Effect of Chaetochromin A, Chaetochromin D and Ustilaginoidin A, Bis (naphtho‐γ‐pyrone) Derivatives, on the Mouse Embryo Limb Bud and Midbrain Cells in Culture

Mouse embryo limb bud (LB) and midbrain (MB) cells were prepared from day 10 mouse embryos and cultured as micromass cell islands for 5 days. Differentiation was determined by the number of stainable foci of differentiated cells, and the concentration at which each compound inhibited the formation of differentiated foci by 50% of the control value (IC 50 ) was estimated according to the method by Flint and Orton (1984). The values of IC 50 of L‐dopa, which is known as a teratogen, were 24 μig/ml in LB cultures and 12 μ/ml in MB cultures, respectively. Teratogenic hazards of three mycotoxins were compared in this system. Chaetochromin A and chaetochromin D, which were new naphtho‐γ‐pyrone dimers produced by Chaetomium sp ., indicated strong inhibition (IC 50 0.13‐0.24 μ/ml) in LB and MB cell cultures, and ustilaginoidin A, which was a naphtho‐γ‐pyrone dimer produced by Ustilaginoidea virens , inhibited at higher concentration than chaetochromins by several‐folds in LB and MB cultures.