Novel Antimicrobial Diterpenoids from Turraeanthus africanus

Abstract

The dichloromethane-methanol (1/1) extract of the stem bark of Turraeanthus africanus (Meliaceae) showed remarkable antimicrobial activity against Cryptococcus neoformans, Staphylococcus aureus and methicillin-resistant S. aureus. Phytochemical investigation of this extract afforded six new diterpenoid derivatives, (+)-16-acetoxy-12,15-epoxylabda-8(17),12,14-triene (3), [16(E),12S,15R]-16-acetoxy-12,15-epoxy-15-isopropoxy-ent-labda-8(17),13(16)-diene (turraeanin A, 4), [16(E),12R,15S]-16-acetoxy-12,15-epoxy-15-isopropoxy-ent-labda-8(17),13(16)-diene (turraeanin B, 5), [16(E),12S,15R]-16-acetoxy-12,15-epoxy-15-methoxy-ent-labda-8(17),13(16)-diene (turraeanin C, 6), [16(E),12R,15S]-16-acetoxy-12,15-epoxy-15-methoxy-ent-labda-8(17),13(16)-diene (turraeanin D, 7) and (12S,13S,15R)-12,15-epoxy-15-methoxy-ent-labd-8(17)-en-16-al (turraeanin E, 9) together with the known compounds, 15,16-epoxy-ent-labda-8(17),13(16),14-triene (1), (+)-pumiloxide (2), ent-labda-8(17),12 (E)-diene-15,16-dial (8) and 16-acetoxy-12(R),15-epoxy-15β-hydroxylabda-8(17),13 (16)-diene (10). Compound 10 was obtained as its acetoxy derivative (10a) and compound 11 was the product of hydrolysis of 6. Antimicrobial activity of the isolates was assayed and compounds 8, 9, 10a and 11 exhibited significant activities.

Key words

Turraeanthus africanus - Meliaceae - antimicrobial activity - diterpenes - labdanes - turraeanin

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