Sesquiterpenoids biogenesis

The details of the isolation of prezizaene (393), and its implication in the biogenesis of the tricyclovetivane group, have been published.The structure of a new sesquiterpenoid, pseudoanisatin (394), related to anisatin has been... 

The biogenesis of many cyclic terpenoids requires a cts-double bond in the acyclic precursor. A cis-double bond is frequently incorporated into the terminal isoprenoid unit via an allylic rearrangement mechanism. Alternatively, a cis unit could be incorporated directly (as rubber). Two results this year highlight some features of this problem. Both geraniol (22) and nerol (23) are derived from all-trans units (i.e. retention of the 4i -proton of mevalonate) so that the cis-double bond of nerol is derived by isomerization. The sesquiterpenoid gossypol (34) is derived from c/s,cis-farnesyl pyrophosphate. Hence in its biosynthesis either... 

Alpinolide peroxide, a secoguaiane-type sesquiterpenoid from Alpinia japonica, has been prepared with complete stereocontrol by autoxidation of a y5,y-butenolide (Scheme 18) [42]. Conceivably, tautomerization of the butenolide to 2-furanol may occur prior to oxygenation. The biogenesis of alpinolide peroxide appears to proceed by a similar pathway [42]. 

A quick glance back at Figure 2.10 will show how the major families of cedarwood sesquiterpenoids are related in terms of their biogenesis, and indeed, how they are related to the sandalwood sesquiterpenoids. Initial... 

The essential oil of Echinops giganteus var. lelyi, a culinary herb from Cameroon, contains many sesquiterpenoids. The most abundant (26.9% of the oil) is silphiperfol-6-ene, (P24.1). The biogenesis of this material from farnesyl pyrophosphate is enzyme mediated but the chemistry of the enzymatic reactions follows the basic principles of carbocation mechanisms (Figure P24). Initial cyclisation of farnesyl pyrophosphate gives the cation (P24.2). Suggest a sequence of cationic reactions which could lead from (P24.2) to (P24.1). This is a particularly difficult problem. If you would like a hint (without having to look at the solution) one will be found at the end of the problems section. 

A new sesquiterpenoid skeleton has been discovered in the form of lactarorufin A (193) isolated from Lactarius rufus. At the present time only the relative stereochemistry of the four asymmetric centres is known and it has been suggested that its biogenesis can be considered in terms of opening of the cyclopropyl-carbinyl cation (194) which has previously been proposed in the marasmic acid biogenesis. In another study of Lactarius species, Magnusson et have... 

An examination of the minor constituents of Cupressus dupreziana has resulted in the isolation of the three alaskane-type sesquiterpenoids (180)—(182) together with the two 1,7-diepi-cedrane derivatives (183) and (184). In view of the importance of absolute stereochemistry in these and related compounds it is regrettable that the [a]o value of only one of them (183) is quoted. Indeed this is all the more surprising when the comparison of [a]o values has played an important role in the proposals of the same authors to account for the distribution and biogenesis of acorane, alaskane, cedrane, 1,7-diepi-cedrane,... 

A further group of compounds having a mixed terpenoid biogenesis embraces a number of sesquiterpenoid derived antibiotics such as grifohn for which the revised structure XV has been advanced [120] and the related compounds... 

Mono- and sesquiterpenes are the main constituents of the essential oils, while the other terpenes are constituents of balsams, resins, waxes, and rubber. Oleoresin is a roughly equal mixture of turpentine (85 % Cio-monoterpenes and 15 % C15- sesquiterpenes) and rosin (C2o-diterpene) that acts in many conifer species as a toxic material to invading insects and their pathogenic fungi [12]. A number of angiosperm species have inducible terpenoid defensive compounds (phytoalexins) [13]. These include both sesquiterpenoid and diterpenoid t)pes. Isoprenoid units are also found within the framework of other natural molecules. Thus, indole alkaloids, several quinones (vitamin K), alcohols (vitamin E, vitamin A formed from p-carotene), phenols, and isoprenoid alcohols (also known as terpenols or polyprenols) also contain terpenoid fragments. The biogenesis. 

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