Chemoenzymatic Total Synthesis of Lansai B

Lansai B is an indole alkaloid whose biosynthesis is not yet elucidated. However, utilizing nature's tools enabled the stereoselective formation of this unique framework, first by providing the substituted tryptophan as starting material and later in the scaffold-building step forming the pyrroloindole motif. For the latter, the C3-methyltransferase from Streptomyces griseoviridis (SgMT) is employed for the diastereoselective methylation. Investigating the scope of the enzyme proved that introducing a bromide in the 5-position was ideal for the synthetic endeavor. With this, the stage was set for the synthesis of lansai B, introducing the prenyl group late via a Suzuki coupling.