Few natural oxindole alkaloids possess an exceptional spiro-[(1,3)oxazinan-3,6'-oxindole] core structure, which results from an unusual oxidative indole rearrangement. The Rauvolfia alkaloid reserpine can be converted into the spirooxindole-1,3-oxazines dioxyreserpine and trioxyreserpine through efficient visible-light catalytic photooxygenation with anthraquinone photocatalysts. A mechanistic investigation sheds new light on the photooxidative rearrangement of reserpine and related monoterpene indole alkaloids, and the spirooxindole-1,3-oxazine products can be valorized by reductive ring opening, to obtain cis-decahydroisoquinolines as new enantiopure synthetic building blocks, as demonstrated for dioxyreserpine.

A common synthetic route to indoxyl and 2‐oxindole alkaloids utilizes the oxidation of indoles to 3‐hydroxyindolenines, followed by acid‐mediated 1,2‐rearrangement. However, controlling the regioselectivity is often challenging and there is an ongoing need for new reaction conditions allowing to steer product selectivity. We report herein that phosphoric acids are ideal organocatalysts for the highly regioselective 1,2‐rearrangement of 3‐hydroxyindolenines to 2‐oxindoles, with predictable product selectivity arising from an efficient dual activation mode.

Tetrahydrocarbazoles and perhydrocyclohepta[b]indoles undergo a catalytic cascade singlet oxygenation in alkaline medium, which leads to chiral tricyclic perhydropyrido‐ and perhydroazepino[1,2‐a]indoles in a single operation. These photooxygenation products are new synthetic equivalents of uncommon C,N‐diacyliminium ions and can be functionalized with the aid of phosphoric acid organocatalysis.

In this study, we report on the modification of a 3,4-diaryl-isoxazole-based CK1 inhibitor with chiral pyrrolidine scaffolds to develop potent and selective CK1 inhibitors. The pharmacophore of the lead structure was extended towards the ribose pocket of the adenosine triphosphate (ATP) binding site driven by structure-based drug design. For an upscale compatible multigram synthesis of the functionalized pyrrolidine scaffolds, we used a chiral pool synthetic route starting from methionine. Biological evaluation of key compounds in kinase and cellular assays revealed significant effects of the scaffolds towards activity and selectivity, however, the absolute configuration of the chiral moieties only exhibited a limited effect on inhibitory activity. X-ray crystallographic analysis of ligand-CK1δ complexes confirmed the expected binding mode of the 3,4-diaryl-isoxazole inhibitors. Surprisingly, the original compounds underwent spontaneous Pictet-Spengler cyclization with traces of formaldehyde during the co-crystallization process to form highly potent new ligands. Our data suggests chiral “ribose-like” pyrrolidine scaffolds have interesting potential for modifications of pharmacologically active compounds.

Dabrafenib (Tafinlar) was approved in 2013 by the FDA as a selective single agent treatment for patients with BRAF mutation-positive advanced melanoma. One year later, a combination of dabrafenib and trametinib was used for treatment of BRAF mutant metastatic melanoma. In the present study, we report on hitherto not described photosensitivity of dabrafenib both in organic and aqueous media. The half-lives for dabrafenib degradation were determined. Moreover, we revealed photoinduced chemical conversion of dabrafenib to its planar fluorescent derivative dabrafenib_photo . This novel compound could be isolated and biologically characterized. Both enzymatic and cellular assays proved that is still a potent BRAF inhibitor. The intracellular formation of from dabrafenib upon ultraviolet irradiation is shown. The herein presented findings should be taken in account when handling dabrafenib both in preclinical research and in clinical applications.