Try chiral columns instead of derivatization.

Chiral Seperation with derivatization are difficult. Try with chiral column by developing the chiral HPLC methods. Seperate the chiral compounds by SFC (Supercritical fluid chromatography).

thank you very much sir for your kind suggestions

Four chiral centers will potentially give 8 individual compounds. Separation won't be easy, perhaps some sort of stereoselective synthesis will help to reduce the number of enantiomers/diastereomers. Or you can start from some precursor where at least several chiral centers have fixed configuration.

With SFC choral separation can be done but not single time and that depends upon the method development of the mixture. Suppose if they have 4 recemic mixture that have to separate twise or three times. First time they can separate two pair of enantiomers then each separated pair again they have to separate the R and S. Single time is never possible.