Sesquiterpene acyclic

Acyclic podands, 24 41 Acyclic sesquiterpenes, aroma chemicals, 3 239... 

A powerful feature of intramolecular C-H insertion is the inherent ability to transform an acyclic ternary stereogenic center into a cyclic quaternary stereogenic center26. It has been demonstrated that the rhodium-catalyzed cyclization of methyl (tf)-2-diazo-6-(4-methylphenyl)-3-oxohep-tanoate to cyclopentanone 6 indeed proceeds with retention of absolute configuration61. The absolute configuration of the latter was confirmed by conversion to the sesquiterpene (+ )-a-cu-parenone. 

Acyclic terpene (Cjo) and sesquiterpene (C15) hydrocarbons find little use in flavor and fragrance compositions. They are relatively unstable and some have a slightly aggressive odor due to their highly unsaturated structure. 

Acyclic terpene and sesquiterpene alcohols occur in many essential oils. These alcohols were formerly isolated from oils in which they are major components. 

Among the acyclic terpene aldehydes, citral and citronellal hold key positions as fragrance and flavor chemicals, as well as starting materials for the synthesis of other terpenoids. Hydroxydihydrocitronellal is one of the most important fragrance materials. Derivatives of these aldehydes, particularly the lower acetals, are also used as fragrance materials. Acyclic sesquiterpene aldehydes are not very important as such, but they contribute to the characteristic fragrance and aroma of essential oils, for example, in the case of a- and /3-sinensal in sweet orange oil. 

For Instance, many terpene derivatives mimic insect hormone actioa Juvabione (15) is the classical example of a juvenile hormone (JH) mimic that prevents egg maturation in Pyrrhocoris bugs. Aromatic terpene ethers (16), methylene dloxyphenyl terpene ethers (17), and other farnesyl derivatives also have JH activity and the latter ones (18) also cause sterility in Pyrrhocoris. For the most part JH active terpenes are among the sesquiterpenes but several monoterpenes also have insect sterilizing effects (19. 20). The acyclic monoterpene cltral reduces the fertility of rats by causing follicular degeneration (21). 

Another sesquiterpene synthase forms trichodi-ene, the parent compound for a family of mycotoxins and antibiotics.97/97a b A different sesquiterpene synthase, present in peppermint and also in a wide range of other plants and animals, forms the acyclic (E)-(J-... 

As in the discussion of the acyclic monoterpene ketones (see 1.1.3) instead of the sesquiterpene ketones, the structurally related compounds neryl-(176) and geranylacetone (169) will be reviewed. Indeed, as mentioned before, neryl- and geranylacetone are the norsesquiterpene -analogues of 6-methyl-5-hepten-2-one, which is the /1-oxidation product of nerol and geraniol, just like neryl- and geranylacetone are the bioconversion products of famesol (see 2.1.1). 

Diterpene isothiocyanates fall into three distinct structural categories regarding their carbon skeletons the acyclic tetraenes (220 and 221), the biflorane framework (including the kalihinol family) (222-238), and the amphilectane framework (including the cyclo- and isocycloamphilectanes) (239-241). Like the sesquiterpene isothiocyanates, most of these compounds were isolated along with the corresponding isocyanate and formamide compounds. 

Exercise 30-1 a. Write out all of the possible carbon skeletons for acyclic terpene and sesquiterpene hydrocarbons that follow the isoprene rule. Do not consider doublebond position isomers. 

Among the other terpenes that have been used as substrate in the MTO-catalyzed oxidation reactions are the bicyclic monoterpenes carene and camphene, the acyclic monoterpene myrcene, fi-citronellene (the reduced form of myrcene), and the bicyclic sesquiterpene (i-caryophyllene (Fig. 6). 

Corey and Yamamoto 233) used the P-oxido synthesis 2341 of trisubstituted olefins for the preparation of the acyclic sesquiterpene famesol 433. In this preparation the isoheptenylphosphonium salt 430 is converted into the hydroxyfamesol derivative 432 by reaction with the tetrahydropyranyl ether — protected hydroxy aldehyde 431 and formaldehyde 205. 432 is converted into famesol 433 via several steps. Other reactions of432 likewise proceeding via several steps lead to 434 which is a positional isomer of a C17-juvenile hormone 233) (Scheme 75). 

Figure 3.3 Sesquiterpenes (C15H24). (A) Farnesene (3,7,11-trimethyl-2l6l10-dodeeatriene) (acyclic). (B) Caryophyllene (bicyclic). Courtesy Spiring Enterprises Ltd.

