Microwave-Assisted Extraction and HPLC-UV-CD Determination of (S)-usnic Acid in Cladonia foliacea

Abstract

During the years, many usnic acid (UA) conjugates have been synthesized to obtain potent endowed with biological properties. Since (S)-UA is less abundant in nature than (R)-enantiomer, it is difficult to source, thus precluding a deeper investigation. Among the lichens producing UA, Cladonia foliacea is a valuable (S)-UA source. In the present work, we report on a rapid HPLC-UV/PAD-CD protocol suitable for the analysis and the identification of the main secondary metabolites present in C. foliacea extract. Best results were achieved using XBridge Phenyl column and acetonitrile and water, which were both added with formic acid as mobile phase in gradient elution. By combining analytical, spectroscopical, and chiroptical analysis, the most abundant analyte was unambiguously identified as (S)-UA. Accordingly, a versatile microwave-assisted extractive (MAE) protocol, assisted by a design of experiment (DoE), to quantitatively recover (S)-UA was set up. The best result in terms of UA extraction yield was obtained using ethanol and heating at 80 °C under microwave irradiation for 5 min. Starting from 100 g of dried C. foliacea, 420 mg of (S)-UA were achieved. Thus, our extraction method resulted in a suitable protocol to produce (S)-UA from C. foliacea for biological and pharmaceutical investigation or commercial purposes.

Methodological Aspects of Green Extraction of Usnic Acid Using Natural Deep Eutectic Solvents

“…Usnic acid (UA) is a phenolic compound with a dibenzofuran structure occurring in the form of two enantiomers ( Figure 1 ) [ 1 ] in several lichen genera ( Alectoria , Cladonia , Evernia , Lecanora , Parmelia , Ramalina , Usnea , and Xanthoparmelia ) as a yellow cortical pigment [ 2 , 3 , 4 , 5 , 6 ]. Nowadays, it is the most extensively investigated lichen secondary metabolite.…”

Chiral 2‐phenyl‐3‐hydroxypropyl esters as PKC‐alpha modulators: HPLC enantioseparation, NMR absolute configuration assignment, and molecular docking studies

“…Velocity representations were used to simulate the ECD spectra. The calculated ECD spectra were the result of a weighted average of the calculated ECD spectra of each conformer based on Boltzmann distribution 32 …”

Combining DoE and MASE: a winning strategy for the isolation of natural bioactive compounds from plant materials

“…In Table 1, when both ethanol and acetone are at their 0 levels (i.e., not used), it indicates consequently that water is used as the extraction solvent. An example of this kind of coding can be found in reference, 41 where the influence of solvents as acetone, ethyl acetate or ethanol in the extraction process is investigated by exploiting a DoE model. The fully coded data of the work taken as an example are reported in Table 2.…”

“…The success of these two models lies in the fact that they highlight the interactions between parameters and require a limited number of experiments. The other experimental designs that emerged during the literature survey are two-level factorial design, 51 Taguchi design, 52 incomplete 3 3 factorial design, 53 orthogonal array, 54,55 3-level design, 56 D-optimal, 57 full factorial design, 41,58 randomized block design, 59 and face-centered central composite design. 60,61 All these models emerged a maximum of three times each during the investigations (Table 4).…”