Cyclopropylmethyldiphosphates are substrates for sesquiterpene synthases: experimental and theoretical results

Sesquiterpene Cyclase BcBOT2 Promotes the Unprecedented Wagner-Meerwein Rearrangement of the Methoxy Group

Presilphiperfolan-8β-ol synthase (BcBOT2), a substrate-promiscuous sesquiterpene cyclase (STC) of fungal origin, is capable of converting two new farnesyl pyrophosphate (FPP) derivatives modified at C7 of farnesyl pyrophosphate (FPP) bearing either a hydroxymethyl group or a methoxymethyl group. These substrates were chosen based on a computationally generated model. Biotransformations yielded five new oxygenated terpenoids. Remarkably, the formation of one of these tricyclic products can only be explained by a cationically induced migration of the methoxy group, presumably via a Meerwein-salt intermediate, unprecedented in synthetic chemistry and biosynthesis. The results show the great principle and general potential of terpene cyclases for mechanistic studies of unusual cation chemistry and for the creation of new terpene skeletons.

Enhancing structural diversity of terpenoids by multisubstrate terpene synthases

Terpenoids are one of the largest class of natural products with diverse structures and activities. This enormous diversity is embedded in enzymes called terpene synthases (TSs), which generate diverse terpene skeletons via sophisticated cyclization cascades. In addition to the many highly selective TSs, there are many promiscuous TSs that accept multiple prenyl substrates, or even noncanonical ones, with 6, 7, 8, 11, and 16 carbon atoms, synthesized via chemical approaches, C-methyltransferases, or engineered lepidopteran mevalonate pathways. The substrate promiscuity of TSs not only expands the structural diversity of terpenes but also highlights their potential for the discovery of novel terpenoids via combinatorial biosynthesis. In this review, we focus on the current knowledge on multisubstrate terpene synthases (MSTSs) and highlight their potential applications.

Enzymatic Synthesis of Diterpenoids from iso-GGPP III: A Geranylgeranyl Diphosphate Analog with a Shifted Double Bond

The analog of the diterpene precursor geranylgeranyl diphosphate with a double bond shifted from C14=C15 to C15=C16 (named iso-GGPP III) has been synthesized and enzymatically converted with six bacterial diterpene synthases; this allowed the isolation of nine unnatural diterpenes. For some of the enzyme-substrate combinations, the different reactivity implemented in the substrate analog iso-GGPP III opened reaction pathways that are not observed with natural GGPP, resulting in the formation of diterpenes with novel skeletons. A stereoselective deuteration strategy was used to assign the absolute configurations of the isolated diterpenes.

Chemoenzymatic Synthesis of a New Germacrene Derivative Named Germacrene F

The new farnesyl pyrophosphate (FPP) derivative with a shifted olefinic double bond from C6-C7 to C7-C8 is accepted and converted by the sesquiterpene cyclases protoilludene synthase (Omp7) as well as viridiflorene synthase (Tps32). In both cases, a so far unknown germacrene derivative was found to be formed, which we name "germacrene F". Both cases are examples in which a modification around the central olefinic double bond in FPP leads to a change in the mode of initial cyclization (from 1→11 to 1→10). For Omp7 a rationale for this behaviour was found by carrying out molecular docking studies. Temperature-dependent NMR experiments, accompanied by NOE studies, show that germacrene F adopts a preferred mirror-symmetric conformation with both methyl groups oriented in the same directions in the cyclodecane ring.

Sesquiterpene Backbones Generated by Sesquiterpene Cyclases: Formation of iso-Caryolan-1-ol and an Isoclovane

New sesquiterpene backbones are accessible after incubation of caryolan-synthase (GcoA) and presilphiperfolan-8-β-ol synthase (BcBOT2) with a non-natural farnesyldiphosphate in which the central olefinic double bond is isomerized toward the methyl group. Two newly formed sesquiterpenoids are reported, a constitutional isomer of caryolan-1-ol (3), which we name iso-caryolan-1-ol (17), and the first terpenoid based on the isoclovane ring skeleton generated enzymatically thus far.

Subrutilane-A Hexacyclic Sesterterpene from Streptomyces subrutilus

Mining of a terpene synthase from Streptomyces subrutilus resulted in the identification of the hexacyclic sesterterpene subrutilane, besides eight pentacyclic side products. Subrutilane represents the first case of a saturated sesterterpene hydrocarbon. Its structure, including the absolute configuration, was unambiguously determined through X-ray crystallographic analysis and stereoselective deuteration. The cyclisation mechanism to subrutilane and its side products was investigated in all detail by isotopic labelling experiments and DFT calculations. The subrutilane synthase (SrS) also converted (2Z)-GFPP into one major product. Additional compounds were obtained from the substrate analogues (7R)-6,7-dihydro-GFPP and (2Z,7R)-6,7-dihydro-GFPP with blocked reactivity at the C6-C7 bond. Interestingly, the early steps of the cyclisation cascade with (2Z)-GFPP and the saturated substrate analogues were analogous to those of GFPP, but then deviations from the natural cyclisation mode occur.

Production of secondary metabolites using tissue culture-based biotechnological applications

Plants are the sources of many bioactive secondary metabolites which are present in plant organs including leaves, stems, roots, and flowers. Although they provide advantages to the plants in many cases, they are not necessary for metabolisms related to growth, development, and reproduction. They are specific to plant species and are precursor substances, which can be modified for generations of various compounds in different plant species. Secondary metabolites are used in many industries, including dye, food processing and cosmetic industries, and in agricultural control as well as being used as pharmaceutical raw materials by humans. For this reason, the demand is high; therefore, they are needed to be obtained in large volumes and the large productions can be achieved using biotechnological methods in addition to production, being done with classical methods. For this, plant biotechnology can be put in action through using different methods. The most important of these methods include tissue culture and gene transfer. The genetically modified plants are agriculturally more productive and are commercially more effective and are valuable tools for industrial and medical purposes as well as being the sources of many secondary metabolites of therapeutic importance. With plant tissue culture applications, which are also the first step in obtaining transgenic plants with having desirable characteristics, it is possible to produce specific secondary metabolites in large-scale through using whole plants or using specific tissues of these plants in laboratory conditions. Currently, many studies are going on this subject, and some of them receiving attention are found to be taken place in plant biotechnology and having promising applications. In this work, particularly benefits of secondary metabolites, and their productions through tissue culture-based biotechnological applications are discussed using literature with presence of current studies.