1QO SOME MISCELLANEOUS UNSAPONIFIABLE LIPIDS 



show a broad absorption peak at about 440 m/J. whereas the reduced forms absorb at about 

 360 niM with no significant absorption at 440. 1, 4-dihydroxyanthraquinones fluoresce in 

 acetic acid solution. The colors given with alcoholic magnesium acetate solutions are 

 characteristic of different hydroxylation patterns (32). Meta hydroxyls give an orange 

 color,- para a purple color, and ortho violet. 



Proof that an isolated compound has the anthracene nucleus may be obtained by dry 

 distillation in the presence of zinc dust. This drastic treatment breaks down anthraqui- 

 none or anthrone derivatives to anthracene which distills over and may be identified by 

 its melting point (216° C. ). Methylated derivatives form 2-methylanthracene (m.p. 245°). 

 These hydrocarbons are easily distinguished from naphthalene (m.p. 80°) which is form- 

 ed from a napthoquinone. 



Characterization of anthraquinone derivatives by means of paper chromatography 

 and electrophoresis has been developed recently by several workers. Paper electro- 

 phoresis methods are described by Core and Kirch (33) and Siesto and Bartoli (34). 

 Betts et al. (35) have chromatographed the glycosides and free anthraquinones on paper. 

 In all of these methods using migration on paper, spots may be detected by spraying with 

 0. 5% magnesium acetate in methanol and heating at 90° C. for five minutes. Character- 

 istic colors appear, as described above (32). 



The pathways, for biosynthesis of anthracene derivatives in plants are still only 

 speculative but generally believed to involve polyacetate condensations possibly as follows 

 (36, 37): 



il % I 

 /\ /\ /\ 



CH2 CH2 CH2 CH3 







ii II 



8 



» \(^2 \^2 \^2 



ANTHRONES 



i 



I 



ANTHRAQUINONES 



It will be seen that such a scheme accounts perfectly for the structure of emodin. For 

 other compounds loss or rearrangement of hydroxyl groups and oxidation or removal of 

 the methyl group are required. Hegnauer (38) has suggested that several different bio- 

 synthetic pathways may be followed, some possibly involving phenylpropane-type inter- 

 mediates. 



