Kinetic resolution of a racemic mixture rests upon chiral discrimination of enantiomers. Each enantiomer is transformed into a product at a different rate. The theoretical yield is then 50% of the product (P) and the unreacted substrate (S).

1. Desymmetrization

   In desymmetrization process , a prochiral mesosubstrate is preferentially transformed into one enantiomers of the product. In the ideal case the yield of the product may be 100 %.

   

2. Deracemization
   
   Racemic mixture is defined as equal amounts of enantiomers of a chiral molecule. In this process racemic substrate is transformed into one enantiomer of the product.

Kinetics

Some functional groups on enzymes such as carboxylic COO- group can act as Bronsted base. Some acidic functional groups are also proton donors. Proton bounded to one of the functional groups result in most active enzyme form. The addition or removal of proton to a critical functional group redistributes the charge on the active site and affects its binding with the substrate. Accordingly the rate of enzymatic reaction is strong function of pH.

Most enzymes follow the kinetics proposed by Michaelis and Menten. Enzyme (E) and substrate (S) first form an enzyme-substrate complex (ES), called the Michaelis-Menten complex. The complex can then either dissociate back to substrate or cross the reaction energy barrier to form enzyme and product (P).

The Michaelis-Menten equation gives the rate of formation of products as :

Where C_S is the concentration of substrate and C_EO is the initial concentration of enzyme.

K_m is known as Michaelis constant. The rate law is derived from following basic assumptions:

1. The first step of binding of substrate to enzyme is faster compared to second step of dissociation of enzyme-substrate complex [ES] to products. Hence 2^nd step is the rate determining step.
   
   
2. At initial stages of reaction, concentration of product is assumed to be zero.
   
   
3. At steady state, the concentration of the intermediate ES is constant.

Rate of formation of product P is given as

.....................(1)

At initial stage of reaction, concentration of product,

Hence,

.......................(2)

Now at steady state condition,

Rate of formation of [ES] = Rate of breakdown of [ES]

Substituting

Or ......................(3) where

The ratio of rate constants, K_m is known as Michaelis constant.

Substituting concentration C_ES from equation (3) in equation (2), rate expression is obtained as

...........................(4)

The total concentration of enzyme is summation of concentration of free enzyme C_E and concentration of enzyme bound to substrate C_ES. Hence total concentration of enzyme C_E0 is given as

Substituting value of C_ES from equation (3) we obtain

       

Or

Substituting C_E in equation (4)

Or

The rate expression is often referred as Michaelis-Menten rate law. This is valid for many enzyme reactions at constant pH.