Mathias Christmann

Mechanistic Characterisation of Two Sesquiterpene Cyclases from the Plant Pathogenic Fungus Fusarium fujikuroi

Two sesquiterpene cyclases from Fusarium fujikuroi were expressed in Escherichia coli and purified. The first enzyme was inactive because of a critical mutation, but activity was restored by sequence correction through site-directed mutagenesis. The mutated enzyme and two naturally functional homologues from other fusaria converted farnesyl diphosphate into guaia-6,10(14)-diene. The second enzyme produced eremophilene. The absolute configuration of guaia-6,10(14)-diene was elucidated by enantioselective synthesis, while that of eremophilene was evident from the sign of its optical rotation and is opposite to that in plants but the same as in Sorangium cellulosum. The mechanisms of both terpene cyclases were studied with various (13) C- and (2) H-labelled FPP isotopomers.

Picomolar, selective, and subtype-specific small-molecule inhibition of TRPC1/4/5 channels

The concentration of free cytosolic Ca2+ and the voltage across the plasma membrane are major determinants of cell function. Ca2+-permeable non-selective cationic channels are known to regulate these parameters, but understanding of these channels remains inadequate. Here we focus on transient receptor potential canonical 4 and 5 proteins (TRPC4 and TRPC5), which assemble as homomers or heteromerize with TRPC1 to form Ca2+-permeable non-selective cationic channels in many mammalian cell types. Multiple roles have been suggested, including in epilepsy, innate fear, pain, and cardiac remodeling, but limitations in tools to probe these channels have restricted progress. A key question is whether we can overcome these limitations and develop tools that are high-quality, reliable, easy to use, and readily accessible for all investigators. Here, through chemical synthesis and studies of native and overexpressed channels by Ca2+ and patch-clamp assays, we describe compound 31, a remarkable small-molecule inhibitor of TRPC1/4/5 channels. Its potency ranged from 9 to 1300 pm, depending on the TRPC1/4/5 subtype and activation mechanism. Other channel types investigated were unaffected, including TRPC3, TRPC6, TRPV1, TRPV4, TRPA1, TRPM2, TRPM8, and store-operated Ca2+ entry mediated by Orai1. These findings suggest identification of an important experimental tool compound, which has much higher potency for inhibiting TRPC1/4/5 channels than previously reported agents, impressive specificity, and graded subtype selectivity within the TRPC1/4/5 channel family. The compound should greatly facilitate future studies of these ion channels. We suggest naming this TRPC1/4/5-inhibitory compound Pico145.

A formal, one-pot β-chlorination of primary alcohols and its utilization in the transformation of terpene feedstock and the synthesis of a C2-symmetrical terminal bis-epoxide.

A one-pot transformation of alkan-1-ols into 2-chloroalkan-1-ols is described. As a practical application, terpene-derived primary alcohols were converted into semiochemicals such as olfactory lactones (aerangis lactone, whisky lactone, and cognac lactone) and pheromones (cruentol and ferrugineol). Using heptane-1,7-diol as a bifunctional substrate, the corresponding bis-epoxide was synthesized by bidirectional synthesis in good yield and high enantioselectivity.

One-Pot Synthesis of 5-Hydroxy-4H-1,3-thiazin-4-ones: Structure Revision, Synthesis, and NMR Shift Dependence of Thiasporine A

An annulation of arylthioamides with 3-bromopyruvic acid chloride to 5-hydroxy-4H-1,3-thiazin-4-ones has been developed. The initial condensation affords two regioisomeric thiazolinone intermediates in a temperature-dependent manner. The synthesis of the 2-aminophenylthiazinone derivative led to the revision of the previously proposed structure of thiasporine A. Synthesis of the revised structure and NMR analysis revealed that thiasporine A had been isolated as a carboxylate.

