CAROTENOIDS 



that carotenoids were formed from the phytyl residues occurring in 

 both chlorophylls a and h. This was made plausible by the chemical 

 conversion of phytol into perhydrolycopene * by the condensation of 

 two molecules of dihydrophytyl bromide in the presence of potassium. ^ 



CH, CHj CH3 CH3 



2 CH3CHCM2CH2CH2CH CHiCHzCH^CH CH2CH2CH2 CH CH2CH2Br 



CH, CH, CH, CH3 CH, CH, CH, ^^^ 



'^CH(CH2)3 CH (CH2)3 Ch (CHj)3 CH (CH2)4 CH fCHj), CH (CH2)3 CH (CH^j CH^ 



CHj \h3 



PerhydroFycopene 



Other suggestions are that phytol and the carotenoids are derived 

 from isoprene ; the carotenoids being formed by addition and sub- 

 sequent dehydrogenation, ' viz. : 



CH3 CH, CH, 



r I I 



CH2 » C - CH = CH2+ CH2=»C- CH « CHj+CHi- C - CH -CHj 



[-2h] I [-2h] 



CH3 CH3 CH, 



r r- I 



CH2=»C- CH=»CH- CH= C-CH — CH-CH— C-CH=CH2 



and phytol by addition followed by hydrogenation, ' viz. : 



CH, CK, CHj 



CH2= C-CH=-CH — CH== C — CH= CH — CH = C— CH= CHj 



[+2h] [+2h] [+2h] I [+2h] [+2h] [+2h] 



CH, CH, CH, 



CH3-CH-CH2-CH2-CH2— CH-CH2-CH2-CH2-CH-CH2— CH3 



Karrer, Helfenstein and Widmer^ suggest that rather than isoprene 

 p-methyl crotonaldehyde may be the fundamental unit, the synthesis 



CH3 CH3 



^C=CH-CH0 + H3C-C=CH-CH0 ^ ^C = CH-CHOH CH^- C = CH -CHO 



^^3 CH, ^^3 CH3 



-HzO CH3 



^ ^C = CH-CH = CH-C=CH-CHO-»- further condensation etc. 



CH,^ c'hj. 



being brought by an aldol type condensation followed by removal of 

 water. 



64 



