Chiral terpene

Scheme 25 Diastereoselective benzannulation with chiral terpene alcohols...

As oxidation also converts the original chiral terpene-derived group to an alcohol, it is not directly reusable as a chiral auxiliary. Although this is not a problem with inexpensive materials, the overall efficiency of generation of enantiomerically pure product is improved by procedures that can regenerate the original terpene. This can be done by heating the dialkylborane intermediate with acetaldehyde. The a-pinene is released and a diethoxyborane is produced.204... 

Stereoselective reduction of some triazolodiazines (derivatives of ring systems 33 and 37) bearing chiral terpene residues has been elaborated by Groselj el al. <2006TA79>. With catalytic hydrogenation, partial saturation of the six-membered ring was experienced, while reaction with borane-methyl sulfide resulted in formation of triazole-boron complexes. 

Ho TL, Enantioselective synthesis Natural products from chiral terpenes, Wiley-Interscience, New York, USA, 1992. 

Ho, Tse-Lok Enantios elective Synthesis Natural Products from Chiral Terpenes, John Wiley Sons. Inc., New York, NY, 1992. 

The world s biggest application of asymmetric catalysis is Takasago Perfumery s synthesis of (-)-menthol from myrcene (see Sections 2.9 and 3.3.1) with about 1500 t/a (menthol and other chiral terpenic substances). The key step is the isomerization of geranyldiethylamine with an Rh -S-BINAP catalyst to citronellal ( )-enamine (eqs. (17)) (BINAP = 2,2 -bis(diphenylphosphine)-l,l -binaphthyl).The geometry of the double bond is 100% E. 

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... 

T.-L. Ho Enantioselective Synthesis Natural Products from Chiral Terpenes Wiley New York, 1992. 

Chiral bromoboranes. The chiral reagents, such as (1), can be prepared from BBrj, Me,SiH, and chiral terpenes (e.g., a-pinene). 

A temperature-dependent NMR spectroscopic study revealed that in solution this species shows dynamic intramolecular coordination of the pendant ether groups, facilitating partial dissociation into the ionic [(3a)2Zr(OTf)]OTf. In the case of the unstable analogues containing cyclopentadienyl ligands 8a and 8b, which bear the much bulkier chiral terpene-... 

Optically active epoxy-terpenes have aroused considerable interest in recent years because of their intermediacy in biosynthetic pathways. Several reports on the syntheses of chiral terpenes have appeared, " among which are the syntheses of / -( + )- and S-(-)-squalene-2,3-oxide from L-glutamic acid (Scheme 1). 

Further, a mathematical model to predict and correlate the flux characteristics of enantiomer(s) and racemate of chiral drugs is described. Finally, the use of eutectics/chiral terpenes to enhance the percutaneous permeation of selected chiral drugs is also discussed. An outline of the skin structure and its barrier function precedes the discussion on enantio-selective skin permeation of chiral drugs in the presence and absence of chiral terpene enhancers. 

Another recent study [57] focused on skin uptake of chiral terpenes. Stereoisomers of menthol have a 9°C lower melting point than racemic compound, while neomenthol enantiomers are present in the liquid state at room temperature, and its racemate melts at 51°C [50]. Changing the solvent composition had no significant effect on the racemate/enantiomers solubility ratio of both terpenes. In further experiments no differences in skin uptake of (+)- or (—)-menthol were examined, but the difference in the melting temperature and solubility of enantiomers vs. racemic compound was reflected in a clear enhancement of racemate skin uptake when compared to pure stereoisomers. In the case of neomenthol, a more than 26° C difference in the melting point resulted in enantiomeric/ racemic uptake ratios of between 2.5 and 8 (depending on the solvent composition). 

Mackay, K.M. Williams, A.C. Barry, B.W. Effect of melting point of chiral terpenes on human stratum corneum uptake. Int. J. Pharm. 2001, 228, 89-97. 

Madiraju, C. Master s thesis. Transport of timolol across hairless mouse skin effect of chiral terpene enhancers. The University of Louisiana at Monroe, LA, 2001. 

Ddii.c. Complexes with Chiral TT-Allyl Ligands. Chirality can be introduced to the TT-allyl moieties of the palladium complexes. Some representative examples are shown in Figure 11. The chiral sources of these 7r-allyl species are chiral terpenes. The terpenes (-)-(3-pinene, pinadiene (for 60), and (+)-3-carene (for 61) reacted with Pd(OAc)2 to give 60, ° and 61, ° respectively. Meanwhile, these terpenes reacted with... 

Ruiz Del Castillo ML, Flores G, Blanch GP, Herraiz M. Effect of thermal treatment during processing of orange juice on the enantiomeric distribution of chiral terpenes. J. Food Prot. 2004 67 1214-1219. 

Ruiz del Castillo, M.L., Blanch, GP, and Herraiz, M., Natural variabdity of the enantiomeric composition of biactive chiral terpenes in Mentha piperita, J. Chromatogr. A, 1054, 87, 2004. 

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