Monoterpene ester

The volatile oil of nutmeg constitutes the compounds monoterpene hydrocarbons, 61-88% oxygenated monoterpenes, i.e. monoterpene alcohols, monoterpene esters aromatic ethers sesquiterpenes, aromatic monoterpenes, alkenes, organic acids and miscellaneous compounds. Depending on the type, its flavour can vary from a sweetly spicy to a heavier taste. The oil has a clovelike, spicy, sweet, bitter taste with a terpeny, camphor-like aroma. 

Peana et al. [68] assessed the effectiveness in vitro of S. sclarea oil and its LC fractions, containing monoterpenic esters and alcohols, against a variety of phytopathogenic fungi which infect different species of host plants (Botrytis cinerea Pers., Fusarium solani (Mart.) Sacc., Phytoph-thora nicotianae var. parasitica (Dastur) Waterh., Rhizoctonia solani... 

Based on these data, it is concluded that monoterpene esters will undergo in vivo hydrolysis in animals to yield the corresponding alcohols and carboxylic acids. Given that the carboxylesterases and lipases catalysing ester hydrolysis are present in all animals, including fish, it is concluded that monoterpene esters will be hydrolysed to yield monoterpene alcohols and simple aliphatic and aromatic acids. Once hydrolysed, the component alcohols and acids are subject to further oxidative metabolism and/or conjugation. 

Intraspeci c, moreover, individual differences have been detected in the volatile composition of the root oils also in the related species A. absinthium. Major components of the roots and of the overground organs proved to be totally different from each other. Our recent investigations (Nemeth, E. et al, unpublished data) showed that independent of the major components of the leaves (P pinene, p-thujone, p-epoxyocimene, p-caryophyllene, etc.), the root oil contained most frequently monoterpenic esters like lavandulyl isovalerate, neryl isovalerate, neryl acetate, and bor-nyl acetate in highest abundance with hardly any sesquiterpenes, in contrary to yarrow. 

The pyrethrins represent a group of six closely-related monoterpene esters and are invaluable insecticidal substances isolated from pyre-thrum flowers, such as Chrysanthemum cinerariaefolium, and several other species in the Asteraceae family. Pyrethrins are indicated for treatment of skin parasites, such as head lice. They block sodium channel repolarization of the arthropod neurons, which leads to parasite paralysis and death. Permethrin is also used to treat head lice infestation. However, the growing resistance of head lice to pyrethrin and permethrin is becoming a serious concern [88]. 

The product of this reaction is geranyl pyrophosphate Hydrolysis of the pyrophosphate ester group gives geramol a naturally occurring monoterpene found m rose oil... 

The enzyme catalyzed reactions that lead to geraniol and farnesol (as their pyrophosphate esters) are mechanistically related to the acid catalyzed dimerization of alkenes discussed m Section 6 21 The reaction of an allylic pyrophosphate or a carbo cation with a source of rr electrons is a recurring theme m terpene biosynthesis and is invoked to explain the origin of more complicated structural types Consider for exam pie the formation of cyclic monoterpenes Neryl pyrophosphate formed by an enzyme catalyzed isomerization of the E double bond m geranyl pyrophosphate has the proper geometry to form a six membered ring via intramolecular attack of the double bond on the allylic pyrophosphate unit... 

Many oxygenated monoterpenes (alcohols, carbonyl compounds, esters) serve as fragrances. Here inexpensive natural starting compounds are a-pinene (4), /1-pinene (5) and limonene (6), with production volumes of about 18000, 12 000, and 30000 t a-1, respectively. 

Citrus oils contain up to 95% monoterpene hydrocarbons (usually limonene, but others as well, e.g., lemon oil also contains a-terpinene and /3-pinene). The important aroma-determining components of citrus oils are functionalized terpenes and aliphatic compounds (predominantly carbonyl compounds and esters), present only in relatively low concentrations [358]. Thus, several methods are employed to concentrate citrus oils on an industrial scale. The monoterpene hydrocarbon... 

