SOME MISCELLANEOUS UNSAPONIFLABLE LIPIDS 93 



Kaufmann and Kessen (10) have described a procedure whereby long-chain aliphatic 

 alcohols are converted to urethanes and these chromatographed on paper impregnated 

 with undecane, using acetic acid/acetonitrile 3:2 as the mobile phase. Spots were detected 

 by forming mercury complexes and showing up the mercury with hydrogen sulfide. 



Gas chromatography has recently demonstrated its great usefulness in separating 

 and identifying leaf wax hydrocarbons (11, 12). The hydrocarbons can first be separated 

 as a group from oxygenated compounds by chromatography on alumina (12). 



Spectral measurements have limited usefulness for characterization of these com- 

 pounds. Where conjugated unsaturation is present, it may be detected by ultraviolet spec- 

 tra as described in Chapter 5. Infrared spectroscopy may be used to determine whether 

 hydroxyl or carbonyl groups are present. X-ray crystallography has been very useful in 

 proving the structure of certain natural, long-chain alcohols, but discussion of this spe- 

 cialized technique is beyond the scope of this book. 



There is no real biochemical evidence regarding the biosynthetic pathways of long- 

 chain, aliphatic hydrocarbons, alcohols and ketones; but it seems evident that they are 

 closely related to the fatty acids, whose biosynthesis is well studied. It is likely that the 

 alcohols and hydrocarbons are made respectively by reduction and decarboxylation of the 

 fatty acids. The few ketones known may possibly be made by decarboxylation of keto acids 

 since, like the hydrocarbons, they have an odd-numbered carbon chain. It is usually be- 

 lieved that following each two-carbon addition in the build-up of fatty acids, reduction of 

 the /3-carbonyl group occurs to form a saturated acid (cf. Chapter 5). If all the steps in 

 this reduction are not carried out, keto compounds, hydroxyl compounds, or unsaturated 

 compounds would result. If chain building went on through several stages without reduc- 

 tion, a /3-polycarbonyl system might result, i. e. : 



o o o 



II II 11 

 RCHjCCHjCCHjCCHjC-S-Enzyme 



Partial reduction could then give rise to polyhydroxy or polyunsaturated systems. Acety- 

 lenic bonds could be introduced by dehydration of the enol form of a carbonyl compound: 



O O OH O O 



II II I II II 



RCH2CCH2COH--RCH = CCH2COH-RC=CCH2COH 



The above speculation provides reasonable pathways of synthesis for most natural com- 

 pounds in this group although there are occasional discrepancies such as the occurrence 

 of even-carbon chain hydrocarbons or the appearance of oxygen attached to a carbon which 

 would be expected to come from the methyl group of acetic acid. Obviously much research 

 is needed in this area of biochemistry. 



PHLOROGLUCINOL DERIVATIVES 



A variety of natural products contain the phloroglucinol nucleus in their structure. 



OH 



phloroglucinol 



