The enzyme mechanism of patchoulol synthase

Different mechanisms for the cyclisation of farnesyl pyrophosphate to patchoulol by the patchoulol synthase are discussed in the literature. They are based on isotopic labelling experiments, but the results from these experiments are contradictory. The present work reports on a reinvestigation of patchoulol biosynthesis by isotopic labelling experiments and computational chemistry. The results are in favour of a pathway through the neutral intermediates germacrene A and α-bulnesene that are both reactivated by protonation for further cyclisation steps, while previously discussed intra- and intermolecular hydrogen transfers are not supported. Furthermore, the isolation of the new natural product (2S,3S,7S,10R)-guaia-1,11-dien-10-ol from patchouli oil is reported.

Isotopic Labelling Experiments and Enzymatic Preparation of Iso-Casbenes with Casbene Synthase from Ricinus communis

Isotopic labelling experiments gave insights into the enzyme mechanism of casbene synthase from Ricinus communis, showing a clear stereochemical course for the cyclisation reaction, in agreement with the reported absolute...

Stereochemical Characterisation of the Non-Canonical α-Humulene Synthase from Acremonium strictum

The non-canonical fungal α-humulene synthase was investigated through isotopic labelling experiments for its stereochemical course regarding inversion or retention at C-1, the face selectivity at C-11, and the stereoselectivity of...

Isoishwarane synthase from Streptomyces lincolnensis

The product of a terpene synthase from Streptomyces lincolnensis has been identified as the new natural product isoishwarane. The enzyme mechanism was studied by isotopic labelling experiments and site-directed mutagenesis.

Amoebocytes facilitate efficient carbon and nitrogen assimilation in the Cassiopea -Symbiodiniaceae symbiosis

The upside-down jellyfish Cassiopea engages in symbiosis with photosynthetic microalgae that facilitate uptake and recycling of inorganic nutrients. By contrast to most other symbiotic cnidarians, algal endosymbionts in Cassiopea are not restricted to the gastroderm but are found in amoebocyte cells within the mesoglea. While symbiont-bearing amoebocytes are highly abundant, their role in nutrient uptake and cycling in Cassiopea remains unknown. By combining isotopic labelling experiments with correlated scanning electron microscopy, and Nano-scale secondary ion mass spectrometry (NanoSIMS) imaging, we quantified the anabolic assimilation of inorganic carbon and nitrogen at the subcellular level in juvenile Cassiopea medusae bell tissue. Amoebocytes were clustered near the sub-umbrella epidermis and facilitated efficient assimilation of inorganic nutrients. Photosynthetically fixed carbon was efficiently translocated between endosymbionts, amoebocytes and host epidermis at rates similar to or exceeding those observed in corals. The Cassiopea holobionts efficiently assimilated ammonium, while no nitrate assimilation was detected, possibly reflecting adaptation to highly dynamic environmental conditions of their natural habitat. The motile amoebocytes allow Cassiopea medusae to distribute their endosymbiont population to optimize access to light and nutrients, and transport nutrition between tissue areas. Amoebocytes thus play a vital role for the assimilation and translocation of nutrients in Cassiopea , providing an interesting new model for studies of metabolic interactions in photosymbiotic marine organisms.

A Boron-Boron Double Transborylation Strategy for the Synthesis of gem-Diborylalkanes

9-Borabicyclo[3.3.1]nonane (H-<i>B</i>-9-BBN) has been used as a catalyst for the sequential double hydroboration of alkynes with pinacolborane (HBpin) to give alkyl gem-di-pinacol boronic esters. This strategy, which is effective for a wide range of terminal alkynes, is predicated upon a key C(<i>sp</i>³)-B / B-H transborylation reaction. Transition-state thermodynamic parameters and 10-boron-isotopic labelling experiments are indicative of an <i>σ</i>-bond metathesis exchange pathway.

A Boron-Boron Double Transborylation Strategy for the Synthesis of gem-Diborylalkanes

9-Borabicyclo[3.3.1]nonane (H-<i>B</i>-9-BBN) has been used as a catalyst for the sequential double hydroboration of alkynes with pinacolborane (HBpin) to give alkyl gem-di-pinacol boronic esters. This strategy, which is effective for a wide range of terminal alkynes, is predicated upon a key C(<i>sp</i>³)-B / B-H transborylation reaction. Transition-state thermodynamic parameters and 10-boron-isotopic labelling experiments are indicative of an <i>σ</i>-bond metathesis exchange pathway.

On the mechanism of ophiobolin F synthase and the absolute configuration of its product by isotopic labelling experiments

The cyclisation mechanism of ophiobolin F synthase AcldOS and the absolute configuration of its product were investigated by isotopic labelling experiments.

Mechanistic characterization of three sesquiterpene synthases from the termite-associated fungus Termitomyces

Three terpene synthases from the termite associated fungus Termitomyces were studied by isotopic labelling experiments and site-directed mutagenesis.