New labdane-type diterpenoids from Leonotis leonurus support circumscription of Lamiaceae s.l.

“Wild cannabis”: A review of the traditional use and phytochemistry of Leonotis leonurus

“…However, repeated chromatography of an acetone extract of the same plant afforded Leonurenone C (3), 9,13:15,16-diepoxylabdane-6β,15α-diol (14), previously reported by Naidoo (2011) a year earlier, and nepetaefolin (4) ( Table 2 and figure 5) which was also found in Leonotis nepetifolia (He et al, 2012).…”

“…Von Dreele et al (1975) also proposed that the absolute configurations of Leonurenone A (1), and 9,13:15,16-diepoxylabdane-6β,15α-diol (epimeric mixture of (14)) were in agreement with the absolute configurations of other known labdanes given the concomitant occurrence of Leonurenone A (1), 9,13:15,16-diepoxylabdane-6β,15α-diol (epimeric mixture of (14)) and nepetaefolin (4) for which the crystal structure had been previously reported (Von Dreele et al,1975). El-Ansari et al (2009) and three known labdane diterpenoids namely, Leoleorin A (Compound Y) (10), Leoleorin B (11) and Leoleorin C (12) which had been reported earlier by Kaplan and Rivett (1968) and Naidoo (2011) (Table 2 and figure 4).…”

“…Phytochemical studies have revealed that terpenoids (mono-, sesqui-and diterpenoids), which are known to be biologically active (Demetzos and Dimas, 2001) are the main compounds found in the plant (Purushothaman and Vasanth, 1988;Pedro et al, 1991), with labdane diterpenes being the most abundant compounds extracted from the leaves (Cragg and Little, 1962;Rivett, 1964;Kaplan and Rivett, 1968;Laonigro et al, 1979;Kruger and Rivett, 1988;McKenzie et al, 2006;Obikeze et al, 2009;Naidoo et al, 2011). Wu et al, (2013) isolated three known labdane diterpenes, known as Leoleorins A (10), B (11) and C (12), and eight new labdane diterpenes, Leoleorins D-J (13-15, 17) and 16-epileoleorin (16) from leaf extracts of L. leonurus.…”

“…The presence of 9, 13:15,16-diepoxylabdane-6β,15α-diol (14), luteolin glycoside (22) and luteolin (21) in this species is known (El-Ansari et al, 2009;Naidoo et al, 2011).…”

“…However, the water extracts did not show antibacterial activity and Klebsiella pneumoniae which is commonly implicated in nosocomial infections was not responsive to leaf extracts. Naidoo et al, (2011) reported that aqueous and methanol/dichloromethane (1:1) extracts of L. leonurus leaves presented 90% growth inhibition when tested at a concentration of 1000 µg/mL against Mycobacterium tuberculosis with rifampicin used as positive control (2 µg/mL). Oyedeji et al, (2005) reported that the major essential oil components of L. leonurus were limonene (7.2-15.6%), β-ocimene (7.5-10.8%), γ-terpinene (4.0-4.7%), β-caryophyllene (15.2-19.6%), α-humulene (4.6-6.5%) and germacrene D (18.9-20.0%) and that the oils exhibited a broad spectrum antibacterial activity against Gram-positive (Bacillus subtilis, Bacillus cereus, Micrococcus kiristinae, Staphylococcus aureus, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Shigella sonnei) bacteria with MIC values ranging from 0.039 -1.25 mg/mL.…”