An appropriate protecting group for the hydroxyl functional group in organic synthesis of a compound containing both a hydroxyl group and a carboxylic acid group is the tert-butyldimethylsilyl TBS group. The TBS group can be selectively introduced to the hydroxyl group using tert-butyldimethylsilyl chloride TBSCl and a base like imidazole or pyridine.The TBS group can be selectively removed without affecting the carboxylic acid group by using mild acidic conditions. One common method for selective removal is using tetrabutylammonium fluoride TBAF in a polar aprotic solvent like THF. This method cleaves the TBS group from the hydroxyl group without affecting the carboxylic acid group. Another option is to use hydrofluoric acid HF in pyridine, which also selectively removes the TBS group without affecting the carboxylic acid group.