Minor bioactive indoles from kimchi mirror the regioselectivity in indole-3-carbinol oligomerization

Kimchi is a globally consumed food with diverse health-benefits, but the low-abundance bioactive compounds in kimchi remain largely neglected. Here we show that kimchi contains a family of low-abundance (0.5–1.6 μg/g, dried weight) high-order indole oligomers derived from indole-3-carbinol (I3C), a breakdown product released from cruciferous vegetables used for producing the traditional subsidiary food. The structure determination of such complex molecules was accomplished by synthesizing linear indole oligomers as standard materials followed by the LC–HR–MS analysis. One indole tetramer (LTe2) is substantially toxic to tumor MV4-11 (IC 50  = 1.94 μM) and THP-1 cells (IC 50  = 7.12 μM). Collectively, the work adds valuable information to the knowledge package about kimchi, and may inspire the generation of indole-based molecules, to which many drugs belong.