From the aqueous acetone extract of burweed fruit, a new thiazinedione and four known phenolic compounds were isolated. The phenolics were identified as caffeic acid, potassium 2-O-caffeoyl quinate, 1,4-di-O-caffeoylquinic acid and 1,2,4-tri-O-caffeoylquinic acid. Based on 1D-NMR experiments and X-ray analysis, the thiazinedione was determined to be 6-hydroxymethyl-7,7-dimethyl-3,7-dihydrobenzo[1,3]thiazine-2,4-dione and named xanthiazone. © 1987 Elsevier Science Ltd. All rights reserved