Terpenes structure

The asymmetric addition of organolithium reagents to arylox azolines has been used to construct highly complex polycyclic terpene structures found in natural products. For example, the asymmetric addition of vinyllithium to chiral naphthyloxazoline 3 followed by treatment of the resulting anionic intermediate with iodoethyl dioxolane 61... 

Terpene structures and their elucidation. Perfum. essential Oil Rec. 43,... 

Exercise 30-7 Camphor can be made on an industrial scale from a-pinene (turpentine) by the following reactions, some of which involve carbocation rearrangements of a type particularly prevalent in the bicyclic terpenes and the scourge of the earlier workers in the field trying to determine terpene structures. 

The sesquiterpenes, diterpenes, and poly terpenes can be considered most simply from a structural point of view as products composed of multiple units of isoprene. Structures currently assigned to some of the sesquiterpenes may have to be revised as the study of terpene chemistry advances, since many of these have been based on the validity of the isoprene rule for terpene structures and exceptions to this rule are becoming known (37). 

The parent compounds, the terpene names, and the fixed numberings recommended by the American committees for the four fundamental bicyclic terpene structures are ... 

Two entirely different approaches to systematizing the numberings of the basic monocyclic and bicyclic terpene structures were suggested in 1952 by G. M. Dyson of England and N. E. Wolff of Princeton University. It was the opinion of the American committees that these proposals needed considerable developmental work by their proponents before they could be properly evaluated. 

Some nudibranchs have adapted to feed on soft corals,270 273 ascidians,274 bryozoans,275 or on other molluscs rather than sponges. The mollusc Ovula ovum was reported to sequester the toxic sarcophytoxide (Structure 2.151) from Sarcophyton sp. and transform it into the less toxic terpene (Structure 2.152),276 but the deoxy metabolite was subsequently found in the soft coral.277... 

The Barton reaction was utilized during the synthesis of various terpenes and has played a crucial role in the elucidation of terpene structures. The Barton nitrite ester reaction was a key step in E.J. Corey s synthesis of azadiradione and perhydrohistrionicotoxin . Even though the yields were low, other ways to access the same intermediates would have been tedious, and afforded lower overall yields than in the applied Barton reactions. 

Thousands of different terpene structures occur in perfume ingredients, both natural and synthetic. The chemistry of terpenes is rich and varied and attempts to understand it have, on many occasions, contributed fundamentally to our total understanding of chemistry. One example is the work of Wagner and Meerwein, whose studies in terpene chemistry led, amongst many discoveries, to elucidation of the rearrangement that bears their names. This work made a very significant contribution to our fundamental understanding of the properties... 

T6) is contradictory to this supposition in that it was deduced that vitamin A deficiency has no effect upon the biosynthesis of sulfated glycosaminoglycans, but that it does increase their turnover rate. From this it was concluded that vitamin A is not necessary for ycosaminogly-can chain biosynthesis. Excess of vitamin A increases the incorporation of [ S]sulfate (Bll). The effects of various derivatives of vitamin A have also been investigated (T6), and citral, a terpene structurally related to vitamin A, also affects glycosaminoglycan biosynthesis (B27). 

However, oils occur in much greater concentrations in fruits and seeds. The so-called essential oils are usually sweet, or aromatic smelling organic compounds which may also contain sulfur and nitrogen in addition to the usual carbon and hydrogen. These oils are often of the terpene class with the general formula (C5Hg) , where n > 1, or may be compound types similar to camphor or other oxidation products associated with the basic terpene structure. 

Substituted furans [63], e.g. the B-methyl fur an unit, are widespread among terpene structures but frequently in oxidized form, for instance, as a-and g-methylene y-i ictones. 

While GC-FID is the traditional method for essential oil quantification, GC-MS is the most common analytical method for component identification. However, the wide concentration range of the analytes (from ppb to percentage levels), as well as the presence of numerous isomers (terpenes and oxygenated terpene structures), make qualitative analysis difficult. In addition, the mass spectra of these compoxmds are usually very similar, so peak identification often becomes very difficult and sometimes impossible. 

Most terpenes share isoprene (2-methyl-1,4-butadiene) as a common carbon skeleton building block. This structural relationship was identified by Wallach in 1887, who recognized that most terpenic structures result from the head-to-tail condensation of isoprene units and this became known as the isoprene rule . Based on this generic rule, terpenes can be classified according to the number of isoprene units (Table 2.1). 

Tarpana alkaloids, isoprenoid alkaloids alktdoids containing a terpene structure, with 10-30 carbon atoms. They are conveniently classified according to the genera in which they occur (Table). 

Most terpene structures can be broken down into multiples of isoprene units. Terpenes contain various functional groups (C=C, OH, C=0) as part of their structures and may be acyclic or cyclic. 

The term bitter principle is used in reference to any one of a group of unrelated constituents responsible for the bitter taste characteristic of many herbs. Most are derived from terpenes, though non-terpene structures such as certain flavonoids and alkaloids are included with the bitters. 

Also known as aromatic aldehydes, these are derived from phenyl-propanoids and lack the terpene structure. They have characteristically sweet, pleasant odours and are found in some of our most well known culinary herbs and spices such as cinnamon and nutmeg. 

As artemisinin has a terpenic structure, its biosynthesis starts in the formation of isopentenyl diphosphate GPP)> as in all the natural terpenoids. In plants, IPP is synthesized either via the mevalonate pathway in the cytosol or via the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway in the plastid. The IPP derived from the mevalonate pathway is generally used in the biosynthesis of sesquiterpenes (such as artemisinin), phytosterols, and triterpenes, and the IPP derived from the non-mevalonate pathway is employed in the biosynthesis of monoterpenes, diterpenes, and tetraterpenes (Fig. 89.15). 

The isoprene rule (337) and its evolved version, the biogenetic isoprene rule (336, 337), have proven to be of fundamental consequence in the development of terpene chemistry. According to the biogenetic isoprene rule, which was formally enunciated by Ruzicka in 1953, terpene structures may be rationalized, or preliminary structures deduced, by accepted reaction mechanisms from hypothesized acyclic precursors such as geraniol, farnesol, geranylgeraniol, etc. Biosynthetic investigations (20, 75, 87, 100, 110, 160, 162, 179, 263) over the past three decades have fully confirmed the biogenetic isoprene rule, and have provided detailed information on several fundamental steps in isoprenoid biosynthesis. 

Of the rearranged eudesmanes, eremophilanes (216) are most prolific ( 150 derivatives). The subject was reviewed in 1977 (314). Two stereochemical classes, 239 and 240, have been recognized in principle, these are related to the eudesmane (222) and intermedeane types (225), respectively. The first member of this class to be characterized was eremophilone (241), which occurs in the wood oil of the Australian tree Eremophila mitchelli, along with other related compounds. This was the first terpene structure not consistent with the isoprene rule and Robinson (327) invoked a 1,2-methyl shift from a eudesmane precursor to rationalize this structure. (-)-Eremoligenol (242) is a component of roots of Ligularia fischeri, while isovalencenic acid (243) has been isolated from vetiver oil. (-h)-Nootkatone (244) was first isolated from the heartwood of Alaska-cedar... 

Sukh Dev 1979 Biogenetic concepts in terpene structure elucidation. Pure Appl Chem 51 837-856... 

Scheme 13.7. Retrosynthetic Analysis of Juvabione with Disconnection to a Terpene Structure...

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