Q54. - Organic Chemistry

Question

Question: Clopidogrel is the generic name for Plavix, a drug used to prevent the formation of blood clots in patients that have a history of heart attacks or strokes. A single enantiomer of clopidogrel can be prepared in three steps from the chiral α-hydroxy acid A. Identify B and C in the following reaction sequence, and designate the configuration of the enantiomer formed by this route as R or S

Step-by-Step Solution

Answer

Answer

 

Compound B

Compound C

The configuration at the chiral carbon of clopidogrel is S

 

Step 1: TsCl - Pyridine reagent

TsCl stands for 4-toluenesulfonyl chloride, a toluene derivative containing sulfonyl chloride.

 

Alcohols when treated with TsCl in the presence of pyridine (a weak base) results in the formation of sulfonate esters.

 

Pyridine is used to use up any HCl formed during the reaction process.  

Step 2: Identification of compounds B and C

• Compound A reacts with methanol in the presence of sulfuric acid to give compound B.

     

           Conversion of compound A to compound B

 

• Compound B reacts with TsCl in the presence of pyridine to give compound C.

     

                      Conversion of compound B to compound C

  

• Compound C reacts with secondary amines to form the desired product, Clopidogrel and the configuration at the chiral carbon of clopidogrel is S (here, the inversion of the configuration takes place).

     

                 Conversion of compound C to clopidogrel