Structural Diversification of Pyrazinone Metabolites via Spontaneous Oxa-Michael Addition in <i>Staphylococcus xylosus</i>

A family of pyrazinone metabolites (1–11) were characterized from Staphylococcus xylosus ATCC 29971. Six of them were hydroxylated or methoxylated, which were proposed to be produced by the rare noncatalytic oxa-Michael addition reaction with a water or methanol molecule. It was confirmed that isopropyl alcohol can also be the Michael donor of the reaction. 1–7 and the synthetic precursor 2a showed significant inhibition of breast cancer cell migration.