II. CHEMISTRY 



141 



vatable and exhibits ultraviolet absorption bands in practically the same" 

 position and intensity as ergosterol. It also shares the property of being 

 somewhat unstable. These facts account for the original misidentification 

 of the provitamin in cholesterol. 



By reactions analogous to the ones used in the synthesis of 7-dehydro- 

 cholesterol, the corresponding 7-dehydro derivatives of several other natural 

 sterols have been made, namely, 7-dehydrositosterol,^^ 7-dehydrostigmas- 



Activat- 



ability Sterol 



+ Ergosterol 

 + Epiergosterol 

 + Lumisterol 



— Pyrocalciferol 



— Isopyrocalciferol 



Side chain 



20 21 22 23 24 

 R = — CH(CH3)-CH=CH-CH(CH3)-CH(CH3)2 



+ 22,23-Oxidoergosterol 



+ 22-Dihydroergosterol \ 



+ 7-DehydrocampesterolJ 



? 7-Dehydroclionasterol\ 



? 7-Dehydrositosterol / 



? 7-Dehydrostigmasterol 



+ 7-Dehydrocholesterol 1 



+ 7-Dehydroepicholesterol/ 



? AS '.22-Cholestatriene-3-ol 



? AS7-Norcholestadiene-3-ol 



? 3-Hydroxy-A5'-choIadienic acid 



? 3,17-Dihydroxyandrostadiene 



R = — CH(CH3)-CH-CH-CH(CH3)-CH(CH3)2 

 R = -CH(CH3)-CH2-CH2-CH(CH3)-CH(CH3)2 



R = — CH(CH3)-CH2-CH2-CH(C2H6)-CH(CH3)2 



R = -CH(CH3)-CH=CH-CH(C2H6)-CH(CH3)2 



R = — CH(CH3)-CH2-CH2CH2CH(CH3)2 



R = -CH(CH3)-CH=CHCH2-CH(CH3)2 

 R = -CH(CH3)-CH2CH2CH2-CH2-CH3 

 R = — CH(CH3)-CH2-CH2-C00H 

 R = —OH 



Fig. 6. The provitamins D and related sterols with double bonds at C-5 and C-7. 

 The sign + means that the sterol becomes antiricketic upon irradiation, the sign — 

 means that the irradiation product exhibits no antiricketic action, and the sign ? 

 means that the sterol has not been adequately tested for activatability. 



terol,"*" 7-dehydrocampesterol,'*^ and 7-dehydroclionasterol.'*^ The structures 

 of these and other sterols unsaturated in the critical C-5 and C-7 positions 

 are shown in Fig. 6. 



A provitamin D of special theoretical interest is 22-dihydroergosterol, 

 which is intermediate in structure between ergosterol and 7-dehydrocho- 

 lesterol, and epimeric on C-24 with 7-dehydrocampesterol. This provitamin 

 was prepared by Windaus and J^anger^^ by saturating the double bond in 



»9 W. Wunderlich, Hoppe-Seijler's Z. physiol. Chem. 241, 116 (1936). 



" O. Linsert, Hoppe-Seyler's Z. physiol. Chem. 241, 125 (1936). 



« W. L. Ruigh, J. Am. Chem. Soc. 64, 1900 (1942); U. S. Pat. 2,378,435 (1945). 



^2 W. Bergmann, A. M. Lyon, and M. J. McLean, J. Org. Chem. 9, 290 (1944). 



" A. Windaus and R. Langer, Ann. 508, 105 (1933). 



