Chiral monoterpenes

Askari C, Hener U, Schmarr HG, Rapp A, Mosandl A, Stereodifferentiation of some chiral monoterpenes using multidimensional gas chromatography, Frese-nius J Anal Chem, 340 768-772, 1991. 

The first separations of enantiomers in GC on cyclodextrin modified column were carried out by Sybilska et al. in 1983 [5], They applied a formamide solution of a-cyclodextrin as a stationary phase in the classical packed column. The column allowed an efficient separation of chiral monoterpenes - a- and P-pinenes into enantiomers. This system of using CDs in GC is characterised by obtaining high enantioselectivity factors, so enantioseparation is still possible for receiving not very efficient packed columns. Unfortunately, the columns appeared to be not very stable at higher temperatures. 

ITie enantiomeric composition of monoterpenic hydrocarbons has been studied in laboratory prepared essential oils from Pinus sylvestris, [20-22], Pinus pence [23], Picea abies [24, 25] and Juniperus communis [21,26, 27]. Seven major chiral monoterpenes have been investigated in different plant tissues. The structural formulas of these compounds are presented below. 

From the investigated chiral monoterpenes 3-carene has been detected in only (+)-form. p-pinene and P-phellandrene has been identified as (-)-P-pinene and (+)-P-phellandrene of a high enantiomeric purity. A small amount of their optical antipodes has also been detected in some samples. 

Chiral monoterpenes including (+)-/)-pinene (116) can induce an excess helicity to achiral 115. The chiral terpene forms a complex preferentially with right- or left-handed helical 115, which exists in a dynamic racemic form. This can be regarded as chiral recognition by the helical oligo(phenyleneethyn-ylene).199... 

C. Askari, U. Hener, H.-G. Schmarr, A. Rapp and A. Mosandl. Stereodifferentiation of some chiral monoterpenes, using multidimensional gas chromatography. Fresenius J. Anal. Chem., 340. 768-772(1991). 

Another reason for the increase in interest in monoterpene synthesis is caused by the use of chiral monoterpenes as synthetic auxiliaries. This has led to the study of the chiral synthesis of some monoterpenoids, which is discussed in the relevant sections. 

Inhibited by chiral monoterpenes from ponderosa pine resin (e.g.> llmonene, -plnene and 6-phellandrene and a-plnene). The greatest enantiomeric effect Is observed with (+)-a-plnene which Is three times more Inhibitory against Ceratocystls than the (-)-antlpode (42,43). In another study using Plnus radlata monoterpenes, (+)-llmonene was shown to be a potent Inhibitor of Diplodea plnea spore germination while (-)-llmonene was Inactive (44). 

Syntheses of (-)-A -THC have utilized the acid-catalyzed condensation of olivetol (9, Scheme 1) with suitable chiral monoterpenes, such as (-h)-c/5- or /ra 5-p-mentha-2,8-dien-l-ol (9,10), (+)-trans-2-czKm epoxide (11,12), p-mentha-2-ene-l,8-diol (13,14), and (-)-cis- or /ra 5-verbenol (15). Other successful approaches to A -THCs are also known (16-21), but a problem common to these methods is created by the fact that a variety of by-products results. Normal and abnormal THCs, few-adducts, open-chain intermediates, starting materials, degradation products as well as double-bond isomers complicate work-up procedures and purifications. Although an improved method has... 

Orth, M., F. Czygan, and V. P. Dedkov. 1999. Variation in essential oil composition and chiral monoterpenes of Achillea millefolium from Iran. 11 681-687. 

The enantiomeric distribution of chiral monoterpenes may greatly vary with the individual compounds. For instance, in higher plants, getmacrene D is present as (—)-enantiomer, while the (-i-)-enantiomer is more likely to occur in lower organisms [22]. In a Myrtus communis essential oil from Algeria limonene was exclusively present in the (-i-)-enantiomeric form, a-pinene with more than 95% in the (-i-)-form, while p-pinene, p-phellandrene, and neomenthol occurred rather as a racemate [26]. 

In the past year, (+)- a -crysanthemic acid has been prepared from a number of readily available chiral monoterpenes, namely (—)-carvone, (+)-limonene, a-terpineol, and (+)-3-carene. Furthermore, an asymmetric synthesis of (liJ)-cw-permethric acid (11) has been achieved by the reaction of 1-menthyl diazoacetate and l,l-dichloro-5-methylpenta-l,3-diene in the presence of the... 

---