Myrtinols A–F: New Anti-Inflammatory Peltogynoid Flavonoid Derivatives from the Leaves of Australian Indigenous Plant Backhousia myrtifolia

Abstract

Our in-house ethnopharmacological knowledge directed our anti-inflammatory investigation into the leaves of Backhousia mytifolia. Bioassay guided isolation of the Australian indigenous plant Backhousia myrtifolia led to the isolation of six new rare peltogynoid derivatives named myrtinols A–F (1–6) along with three known compounds 4-O-methylcedrusin (7), 7-O-methylcedrusin (8) and 8-demethylsideroxylin (9). The chemical structures of all the compounds were elucidated by detailed spectroscopic data analysis, and absolute configuration was established using X-ray crystallography analysis. All compounds were evaluated for their anti-inflammatory activity by assessing the inhibition of nitric oxide (NO) production and tumor necrosis factor- α (TNF-α) in lipopolysaccharide (LPS) and interferon (IFN)-γ activated RAW 264.7 macrophages. A structure activity relationship was also established between compounds (1–6), noting promising anti-inflammatory potential by compounds 5 and 9 with an IC50 value of 8.51 ± 0.47 and 8.30 ± 0.96 µg/mL for NO inhibition and 17.21 ± 0.22 and 46.79 ± 5.87 µg/mL for TNF-α inhibition, respectively.

A Method and Formula for the Quantitative Analysis of the Total Bioactivity of Natural Products

“…Using already available purification yields and potency data from a previous structural identification study of anti-inflammatory compounds in Grey Myrtle [ 14 ], it was hypothesized that it is possible to quantify the overall bioactivity of a medicinal plant based on the individual potency of isolated compounds/fractions with certain bioactivity through a purification and isolation process, including sequential extraction and chromatographic separation. In most cases, for the investigation of the therapeutic potential of a medicinal plant and compound(s) of interest, the following two main questions are asked: What is the potency (EC 50 or EDV 50 ) value for the single solvent (ethanolic) extract or fraction?…”

“…B. myrtifolia leaves were subjected to either a single extraction with EtOH or sequential extractions with Hexane, DCM, EtOAc, EtOH, MeOH, and water. The anti-inflammatory potency of the extracts was determined in LPS- and IFN-γ-activated RAW 264.7 macrophages using NO production as a pro-inflammatory readout ( Table 1 ) [ 14 ].…”

“…In a second experimental calculation, it was determined how much of the total bioactivity from the sequential DCM extract was recovered after HPLC purification, where 17 different fractions were isolated [ 14 ]. In addition to the total bioactivity, the total yield of the sum of the fractions compared to the yield of the original TCM extract was also calculated to estimate how much material was lost during the HPLC purification process ( Table 3 ).…”

“…It has to be noted that a manuscript describing the structural identification of all the compounds of B. myrtifolia has been published in detail and that the methods below are only an excerpt of the methods described in the published journal article [ 14 ]. The leaves of B. myrtifolia were collected from the Australian Botanic Garden at Mount Annan (NSW, Australia).…”

“…The original data supporting the reported results are available in an original publication, which includes the structural identification of all active compounds [ 14 ].…”