142 VITAMIN D GROUP 



the side chain of ergosterol. To do this, ergosteryl acetate was heated with 

 maleic anhydride to form an addition product in which the two double 

 bonds in ring B were saturated. The double bond at C-22 was then hydro- 

 genated, after which the maleic anhydride was thermally split from the 

 molecule, thus restoring the double unsaturation in ring B which is essential 

 for activation. The free provitamin was obtained by saponification of the 

 ester. 



Ten other sterols with double bonds at C-5 and C-7 are also known. 

 Their structures are included in Fig. 6. Epiergosterol is prepared by the 

 reduction of ergosterone with aluminum isopropylate.*^ It has not been 

 obtained pure, but has been made free from ergosterol. Lumisterol is the 

 initial irradiation product of ergosterol.^*' *^ It has not been found in nature, 

 but it undoubtedly occurs in natural products where vitamin D is being 

 formed by insolation. Pyrocalciferol and isopyrocalciferol are thermal trans- 

 formation products of calciferol.'** 22 , 23-Oxidoergosterol has been prepared, 

 but the details of its synthesis were not disclosed. ^^ Rosenberg^^ surmises 

 that it was made by treating the maleic anhydride addition product of an 

 ergosterol ester with a mild oxidizing agent to form the 22 , 23-oxido com- 

 pound, which upon thermal decomposition would yield the 22,23-oxido- 

 ergosterol ester. 7-Dehydroepicholesterol has been made by applying the 

 reactions in Fig. 5 to epicholesterol,^^ and also, in poor yield, by reducing 

 dehydrocholestenone with aluminum isopropylate.^^ A* •'' -^--Cholestatriene- 

 3-ol has been identified*" indirectly as one of the provitamins of Myiilus 

 edulis; it has not been prepared synthetically. A* ■^-Norcholestadiene-3-ol 

 has been made by a series of reactions from the oxidation products of 

 sitosterol.*^ 3-Hydroxy-A*'^-choladienic acid is obtained by the pyrolysis of 

 the dibenzoate of methyl 3,7-dihydroxy-A*-cholenate in dimethylaniline.*^ 

 3 , 17-Dihydroxyandrostadiene is made from androstenediol by reactions 

 analogous to those in Fig. 5.*^ 



Besides the chemically definite provitamins cited in the preceding para- 

 graphs, there are provitamins of unknown structure which will be consid- 

 ered under the heading, Provitamins D of Invertebrates. There are also 



" A. Windaus and K. Buchholz, Ber. 72, 597 (1939). 



*^ A. Windaus, A. Liittringhaus, and P. Busse, Nachr. Ges. Wiss. Gottingen, Math. 



physik. KL, Fachgruppe III, 150 (1932). 

 ^« A. Windaus, K. Dithmar, and E. Fernholz, Ann. 493, 259 (1932). 

 « K. Dimroth and J. Paland, Ber. 72, 187 (1939). 

 48 A. Windaus and J. Naggatz, Ann. 542, 204 (1939). 

 " A. Windaus and 0. Kaufmann, Ann. 542, 218 (1939). 

 f^o J. van der Vliet, Rec. trav. chim. 67, 246, 265 (1948). 

 "C. G. Alberti, B. Camerino, and L. Mamoli, Helv. Chim. Acta 32, 2038 (1949); 



33, 229 (1950). 

 52 G. A. D. Haslewood, /. Chem. Soc. 1938, 224. 

 "A. Butenandt, E. Hausmann, and J. Paland, Ber. 71, 1316 (1938). 



