Antimicrobial evaluation of clerodane diterpenes from Polyalthia longifolia var. pendula

Phytochemical investigation of the ethanolic extract of leaves of Polyalthia longifolia var. pendula has led to the isolation of seven clerodane diterpenoids and five alkaloids. (-)-14, 15-bisnor-3, 11E-kolavadien-13-one (1), (-)-16-oxocleroda-3,13(14)E-dien-15-oic acid (2), (-)-16alpha-hydroxycleroda-3,13 (14)Z-dien-15,16-olide (3), (+)-(4-->2)-abeo-16(R/S)-2, 13Z-kolavadien-15, 16-olide-3-al (4), (-)-3beta, 16beta-dihydroxycleroda-4(18), 13(14)Z-dien-15,16-olide (5), (-)-3, 12E-kolavadien-15-oic acid-16-al (6), (-)-labd-13E-en-8-ol-15-oic acid (7), liriodenine (8), (-)-anonaine (9), (+)-isoboldine (10), (-)-asimilobine (11) and hordenine (12) have been isolated. This is the first report of 1, 6 and 10 from this plant species while 12 is reported for first time from this genus. Clerodane derivatives 1-7 were evaluated for their antimicrobial activity. Diterpene 3 was found to be most potent agent with MIC value of 6.25 microg/mL against Staphylococcus aureus and Sporothrix schenckii.