Electronic Supplementary Information Synthesis of chromenoindole derivatives from Robinia pseudoacacia Lisa Dejon, Hamdoon Mohammed, Peng Du, Claus Jacob and Andreas Speicher* Experimental section (1) Isolation of compound 1 from the root of Robinia pseudoacacia Roots of Robinia pseudoacacia (typically 3.0 kg per batch) were collected freshly from trees found in the Botanical Garden of Al-Azhar University, Nasr City, Cairo, Egypt. They were cleaned and air dried for 1-2 weeks, and subsequently grinded down manually. The powder (usually around 850.0 g) was extracted 5 times with 4 L of 70 % ethanol. The ethanolic extracts were combined and the solvent was removed at 40°C under vacuum to dryness. 95.0 g of ethanolic extract were obtained from 3.0 kg of wet root material. The extract was re-dissolved in H 2 O and the insoluble material was removed by filtration. The water-soluble fraction (62.0 g) was then washed three times with petroleum ether to remove any fatty acids and subsequently extracted three times with ethyl acetate and then with n-butanol, respectively. The solvent was removed at 40°C under vacuum to yield 5.0 g of ethyl acetate extract and 8.5 g of n-butanol extract. These extracts were dissolved in methanol, combined and applied to silica gel chromatography (CH 2 Cl 2 :CH 3 OH, 80:20) to yield five fractions, of which three contained material in excess of 100.0 mg. These fractions were purified further individually by Sephadex LH-20 chromatography (using methanol as running solvent), ultimately resulting in five chemically pure compounds. The latter were characterized by one- and two-dimensional 1 H- and 13 C-NMR and mass spectrometry. Ultimately, these compounds were identif ied as one known dihydroflavone, 7,4’ -dihydroxy-dihydroflavone (a compound found in many plants 11 ), three chalcons, i.e. 2’-hydroxy-chalcone, 4,2’,4’ - trihydroxychalcone and 2’ -hydroxy-2,3-dimethoxy-chalcone, and the hitherto unknown compound 1. 1 1 M.J.C. Falcao, Y.B.M. Pouliquem, M.A.S. Lima, N.V. Gramosa, L.V. Costa-Lotufo, G.C.G. Militao, C. Pessoa, M.O. De Moraes, E.R. Silveira, J. Nat. Prod. 2005, 68, 423-426. Electronic Supplementary Material (ESI) for Medicinal Chemistry Communications This journal is © The Royal Society of Chemistry 2013