Structural elucidation of two unique antimicrobial Cassane – type tricyclic diterpenes from the root of CALLIANDRA PORTORICENSIS (JACQ)-BENTH (FABACEAE).

Abstract

The burden of infectious diseases by bacteria and fungi had constituted a great concern to the entire human population. Calliandra portoricensis (Fabaceae) had been widely used over the years in ethnomedicine for the; treatment of various ailments such as swollen gum, tooth and throat inflammation often associated with microbial infections. At present, no active antimicrobial compound has been reported from this specie. The aim of this research was to identify, isolate and characterize the antimicrobial compounds from the root of C. portoricensis. The pulverized root sample (0.8 Kg) was extracted by successive cold maceration respectively for 72 hr. The most bioactive ethyl acetate extract (4.61 gm) was subjected to chromatographic column fractionation (Silica Gel G, 200-400 mesh-stationary phase). Gradient mixtures of n-hexane: ethyl acetate: methanol (4:0:0; 3:1:0; 2:2:0; 1:3:0; 0:1:0; 0:3:1; 0:2:2; 0:1:3; 0:0:4; – v/v/v) were used for elution. Agar well diffusion method was adopted for the bioassays susceptibility tests and MIC determinations. Clinically viable human pathogens for the tests were; Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Klebsiella pneumonia, Streptococus fecalis, Candida albicans and Aspergillus niger. Two major fractions (F_A and F_B) active against the test organisms were pooled the most active fraction F_B on further purification by preparative TLC (Silica Gel G, 0.5 mm thickness), yielded bioactive pure commands C₁ (9 mg) and C₂ (8 mg). Both compounds exhibited MIC values of 125.00±0.70 µg per milliliter  against Candida albicans and Aspergillus niger These activities were found to be quite significant with respect to the reference controls (Ciprofloxacin and fluconazole) at P < 0.05. Characterization of C₁ and C₂ by spectroscopic analysis (UV, MS, FT – IR and NMR), identified two novel compounds as Cassane - type tricyclic diterpenoids. C₁ (Molecular Mass: 340, C₂₀ H₃₆ O₄) is (5,10- 8,9- 12,13)-seco_- 4,4,10 – trimethyl, 7 – hydroxy, 14 – hydroxymethyl, 16 – keto, 13(15) – ene – cassane furanoditerpene and compound C₂ (Molecular Mass: 418, C₂₄ H₃₄ O₆) is (12,13)- seco_- 12, 14 – epoxy, 12(16) -Oxo – 16(17), 13(15) – diene, 4, 10, 17 – trimethyl, 4, 7 – di – aceto cassanoate The Cassane - type diterpenoids have been reported for promising antimicrobial properties.