What is "mesylate"

n. (context organic chemistry English) methanesulfonate

In chemistry, a mesylate is any salt or ester of methanesulfonic acid (CHSOH). In salts, the mesylate is present as the CHSO 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 CHSOO–R, abbreviated MsO–R, where R is an organic substituent. Mesylate is considered a leaving group in nucleophilic substitution reactions.