Monoterpene aldehydes

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... 

Stingless bees lay chemical trails with mandibular gland constituents which have been identified as normal aliphatic alcohols or monoterpene aldehydes. Trigona spinipes generates a trail with a mixture of 2-heptanol, 2-undecanol, and 2-tridecanol, and it has been possible to successfully lay artificial trails with these alcohols (136). Trail following in workers of Trigona subterranea is released by citral (130), the stereoisomers of which are also utilized as alarm pheromones and defensive compounds. Such pheromonal parsimony appears to be especially typical of eusocial bees and ants. 

Essential oil recovery and composition showed variation with maturity. C. sativum L. fruits grown in Tunisia gave essential oils at the initial, middle and final stages of maturity, with yields of 0.01, 0.12 and 0.35%, respectively. Essential oil at the first stage of maturity consisted mainly of monoterpene alcohols (14.6%), especially linalool (10.96%). Other constituents were monoterpene aldehydes (2.07%), ethers, hydrocarbons and monoterpene ketones, as well as phenols and sesquiterpenes. 

A monoterpenal, or monoterpene aldehyde, is a monoterpene with an aldehyde functional group. 

Figure 3.8 Aldehydes. Citronellal (C H180), monoterpene aldehyde. Courtesy Spiring Enterprises Ltd.

Crocins (II) that are glycosyl esters of crocetin (I) are the major components of saffron. Crocins (trans and cis isomers) belong to the family of carotenoids that are water-soluble. Safranal (III), a monoterpene aldehyde and picrocrocin (IV) precursor of safranal are also main components. 

Monoterpene aldehydes, isophorone and isophorone-related compounds have been also found in saffron. Zarghami and Heinz [3] have identified six new isophorone-related compounds listed in Table 1 from ether extracts of saffron by IR, NMR, UV and MS. In the same table are listed the most common volatiles of saffon. The structures of carotenoid derived volatiles found by various researchers are shown below (scheme 3). 

The preferred rotational conformations of acetyl and formyl groups can be predicted by temperature-dependent c.d. measurements, and the technique has been applied to some monoterpene aldehydes. The sign of the Cotton effect has been related to the chirality of a series of Ti-molecular complexes of monoterpene (and other) hydrocarbons with tetracyanoethylene. Inconclusive results found with (-h )-sabinene were ascribed to complexation with the cyclopropane ring. °... 

In the presence of oxygen, ketyl radicals and those derived from their hydrogen donors are converted to peroxy radicals. Figure 6.15 shows an example of an aldehyde photolyzed in ethanol. These peroxy radicals are often quite susceptible to loss of HOO and subsequent production of hydrogen peroxide (see Equations 4.10 and 4.23 in the Oxidation chapter). Citral (25), a naturally occurring monoterpene aldehyde that is abundant in Citrus species and other plants, has been shown to be phototoxic, perhaps by this mechanism (Asthana et al., 1992). 

C10H14O, Mr 150.22, oil. Monocyclic monoterpene aldehyde occurring in both enantiomeric forms (/ )-(- )- and(S)-(-)-P.,bp. 104°C(900 Pa), [o]d 150.7°. LD50 (rat p. 0.) 2500 mg/kg. (-)-P. constitutes ca. 50% of Perilla oil from Perilla arguta and P. frutescens var. crispa (Lamiaceae), (+)-P. constitutes ca. 60% of the Philippine Sulpicia oil from Sulpicia orsuami and also occurs in Siler trilobum, Siam latifolium. Citrus reticulata, and other plants. The ( )-oxime of (5)-(-)-P. is used in Japan as a sweetener Perilla sugar and has a 2000-fold higher sweetness than saccharose. 

C,oH,40, Mr 150.22, bp. 72 C (4 hPa). A monocyclic monoterpene aldehyde. S. is the odor principle of saffron and is formed from the bitter saffron gluco-side picrocrocin [CisHjjO, Mr 330.38, mp. 156°C, [a]g -58° (H2O)]. S. acts as an androtermone, i.e., the substance determining the male gender of the green alga Chlamydomonas eugametus. S. occurs in saffron oil (Crocus sativus, Iridaceae) and is prepared from, e.g., citral. ... 

Naturally abundant monoterpene aldehydes include (-)-perillaaldehyde in mandarin peel oil Citrus reticulata, Rutaceae) and Perilla arguta (Labiatae) as well as phel-landral in the oil of water fennel Phellandrium aquaticum, Umbelliferae)... 

