Constitution of Yohimbine

IT has been suggested by D. G. Harvey, E. J. Miller and W. Robson in a recent publication¹ on the colour reactions of tryptophan and allied compounds-among them the alkaloid yohimbine-that the formation of a blue colour in sulphuric acid containing a trace of oxidizing agent is characteristic of the 4-carboxytetrahydro-β-carbolines. The presence in yohimbine of both tetrahydro-β-carboline and carb-oxylic acid (actually carbomethoxyl) residues has been recognized for some time, and it is clear from the formation in good yields of 2: 3-dimethylbenzoic acid from ketodihydroyobyrine², and of harman and m-toluic acid from tetradehydroyohimbic acid³, that the carbomethoxyl must be attached to the yohimbine skeleton, which is as depicted, in ring E at position 16.