Di terpenoid

Tanaka, H. and Asakawa, Y. 1996. Sesqui- and di-terpenoids from the liverwort Junger-... 

Since last year s Specialist Report, the emphasis in the di terpenoid alkaloid field has focused on structure determination, both by X-ray crystallography and by chemical and spectral methods. Some interesting synthetic approaches to diterpenoid alkaloids have also been reported. The total volume of work on diterpenoid alkaloids reported this year, however, is much less than in Chapter 16 of last year s Report, which covered a longer period and was intended to give a background to the subject. 

Savona, G. etal. 1978. Salviarin, a new di-terpenoid from Salvia splendent Journal of the Chemical Society, Perkins Transactions i 643—546. 

Taxol is one of the structurally more complex members of the approximately 400 defined taxane di terpenoid family of the Taxus species, most of which are based upon the unique taxane skeleton, pentamethyl[9.3.1.0]tricyclopentadecane 108. The taxane nucleus bears three stereocenters, and taxol itself bears 11 such centers. The large number of possible stereoisomers is the reason for the difficulties of taxol total syntheses (Figure 4.49). 

Chemistry of taxol, anticancer di terpenoid with oxethane cycle as a part of fused system 98PAC331. 

A-like Taxadiene 5a-hydroxylase Di terpenoids Paclitaxel [231]... 

From a chemical point of view, vegetable resins are a complex mixture of mono-, sesqui-, di- and triterpenes, which have, respectively, 10, 15, 20 and 30 carbon atoms per molecule. The mono- and sesquiterpenes are both present in most resins. The di- and triterpenes are rarely found together in the same resin, which means that terpenic resins can be divided into two main classes. Table 1.5 lists the botanical origin and the kind of terpenoid compounds of some natural resins. 

In this presentation, bioactivity-directed isolation and stmcture elucidation of the active constituents will be given. Structures of the constituents, which form namely terpenoids (sesqni, di- and triterpenoids) were based on spectroscopic tech-niqnes, particnlarly intensive NMR and Mass spectroscopies. 

Other phenolic compounds of commercial importance include the terpenoids, including mono, di, tri, and sesquiterpenes. While most of these are used as essential oils, fragrances, and flavors in various products, they are toxins in certain species. For example the sesquiterpene lactones of the Centaurea species cause an irreversible Parkinson s-like condition in horses called nigro-pallidal encephalomalacia. This is a lethal condition and the prognosis for recovery is grave in most cases, affected horses should be euthanized before reaching the terminal stages. 

German for turpentine) and there are approximately 15000 terpenes. Terpenes are lipophilic, and the building blocks are five-carbon units with the branched carbon skeleton of isopentane. The basic units are sometimes called isoprene (F ig. 11.5fl), because heat decomposes terpenoids to isoprene. Depending on the number of C5 units fused, we distinguish mono- (Cio), sesqui- (C15), di- (C20), tri-(C30), tetra- (C40) and polyterpenoids [(Cs) , with n > 8]. Alpha-Pinene and bor-neol (Fig. 11.56) are examples of monoterpenes. 

Streibl M, Herout V, Terpenoids-especially oxygenated mono-, sesqui-, di-, and triterpenoids, in Eglinton G, Murphy MTJ (eds.). Organic Geochemistry Methods and Results, Springer-Verlag, Berlin, pp. 401—424, 1969. 

A variety of alkaloids based on mono-, sesqui-, di-, and tri-terpenoid skeletons have been characterized, but information about their formation in nature is still somewhat sparse. Monoterpene alkaloids are in... 

Several terpenoids, particularly those with a lactone moiety, have been examined for plant growth-regulating activity. Incidentally, several of these compounds exhibit anti-tumor and insecticidal activity. They are classified into mono-(CjQ), sesqui-(Ci5), di-(C2Q), tri-(Cgg) and tetraterpenes (C40) Some representative candidates among these classes possessing biological activity are as follows ... 

Tables 2-5 list monoterpenoids (Mo), sesquiterpenoids (Sq), diterpenoids (Di), and retinoids (Re), sesterterpenoids (St), meroterpenoids and miscellaneous terpenoids (Me), respectively, discussed in this review. The bioassay systems in which the compounds exhibited inhibitory effects, together with the major sources of the compounds, are included in the Tables. Most of these terpenoids are isolated from natural sources, and their structures are shown in Figs. (2)-(5). Some terpenoids which exhibit significant and/or a broad range of chemopreventive and anti-inflammatory activities are discussed below.

Both cell cultures and animal studies have shown that many of the naturally occurring mono-, sesqui-, di-, sester-, and meroterpenoids as well as retinoids possess potentially chemopreventive activities. Terpenoids are minor but ubiquitous components of our diet, and have the advantage of being non-toxic or relatively non-toxic to humans. More mechanistic-oriented basic research is needed to elucidate the mechanisms of action. Studies of derivatives of these naturally occurring terpenoids are also necessary to elucidate the structure-activity relationship and to guide the development of novel chemopreventive agents. 

There have been a number of previous reviews on microbial oxidations of teipenes. Monoter-penes are often degraded progressively after an initial hydroxylation step, but di-, tri- and sesqui-tetpenes can be converted more selectively, to accumulate useful quantities of hydroxyla products. Less systematic work on the microbial oxidation of terpenoids has l n carried out than in the case of steroids, and therefore prediction of the regio- and stereo-chemistry is scarcely possible. 

Piretti, M. V, Ghedini, M., Serrazanetti, G. (1976). Isolation and identification of the polyphe-nolic and terpenoid constituents of Vitis vinifera. v. Trebbiano variety. Annali di Chimica, 66, 429-437. 

Without proposing an entire biosynthetic pathw ay, draw the appropriate precursor, eithci geranyl di[)hosi hate or fainesyl diphosphate, ir. a confo ination that sliows a likeness to each of the following terpenoids ... 

C15), di- (C20), sester- (C25), tri- (C30), tetra- (C40), and poly- carboxylic acids and their esters, which makes terpenoids the... 

The universal precursors to terpenoids, the C5-compounds dimethylallyl pyrophosphate (DMAPP) and isopentenyl pyrophosphate (IPP), originate from two pathways in plants (Fig. 1). The mevalonate (MEV) pathway is well described in many eukaryotic organisms. This pathway is present in the cy-tosol/endoplasmic reticulum of plants. More recently, another pathway has been described, the 2C-methyl-D-erythritol-4-phosphate (MEP) pathway, which is found in the plastids of plants (19). The localization of the different pathways and the plastid-directing transit peptides found in hemi-TPS, mono-TPS, and di-TPS, but not in sesqui-TPS, result in the production of terpenoids from at least two different precursors pools. 

In summary, these important investigations have rationalized the stereochemistry of the 1,3-hydride shift (which transfers a positive centre from C-10 or C-11 at the distal end of FPP to C-1 and so allows initiation of further isomerization or a second cyclization of the Cio or Ci i ring) on the basis of the ring size of the products. This presumably results from fixation of specific conformations of the intermediates on a hypothetical enzyme surface. The larger diversity of structure for sesquiterpenoids than for di- or tri-terpenoids could then reflect the larger conformational flexibility of a Cio or Cii ring (which are often involved in the formation of the former) than of the Ce rings that are usually implicated in the latter. 

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