Vitamin B₁₂

The theme for this year’s National Chemistry Week is Marvelous Metals. One reason that metals are marvelous is that many of them can combine with organic structures to make organometallic compounds that are essential for life.

One example is former Molecule of the Week chlorophyll, in which the metal is magnesium. This week’s molecule, vitamin B₁₂, contains a cobalt atom, a rarity in natural products.

The basic vitamin B₁₂ structure has several chemical forms that differ by the substituent on the central cobalt atom. The one shown in the images, with a cyanide group bonded to cobalt, goes by the name cyanocobalamin. It is a manufactured form of the vitamin that is made from natural forms and used in supplements because it is highly bioavailable.

Vitamin B₁₂ has an extensive history. Some highlights:

• 1849–1947: Once pernicious anemia was identified, it was found to respond well to liver extracts, which were then used for treatment.
• 1948: Mary Shaw Shorb at the University of Maryland (College Park), Karl A. Folkers at Merck (then in Rahway, NJ), and colleagues isolated vitamin B₁₂ from several sources, including liver.
• 1956: Crystallographer Dorothy Crowfoot Hodgkin at Oxford University (UK) determined the structure of vitamin B₁₂.
• 1973: Robert B. Woodward at Harvard University (Cambridge, MA), Albert Eschenmoser at the Swiss Federal Institute of Technology in Zurich (ETH Zurich), and almost 100 co-workers completed the total synthesis of the vitamin.

Hodgkin received the 1964 Nobel Prize in Chemistry for her structure studies on vitamin B₁₂ and other complex molecules. Woodward and Eschenmoser had been awarded earlier Nobels for their achievements in natural product synthesis.

Vitamin B₁₂ is found in every cell in the body and has multiple functions, including acting as a cofactor in DNA synthesis. Animal-based foods (meat, milk, and eggs) are the primary sources; vegetarians, especially vegans, must include plant- or bacterium-derived vitamin B₁₂ supplements in their diets.

Vitamin B₁₂ is indeed a molecule to celebrate during National Chemistry Week!