576 VI. CAROTENOIDS AND RELATED COMPOUNDS 



C4oH5803,^** which is beheved to represent the correct composition. It has 

 been demonstrated by catalytic hydrogenation that there are ten double 

 bonds; five acetic acid molecules also originate on strenuous oxidation-^ 

 according to the procedure of Kuhn and L'Orsa.^" Of the oxygen atoms, 

 two occur in hydroxyl groups, as determined by the esterification reaction 

 and the Zerewitinoff test. Although this carotenol will not react with 

 hydroxylamine, as would be expected if the third oxygen were present in a 

 carbonyl group, there is considerable evidence that a ketone group does 

 exist. Kuhn and Brockmann*^ found that the diketone semi-/3-carotenone 

 only partially reacts with hydroxylamine, as it gives a monoxime instead 

 of the expected dioxime. This latter compound exhibits a spectroscopic 

 picture similar to that of capsanthin, which might suggest that a carbonyl 

 group is present in the latter. The presence of the ketone group was proved 

 by the demonstration that esterification of the reduced capsanthin resulted 

 not in two but in three acetyl groups entering into combination. This 

 must indicate that the unreduced pigment is a dihydroxy-ketone. 



Since capsanthin possesses no biological activity, it would seem highly 

 improbable that it contains an unsubstituted ^S-ionone ring. Presumably 

 one hydroxyl occurs there, and it probably occupies the same position on the 

 ionone ring as in zeaxanthin, with which capsanthin is frequently asso- 

 ciated. On decomposition of capsanthin with permanganate, both a,a- 

 dimethylsuccinic acid and dimethylmalonic acid are formed, but no acetone 

 results.^" Zechmeister and Cholnoky^^'^'^i have proposed the following 

 formula for capsanthin : 



HsC CHj H,C CHj 



C CHj CH3 CH3 CH3 ^c^ 



/\ hhIhhhIhhhhIhhhIhh /\ 



HzC C • C : C • C: C • c: C • C : C • c: C • C: C • C: C • C: C • C : C- C=0 CH? 



hJ II l/H 



C C CHj C 



HO^ \ z' \ / \ / \0H 



C CH3 HjC C 



H2 He 



Capsanthin 



b. Occurrence. Capsanthin occurs in a number of plants belonging to 

 the Solanaceae. The principal source is the paprika grown in Hungary 

 and Spain {Capsicum frutescens) from which its name is derived. The 

 paprika is the same as the South American Perfection pimento. ^^^ Cap- 

 santhin also occurs in another pepper, the Japanese chili {Capsicum frutes- 

 cens japonicurn) .^'^^ The presence of capsanthin in the anthers of the 

 tiger lily {Lilium tigrinum), in conjunction with antheraxanthin, was 

 demonstrated by Karrer and Oswald.^^^ In all these cases, the capsanthin 



3'" L. Zechmeister and L. v. Cholnoky, Ann., 516, 30-45 (1935). 

 "1 L. Zechmeister and L. v. Cholnoky, Ann., 523, 101-118 (1936). 

 372 W. L. Brown, J. Biol. Chem., 110, 91-94 (1935). 



