Collective synthesis of kauralexins, maize phytoalexins isolated from Zea mays , and their putative biosynthetic intermediates

We herein report the collective synthesis of all known kauralexins (A1-A4 and B1-B4) and their putative biosynthetic intermediates isolated from Zea mays via a practical and scalable route. Our synthetic approach enabled stereoselective construction of key intermediates, clarified the stereochemical relationship between kauralexin A4 and annoglabasin E, and provided the first complete NMR spectroscopic data for kauralexins. Furthermore, we developed an efficient method for the selective synthesis of ent-isokaurene derivatives, facilitating the preparation of various oxidation products implicated in kauralexin biosynthesis. Our synthetic ent-kaurane library serves as valuable tools for biochemical investigations aimed at elucidating enzymatic functions involved in diterpenoid metabolism.