208 VITAMIN D GROUP 



wavelengths 304 and 315 m/x. Heilbron et al}^^ suggested that the extra 

 bands might be those of cholesterilene, which is non-activatable and hence 

 irrelevant. Other studies with specially purified cholesterol are discussed in 

 the author's review of the multiple nature of vitamin D.^'* It will suffice 

 here to note that Hathaway and Lobb^^^ performed chick-rat assays on the 

 irradiation product of cholesterol which had been purified via the dibro- 

 mide. They found that its efficacy ratio was very low, in a class with that 

 of irradiated ergosterol. Since no known cholesterol derivative has a low 

 efficacy ratio, and since ergosterol could not have survived bromination and 

 could not have been formed anew from a sterol of lower molecular weight, 

 it must be concluded that the irradiated purified cholesterol contained a 

 new form of vitamin D. Presumably the provitamin was the substance 

 which showed the absorption bands in the Bills preparation, and which orig- 

 inated during or after the debromination of the cholesterol dibromide. 



Koch et al,^^^ in a series of papers summarized^^^ in 1935, found that by 

 strongly heating highly purified cholesterol in the presence of traces of 

 oxygen, the provitamin D activity could be enhanced 100 times. The typi- 

 cal provitamin spectrum was not observed, but it may have been present 

 and obscured by a strong general absorption. WaddelP''^ found that by 

 heating the cholesterol in the presence of water, the provitamin D activity 

 could be enhanced 100 to 150 times. The vitamin D from heat-treated cho- 

 lesterol was found by Hathaway and Lobb^'*^ and WaddelP^^ to have a high 

 efficsicy ratio in chick-rat assays. This fact, together with the later work 

 on the synthesis of provitamins D, makes it seem probable that the pro- 

 vitamin formed by heating cholesterol is 7-dehydrocholesterol. Unless this 

 assumption is disproved, one cannot regard the vitamin D from irradiated 

 heat-treated cholesterol as a new form. 



(15) Meunier and Thibaudet^^^ have prepared a monoiodocalciferol, m.p. 

 150°, which is at least as potent as the parent substance. Removal of the 

 iodine with hyposulfite yielded tachy sterol. 



(16) Bills and McDonald^^^ treated ergosterol with ethyl nitrite, and then 

 treated the product with isopropylamine, obtaining a substance which 

 showed a trivial antiricketic action with rats. Since the conventional form_ 



333 I. M. Heilbron, R. A. Morton, and W. A. Sexton, Nature 121, 452 (1928). 



334 M. L. Hathaway and D. E. Lobb, J. Biol. Chem. 113, 105 (1936). 



336 F. C. Koch, E. M. Koch, and I. K. Ragins, /. Biol. Chem. 85, 141 (1929); E. M. 

 Koch, F. C. Koch, and H. B. Lemon, ?6{d. 85, 159 (1929); M. L. Hathaway and 

 F. C. Koch, ibid. 108, 773 (1935). 



336 E. M. Koch and F. C. Koch, Science 82, 394 (1935). 



337 J. Waddell, U. S. Pat. 2,028,364 (1936). 



338 P. Meunier and G. Thibaudet, Compt. rend. 223, 172 (1946). 



339 C. E. Bills and F. G. McDonald, cited by C. E. Bills, Cold Spring Harbor Symposia 

 Quant. Biol. 3, 328 (1935). 



