Theoretical study of the rearrangement reaction in bisorbicillinoid biosynthesis: insights into the molecular mechanisms involved.

Bisorbibutenolide and bisorbicillinolide are polyketide compounds with complex skeletons that are formed by the dimerization of sorbicillin. These compounds have long been of interest, with several reports of their biosynthesis, biological activity, and total synthesis. In this study, we theoretically investigated the detailed biosynthetic mechanism of the rearrangement reaction to form bisorbicillinolide. We showed that the presence of water molecules facilitates the intramolecular aldol reaction, determined the rate-limiting steps, and revealed that a cyclopropane intermediate is formed during the rearrangement process. Although computational chemistry has been widely applied to the carbocation chemistry present in terpene biosynthesis, it has seldom been used to investigate the carbonyl chemistry responsible for polyketide biosynthesis. This study shows that computational chemistry is a useful tool for studying anionic skeletal rearrangement reactions.