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The Structural Formula for Cholesterol

Cholesterol, C27H45-OH, is a polycyclic zoosterol (animal steroid) which can probably best be visualized by considering features independently: the basic ring structure, the minor modifications to the ring structure and the eight-carbon aliphatic chain. Once the basic chemical layout is understood, a space-filling model completes the visualization. Cholesterol is not merely found in food, but is made within the human body.

  1. Ring Structure

    • The ring portion of cholesterol is the four-ringed cyclopentanophenanthrene structure. It is given a very specific numbering as seen in the diagram.

    The Eight-Carbon Chain

    • The eight-carbon chain is attached at carbon 17 of the ring system, and possesses the simple structure
      [ - H2(CH3)C -- (CH2)3 -- CH(CH3)2]
      [2,6-dimethyl-hexyl - ]

      From left to right in the formula, the carbons in this chain are numbered 21, 20, 22, 23, 24, 25, 26 and 27.

    Minor Modifications

    • The minor modifications are a hydroxyl group at the carbon-3 position, a double bond at the carbon-5 to carbon-6 position and two methyl groups---one at the carbon-10 position (it receiving the number 19) and one at the carbon-13 position (it receiving the number 18).

    Isoprene Rule

    • The synthesis of many complex natural substances can be explained in simple rules. The isoprene rule can be used to derive the triterpene molecule, squalene. As Woodward and Bloch demonstrated in 1953, squalene, in turn, can be cyclized in a cholesterol synthesis. Isoprene has the very simple chemical structure
      H2C=C(CH3)-CH=CH2.

    Isopentenyl Pyrophosphate (IPP)

    • The isoprene units making up the building blocks of such structures do not actually come from isoprene itself but from isopentenyl pyrophosphate, which possesses the structure
      H2C=C(CH3)-CH=CH-O-P(O)(OH)-O-P(O)(OH)2.
      It is actually this natural-occurring substance that is responsible for the formation of cholesterol. Notice the similarity of this substance to that of isoprene. The only difference is that one of the hydrogens of the isoprene is replaced by the pyrophosphate portion of the molecule.

    Structure First Proven

    • Little was known about cholesterol until the work of A. Windhaus and H. Wieland, who completely elucidated its chemical structure in 1932.

    Role Cholesterol Plays in the Human Body

    • Helmut Schrott, M.D., a professor of epidemiology in the University of Iowa College of Public Health and director of the UI Lipid Research Clinic, is quoted as saying,
      "Cholesterol is needed for cell wall functioning and for the production of hormones, such as estrogen and testosterone..."
      [University of Iowa Health Clinics - "Health Reports"]

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