Introduction To Tos

Tosyl (Tos) is a relatively stable amino protecting group, which is stable to alkaline hydrolysis and catalytic reduction. In addition to being used as a protecting group for α-amino in the early days, Tos is generally used as a side chain protecting group for basic amino acids.

Introduction of Tos

Tos can be introduced by toluenesulfonyl chloride in the presence of NaOH, NaHCO₃ or other organic bases.

Removal of Tos

Tos can withstand various conditions such as general acid hydrolysis (TFA and HCl, etc.), saponification, and catalytic hydrogenolysis. It is commonly removed by treatment with Na/naphthalene, Na/NH₃ (liquid) and Li/NH₃ (liquid). HBr/phenol and Mg/MeOH are also relatively good methods for removing Tos. It is worth noting that the operation of Na/NH₃ (liquid) is more troublesome and will cause some peptide bond breakage and peptide chain damage. In addition, the Tos group can sometimes be removed under HF/MeCN reflux conditions.

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