Total synthesis of rosette inhibitor IOR allows its functional analysis and evaluation of sulfonolipid-based chemical probes

The predatory choanoflagellate Salpingoeca rosetta has emerged as important model systems to study the evolution of multicellularity and chemical origin of bacterial-eukaryote communication mechanisms. In this study we elaborated on the function and possible proteogenic binding partners of the bacterial sulfonolipid IOR-1A, which serves as bacterial inhibitor of rosette formation in S. rosetta. To study the function of IOR-1A, a new, modular and scalable total synthesis of IOR-1A (six steps, 30% overall yield) was developed, which features a decarboxylative cross-coupling reaction of a desymmetrized tartaric acid derivative carrying a protected sulfonic acid moiety with an alkyl zink reagents of choice. Synthesis of twelve IOR derivates, including fluorescent and photoaffinity-based probes, allowed to determine the abundance of IOR-1A, evaluation of structure-activity relations, localization studies within S. rosetta and de novo chemical proteomic identification of IOR-binding proteins in bacteria and S. rosetta. The combined results will catalyse future studies aiming at deciphering the biochemical basis of cell differentiation processes within rosette formation of S. rosetta.