Enzymatic acylation: assessing the greenness of different acyl donors

The hydrolase-catalyzed esterification of alcohols is the best established enzymatic transformation in today's organic chemistry, along with the corresponding ester hydrolysis. Over the years, various different acyl donors have been proposed to overcome the major limitation of the condensation of an alcohol and an acid, the unfavourable equilibrium. This review aims at screening the actual number of applications of the different acyl donors, and at assessing the greenness (or lack thereof) of the most applied among them. Indeed, the use of an enzyme to catalyze an esterification is often regarded as sufficient to define the whole transformation as green. However, this definition can easily be misinterpreted if the contribution of the acyl donor to the overall process is overlooked, as is often the case. Aiming at filling this gap, this contribution evaluates the advantages and disadvantages of the acyl donors, and assesses their green credentials using an efficient tool in strategic planning, a strengths-weaknesses-opportunities-threats (SWOT) analysis. A calculation of the atom economy and E-factor for representative acylations involving each donor is included, as well as an analysis of the adherence of each process to the twelve principles of Green Chemistry.