II. CHEMISTRY AND INDUSTRIAL PREPARATION 



47 



single maximum at (>()4 mM, ^l^m. 3400. Under similar conditions ncoret- 

 inene gives a maximum at 662 m^u. The enzyme system of Hubbard and 

 Wald failed to synthesize rhodopsin when either retinenei or neoretinene 

 was added to it.^^' The biopotency of what may be the all-/rans vitamin A 

 aldehyde has been reported as essentially the same as that of natural 

 crystalline vitamin .Vi.'"' A more recent determination is given as 2.8 X 10* 



TABLE XII 

 Physical Properties of Vitamin A Aldehydes (Retinenes) 



(Aldehyde Retinene) 



M.p. 



Amaxt 

 mpL 



1 cm. 



Solvent 



References 



2,3,4,5-Tetra-</ans 

 (Retinenei) 



2,3,4, 5-Tetra-trans 

 semicarbazone 



2,4,5-Tri-<rans 3-cts 



(retinene?) 

 2,4,5-Tri-<7-ans Z-cis 



semicarbazone 

 2,S,i-Tr'\-trans 5-cis 



(neoretinene) 

 2,d,4-Tri-trans 5-cis 



semicarbazone 



193-195' 



185' 



371 



1610 Chloroform 



167 



I.U. per gram.* The biopotency of the 3-cis isomer is also the same as that 

 of vitamin Ai.^*^ 



5. Vitamin A Acid 



Vitamin A acid has not been isolated from natural sources, although it 

 could conceivably be formed from vitamin A, However, it has been syn- 

 thesized by several investigators (see p. 34). The all-^rans form is a crystal- 

 line product which has the properties shown in Table XHI. The spectro- 

 scopic data were determined in ethanol. 



The a\\-trans vitamin A acid has a biopotency of about two-thirds that 

 of crystalline vitamin Ai. 



