110 SOME MISCELLANEOUS UNSAPONIFIABLE LIPIDS 



two other groups with the empirical formula CgHuON. These groups may be attached by 

 ether linkages. It seems likely that these pigments exist in plants in a more complex 

 form which is broken down during extraction. 



Hypericin is very dark red and only slightly soluble in organic solvents. In sulfuric 

 acid it is green with a red fluorescence. In aqueous sodium hydroxide, unlike the anthra- 

 quinones, it also gives a green solution. Hypericin is isolated from dried flowers of 

 Hypericum perforatum by first extracting with ether to remove carotenoid pigments and 

 then extracting the hypericin with methanol. Methanolic HCl is added to give an HCl con- 

 tent of 2. 5% and the solution allowed to stand at 0° C. for two days. Crystalline hypericin 

 separates out. It is washed with boiling benzene and methanol and crystallized from pyr- 

 ridine solution by adding methanolic HCl. This crystalline preparation is contaminated 

 with pseudohypericin unless the plant used contained only hypericin. Pyridine is the best 

 solvent for hypericin, and in pyridine solution it shows absorption bonds at 519, 557 and 

 603 niju. KuCera (41) has developed a paper chromatographic method for determination 

 of hypericin in plants. 



The structure of hypericin is obviously similar to that of the dianthrones (e. g. sen- 

 nidin). Emodin anthrone is a minor constituent of Hypericum plants and it seems likely 

 that hypericin is formed by ring closure between two such molecules. A careful search 

 has revealed the presence in the plants of several presumed intermediates in the conver- 

 sion of emodin anthrone to hypericin. The closure of the 4-4' and 5-5' rings is cata- 

 lyzed by light; and by working in the dark a dehydrodian throne of the following structure 

 could be isolated: 



This is evidently derived from two molecules of emodin anthrone and is converted by 

 light into hypericin. The first ring-closure at 5 - 5' gives rise to protohypericin. 



GENERAL REFERENCES 



Bohlmann, F. and Mannhardt, H. J. , "Acetylenverbindungen im Pflanzenreich" Fortschr. 



Chem. Org. Naturstoffe 14 1 (1957). 

 Deuel, H. J., The Lipids 1 pp. 305-319, 372-383, 402-404, Interscience Publishers, 



N. Y. , 1951. 

 Hoffmann -Ostenhof, O. , "Ein und zweikernige Chinone" in Paech and Tracey 3 359. 

 Hoffmann -Ostenhof, O. , "Vorkommen und biochemisches Verhalten der Chinone" Fortschr. 



Chem. Org. Naturstoffe 6 154 (1950). 



