Antimicrobial napthoquinones from the roots of aloe secundiflora

Abstract

Two new naphthoquinones, 5 - hydroxy - 3,6 - dimethoxy - 2 - methylnaphthalene - 1,4 - dione ( 1 ) and 5,8 - dihydroxy - 3 - methoxy - 2 - methylnaphthalene - 1,4 - dione ( 2 ), were isolated from the roots of A. secundiflora together with the kn own 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 . 5 - Hydroxy - 3,6 - dimethoxy - 2 - methylnaphthalene - 1,4 - dione showed activity against Candida albicans and Microsporum gypseum with zones of inhibition of 16 and 10 mm respectively. At the same time, 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) ; with 5 - hydroxy - 3,6 - dimethoxy - 2 - methylnaphthalene - 1,4 - dione also showing cytotoxicity against the Vero cell - line (IC 50 = 10.2 μg/mL).