Researches have shown that cleavage of the β-lactone ring results in loss of inhibitory activity of the inhibitors, which makes the β-lactone structure a crucial part in biological activity.[1][2] The lactone ring structure binds irreversibly to the active site of the lipase and forms covalent bond, which leads to inhibition.[32] Most natural lipase inhibitors differ only in the structure of the side chains and the nature of the linked amino acids, but have the same β-lactone ring[5] in (S)-configuration as a primary structure.[4] Besides the role of the β-lactone ring in structure-activity relationship, the nature of the functional groups (e.g. ester or ether and the chain length at the β-site) also matter.[5] However a trans-position of the side-chains on the β-lactone ring is crucial for its activity.[33]