zolinone alkaloid tryptanthrin (indolo[2,1-b]quinazoline-6,12dione, 2) (Figure 1). Isolation of wrightiadione from W. tomentosa and its structure determination by NMR spectroscopy and X-ray crystallography, as well as a finding of cytotoxic activity against leukemia cells, were first reported in 1992. 14 More recently, wrightiadione has been reported in extracts of W. pubescens 11 and W. religiosa (Teijsm. & Binn.) Benth. Ex Kurz 15 with identification by spectroscopic data interpretation.Tryptanthrin (2) has been known for more than 100 years, 16−18 although it was first isolated from plant sources more recently. 19−23 Structure elucidation by X-ray crystallography in combination with other methods including NMR spectroscopy has been reported, 24−26
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