Essential oils may comprise volatile compounds of terpenoid or non-terpe-noid origin. All of them are hydrocarbons and their oxygenated derivatives. Some may also contain nitrogen or sulphur derivatives. They may exist in the form of alcohols, acids, esters, epoxides, aldehydes, ketones, amines, sulphides, etc. Monoterpenes, sesquiterpenes and even diterpenes constitute the composition of many essential oils. In addition, phenylpropanoids, fatty acids and their esters, or their decomposition products are also encountered as volatiles [1-16, 21-33, 36-38]. 

Esters of benzenoid and monoterpenic acids and alcohols as well as unsaturated carboxylic acids such as tiglic acid 142 and angelic acid 143 (Structure 4.43) are found in essential oils [60, 61]. 

Lemon peel oil is much more valuable than its juice therefore, extensive research efforts have been expended to determine its natural composition as a way to detect adulteration as well as to determine quality factors [6, 31, 32]. However, a few studies on lemon juice volatiles can be found [33-35]. Lemon oils are notable for possessing relatively low levels of limonene (more than 70%) and relatively high levels of a-pinene (1-2%), -pinene (6-13%), sabinene (1-2%) and y-terpinene (8-10%) [32]. The relatively high concentration of -pinene is thought to instil the green peely odour of lemon oil. The concentrations of aliphatic and monoterpenic aldehydes, (especially citral) as well as those of esters and alcohols are critical components in the perceived quality of the oil. As lemon oil is unstable, quality can deteriorate with improper storage, resulting in... 

The aroma of intact black currant fruit is mostly produced by anabolic pathways of the plant, and production of fruit volatiles occurs mainly during a short ripening period [112]. The aroma profile of black currant shares similarities with that of other berry fruits, although terpenes are more abundantly present in black currant [107]. Black currant is mainly used for the production of juice. Over 150 volatile compounds have been reported from either black currant berries and/or juice, of which the major groups are monoterpenes, sesquiterpenes, esters and alcohols [107]. Processing of berries to juice has been shown to lead to major changes in the aroma composition [113-118]. 

Important aroma compounds of black currant berries have been identified mainly by GC-O techniques by Latrasse et al. [119], Mikkelsen and Poll [115] and Varming et al. [7] and those of black currant nectar and juice by Iversen et al. [113]. The most important volatile compounds for black currant berry and juice aroma include esters such as 2-methylbutyl acetate, methyl butanoate, ethyl butanoate and ethyl hexanoate with fruity and sweet notes, nonanal, /I-damascenone and several monoterpenes (a-pinene, 1,8-cineole, linalool, ter-pinen-4-ol and a-terpineol) as well as aliphatic ketones (e.g. l-octen-3-one) and sulfur compounds such as 4-methoxy-2-methyl-butanethiol (Table 7.3, Figs. 7.3, 7.4, 7.6). 4-Methoxy-2-methylbutanethiol has a characteristic catty note and is very important to blackcurrant flavour [119]. 

Mango is one of the most popular and best known tropical fruits [44] and possesses a very attractive and characteristic flavour. Some authors reported great differences in flavour compounds (including esters, lactones, monoterpenes, and sesquiterpenes) [14]. 

A wide range of volatile compounds from Indian mango were identified by pioneer group research [20,21]. Esters, lactones, monoterpenes, sesquiterpenes, and furanones were among the volatiles. It has been suggested that the ratio of palmitic to palmitoleic acids determines the flavour quality of the ripe fruit, a ratio of less than 1 resulting in strong aroma and flavour [44]. 

Volatiles of three cultivars of mango (Jaffna, Willard, and Parrot) from Sri Lanka were analysed, and among the 76 components identified, monoterpenes and sesquiterpenes hydrocarbons were described as the major contributors [42]. Variations in the amounts of esters, ketones, and alcohols were also related. 

The remarkably efficient cyclopropanation reaction with an in-situ-generated zinc carbenoid, Eq. (61) provided a straightforward synthesis of the monoterpene sabinene (42) starting from the P-keto ester 41 [58],... 

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