| Summary: | Terpenes and terpenoids make up one of the largest and most structurally diverse families of natural products with known compounds numbering in the tens of thousands. A significant proportion of terpenoids are secondary metabolites, which display a wide range of biological activities, and consequently many have found uses as therapeutic drugs, most notably paclitaxel, the anti-cancer agent; and artemisinin, a key drug in anti-malarial therapies. Due to the challenges in synthesising these highly complex compounds in satisfactory yields the majority of the supply of these drugs is still extracted from natural sources or produced semi-synthetically from naturally extracted compounds. Terpene synthases convert the linear isoprenyl diphosphates, precursors of all terpenoids, into complex hydrocarbon skeletons, which are often naturally further derivatised by P450 cytochromes. Recently there have been advances in exploiting terpene synthases for the production of terpenoid precursors, but despite these advances selectively derivatising the hydrocarbon skeleton remains the major barrier to the conversion of these skeletons to therapeutically viable compounds. This thesis focuses on exploring methods of generating simple terpenoids from terpene synthases. The project is divided into two parts both designed to investigate methods of generating simple terpenoids. The first part focuses on germacradien-4-ol synthase (GdolS), a recently discovered bacterial sesquiterpene synthase, which incorporates water in the cyclisation cascade to generate a single terpene alcohol. This enzyme was characterised and the mechanism probed using substrate analogues and single-point mutations to elucidate how GdolS is able to incorporate water into its product while still protecting the highly reactive carbocation intermediates. Our data indicated that germacradien-4-ol synthase catalyses the loss of the diphosphate group and ring closure in a stepwise manner, followed by a 1,3-hydride shift to generate a long-lived allylic-carbocation intermediate. We propose this carbocation is then quenched by water ingress into the active site due to loop movement. The second part of the project involved the synthesis of a range of farnesyl diphosphate analogues designed to offer means of trapping carbocation intermediates in the catalysis by a range of sesquiterpene synthases. These analogues were primarily epoxy-FDPs, designed to produce simple terpenoids with hydroxy- and epoxy-functionalities. While a number of the prepared analogues were turned over by the tested sesquiterpene synthases two, 10,11-epoxy-FDP and 10-hydroxy-11-ene-FDP, were able to intercept the farnesyl cation upon loss of the diphosphate group, to generate a novel macrocyclic ether.
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