New nitro-benzo[c]phenanthridine and indolopyridoquinazoline alkaloids from Zanthoxylum atchoum

Abstract

• Isolation and characterization of four new compounds: two benzophenanthridine and two indoloquinazoline alkaloids from Zanthoxylum atchoum . • First report of a nitro group on the biosynthesis of the natural benzo[ c ]phenantridine alkaloids. • Interesting analysis of deuterium exchange during the 1 H-NMR experiments. • Potent antibacterial activity for the new nitro-benzophenanthridine alkaloid. The first phytochemical investigation of the roots of Zanthoxylum atchoum has led to the isolation of two new nitro-benzo[ c ]phenanthridine alkaloids 6-nitronitidine ( 1 ) and 6-nitro-8-methoxy-7,8-dihydronitidine ( 2 ), two new salts of indolopyridoquinazoline alkaloids 3-hydroxy-8,13-dihydro-14-methyl-5-oxo-7 H -indolo[2’,3’:3,4]pyrido[2,1- b ]quinazolin-14-ium ( 3 ) and its zwitterionic form 3-phenolate-8,13-dihydro-14-methyl-5-oxo-7 H -indolo[2’,3’:3,4]pyrido[2,1- b ]quinazolin-14-ium ( 4 ) along with 18 ( 5 – 22 ) known compounds. Their chemical structures were elucidated by spectroscopic analysis including 1D and 2D NMR and MS techniques. This is the first report of the nitro group on the biosynthesis of the natural benzo[ c ]phenantridine alkaloids. Compound 2 exhibited potent antibacterial activity against Staphylococcus aureus of MIC 50 = 4 μg·mL −1 . La première étude phytochimique des racines de Zanthoxylum atchoum a conduit à l’isolement de deux nouveaux alcaloïdes nitro-benzo[ c ]phénanthridine, le 6-nitronitidine ( 1 ) et 6-nitro-8-méthoxy-7,8-dihydronitidine ( 2 ), de deux nouveaux sels d’indolopyridoquinazoline, le 3-hydroxy-8,13-dihydro-14-méthyl-5-oxo-7 H -indolo[2’,3’:3,4]pyrido[2,1- b ]quinazolin-14-ium ( 3 ), et sa forme zwittérionique, le 3-phénolate de 8,13-dihydro-14-méthyl-5-oxo-7 H -indolo [2’,3’:3,4]pyrido[2,1- b ]quinazolin-14-ium ( 4 ), et de 18 composés connus ( 5 – 22 ). Leurs structures chimiques ont été élucidées par analyse des techniques spectroscopiques 1D et 2D-RMN et SM. C’est le premier rapport d’un groupement nitro dans la biosynthèse de benzo[ c ] phénantridines naturelles. Le composé ( 2 ) montre une puissante activité antibactérienne contre Staphylococcus aureus , avec une CMI50 = 4 μg·mL −1 .