Enantiogroup‐Differentiating Biocatalytic Reductions of Prochiral Cs‐Symmetrical Dicarbonyl Compounds to meso Compounds

The stereoselective reduction of symmetrical prochiral dicarbonyl compounds bearing enantiotopic carbonyl groups yields several stereogenic centers in one step. In a proof-of-concept study, a new approach is described for the enzymatic desymmetrization of 5-nitrononane-2,8-dione via sequential biocatalytic reduction steps utilizing ketoreductases to yield all possible diastereomers of 5-nitrononane-2,8-diol.

Identification of an (−)‐englerin A analogue, which antagonizes (−)‐englerin A at TRPC1/4/5 channels

(−)‐Englerin A (EA) is a potent cytotoxic agent against renal carcinoma cells. It achieves its effects by activation of transient receptor potential canonical (TRPC)4/TRPC1 heteromeric channels. It is also an agonist at channels formed by the related protein, TRPC5. Here, we sought an EA analogue, which might enable a better understanding of these effects of EA.

Synthesis and Structure Revision of Dichrocephones A and B

Herein, we report the first enantioselective synthesis of dichrocephonesu2005A and B, which are cytotoxic triquinane sesquiterpenes with a dense array of stereogenic centers within a strained polycyclic environment. Key features include the application of a catalytic asymmetric Wittig reaction, followed by stereoselective functionalization of the propellane core into a pentacyclic intermediate. Double reductive ring cleavage yielded the proposed structure of dichrocephoneu2005A. Mismatched spectroscopic data for our synthetic material compared to the natural isolate led us to revise the previously proposed configuration based on biosynthetic considerations and NMR calculations. Implementation of these findings culminated in the synthesis of dichrocephonesu2005A and B.

Synthesis of Highly Enantioenriched Propelladienes and their Application as Ligands in Asymmetric Rh-Catalyzed 1,4-Additions

The first synthesis of highly enantioenriched [4.3.3]propelladienes is reported. The novel bridged bicyclo[3.3.0] dienes were applied as steering ligands in the rhodium-catalyzed asymmetric arylation of cyclic enones. The catalytic system showed high catalytic activity, and the 1,4-adducts were obtained in good to excellent yields (46-99%) with enantioselectivities up to 96% ee.

Towards a comprehensive understanding of the structural dynamics of a bacterial diterpene synthase during catalysis

Terpenes constitute the largest and structurally most diverse natural product family. Most terpenoids exhibit a stereochemically complex macrocyclic core, which is generated by C–C bond forming of aliphatic oligo-prenyl precursors. This reaction is catalysed by terpene synthases (TPSs), which are capable of chaperoning highly reactive carbocation intermediates through an enzyme-specific reaction. Due to the instability of carbocation intermediates, the proteins’ structural dynamics and enzyme:substrate interactions during TPS catalysis remain elusive. Here, we present the structure of the diterpene synthase CotB2, in complex with an in crystallo cyclised abrupt reaction product and a substrate-derived diphosphate. We captured additional snapshots of the reaction to gain an overview of CotB2’s catalytic mechanism. To enhance insights into catalysis, structural information is augmented with multiscale molecular dynamic simulations. Our data represent fundamental TPS structure dynamics during catalysis, which ultimately enable rational engineering towards tailored terpene macrocycles that are inaccessible by conventional chemical synthesis.The bacterial diterpene synthase CotB2 catalyses the cyclisation of geranylgeranyl diphosphate to cyclooctat-9-en7-ol. Here the authors present various CotB2 structures including a trapped abrupt reaction product that were used for molecular dynamic simulations and allowed them to model all intermediates along the reaction cascade.

Synthesis of Enantioenriched Bromohydrins via Divergent Reactions of Racemic Intermediates from Anchimeric Oxygen Borrowing

We report a chiral phosphoric acid catalyzed bromocyclization/regiodivergent reaction of racemic intermediates sequence, which is enabled by anchimeric oxygen borrowing. Different types of alkenes are applicable, and both enantiomers of the bromohydrin products were obtained in generally excellent yields and enantioselectivities. In addition, an example of enantioconvergent synthesis from the two isomeric products is presented.