The 1928 Nobel Prize in Chemistry was awarded to Adolf Windaus for his work elucidating the structure of vitamin D3. Vitamin D3 was isolated around 1936 by Brockmann from the liver oil of the tuna fish. The unsaponifiable fraction was partitioned between 90% methanol and a petroleum compound to separate vitamins A and D3. The residue from the petroleum phase contained vitamin D3 to be purified by multiple chromatography.

In the body, Vitamin D3 is synthesized in the following manner:

Step1. Vitamin D3 is synthesized from 7-dehydrocholesterol, a derivative of cholesterol, which is then photolyzed by ultraviolet light in 6-electron conrotatory electrocyclic reaction. The product is Previtamin D3.

Step 2. Previtamin D3 then spontaneously isomerizes to Vitamin D3 (cholecalciferol) in a antarafacial hydride [1,7] sigmatropic shift

Step 3. Vitamin D3 is then hydroxylated in the liver to 25-hydroxycholecalciferol (calcidiol) and stored until it is needed. 25-hydroxycholecalciferol is further hydroxylated in the kidneys to the main biologically active form 1,25-    dihydroxycholecalciferol (calcitriol) in a tightly regulated fashion. Calcitriol is represented below right (hydroxylated Carbon 1 is on the lower ring at right, hydroxylated Carbon 25 is at the upper right end).


Figure 1. Vitamin D3 synthesis

Step 1  step1.png
Step 2
Step 3


Question #00010

7-dehydrocholesterol is found to be optically active. How many stereoisomers are possible for this compound?

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