Total synthesis of cassane-type diterpenoid pikrosalvin

This paper presents the first successful total synthesis of pikrosalvin, a compound naturally derived from Salvia officinalis, grounded on the structural framework delineated by Brieskorn and Fuchs. Our synthetic approach was underpinned by a biomimetic strategy inspired by the Stork–Eschenmoser hypothesis for the biosynthesis of terpenes via polyene cyclization. Starting with commercially available vanillic acid and geraniol, we strategically assembled pikrosalvin's structural core, consisting of a decalin A/B ring, an aromatic C ring, and a butyrolactone D ring. Challenges related to protective groups and specific catalytic conditions were effectively addressed, resulting in high product yields. We further demonstrated the efficacy and broad applicability of a combined-acid-catalyzed polyene cyclization methodology in the context of complex natural product synthesis. This study sets the stage for future biological and pharmacological investigations of pikrosalvin.     

Pyrroloquinoline Quinone Aza-Crown Ether Complexes as Biomimetics for Lanthanide and Calcium Dependent Alcohol Dehydrogenases**

Understanding the role of metal ions in biology can lead to the development of new catalysts for several industrially important transformations. Lanthanides are the most recent group of metal ions that have been shown to be important in biology, that is, in quinone-dependent methanol dehydrogenases (MDH). Here we evaluate a literature-known pyrroloquinoline quinone (PQQ) and 1-aza-15-crown-5 based ligand platform as scaffold for Ca²⁺, Ba²⁺, La³⁺ and Lu³⁺ biomimetics of MDH and we evaluate the importance of ligand design, charge, size, counterions and base for the alcohol oxidation reaction using NMR spectroscopy. In addition, we report a new straightforward synthetic route (3 steps instead of 11 and 33 % instead of 0.6 % yield) for biomimetic ligands based on PQQ. We show that when studying biomimetics for MDH, larger metal ions and those with lower charge in this case promote the dehydrogenation reaction more effectively and that this is likely an effect of the ligand design which must be considered when studying biomimetics. To gain more information on the structures and impact of counterions of the complexes, we performed collision induced dissociation (CID) experiments and observe that the nitrates are more tightly bound than the triflates. To resolve the structure of the complexes in the gas phase we combined DFT-calculations and ion mobility measurements (IMS). Furthermore, we characterized the obtained complexes and reaction mixtures using Electron Paramagnetic Resonance (EPR) spectroscopy and show the presence of a small amount of quinone-based radical.