Trifluoroacetic acid → 5-(S)-Acetamidomethyl-3-[4'-triphenylmethylthio-3'-fluorophenyl]oxazolidine-2-one

BAL resin immobilized 5-(S)-Aminomethyl-3-[4′-triphenylmethylthio-3′-fluorophenyl]-oxazolidine-2-one (5.00 g, 2.05 mmol) was suspended in 5% trifluoroacetic acid and 2.5% triisopropylsilane in dichloromethane (50 mL), and the mixture was agitated for 1 h. The resin was filtered and the procedure repeated with fresh 5% trifluoroacetic acid and 2.5% triisopropylsilane in dichloromethane (50 mL) for another 30 minutes. The resin was filtered and washed liberally with dichloromethane. Resulted thiol resin was immediately suspended in a mixture of acetic anhydride (20 mL) and pyridine (30 mL) in DCM (50 mL), and the mixture was agitated overnight at r.t. The resin was filtered, washed liberally with dichloromethane and dried under vacuum.