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Chemistry of Essential Oils
Published in K. Hüsnü Can Başer, Gerhard Buchbauer, Handbook of Essential Oils, 2020
Geranyl pyrophosphate (68) is the precursor for the monoterpenoids. Heterolysis of its carbon–oxygen bond gives the geranyl carbocation (69). In natural systems, this and other carbocations discussed in this chapter do not exist as free ions but rather as incipient carbocations held in enzyme active sites and essentially prompted into cation reactions by the approach of a suitable reagent. For the sake of simplicity, they will be referred to here as carbocations. The reactions are described in chemical terms but all are under enzymic control, and the enzymes present in any given plant will determine the terpenoids it will produce. Thus, essential oil composition can give information about the genetic makeup of the plant. A selection of some of the key biosynthetic routes to monoterpenoids (Devon and Scott, 1972) is shown in Figure 6.15.
The Plant Kingdom
Published in Spyridon E. Kintzios, Maria G. Barberaki, Evangelia A. Flampouri, Plants That Fight Cancer, 2019
Biosynthesis in plant cells: terpenoids are all derived from mevalonic acid or a closely related precursor. The pyrophosphate of alcohol farnesol is a key intermediate in terpenoid biosynthesis, particularly leading to the formation of diterpenoids, triterpenoids, and sterols. Monoterpenoids are derived from geranyl pyrophosphate.
Carotenoids
Published in Ruth G. Alscher, John L. Hess, Antioxidants in Higher Plants, 2017
Kenneth E. Pallett, Andrew J. Young
This pathway involves the formation and subsequent conversion of the isoprenoid precursor, mevalonic acid (MVA) to isopentenyl pyrophosphate (IPP). This common five-carbon unit of isoprenoids undergoes isomerization to dimethyl allyl pyrophosphate (DMAPP), which then condenses with another IPP to form geranyl pyrophosphate (GPP). Condensation with two further IPP units results in the formation of geranyl geranyl pyrophosphate (GGPP), which is the precursor for carotenoids. This polymerization of IPP occurs in the stroma of the chloroplast. For a more detailed consideration of the general isoprenoid pathway, its enzymology and significance in carotenoid biosynthesis, see Qureshi and Porter,1 Poulter and Rilling,2 Dogbo and Camara,3 and Lutzow and Beyer.4
Novel approaches for the development of direct KRAS inhibitors: structural insights and drug design
Published in Expert Opinion on Drug Discovery, 2022
Kashif Haider, Anku Sharma, M Shahar Yar, Prasanna Anjaneyulu Yakkala, Syed Shafi, Ahmed Kamal
In human cells, major RAS oncogenes include KRAS, NRAS, and HRAS encode for KRAS (4A and 4B), HRAS, and NRAS, respectively. In RAS protein, the catalytic site has much higher similarity among all isoforms, which contains P-loop, switches I and II and RAS-effector interaction interfaces. RAS GTPases contain a CAAX motif, which serves as the substrate for a series of post-translational modifications. These modifications include initial prenylation by the covalent attachment of farnesyl pyrophosphate or geranyl pyrophosphate at the CAAX box (termed as farnesylation and geranylation, respectively), whereas HRAS can be only farnesylated. Most of the RAS proteins can be farnesylated and as well as geranylated. After prenylation, three-terminal amino acid residues (AAX) are removed at the endoplasmic reticulum. The carboxy group of terminal cysteine is methylated by an enzyme called isoprenylcysteine carboxymethyltransferase (ICMT). Except for KRAS4B, other RAS proteins then undergo palmitoylation at the adjacent cysteine residue and are transported to the plasma membrane by active vesicular transport [3]. Finally, the inner membrane of RAS activation is controlled through positive guanine nucleotide exchange factors (GEFs) and negative GTPase activating proteins (GAPs) (Figure 1) [4].
An evidence-based review of neuronal cholesterol role in dementia and statins as a pharmacotherapy in reducing risk of dementia
Published in Expert Review of Neurotherapeutics, 2021
Siddhartha Dutta, Sayeeda Rahman, Rahnuma Ahmad, Tarun Kumar, Gitashree Dutta, Sudeshna Banerjee, Abdullahi Rabiu Abubakar, Adekunle Babajide Rowaiye, Sameer Dhingra, Velayutham Ravichandiran, Santosh Kumar, Paras Sharma, Mainul Haque, Jaykaran Charan
In vitro and animal studies have also shown a crucial role of statins in AD therapy [166]. In support of the mechanism of statin action on APP, it is postulated that it significantly reduces the levels of Aβ 42 and Aβ 40 in vitro and in vivo experiments [167]. Statins also block the synthesis of mevalonate and consequently the production of its isoprenoid derivatives, such as farnesyl pyrophosphate and geranyl pyrophosphate (Figure 3). Farnesyl pyrophosphate and geranyl pyrophosphate, respectively, modulate the farnesylation and geranylation of various proteins such as the GTPases, Rho, and Rab proteins [156]. The post-translational modification of cell-signaling proteins, such as Ras and Rho might affect the neurons’ metabolic activity and amyloid standard processing [168,169].
The genus Perovskia Kar.: ethnobotany, chemotaxonomy and phytochemistry: a review
Published in Toxin Reviews, 2021
Majid Mohammadhosseini, Alessandro Venditti, Abolfazl Akbarzadeh
Another polycyclic terpenoid was isolated from P. abrotanoides Karel. for the first time by Parvez et al. (1992). This compound which is trivially called perovskone (40) is a heptacyclic isoprenoid and conjugated diterpene-monoterpene with 6/7/6/6/5 membered carbon ring skeleton fused with two tetrahydrofuran rings. Biogenetically, it may be resulted from the addition of geranyl pyrophosphate to an icetexone precursor. In 1993, another compound with a complex rearranged structure, namely peradione (41) was isolated from the same plant species by Ahmad et al. (1993). It is also interesting to note that these kinds of natural products showed a pronounced antiprotozoal activity (Tabefam et al. 2018b), but none of the compounds isolated from Perovkia spp has been tested in this context of bioactivities until now and this could be an argument which deserves further studies.