670 VII. VITAMINS A 



The best preparation of Carr and Jewell had an extinction value, E (1%, 

 1 cm.), of 1600, contrasted with the figures obtained by Heilbron et al.,^'' 

 i.e., 1370 for a halibut distillate, 1330 for a distillate of sturgeon liver oil, 

 and 1350 and 1250 for two samples prepared by Karrer.^" 



Holmes and Corbet'^ were the first to prepare vitamin A in crystalline 

 form. They accomplished this by prolonged cooling of a vitamin A con- 

 centrate dissolved in methyl alcohol containing small amounts of water at 

 temperatures below — 50°C. The concentrates were prepared from the 

 liver oils of the Japanese ishinagi (Stereolepis ishinagi) and of the mackerel 

 (Scomber scomhrus). The vitamin A separated in the form of yellow 

 rosettes with a melting point of 7.5-8.0°C. ; it had an extinction maximum 

 of 2100 and a biological potency of 3,000,000 International Units per gram. 

 The results as regards melting point and biological potency were later con- 

 firmed by Mead.^^ However, Baxter and Robeson^^ demonstrated that 

 the crystals isolated from methanolic solution contained approximately 

 10% of methyl alcohol of crystallization. The latter workers prepared 

 vitamin A samples having identical extinction maxima of 1750, and melt- 

 ing points of 63-64 °C., from shark liver, ling cod liver (Moloa vulgaris), 

 black sea bass or California jewfish liver (Stereolepis gigas), and halibut 

 (Hippoglossus hippoglossus) visceral oils, which originally had such varied 

 extinction coefficients as 100, 129, 317, and 72, respectively. They em- 

 ployed vacuum distillation, saponification, and crystallization from ethyl 

 formate at low temperatures. 



Further progress in determining the nature of vitamin A resulted from 

 the preparation of crystalline derivatives. In 1935 Hamano^^'^^ first suc- 

 ceeded in preparing a /3-naphthoate and an anthraquinone-/3-carboxylate 

 from several fish liver oil concentrates. Mead^^ later confirmed these re- 

 sults, while Baxter and Robeson ^^■^'^ subsequently synthesized a number of 

 additional esters. The nature and properties of these crystalline products 

 are included in Table 1. The crystalline structure of the vitamin A alcohol, 

 both from ethyl formate and from methyl alcohol, is shown in Plate 1. 

 Photographs of the acetate and succinate esters are found in Plate 2, while 

 those of the palmitate and /3-naphthoate are given in Plate 3. 



^" I. M. Heilbron, W. E. Jones, and A. L. Bacharach, Vitamins and Hormones, 2, 1.55- 

 213 (1944). 



31 H. N. Holmes and R. E. Corbet, /. Am. Chem. Soc, 59, 2042-2047 (1939). 



32 T. H. Mead, S. W. F. Underbill, and K. H. Coward, Biochem. J., 33, 589-600 

 (1939). 



" J. G. Baxter and C. D. Robeson, J. Am. Chem. Soc, 64, 2411-2416 (1942). 

 34 S. Hamano, Sci. Papers Inst. Phys. Chem. Research Tokyo, 28, 69-73 (1935). 

 ^ S. Hamano, Sci. Papers Inst. Phys. Chem. Research Tokyo, 32, 44-49 (1937). 

 3« J. G. Baxter and C. D. Robeson, J. Am. Chem. Soc, 64, 2407-2410 (1942). 

 " J. G. Baxter and C. D. Robeson, Science, 92, 203-204 (1940). 



