane natural products isolated since 2009, provides an overview of new synthetic approaches to the icetexane problem, and proposes an additional classification of icetexanes based on novel structures that are unlike previously isolated materials.

Gold-Catalyzed Synthesis of Icetexane Cores: Short Synthesis of Taxamairin B and Rosmaridiphenol

We report the short synthesis of two natural products, rosmaridiphenol and taxamairin B, from key intermediates 5a and 5b, which were prepared from enynals 8a and 9b, respectively, by using a gold-catalyzed cyclization reaction. This approach can be widely applied in the synthesis of [6,7,6]-fused tricyclic compounds found in many icetexane diterpenoids.