Crystal structure of tryptanthrin (indolo[2,1-b]quinazoline-6,12-dione)

The structure of tryptanthrin, an antibiotic produced by the yeast Candida lipolytica has been determined by X-ray crystallographic analysis. The structure has been solved by direct methods and refined by block-diagonal least-squares to R 0·089 using 1207 independent reflections. The crystals are monoclinic, space group P21/c, with a= 7·46, b= 7·66, c= 20·78 Å; β= 109·0°, Z= 4. Tryptanthrin has thus been proved to be indolo[2,1-b]-quinazoline-6,12-dione: the structural features are consonant with the spectroscopic behaviour.