Cysteine selective tritylation

Scheme 7 Selective deprotection of the trityl group for farnesylation under acidic conditions and subsequent deprotection of the second cysteine under reductive conditions.

The selective removal of the S-benzoyl group in the presence of other S-protected cysteine residues was studied by Zervas et al. [88] who prepared the insulin fragment, (66). The S-benzoyl groups were removed with 0.55N-sodium methoxide in methanol-DMF. In a related study [89] the S-benzoyl group was removed in the presence of the S-benzhydryl and S-trityl groups (18c, d). 

---