Juvenile hormone III, an acyclic sesquiterpene epoxide, was also synthesized from (S)-25 by submitting the acetate of (S)-25 to the... 

A major focus of our research program has been the development of synthetically useful radical-mediated methodologies in recent years. Our interest in this area was partly initiated by asking how to generate five- and six-membered ring radicals from acyclic radical precursors. This problem has been unsolved in radical chemistry due to a disfavored 5-endo cyclization in pentenyl radical cyclizations. This simple but intriguing curiosity led us to study radical reactions of yV-aziridinylimines. The outcome of this research is the development of a novel consecutive carbon-carbon bond formation approach, which has tremendous synthetic potential. This review provides a full account of radical cyclizations of V-aziridinylimines and their applications to sesquiterpene natural products. 

A number of hydrocarbon fractions from liquefaction products produced at GFETC from the coals studied here were investigated using selected ion profiles of the capillary GC/MS data. None of the hydrocarbon biological markers other than the acyclic alkanes already discussed were detected. There were no sesquiterpenes, sesquiter-panes, steranes, triterpanes or other cyclic terpenoids found. 

Acyclic dienamines are relatively unstable, but very reactive towards electron-poor dienophiles as describe in a review article (1984). A more recent example shows the preparation of sterically encumbered 1-amino-1,3-diene (125) and its, nevertheless, efficient and highly stereoselective [4 + 2] cycloaddition to dimethyl fumarate (Scheme 32). Elimination of pyrrolidine, by heating the non-iso-lated cycloadduct with acetic anhydride, afforded hexahydronaphth ene (126), a key intermediate for a synthesis of drimane-type sesquiterpenes. 

The Ci5 terpenoids known as sesquiterpenoids are the most chemically diverse group of terpenoids known in nature. Like monoterpenoids, many sesquiterpenoids contribute to the flavor and fragrances of a variety of plant products. To date about 10,000 sesquiterpenoids are known (32), and in the plant kingdom they commonly occur as hydrocarbons, alcohols, aldehydes, ketones, carboxylic acids, lactones, and oxiranes. The acyclic sesquiterpene hydrocarbons a- and p-farnesenes (HI and H2, respectively) (Fig. 8) are constituents of the oils... 

An acyclic sesquiterpene glycoside, mukurozioside Ilb (13), which was identified previously fi om Sapindus mukurossi Gaertn. (Sapindaceae) [68], was isolated fi om the fruits of Sapindus rarak DC. (Sapindaceae) from Indonesia (6.8% w/w yield) [47]. The sweetness of this compoimd has been rated as about the same as that of 2% sucrose by a small taste panel [47]. This is the first acyclic sesquiterpene glycoside fi-om a plant source to have been determined to have a sweet taste. Altiiough its sweetness potency is equivalent to those of the bulk sweeteners, this... 

The Amazon Indians Waiapi living in the West of Amapa State of Brazil, treat malaria with an inhalation of vapor obtained from leaves of Viola surinamensis. The antimalarial activity of the aromatic volatile plant extracts from leaves, showed that nerolidol (an acyclic oxygenated sesquiterpene) was identified as one of the active principles (36). Another recent study suggested the presence of an active isoprenoid pathway for biosynthesis of isoprenic chains of coenzyme Q in P. falciparum (37), parasites treated with nerolidol showed decreased ability to synthesize coenzyme Q in all intraerythrocytic stages. A challenge would be to now identify which African medicinal plants contain similar chemistry. 

Two elements of the cyclization have yet to be addressed the isomerization of geranyl pyrophosphate to linalyl pyrophosphate (or the equivalent ion-pair) and the construction of bicyclic skeleta. Studies on the biosynthesis of linalool (61), and on the analogous nerolidyl system in the sesquiterpene series (52), have shown this allylic transposition to occur by a net suprafacial process, as expected. On the other hand, the chemical conversion of acyclic or monocyclic precursors to bicyclic monoterpenes, under relevant cationic cyclization conditions, has been rarely observed (47,62-65) and, thermodynamic considerations notwithstanding (66), bicyclizations remain poorly modeled. 

Steroids are formed from two sesquiterpene molecules—farnesyl pyrophosphate— which are attached to each other tail to tail to give the acyclic squalene (SOC-atoms) this undergoes complex reactions involving a cyclisation to tetracyclic or pentacychc ring systems, especially cholesterol. 

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