766 



VIII. PROVITAMINS D AND VITAMINS D 



prepared in pure form. It rapidly undergoes a transformation to tachy- 

 sterol.i^^ 



The methods employed for the preparation of tachysterol and for its 

 purification differ considerably from those used in the synthesis of lumi- 

 sterol. The destruction of ergosterol is allowed to proceed to 60% in- 

 stead of to the 40% limit as in the preparation of lumisterol; shorter wave 

 lengths are used in the irradiation than in the synthesis of lumisterol. 

 The first step in the preparation of tachysterol from the irradiation mix- 

 ture involves the separation of unchanged ergosterol by crystallization from 

 a methanol solution. Tachysterol can then be isolated from the irradia- 

 tion mixture as an addition product of citraconic anhydride. On thermal 

 decomposition, the adduct yields tachysterol. It can be further purified 

 by the preparation of tachysteryl-3,5-dinitro-4-methylbenzoate, which 

 forms well-shaped crystals. This method was first used by Windaus, von 

 Werder, and Liittringhaus"*^ in 1932. 



250 300 250 300 250 300 250 300 250 300 250 300 m/* 



P'ig. 6. Absorption curves of ergosterol uml its irradiation products 

 in 0.2% ethereal solution." 



Tachysterolo is an isomer of both ergosterol and lumisterol, since they 

 all have an identical empirical formula. However, it differs markedly in 

 reaction from each of its precursors. For example, it contains 4 double 

 bonds instead of the 3 found in ergosterol or lumisterol,. When tachy- 

 sterol. acetate is treated with citraconic anhydride, the addition product 

 formed has one less double bond; 2 additional double bonds can be demon- 

 strated in this adduct by catalytic hydrogenation. A fourth double bond 

 which can be hydrogenated was demonstrated V)y treatment with per- 

 benzoic acid.'*^ 



Since tachysterol. has 4 double l)onds, only 3 rings instead of 4 are re- 

 {[uired to .satisfy the valence requirements. The fourth additional double 

 Ijond which results from the ring opening must be in conjugation with the 

 other 2 double bonds in ring B, as indicated l)y the absc^ri^tion spectrum. 



"5 A. Windaus and E. Auhagen, Z, phijsiol. Cheni., 1!)6, 108-120 (1931). 



