Antibacterial and antioxidant activities of flavonoids from Lannea alata (Engl.) Engl. (Anacardiaceae)

Two new prenylated flavonoids, lanneaflavonol (1) and dihydrolanneaflavonol (2) together with the known compounds myricetin-3-O-alpha-rhamnopyranoside (myricitrin) (3) and myricetin-3-O-alpha-arabinofuranoside (betmidin) (4), lupeol (5) and sitosterol (6) were isolated from the roots of Lannea alata. Compounds 1-4 exhibited good antibacterial and radical scavenging activity with the glycosides 3 and 4 showing better antioxidant activity than the aglycones 1 and 2 and myricetin-3-O-alpha-arabinofuranoside (4) showing the best antimicrobial activity followed by the aglycones 1 and 2. Betmidin (4) with an arabinose moiety at the 3-O-position showed the best antibacterial activity against Gram-positive bacteria, followed by the prenylated dihydroflavonol (2), whilst the prenylated linear flavonol (1) showed limited activity against Gram-negative bacteria. The arabinofuranoside (4) followed by the rhamnopyranoside (3) showed the best antioxidant activity comparable to that of ascorbic acid. The biological activities justify the ethnomedicinal uses of the plant in the management of diseases associated with Gram-positive bacteria, such as being used to treat injuries and wounds. (C) 2013 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.