Naphthoquinones from the roots of Aloe secundiflora

Abstract

Two new naphthoquinones, 5-hydroxy-3,6-dimethoxy-2-methylnaphthalene-1,4-dione and 5,8-dihydroxy-3-methoxy-2-methylnaphthalene-1,4-dione, were isolated from the roots of Aloe secundiflora together with the known compounds chrysophanol, helminthosporin, isoxanthorin, ancistroquinone C, aloesaponarins I and II, aloesaponols I and II, laccaic acid d methyl ester and asphodelin. The structures were elucidated based on spectroscopic evidence. This appears to be the first report on the occurrence of naphthoquinones in the genus Aloe. Aloesaponarin I and 5-hydroxy-3,6-dimethoxy-2-methylnaphthalene-1,4-dione showed anti-bacterial activity against Mycobacterium tuberculosis with MIC values of 21–23 μg/mL in the Microplate Alamar Blue Assay (MABA) and Low Oxygen Recovery Assay (LORA); 5-hydroxy-3,6-dimethoxy 2-methylnaphthalene-1,4-dione also showed cytotoxicity against the Vero cell line (IC50 = 10.2 μg/mL). Graphical abstract Two new naphthoquinones which include 5-hydroxy-3,6-dimethoxy-2-methylnaphthalene-1,4-dione (1) were isolated from the roots of Aloe secundiflora. Compound 1 and aloesaponarin I showed antibacterial activity against Mycobacterium tuberculosis....................... Image for unlabelled figure Highlights ► Two new naphthoquinones were isolated from the roots of Aloe secundiflora. ► This is the first report on the occurrence of naphthoquinones in the genus Aloe. ► Antibacterial activity of selected metabolites against Mycobacterium tuberculosis is described. Keywords Aloe secundiflora; Asphodelaceae; Roots; Naphthoquinone; 5-Hydroxy-3,6-dimethoxy-2-methylnaphthalene-1,4-dione; 5,8-Dihydroxy-3-methoxy-2-methylnaphthalene-1,4-dione; Anthraquinone; Aloesaponarin I; Mycobacterium tuberculosis