Advices For Studying Organic Chemistry

Squalene

H 3 C

H 3 C

H 3 C

HO CH

3

CH 3

Lanosterol

CH 3

3

H H

H

Cholestero

1. Cholesterol is the biochemical precursor of cortisone, estradiol, and testosterone.
   
   
   1. Cholesterol is the parent of all of the steroid hormones and bile acids in the
   
   
   
   

squalene, consisting of a

linear polyalkene chain of 30 carbons.

3. From squalene, lanosterol, the first cyclic precursor, is created by a remarkable
   set of enzyme-catalyzed addition reactions and rearrangements that create four
   and seven stereocenters.

1. In theory, 2^7 (or 128) stereoisomers are possible.

4. Polyene Cyclization of Squalene to Lanosterol
   
   
   1. The sequence of transformations from squalene to lanosterol begins by the
      enzymatic oxidation of the 2,3-double bond of squalene to form
   
   
   
   

lkene addition reactions begin through a chair-boat-chair

conformation transition state.

i) Protonation of (3S)-2,3-oxidosqualene by squalene oxidocyclase gives the

oxygen a formal positive charge and converts it to a good leaving group.

H C

HO l

body.

2. The last acyclic precursor of cholesterol biosynthesis is

fused rings

(3S)-2,3-oxidosqualene [also called squalene 2,3-epoxide].

2) A cascade of a