Scandium-Catalyzed Skeleton Conversion of Lathyrane to Lathyranone-Type Euphorbia Diterpenes

Rearrangement of the Tetra- and Tricyclic Skeletons of Pepluanol B to Access the Core Structures of Tigliane- and Myrsinane-Type Euphorbia Diterpenes

Pepluanol B is a new Euphorbia diterpene with an unprecedented tetracyclic backbone. However, its biogenetic relationship with known Euphorbia diterpenes is unclear. We report herein that its β-hydroxyl ketone motif could undergo a base-promoted retro-aldol/aldol process in two pathways and afford the skeletons of tigliane- and myrsinane-type Euphorbia diterpenes through the formation of the C8-C14 and C7-C13 bonds, respectively. The retro-aldol/aldol cascade indicates that pepluanol B is possibly a biosynthetic precursor of lathyranes and other relevant dipterpenes.

Photo-induced scandium-catalyzed biomimetic skeleton conversion of lathyrane to naturally rare eupholathone Euphorbia diterpenes

The naturally scarce eupholathone-type euphornin E (1) was efficiently prepared from abundant lathyrane-type Euphorbia factor L1via a visible-light-induced Sc(OTf)3-catalyzed tandem process. Eupholathones 2 and 3 were also smoothly obtained by changing the reaction solvent. This route provides a convenient method for easily constructing scarce eupholathone- from lathyrane-type Euphorbia diterpenes, and confirms the biogenetic relationship between them from a chemical standpoint. Notably, compound 1 exhibited good anti-HIV activity.

Discovery of myrsinane-type Euphorbia diterpene derivatives through a skeleton conversion strategy from lathyrane diterpene for the treatment of Alzheimer's disease

A series of novel myrsinane-type Euphorbia diterpene derivatives (1-37) were synthesized from the abundant natural lathyrane-type Euphorbia factor L3, using a multi-step chemical process guided by a bioinspired skeleton conversion strategy, with the aim of discovering potential anti-Alzheimer's disease (AD) bioactive lead compounds. The synthesis process involved a concise reductive olefin coupling reaction through an intramolecular Michael addition with a free radical, followed by a visible-light-triggered regioselective cyclopropane ring-opening. The cholinesterase inhibitory and neuroprotective activities of the synthesized myrsinane derivatives were evaluated. Most of the compounds showed moderate to strong potency, highlighting the importance of ester groups in Euphorbia diterpene. In particular, derivative 37 displayed the most potent acetylcholinesterase (AChE) inhibition, with an IC50 value of 8.3 μM, surpassing that of the positive control, tacrine. Additionally, 37 also showed excellent neuroprotective effect against H2O2-induced injury in SH-SY5Y cells, with a cell viability rate of 124.2% at 50 μM, which was significantly higher than that of the model group (viability rate 52.1%). Molecular docking, reactive oxygen species (ROS) analysis, immunofluorescence, and immunoblotting were performed to investigate the mechanism of action of myrsinane derivative 37. The results indicated that derivative 37 may be a promising myrsinane-type multi-functional lead compound for the treatment of Alzheimer's disease. Furthermore, a preliminary SAR analysis was performed to study the acetylcholinesterase inhibitory and neuroprotective activities of these diterpenes.

Visible-Light-Promoted Tandem Thiol-Ene Click Reaction/Transannular Cyclization and Regioselective Cyclopropane Ring-Opening to Construct Sulfur-Containing Euphorbia Diterpenes

The biorelevant sulfur-containing Euphorbia diterpenes with scarce 5/7/6/3 premyrsinane- and 5/7/6 myrsinane-type backbones were easily constructed from naturally abundant lathyrane-type Euphorbia factor L₃ by visible-light-triggered tandem thiol-ene click reaction/transannular cyclization and regioselective cyclopropane ring-opening. The selenide diterpene was also successfully obtained to verify the system universality. This concise synthesis route gives an efficient strategy for obtaining structurally diverse Euphorbia diterpenes under very mild conditions and provides a promising anti-HIV bioactive premyrsinane diterpene 3h.