Thioester

A thioester contains the linkage $\mathrm{R}-\mathrm{C}(=\mathrm{O})-\mathrm{S}-{\mathrm{R}}^{\prime }$, in which sulfur replaces the single-bonded oxygen of an ordinary ester. It is an acyl group joined to a sulfur-containing substituent; it is not the same structural class as a compound with a C=S double bond.

Coenzyme A carries acyl groups through a thioester linkage. Nucleophilic attack at the carbonyl carbon can transfer the acyl group, coupling chemical transformations through an activated carrier. The familiar usefulness of this linkage concerns the free-energy change of the overall transfer or hydrolysis reaction, rather than an isolated “high-energy bond” acting as a store of released energy when simply broken.