Contiguous Quaternary Carbons: A Selection of Total Syntheses

Total synthesis and target identification of marine cyclopiane diterpenes

Marine cyclopianes are a family of diterpenoid with novel carbon skeleton and diverse biological activities. Herein, we report our synthetic and chemical proteomics studies of cyclopiane diterpenes which culminate in the asymmetric total synthesis of conidiogenones C, K and 12β-hydroxy conidiogenone C, and identification of Immunity-related GTPase family M protein 1 (IRGM1) as a cellular target. Our asymmetric synthesis commences from Wieland-Miescher ketone and features a sequential intramolecular Pauson-Khand reaction and gold-catalyzed Nazarov cyclization to rapidly construct the 6-5-5-5 tetracyclic skeleton. The stereocontrolled cyclopentenone construction is further investigated on complex settings to demonstrate its synthetic utility. Furthermore, using an alkyne-tagged conidiogenone C-derived probe, IRGM1, a master regulator of type I interferon responses, is identified as a key cellular target of conidiogenone C responsible for its anti-inflammatory activity. Preliminary mechanism of action studies shows that conidiogenone C activates IRGM1-mediate dysfunctional mitochondria autophagy to maintain mitochondria quality control of inflammatory macrophages.

Hydrated [3+2] Cyclotelomerization of Butafulvenes to Create Multiple Contiguous Fully Substituted Carbon Centers

The construction of multiple continuous fully substituted carbon centers, which serve as unique structural motif in natural products, is a challenging topic in organic synthesis. Herein, we report a hydrated [3+2] cyclotelomerization of butafulvenes to create contiguous fully substituted carbon backbone. In the presence of scandium triflate, all-carbon skeleton with spiro fused tricyclic ring can be constructed in high diastereoselectivity by utilizing butafulvene as the synthon. Mechanistic studies suggest that this atom-economic reaction probably proceeds through a synergistic process containing butafulvenes dimerization and nucleophilic attack by water. In addition, the tricyclic product can undergo a series of synthetic derivatizations, which highlights the potential applications of this strategy. The recyclability of Sc(OTf)3 has also been demonstrated to show its robust performance in this hydrated cyclotelomerization.

Concise Total Synthesis of Salimabromide

We achieved a concise total synthesis of salimabromide by using a novel intramolecular radical cyclization to simultaneously construct the unique benzo-fused [4.3.1] carbon skeleton and the vicinal quaternary stereocenters. Other notable transformations include a tandem Michael/Mukaiyama aldol reaction to introduce most of the molecule's structural elements, along with hidden information for late-stage transformations, an intriguing tandem oxidative cyclization of a diene to form the bridged butyrolactone and enone moieties spontaneously, and a highly enantioselective hydrogenation of a cycloheptenone derivative (97% ee) that paved the way for the asymmetric synthesis of salimabromide.