Terpenoids linalool

Uses ndReactions. a-Pinene (8) is useful for synthesizing a wide variety of terpenoids. Hydration to pine oil, acid-catalyzed isomerization to camphene, thermal isomerization to ocimene and aHoocimene, and polymerization to terpene resins are some of its direct uses. Manufacture of linalool, nerol, and geraniol has become an economically important use of a-pinene. 

Experiment 2. Effects of terpenoid allelochemicals on pollen germination The effects of the terpenoids found in many allelopathically active plants are dependent on the concentration of the active matter (Fig. 4). Linalool, cymol, citral, gaillardine and austricine excreted by many flowers, stimulated the pollen germination upto 10 7-1()" M concentrations and depress in higher ones. Rodriguez et.al (1976) described the biological effects of some sesquiterpene lactones, which are allelochemicals. 

Adults of some species also produce 4-oxo-( )-2-alkenals. Other types of simple compounds that have been found in the defensive secretions of true bugs include common terpenoids such as a- and (3-pinenes, limonene, linalool, and Z, -oc-farnesene, and simple aromatic compounds such as benzyl alcohol, ben-zaldehyde,p-hydroxybenzaldehyde, methyl p-hydroxybenzoate,phenylethanol, and guaicol. In general, although a number of species may share particular components, each species does appear to produce its own particular blend. In at least one species, the blend of defensive compounds is reported to vary with season and/or diet [36]. 

Another heterocyclization is presented by Panifilow et al. Cyclic acetals and ethers are obtained by electrochemical oxidation of the terpenoid alcohol linalool 57 in methanol containing alkaline and sodium methoxide as electrolyt [102]. Anodic oxidation of the C(6)-C 7) double bond of linalool leads to the radical cation 58. In addition to direct methoxylation of the radical cation an attack on the hydroxyl group takes place. After a second one-electron oxidation and following methoxylation the regioisomeric cyclic acetal and a subsequent 1,2-hydride shift, the cyclic acetal 60 and the cyclic ether 61 are finally formed in yields of 16 and 24%, respectively (Scheme 13). As shown by Utley and co-workers bicyclic lactones 65 and 66 can be synthesized by anodic oxidation... 

Heating (cooking) seems to produce certain terpenoids. In some vegetables, such as tomatoes and potatoes, there is a considerable increase in the formation of some terpene alcohols, including linalool, a-terpineol and terpinen-4-ol during heat treatments. 

Approximately 230 volatile compounds have been identified in raspberry fruit [35]. The aroma of raspberries is composed of a mixture of ketones and aldehydes (27%) and terpenoids (30%), alcohols (23%), esters (13%) and furanones (5%). The raspberry ketone (Fig. 7.5) along with a-ionone and jS-ionone have been found to be the primary character-impact compounds in raspberries. Other compounds such as benzyl alcohol, (Z)-3-hexen-l-ol, acetic acid, linalool, geraniol, a-pinene, jS-pinene, a-phellandrene, jS-phellandrene and jS-caryophyllene contribute to the overall aroma of mature red raspberries [101-105]. The most important character-impact compounds of raspberries are summarised in Table 7.3. 

Blueberry consists of cultivated highbush blueberries Vaccinium corymbo-sum) and wild lowbush blueberries Vaccinium august ifolium). The aroma of cultivated and wild blueberries is dominated by long-chain alcohols, esters and terpenoids. Forney [43] reported that y-butyrolactone, a-terpineol, 6-ethyl 2,6-decadiene-4,5-diol, linalool, benzaldehyde and 2-ethyl-2-hexenal contribute to the aroma of fresh, whole highbush blueberries using GC-O analysis. In... 

Monoterpenes, 10-carbon-containing terpenoids, are composed of two isoprene units, and found abundantly in plants, e.g. (+)-limonene from lemon oil, and (—)-linalool from rose oil. Many monoterpenes are the constituents of plant volatile oils or essential oils. These compounds are particularly important as flavouring agents in pharmaceutical, confectionery and perfume products. However, a number of monoterpenes show various types of bioactivity and are used in medicinal preparations. For example, camphor is used in liniments against rheumatic pain, menthol is used in ointments and liniments as a remedy against itching, bitter-orange peel is used as an aromatic bitter tonic and as a remedy for poor appetite and thymol and carvacrol are used in bactericidal preparations. 

