The structures of xenorine A–C from the entomopathogenic bacterium Xenorhabdus indica

Three new compounds, xenorine A-C, along with six known compounds were isolated from the cultured broth of Xenorhabdus indica. The chemical structures of these compounds were elucidated mainly by analysis of 1D and 2D NMR and MS data. The major metabolites were dioxopiperazines. In addition, 5,6,11,11a-tetrahydro-1H-imidazo[1′,5′:1,6]pyrido[3,4-b]indole-1,3(2H)-dione, previously described as synthetic product, was isolated as a natural product. The absolute configuration was determined using quantum chemical time-dependent density functional theory calculations. The six known compounds showed weak in vitro immunosuppressive activity towards concanavalin-A- and lipopolysaccharide -induced proliferation of mice splenocytes.