Dear Tao xu ,

Its very simple, take MTPA in any form(+)(-) and to that add 0.5eq of EDC - 1-ethyl-3(3-dimethylaminopropyl)carbodiimide and DMAP-dimethylaminopyridin (0.4eq) in DCM-dichloromethane  shake it and keep it for 15hrs, the perfect esterification will takes place.,

Another one very simple method also available,  MTPA with DMAP/Et3N with DCM keet it room temperature for 15hr,  for this type of compound the reaction will takes place very slow manner..,

you use either one method you will get result without any problem.,

Hope you may clear now.,

Good Luck & Regards

R.Selva.......

DMAP with Et3N in Dichloromethane for 15hours will give perfect result.,..

MTPA in any form(+)(-) and to that add 0.5eq of EDC - 1-ethyl-3(3-dimethylaminopropyl)carbodiimide and DMAP-dimethylaminopyridin (0.4eq) in DCM-dichloromethane  shake it and keep it for 15hrs, it will be perfect for you.,

and other method also most easy for your reaction, time should need to keep 15hrs it's very slow process

thank you for your answers

best regards

Consider Tom Hoye's  protocol on the subject.

See: Nature Protocols 2, 2451 - 2458 (2007)

Cheers.