13 PETALOXANTHIN 317 



ascribe this change to cis-trans isomerism and distinguish three neo-celaxan- 

 thins* : 



Solvent Absorption maxima in petroleum ether 



Neocelaxanthin A . . 534 497 464 (433.5) m// 



Neocelaxanthin B . . 530 493.5 460 (431.5) m/< 



Neocelaxanthin C . . 536 496.5 461 (432) m/^ 



The neotonilins, also obtained by le Rosen and Zechmeister, exhibit 

 spectral properties similar to the neocelaxanthins, but can be easily separated 

 from the latter by chromatography on calcium hydroxide. (The two natural 

 pigments can be separated in the same way). 



13. PETALOXANTHIN C4oH5g03** 



History and Occurrence 



The blossoms of Cucurhita Pepo were first examined for carotenoids in 

 1914 by MiCHAUD and Tristan*^ In 1936, Zechmeister, Beres and Ujhelyi^" 

 isolated from this source a new phytoxanthin, for which they proposed the name 

 petaloxanthin. (The obvious name cucurbitaxanthin could not be used as this 

 had already been employed by Suginome and Ueno to designate lutein 

 obtained from Cucurhita maxima Duch^^). Petaloxanthin has so far only been 

 found in pumpkin blossoms. 



Preparation^'^ 



1 kg of material (from male pumpkin blossoms) is exhaustively extracted with 

 ether in the cold. The combined extracts are concentrated and the residue is 

 saponified with methanolic potassium hydroxide at room temperature. The reaction 

 mixture is covered with petroleum ether and the pigments are divided into an 

 epiphasic and hypophasic fraction by addition of a little water. The pigments of 

 the hypophasic fraction are extracted with ether and the solution is washed and 

 dried, and the solvent evaporated. The residue is dissolved in a little carbon di- 

 sulphide, a small portion remaining undissolved. This less soluble fraction is dissolved 

 in more carbon disulphide. The solution is slightly cooled to precipitate colourless 

 impurities and the mother liquors are twice chromatographed on calcium carbonate. 

 The petaloxanthin is eluted with methanol-containing ether and crystallised from 

 a mixture of carbon disulphide and petroleum ether. From 1 kg of ground blossoms, 

 20 mg of pigment are obtained in this way. 



Chemical Constitution 



Very httle is at present known regarding the structure of petaloxanthin. 

 The molecular formula C40H56O3 or C4oH5g03, the absorption spectrum (maxima 



* None of these isomerisation products were obtained in a crystalline state. 

 ** The formula C40H58O3 is also a possible one for petaloxanthin. 



References p. 241—343 ■ 



