<jats:p> Analysis by <jats:sup>1</jats:sup>H and <jats:sup>13</jats:sup>C nmr spectrometry showed that caerulomycin D, a new metabolite isolated from S. caeruleus, possessed a novel ring system and had the structure (2S,3R,4R,4aS,10aS)-3,4,4a,10a-tetrahydro-4-hydroxy-3,4a-diniethoxy-2-methyl-9-(2-pyridyl)-2H-pyrano[3′,2′:5,6]-p-dioxino[2,3-c]pyridine-7-carboxaldenyde (E)-oxime.