A Classic Photochemical Approach Inducing an Unexpected Rearrangement: Exploring the Photoreactivity of Pentacyclic Triterpenic Acids

The discovery of new bioactivities is closely related to the generation of novel scaffolds, and in the past few years different strategies have been proposed to obtain unknown architectures from the manipulation of known compounds. In the present study, we exploited a vintage photochemical approach for the discovery of an unexpected pathway of reactivity related to Δ¹-3-oxo-pentacyclic triterpenic acids gaining access to a new class of natural-unnatural 5(10→1)abeo-pentacyclic triterpenic acids.

Identification of a Strigoterpenoid with Dual Nrf2 and Nf-κB Modulatory Activity

The sesquiterpene-coumarin ether samarcandone provided a suitable framework to replace the apocarotenoid A-C ring system of strigol (1), replicating, after linking to a butenolide moiety, the activity of the natural phytohormone on Nrf2 and also showing potent NF-kB inhibitory activity, overall modulating two critical pathways of inflammation and cancer.

Triterpenoid Hydroxamates as HIF Prolyl Hydrolase Inhibitors

Pentacyclic triterpenoid acids (PCTTAs) are pleiotropic agents that target many macromolecular end-points with low to moderate affinity. To explore the biological space associated with PCTTAs, we have investigated the carboxylate-to-hydroxamate transformation, discovering that it de-emphasizes affinity for the transcription factors targeted by the natural compounds (NF-κB, STAT3, Nrf2, TGR5) and selectively induces inhibitory activity on HIF prolyl hydrolases (PHDs). Activity was reversible, isoform-selective, dependent on the hydroxamate location, and negligible when this group was replaced by other chelating elements or O-alkylated. The hydroxamate of betulinic acid (5b) was selected for further studies, and evaluation of its effect on HIF-1α expression under normal and hypoxic conditions qualified it as a promising lead structure for the discovery of new candidates in the realm of neuroprotection.

Cannabichromene

Cannabinochromene (CBC, 1a) is the archetypal member of a class of more than twenty isoprenylated 5-hydroxy-7-alkyl(aralky)benzo[2 H]pyranes first reported from Cannabis sativa L. but also occurring in unrelated plants ( Rhododendron species) as well as liverworts and fungi. The chemistry, synthesis, and bioactivity of CBC (1a) is reviewed, highlighting its underexploited pharmacological potential and rich chemistry.