New bioactive compounds from Aloe hijazensis

Abstract

The chemical constituents and biological activities of leaves and roots of Aloe hijazensis, collected in Saudi Arabia, are reported here for the first time. Twenty-two compounds were obtained, among them eight hydroxyquinones: aloe-emodin (1), emodin (2), chrysophanol (3), aloesaponarin II 3-methyl ether (4), ziganein (5), ziganein-5-methyl ether (6a), aloesaponarin I (7) and chrysophanein (8), the dihydro-isocoumarin feralolide (9), 4,7-dichloro-quinoline (10), the triterpene lupeol (11), the anthrone aloin (12), three aloenin derivatives, aloenin (13) ethylidene-aloenin (14), and aloenin B (15), four flavonoids, quercetin (16), kaempferol (17) cosmosiin (18) and isovitexin (19), and cinnamic acid (20) and two further analogues, caffeic acid (21) and ferulic acid (22). While 15 of the isolated compounds were found in the leaves, 12 were isolated from roots of the plant. Compounds 6a and 10 are reported as new natural constituents, while the compounds 4, 5, 8, and 18 are reported here for the first time from Aloe spp. The structures of the compounds were deduced by intensive studies of their UV, NMR, MS data and by comparison with related structures. The biological activity of plant extracts was studied against various microbial strains, and potent anti-bacterial and anti-fungal activities were found.

Keywords:

• Aloe hijazensis
• dichloroquinoline
• potent anti-microbial extracts
• anthraquinones

Acknowledgements

The authors are thankful for Dr M.M. El-Safty, Central Laboratory for Veterinary Biologics (CLEVB), Cairo for evaluation of anti-microbial activities. We thank Dr H. Frauendorf and Mr R. Machinek for MS and NMR measurements.