Citral a doubly unsaturated monoterpene aldehyde, M, 152.24. A mixture of cis and Irons isomers is a component of many essential oils. C.A (trans-C., geranial) b.p.,2 110-112 "C, P20 0.8898, n J 1.4894. CB (cis-C., neral) b.p.12 102-104°C, pjo 0.8888, /Id 1.4891. C. is a component of complex insect pheromone mixtures. When heated, it is converted to isocitral, and it undergoes photocyclization to photocitral A. Conversion of C. to pseudoionone with acetone is important as the first step in the industrial synthesis of vitamin A. In the perfume and food industries C. is the most important of the aliphatic monoterpenes. 

Aldehydes are highly reactive compounds in which one hydrogen atom is bonded to a carbonyl group at the end of a hydrocarbon chain. Monoterpene aldehydes such as those found in citrus oils correspond to their respective alcohol note their names end in al , hence geraniol, citronellol (alcohols) geranial, citronellal (aldehydes). 

Citronellal is a monocyclic monoterpene aldehyde with high concentrations found in the essential oils of Corymbia citriodora, M. officinalis, and various Cymbopogon species. It is used for perfuming soaps and other products (Bornscheuer et al., 2014 O Neil, 2006). Only one study described biotransformation of citronellal in rabbits. Ishida et al. could isolate three neutral metabolites of (+)-citronellal in the urine of rabbits (Figure 9.11). An additional acidic metabolite was formed as the result of regioselective oxidation of the aldehyde and dimethyl allyl groups (Ishida et al., 1989). Based on animal data, metabolism of citronellal is also expected in humans. 

Chlorella species are excellent microalgae as oxidation bioreactors as mentioned earlier. Treatment of monoterpene aldehydes and related aldehydes were reduced to the corresponding pri mary alcohols, indicating that these green algae possess reductase. 

Biotransformation of Monoterpenoids by Microorganisms, Insects, and Mammals 14.3.2 Monocyclic Monoterpene Aldehyde... 

Molecular structures of monoterpenoids are present as three major types acyclic, monocyclic and bicyclic. Oxygenated derivatives of acyclic monoterpenes are more widespread in nature than acyclic monoterpenes themselves. Such derivatives are the monoterpene alcohols citronellol and geraniol, or the monoterpene aldehydes citronellal and geranial. Mononocyclic monoterpene hydrocarbons are exemplified by limonene, which is a major component of orange and lemon peel oils, and p-phellandrene, which is emitted by conifer trees under biotic stress. These compounds are relatively common in nature. Bicyclic monoterpenes are represented by the aforementioned a-pinene, one of the most abundant and important monoterpenes. 

Machado M, Pires P, Dinis AM, Santos-Rosa M, Alves V, Salgueiro L, Cavaleiro C, Sousa MC (2012) Monoterpenic aldehydes as potential anti-leishmania agents activity of Cymbopogon citratus and citral on L. infantum, L. tropica and L. major. Exp Parasitol 130(3) 223-231... 

Zarghami, N. S., and D. E. Heinz Monoterpene Aldehydes and Isophorone-Related Compounds of Saffron. Phytochem. 10, 2755 (1971). 

Almost aU saturated aliphatic aldehydes, starting with formaldehyde (methanal) and ending with dodecanal, are important odour-active compounds. Particularly important odour-active compounds are monoterpenic aldehydes. 

The ahcycHc monoterpenic aldehyde safranal has a different biochemical origin, and is the main characteristic odorous component of saffron Crocus sativus, Iridaceae). Safranal is classified as a degraded carotenoid (apocarotenoid) as it is produced from zeaxanthin via hydrolysis of the bitter intermediate picrocrocin. Degradation of carotenoids produces a number of other aromatic compounds (see Section 9.9.5.2). A list of the names of major terpenoid aldehydes is shown in Table 8.11. 

Aliphatic aldehydes with between 1 and 7 carbon atoms in the molecule generally have a sharp, pungent and sometimes rancid aroma, while aldehydes with 8-14 carbon atoms (including monoterpenic aldehydes) are generally characterised by a pleasant aroma. Higher aldehydes are usually odourless. 

The monoterpenic aldehyde (-)-perillaldehyde, also known as per-iUal (see Section 8.2.4.1.1), which occurs in small quantities as a... 

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