On the Role of Hydrogen Migrations in the Taxadiene System.

Taxa-4,11-diene is made by the taxa-4,11-diene synthase (TxS) from Taxus brevifolia. The unique reactivity of the taxane system is characterised by long distance hydrogen migrations in the biosynthesis. This study demonstrates that selective long range hydrogen migrations also play a role in the high energy process of the EI-MS fragmentation of taxa-4,11-diene.

Unusual Reaction of Isocyanides with Aromatic Aldehydes Catalyzed by a Supramolecular Capsule.

The supramolecular resorcinarene hexameric capsule efficiently promotes the unprecedented reaction between isocyanides and electron-deficient aromatic aldehydes leading to the formation of imines and carbon monoxide. The mechanism of the reaction was investigated via isotope labelling, kinetic analysis of the reaction, computational studies and the independent synthesis of a proposed intermediate. Control experiments indicate that the formation of the key aziridinone intermediate is limited to the cavity of the capsule.

Skeletal Rearrangements in the Enzyme-Catalysed Biosynthesis of Coral-Type Diterpenes from Chitinophaga pinensis.

Two diterpene synthases from the bacterium Chitinophaga pinensis were characterised. The first enzyme mainly produced the rearranged diterpene palmatol, a compound known from octocorals, while the second enzyme made the new coral-type eunicellane chitinol. The mechanisms of both enzymes were deeply studied through isotopic labelling experiments, DFT calculations, and with a substrate analog containing a saturated double bond, resulting in the formation of derailment products that gave additional insights into the nature of the cyclisation cascade intermediates.

Biosynthesis of the Non-Canonical C Sesquiterpenoids Chlororaphen A and B from Pseudomonas Chlororaphis.

Chlororaphens A and B are structurally unique non-canonical C sesquiterpenoids from Pseudomonas chlororaphis that are made by two SAM-dependent methyltransferases and a type I terpene synthase. This study addresses the mechanism of their formation in isotopic labelling experiments and DFT calculations. The results demonstrate an astonishing complexity with distribution of labellings within a cyclopentane core that is reversely connected to two acyclic fragments in chlororaphen A and B.

Common Biosynthesis of Non-Canonical C Terpenes through a Fragmentation-Recombination Mechanism.

The biosynthesis of six recently reported non-canonical C sesquiterpenoids named after ancient Greek philosophers, archimedene, aristotelene, eratosthenene, pythagorene, α-democritene and anaximandrene, was investigated through density functional theory (DFT) calculations and isotopic labeling experiments. The results revealed for all compounds except archimedene a unique fragmentation-recombination mechanism as previously demonstrated for sodorifen biosynthesis, in addition to a remarkable "dancing" mechanism for anaximandrene biosynthesis.