Nature-driven approaches to non-natural terpene analogues.

Covering: up to 2019The reactions catalysed by terpene synthases belong to the most complex and fascinating cascade-type transformations in Nature. Although many accept only one natural terpene precursor and convert it with high selectivity into only one product, several of these remarkable biocatalysts were recently shown to have a surprising plasticity towards non-natural substrate analogues. For an easy access to the topic also for readers who are new to the field, this review will first briefly cover the principles of natural terpene biosynthesis. This is followed by a chapter that highlights purely chemical transformations mimicking terpene synthase catalysed reactions. Then, the main focus of this article will shed light on the recent advances of terpene synthase catalysed transformations of synthetic substrate analogues. As will be demonstrated, a simple conceptual approach extensively broadens the chemical space that can be reached with terpene synthases.

Exploiting the Synthetic Potential of Sesquiterpene Cyclases for Generating Unnatural Terpenoids.

The substrate flexibility of eight purified sesquiterpene cyclases was evaluated using six new heteroatom-modified farnesyl pyrophosphates, and the formation of six new heteroatom-modified macrocyclic and tricyclic sesquiterpenoids is described. GC-O analysis revealed that tricyclic tetrahydrofuran exhibits an ethereal, peppery, and camphor-like olfactoric scent.

Mechanistic Similarities of Sesquiterpene Cyclases PenA, Omp6/7, and BcBOT2 Are Unraveled by an Unnatural "FPP-Ether" Derivative.

The sesquiterpene cyclases pentalenene synthase (PenA) and two Δ6-protoilludene synthases Omp6 and Omp7 convert a FPP ether into several new tetrahydrofurano terpenoids, one of which is also formed as the main product by the sesquiterpene cyclase BcBOT2. Thus, PenA, Omp6/7, and BcBOT2 follow closely related catalytic pathways and induce similar folding of their diphosphate substrates despite low levels of amino acid sequence similarity. Some of the new terpenoids show pronounced olfactoric properties.

Methyl-Shifted Farnesyldiphosphate Derivatives Are Substrates for Sesquiterpene Cyclases.

New sesquiterpene backbones are accessible after biotransformation of presilphiperfolan-8ß-ol synthase (BcBOT2), a fungal sesquiterpene synthase, with non-natural farnesyldiphosphates in which methyl groups are shifted by one position toward the diphosphate terminus. One of the macrocycles formed, a new germacrene A derivative, undergoes a Cope rearrangement to iso-ß-elemene. Three of the new terpenoids show olfactoric properties that range from an intense peppery note to a citrus, ozone-like, and fruity scent.

Sensitivity of human pluripotent stem cells to insulin precipitation induced by peristaltic pump-based medium circulation: considerations on process development.

Controlled large-scale production of human pluripotent stem cells (hPSCs) is indispensable for their envisioned clinical translation. Aiming at advanced process development in suspension culture, the sensitivity of hPSC media to continuous peristaltic pump-based circulation, a well-established technology extensively used in hydraulically-driven bioreactors, was investigated. Unexpectedly, conditioning of low protein media (i.e. E8 and TeSR-E8) in a peristaltic pump circuit induced severe viability loss of hPSCs cultured as aggregates in suspension. Optical, biochemical, and cytological analyses of the media revealed that the applied circulation mode resulted in the reduction of the growth hormone insulin by precipitation of micro-sized particles. Notably, in contrast to insulin depletion, individual withdrawal of other medium protein components (i.e. bFGF, TGFß1 or transferrin) provoked minor reduction of hPSC viability, if any. Supplementation of the surfactant glycerol or the use of the insulin analogue Aspart did not overcome the issue of insulin precipitation. In contrast, the presence of bovine or human serum albumin (BSA or HSA, respectively) stabilized insulin rescuing its content, possibly by acting as molecular chaperone-like protein, ultimately supporting hPSC maintenance. This study highlights the potential and the requirement of media optimization for automated hPSC processing and has broad implications on media development and bioreactor-based technologies.