BILADIENES-(a,b) AND RELATED SUBSTANCES 



125 



called phylloerythrin {1770).) The difference in color between the two classes 

 is by no means always as distinct as the names "violins" and "purpurins" 

 would indicate, and the bilipurpurins again comprise several structural 

 types, the first of which were observed by Lemberg and Lockwood (1711). 

 Hence Lemberg (1771,1712) used the terms biliviolins type I for Siedel's 

 biviolins, and biliviolins type II and type III for two distinct types of bili- 

 purpurins. IMeanwhile, still other types of bilipurpurins have been found by 

 Siedel and co-workers. Since only biliviolinoid mesobiladienes have been 

 found so far in nature, and the various types of biliviolinoid oxidation prod- 

 ucts have only been obtained in the test tube, and since no simple chemical 

 names are av'ailable, it simplifies matters to refer to Siedel's nomenclature. 

 Both biliviolins and bilipurpurins are again summarized under the term 

 "biliviolinoid substances'" which should be used to describe any natural 

 product of still unknown structural type which possesses the spectroscopic 

 properties of biliviolins. 



5.2. Mesobiliviolin (Mesobiliviolin Type I, Lemberg) 



5.2.1. Structure. The "mesobiliviolin" obtained by Fischer and 

 Niemann (858) by oxidation of mesobilane with ferric chloride was a 

 complicated mixture, in which Lemberg (1673,1680,1690) established 

 the presence of mesobilene-(b), mesobilierythrin, and mesobiUverdin 

 in addition to mesobiliviolhi. When its solution in chloroform-ether 

 (1:1) is passed through a column of talc, the violet ring of meso- 

 biliviolin migrates in front of the red ring of mesobilierythrin (Siedel, 



M E M P 



P M M E 



+ 



HO 



H H " ' 



H2 



MEMP PMME 



H 



A ApA ApA A 



-^ XT L XT ( XT 



H 



H 



H. g 



^OH 



Fig. 15. Synthesis of mesobiliviolin (Siedel). 



2550). Siedel thus isolated mesobiliviolin. He also synthesized it 

 by condensation of formylneoxanthobilirubinic acid with isoneobili- 

 rubinic acid (Fig. 15). Since oxidation of the methylene groups of 



