Tetracyclic terpenoids from Dasyscyphus niveus, dasyscyphins D and E

Naturally Occurring Norsteroids and Their Design and Pharmaceutical Application

The main focus of this review is to introduce readers to the fascinating class of lipid molecules known as norsteroids, exploring their distribution across various biotopes and their biological activities. The review provides an in-depth analysis of various modified steroids, including A, B, C, and D-norsteroids, each characterized by distinct structural alterations. These modifications, which range from the removal of specific methyl groups to changes in the steroid core, result in unique molecular architectures that significantly impact their biological activity and therapeutic potential. The discussion on A, B, C, and D-norsteroids sheds light on their unique configurations and how these structural modifications influence their pharmacological properties. The review also presents examples from natural sources that produce a diverse array of steroids with distinct structures, including the aforementioned A, B, C, and D-nor variants. These compounds are sourced from marine organisms like sponges, soft corals, and starfish, as well as terrestrial entities such as plants, fungi, and bacteria. The exploration of these steroids encompasses their biosynthesis, ecological significance, and potential medical applications, highlighting a crucial area of interest in pharmacology and natural product chemistry. The review emphasizes the importance of researching these steroids for drug development, particularly in addressing diseases where conventional medications are inadequate or for conditions lacking sufficient therapeutic options. Examples of norsteroid synthesis are provided to illustrate the practical applications of this research.

An Access to Benzo[a]fluorenes, Benzo[b]fluorenes, and Indenes Triggered by Simple Lewis Acid

This report illustrates BF₃·OEt₂ promoted intramolecular cascade cycloaromatization of 1,7-ynones toward synthesizing structurally diverse benzofluorene scaffolds. Remarkably, the present protocol promotes the formation of two consecutive C-C bonds intramolecularly and undergoes aromatization under mild reaction conditions to afford the tetracyclic benzo[a]fluorene frameworks. Besides, the formation of indenes was observed when 1-bromo-2-iodoarenes are relatively more electron-rich when compared with the one originating from the terminal arylacetylenes, under controlled conditions, wherein triple bond polarity has been just reversed due to the change of electronic effects exerted by the strong +M group of 1-bromo-2-iodoarenes, which is in conjugation to the connected triple bond. The same concept to generate indenes has also been extended by using aliphatic alkyne tethered ynones. Further, it was noticed that 1,7-ynones bearing the more electron-rich 1-bromo-2-iodoarenes than the arene ring arriving from the terminal arylacetylenes lead to benzo[b]fluorenes, under thermodynamic conditions, instead of delivering the benzo[a]fluorenes. In addition, this method features metal-free conditions, easily accessible starting materials, operational simplicity, gram-scale synthesis, and a wide range of substrate scopes.

Divergent Entry to Walsucochin Nortriterpenoids: Total Syntheses of (±)-Walsucochin A and (±)-Walsucochinoids C-F

Nortriterpenoids isolated from Walsura cochinchinensis have attracted much attention from both synthetic and medicinal chemists, yet only recently have efficient synthetic approaches to any members appeared. Shown here is that the common intermediate with a 6/6/5/6-fused tetracyclic ring nucleus can be converted to walsucochin family members. The first total syntheses of (±)-walsucochin A, (±)-walsucochinoids C-F, and their analogues were achieved in this work.

Remote C-H Activation Strategy Enables Total Syntheses of Nortriterpenoids (±)-Walsucochin B and (±)-Walsucochinoids M and N

Total syntheses of (±)-walsucochin B and (±)-walsucochinoids M and N have been achieved from farnesyl bromide. The key steps of the synthetic sequence are the titanocene-mediated radical cyclization and base-induced cycloaromatization for the rapid construction of the 6/6/5/6-fused tetracyclic skeleton. Importantly, a Cu-mediated remote C-H hydroxylation reaction has been developed to site-selectively install the oxygen function at the C-7 position of the target molecules, thus solving the biggest challenge for the synthesis of the compounds.

Total synthesis of (−)-akaol A via a conformational constraint strategy

Our synthesis of akaol A features a well-designed Friedel–Crafts cyclization, which ensures a cis-fused B/C ring through a conformational constraint strategy.