Antimicrobial activity of various parts of Polyalthia longifolia var. pendula: isolation of active principles from the leaves and the berries

Methanol extracts of leaves, stem, twigs, green berries, flowers, roots, root-wood and root-bark of Polyalthia longifolia var. pendula, were tested for their antibacterial and antifungal potentials. Bioassay monitored isolation work on the methanol extract of leaves and berries which possess promising antibacterial activity led to the isolation of seven clerodane diterpenoids, 16(R and S)-hydroxy-cleroda-3,13(14)Z-dien-15,16-olide (1), 16-oxo-cleroda-3,13(14)E-dien-15-oic acid (2), methyl-16-oxo-cleroda-3,13(14)E-dien-15-oate (3), 2-oxo-kolavenic acid (4), 16 (R and S)-hydroxy-cleroda-3,13(14)Z-dien-15,16-olide-2-one (5), (4-->2)-abeo-16(R and S)-hydroxy-cleroda-2,13(14)Z-dien-15,16-olide-3-al (6), 3beta,16alpha-dihydroxy-cleroda-4(18), 13(14)Z-dien-15,16-olide (7), while kolavenic acid (8) and solidagonal acid (9) were obtained from the root-wood. Diterpenoids 1 and 8 were also obtained from the root-bark. It is the first report of the isolation of 7 and 9 from this source, and clerodane 3 was obtained as a natural product for the first time. Clerodanes 1, 2, 5, 6 and 7 were found to be active antimicrobial agents with MIC values ranging between 7.8 and 500 microg/mL. Diterpenoid 1 emerged as the most active antimicrobial agent. The acetyl derivative (10) of 1 and the methyl derivative (3) of 2 were found to be less active than the parent compounds. A complex of allantoin was also obtained from the berries, which on hydrolysis furnished pure allantoin (11).