II. CHEMISTRY 205 



(1) Of the minor forms, the best known is vitamin D4, produced by the 

 irradiation of 22-dihydroergosterol. Windaus and Trautmann'-" in 1937 

 prepared this vitamin in crystalHne form. Windaus and GiintzeP-^ repeated 

 the preparation, and also isolated other members of the irradiation series, 

 namely, lumisteroU, tachysteroU, and suprasterol II4. Vitamin D4 crystal- 

 lizes out of acetone in long needles, m.p. 96° to 98°, [af^ = +85.7° in 

 acetone, spectrum similar to that of calciferol.^-' The potency of the crystal- 

 line vitamin amounts to 20,000 to 30,000 I.U. per milligram for the rat^^o 

 (50% to 75 % of the value of D2 or D3). The chick-rat efficacy ratio of vi- 

 tamin D4 may be estimated, from the findings of McDonald^® and Grab," 

 at about 20%, which places it between Do (1 %) and D3 (100%), quite in 

 keeping with its structure. Vitamin D4 ranks as a minor form only because 

 it has received no practical application. 



(2) The vitamins D produced by the irradiation of mollusk provitamins 

 are obscure forms chemically but important commercially because they are 

 widely used in poultry feeding. As indicated in the discussion headed Pro- 

 vitamins D of Invertebrates, the provitamins of different mollusks, even 

 when "pure" spectrographically, differ from each other and from any chem- 

 ically known form of provitamin D. They are probably mixtures, perhaps 

 containing some 7-dehydrocholesterol and occasionally a little ergosterol, 

 but predominantly composed of other sterols, such as the provitamin Dm of 

 Petering and WaddelP' which appears to have 29 carbon atoms. The vi- 

 tamin D obtained from pro\'itamin D^ is notable for exhibiting a chick- 

 rat efficacy ratio somewhat above 100%. "^' '-'' It has been crystallized in 

 the form of its 3 , 5-dinitrobenzoate, m.p. 128° to 128.5°, [a]j, = +92° in 

 chloroform. 1'^ Even though this may not be a pure substance, there is no 

 doubt but that it represents an obscure vitamin D characterized by high 

 efficacy and high molecular weight. 



(3) In the discussion of \'itamin D in fish oils, it was shown that several 

 forms are present, although only D2 and D3 have been identified. One of 

 the minor forms detected in cod liver oil by Hickman and Gray'^^ exhibited 

 a boiling point in molecular distillation so low as to suggest the absence of 

 any side chain in the molecule at C-17. This form, in a chick-rat assay, was 

 found to have an efficacy ratio of between 25 % and 50 %. It must be re- 

 garded as a distinct form of vitamin D. 



(4) It has been amply demonstrated by Waddell,*^ Bills et al.,^^'^ Remp 

 and Marshall,^-^ ^^d others that, rat unit for rat unit, vitamin D3 and cod 

 liver oil are about equally effective for chicks. From this has come the un- 



320 A. Windaus and G. Trautmann, Hoppe-Seyler's Z. physiol. Cherti. 247, 185 (1937); 

 .A. Windaus, U. S. Pat. 2,128,199 (1938). 



321 A. Windaus and B. Giintzel, Ann. 538, 120 (1939). 



322 D. G. Remp and I. H. Marshall, /. Nutrition 15, 525 (1938). 



