Protection for the Thiol Group

Protection for the thiol group is important in many areas of organic research, particularly in peptide and protein syntheses that often involve the amino acid cysteine. Thiols are also more nucleophilic than alcohols, especially in basic solution. Thioethers are in general formed by reaction of the thiol, in a basic solution, with a halide. Much of the chemistry used for the protection of a thiol can also be used for the protection of the selenol group, which is not nearly as common in organic synthesis, but is important in connection with selenocysteine. This chapter presents reaction steps for forming S-p-methoxybenzyl thioether, s-alkyl thioethers, S-2,4,6-trimethoxybenzyl thioether (Tmob–SR), sulfenyl derivatives, s–p derivatives and s-acetyl derivatives.