Chapter 6 



MISCELLANEOUS 

 UNSAPONIFIABLE LIPIDS 



The compounds grouped together in this chapter are very different in most chemical 

 properties, but similar in the fact that they are soluble in lipid solvents rather than in 

 water and not saponified by alkali. The anthraquinones fit the above description, however, 

 they normally occur in plants not free but as water-soluble glycosides. All of the com- 

 pounds included appear to be biosynthetically related in being derived by condensation of 

 several molecules of acetate (or, more specifically, malonyl-coenzyme A). Thus they 

 are also closely related to the long chain fatty acids discussed in Chapter 5. Speculation 

 regarding biosynthesis of all such polyacetate compounds may be found in articles by Birch 

 (1, 2). Because of the diversity of properties shown by compounds in this chapter discus- 

 sions of isolation, characterization and biosynthesis are included under each separate sec- 

 tion rather than for the chapter as a whole. 



LONG CHAIN HYDROCARBONS 

 ALCOHOLS AND KETONES 



The most familiar long-chain aliphatic compounds are the fatty acids discussed in 

 Chapter 5, and it is not often realized that they are only one representative of this class 

 of plant constituents. The normal, aliphatic hydrocarbons found in plants usually have an 

 odd number of carbon atoms, and it seems evident that they are derived by loss of carbon 

 dioxide from even-carbon fatty acids: 



CH3(CH2)nCOOH-CH3(CH2)n-iCH3 + CO2 



Tracer experiments have supported this pathway (3). The lowest natural member of this 

 group, n-heptane, occurs as a constituent of the turpentine from several species of pine. 

 The turpentines of Pinus Jeffrey i and P. sabiniana are nearly pure n-heptane and contain 

 no terpene hydrocarbons. Higher molecular weight hydrocarbons are often found in plant 

 cuticle and pollen waxes where their chainlength generally falls in the range C25 - C37. 

 Commercial candelilla wax from Euphorbia spp. contains 50-60% n-hentriacontane 

 (C3iHe4). Cuticle waxes of several common fruits have n-nonacosane (C29H60). The un- 

 saponif table material in olive oil contains hydrocarbons ranging from C13 - C28. Unsatu- 

 rated, normal, aliphatic hydrocarbons occur more rarely but are known. The horsetail, 

 Equisetum palustre, contains a hydrocarbon with the empirical formula C21H42 -- thus 

 one double bond (4); Costus oil (Saussurea lappa) has aplotaxene (heptadeca-1, 8, 11, 14- 

 tetraene) (5); and five acetylenic hydrocarbons have been found in Coreopsis spp. (6). 

 These latter compounds are interesting because of the widespread occurrence of acetylenic 

 derivatives in the Compositae. AH five of the coreopsis compounds are C13 hydrocarbons. 

 One was shown to have the following structure: 



CH2 = CH-CH = CH-C=C-C = C-C = C-CH = CHCH3 



Similar compounds seem to occur in other composites as well, and some contain a benzene 

 rii^ at one end of the aliphatic chain, e.g.: 



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