SOME MISCELLANEOUS UNSAPONIFL\BLE LIPIDS 97 



2. An acyl group is always present at C-2. 



3. Extra methyl groups are common, often giving the superficial appearance of 

 a terpenoid structure. 



The simple phloroglucinol derivatives may be extracted from plant tissues using 

 organic solvents such as ether and then further purified by taking advantage of their phe- 

 nolic properties -- e. g. extraction from organic solvents with sodium hydroxide solution. 

 Purification of hop constituents of this type has been achieved using countercurrent dis- 

 tribution between phosphate buffer and iso-octane (16). 



These phloroglucinol derivatives are for the most part colorless, crystalline com- 

 pounds, although some (e.g. ceroptene) are yellow pigments. Those that have a free 

 phenolic hydroxyl group show typical phenol reactions such as giving a color with ferric 

 chloride. Heating with sodium hydroxide and zinc dust causes reductive removal of the 

 2-acyl group, and the resulting derivatives give a red color with vanillin-cone, hydro- 

 chloric acid. Identification of these derivatives has been an important procedure in struc- 

 ture determination. The infrared and ultraviolet spectra of 2-acyl-cyclohexane-l, 3- 

 diones have been discussed by Chan and Hassall (17). They generally have one absorption 

 maximum in the range 223-233 m^ and another at 271-293 m/i . Godin (18) has separated 

 crude filicin from male fern (Aspidium) into several different phloroglucinol derivatives 

 using paper chromatography in an aqueous solvent containing sodium carbonate and sodium 

 sulfite. Spots were revealed by the diazonium reaction. Phloroglucinol derivatives of 

 Dryopteris were separated on buffered filter paper impregnated with formamide and a 

 benzene/ chloroform solvent (19). 



Details of the biosynthesis of these phloroglucinol derivatives are completely obscure 

 especially with regard to the origin of C-methyl groups. Birch (2) has made important 

 suggestions in this area which should be tested by experiment. 



CHROMONES 



The chromone nucleus with its numbering system is as follows: 



Naturally -occuring chromones generally have a methyl group at C-2 and are oxygenated 

 at C-5 and C-7. Thus despite their overall resemblance to the carbon skeleton of the 

 coumarins (Chapter 4), they may be regarded as derived from the condensation of five 

 molecules of acetic acid. The coumarins, on the other hand, are probably derived by the 

 shikimic acid pathway which rarely results in oxygenation at C-5: 