Terpenoids (E)-Linalool oxide 59,43, 68 Floral, green, rose, sweet 190... 

Terpenoid alcohols appeared early in the history of synthetic perfumery because several were readily available from inexpensive essential oils. Alpha-terpineol, citronellol and linalool shown in Figure 7 are important constituents of pine stump oil, citro-nella oil and rosewood oil, respectively. The fourth material listed, hydroxycitronellal, is a hydroxy aldehyde which perhaps has a questionable place in this discussion. It is included because it is one of the most important fragrance chemicals used today. "Hydroxy" is almost a perfume unto itself. Its soft flowery, linden blossom odor blends very well in many floral perfumes. 

Three new monoterpenoid lactones, (28)—(30), isolated from the urine of koala bears fed on Eucalyptus punctata, appear to have arisen from the cyclization of carboxylic acids formed as hydrolysis products of glucuronide conjugates from the metabolism of a- and /3-pinenes.70 Linalool injected into various plant species has been claimed to be converted into a-terpineol and other monoterpenoids.71 However, direct interconversions cannot be inferred from this type of non-radioactive tracer study. The terpenoids alleged to be produced may well be stress metabolites or be formed b secondary processes that perturb the usual pattern of terpenoid formation. 

The flavour properties of the citrus oils are based on compounds like aldehydes, esters and alcohols. Aldehydes play the most important role in citrus flavours. Mainly the saturated C-8, C-10 and C-12 long-chain constituents as well as the terpenoid aldehydes citral (a mixture of neral and geranial) and citronellal form the basic notes of the fresh and pleasant citms flavour. Also sesquiterpene aldehydes and ketones, such as sinensal or nootkatone, are significant for citms flavours. The aldehyde content, therefore, is frequently used as a quality criterion for citms oils. Important citms alcohols are linalool, octanol, a-terpineol (especially in distilled lime oil) and ter-pinen-4-ol. Furthermore, esters contribute to the flavour properties of citms oils. Especially the acetates of geraniol and nerol and, to a lesser extent, citronellol are... 

Figure 2. Structures of terpenoids chemically formed from linalool (1 ) at pH 3.5 (cf. Fig.1-4). (2) 2,4(8)-p-menthadiene (3) B-myrcene (4) a-phellandrene (5) cx-terpinene (6) limonene (7) B-phellandrene (8) (Z)-ocimene (9) y-terpinene (10) (E)-ocimene (11) p-cymene (12) terpinolene (13) (E,Z)-alloocimene (14) (E,E)-alloocimene (15) a-terpineol (16) 3,7-dimethyl-l-oct-ene-3,7-diol (17) 1,8-cineole (18) 2,2,6-trimethyl-2-vinyl-te-trahydropyran.

Figure 4. Structures of terpenoids formed from linalool (1) by Botrytis cinerea. (19)>(20) (E)- and (Z)-2,6-dimethyl-2,7-octadie-ne-l,6-diol (21),(22) (Z)- and (E)-linalool oxides, furanoid (23),(24) (Z)- and (E)-linalool oxides, pyranoid (25),(26) (Z)-and (E)-linalool oxide acetates, pyranoid (27) 3,9-epoxy-p-menth-1-ene (28) 2-vinyl-2-methyl-tetrahydrofuran-5-one.

Figure 5. Quantitative distribution of terpenoids (19)-(28) (cf. Fig.4) formed from linalool (1) by three strains of Botrytis cinerea (a = 5901/2 b = 5909/1 c = 5899/4).

Conceptually, it is interesting to speculate on the bioconversion of inexpensive secondary metabolites to others of greater value. Along these lines, Schreier and co-workers use Botrytis cinera to convert linalool to a series of other terpenoids as well as to the furanoid and pyranoid linalool oxides. Reactions of this type are good examples of converting inexpensive, available aroma chemicals to higher valued products. 

Geraniol/Nerol, linalool, citronellol, citronellal and citral are five of the most important terpenoids as far as the perfume industry is concerned. Apart from citral, they are all used as such in perfumes. The alcohols and their esters are particularly important. All of them are key starting materials for other terpenoids, and will be discussed later. Figure 4.1... 

Finely it is of interest that the acetonyHdene diol shown has been both used for the chroman portion of 2R,4 R,8 R-a-tocopherol and also transformed into (3R)-(-)-linalool and thus affords a stereochemial correlation with this terpenoid (ref. 116). 

---