In chemistry, a mesylate is any salt or ester of methanesulfonic acid (CH3SO3H). In salts, the mesylate is present as the CH3SO3− anion. When modifying the International Nonproprietary Name of a pharmaceutical substance containing the group or anion, the correct spelling is mesilate (as in imatinib mesilate, the mesylate salt of imatinib).
Mesylate esters are a group of organic compounds that share a common functional group with the general structure CH3SO2O-R , abbreviated MsO-R, where R is an organic substituent. Mesylate is considered an excellent leaving group in nucleophilic substitution reactions.
Mesyl is the term for the methanesulfonyl or CH3SO2- (Ms-) functional group. For example, methanesulfonyl chloride is often referred to as mesyl chloride.
Mesylates may be prepared using an alcohol and methanesulfonyl chloride in the presence of a base, often amine bases such as triethylamine. Mesylates can also be prepared by combining an alcohol, methanesulfonic anhydride and base, although this method is generally used only if the nucleophilicity of chloride is a concern.