**4.2 Extraction of secondary metabolites for drug discovery or commercial purposes**

### *4.2.1 Alkaloids*

Alkaloids are a well-known class of secondary metabolites characterized by basic nitrogen. Over the years, many active alkaloids have been extracted via MW irradiation, e.g. ephedrine alkaloids, cocaine, and ergot alkaloids [35–37]. Unfortunately, results obtained for many of them have been comparable or worst if compared with the traditional method [38]. Nevertheless, microwaves have also spurred the discovery of new active alkaloids at the early stage of drug discovery. MASE protocols can be exploited to extract different alkaloids (examples are reported in **Figure 3**) from different botanicals like tuberous roots, leaves, and seeds [37, 39, 40].

As an example of MASE applied to the extraction of alkaloids, Pan et al. obtained a good recovery of caffeine and polyphenols from the leaves of green tea (*Thea sinensis* L.). MASE provided high extraction and selectivity, required a short time, and less labour-intensive, thus resulting in an efficient method in comparison with the conventional extraction procedures [41].

**43**

**Figure 3.**

*Microwave-Assisted Solid Extraction from Natural Matrices*

Xiong et al. developed an efficient MASE protocol, within a drug discovery process, for the isolation of bioactive alkaloids (e.g. liensinine, isoliensinine, neferine, dauricine, nuciferine, **Figure 3**) from *Lotus plumule*. The optimal extraction conditions required a 65% aqueous methanol as a solvent and irradiation at 200 W for 260 seconds [42]. Another interesting example, reported by Zhou et al., is the microwave-assisted aqueous two-phase extraction, useful for rapid and simultaneous extraction and separation of alkaloids. This technique was applied to *Radix Sophorae tonkinensis*. The optimum conditions were summarized as follows: ethanol/Na2HPO4 as the extraction solvent, 100 mesh as particle size, 1:75 of S/L ratio, irradiating at 90°C for 5 min [43]. Matrine, sophocarpine, oxymatrine, oxysophocarpine, 5α-hydroxysophocarpine, sophoranol, cytisine, N-methylcytisine, and

Recently, Belwal et al. reported an optimized MASE protocol, defined by multicomponent analysis, for the extraction of berberine (**Figure 3**) and polyphenols from diverse species of *Berberis*. The medical properties of berberine (anti-diabetic, hepato-protectant, anti-arthritic, antioxidants, anti-microbial, neuro-protective, and hypo-lipidemic activity) are widely recognized, and it is used in pharmaceuticals and nutraceuticals preparation. In this study, multi-component analysis (MCA) has been used to extract berberine and polyphenols from *B. jaeschkeana* roots under microwave-assisted extraction (MAE) conditions. All the variables, above described, were considered under 42 experiments and the results of the model showed significant model fitness. Under optimized MAE condition, (i.e. 100% methanol, pH 2.0, 598 W, 2 min of irradiation time), the berberine and palmatine (**Figure 3**) contents were recorded in 4.6% and 2.0%, respectively. Under the optimized condition, the

Regarding the alkaloids employed as drugs, or of interest for the toxicological use and/or abuse, few extractive procedures by MASE are reported in the literature. As an example, Brachet et al. extracted cocaine and benzoylecgonine from

yield of alkaloids was found closer to the models' predicted value [34].

*DOI: http://dx.doi.org/10.5772/intechopen.95440*

sophoridine were efficiently extracted.

*Examples of alkaloids extracted via the MASE approaches.*

*Microwave-Assisted Solid Extraction from Natural Matrices DOI: http://dx.doi.org/10.5772/intechopen.95440*

**Figure 3.**

*Microwave Heating - Electromagnetic Fields Causing Thermal and Non-Thermal Effects*

been obtained in high yields and short times [34].

plant grown under stress conditions.

a low amount of natural matrix.

**purposes**

seeds [37, 39, 40].

*4.2.1 Alkaloids*

HPLC analysis is suitable for the rapid screening of plant materials collected in different environmental conditions, and to determine the best ecological conditions for its cultivation. To extract vitexin and isovitexin from *Crotalaria sessiliflora,* Tang et al. exploited a microwave-assisted cloud-point extraction (MACPE). MACPE combines cloud-point extraction (CPE) with MAE. This has emerged as a technique to extract and separate bioactive compounds from medicinal plants [32]. Of note, using MACPE, hydrophobic compounds present in the aqueous phase can be favorably extracted into the hydrophobic core of micelles [33]. Applying MACPE, vitexin and isovitexin have

MASE can also be applied to study the effect of micronutrients or pollutants on secondary metabolites production. Amri et al. investigated the impact of soil copper (II) concentrations on nutrient uptake and the antioxidant system of *Marrubium vulgare*. Owing to waste deposition and agricultural practices, copper (II) tends to accumulate in high and toxic concentrations, leading to an alteration of the vital physiological or biochemical functions of the plants. As it is the case of *M. vulgare,* these effects may have a great impact on human health, since such a plant is used worldwide for its medicinal properties. To perform the study, the Authors selected marrubiin (**Figure 2**) as a reference compound, since it is the main secondary metabolite produced by *M. vulgare* leaves. A MASE protocol was developed for the easy extraction of marrubiin. This procedure allowed to evaluate the quality of a wide range of samples of white horehound. To optimize the process, the Authors used the statistical DoE approach. DoE findings indicated that the highest extraction efficiency of marrubiin with high repeatability was obtained using 100% ethanol at 120°C for 15 min, with significant benefits in terms of extraction times and environmental impact, given that ethanol is completely biodegradable. The MASE methodology may be applied for the characterization of *M. vulgare* herbal drug samples, thus evaluating their exposure to abiotic stress, revealing their phytochemical status, and facilitating the identification of raw materials obtained from a

To sum up, MASE procedures is a versatile technique suitable for the evaluation of the plant productivity, and to assess the quality of vegetal matrices, since it is fast, reproducible, suitable for extraction of a large number of samples and requires

**4.2 Extraction of secondary metabolites for drug discovery or commercial** 

Alkaloids are a well-known class of secondary metabolites characterized by basic nitrogen. Over the years, many active alkaloids have been extracted via MW irradiation, e.g. ephedrine alkaloids, cocaine, and ergot alkaloids [35–37]. Unfortunately, results obtained for many of them have been comparable or worst if compared with the traditional method [38]. Nevertheless, microwaves have also spurred the discovery of new active alkaloids at the early stage of drug discovery. MASE protocols can be exploited to extract different alkaloids (examples are reported in **Figure 3**) from different botanicals like tuberous roots, leaves, and

As an example of MASE applied to the extraction of alkaloids, Pan et al. obtained a good recovery of caffeine and polyphenols from the leaves of green tea (*Thea sinensis* L.). MASE provided high extraction and selectivity, required a short time, and less labour-intensive, thus resulting in an efficient method in comparison

with the conventional extraction procedures [41].

**42**

*Examples of alkaloids extracted via the MASE approaches.*

Xiong et al. developed an efficient MASE protocol, within a drug discovery process, for the isolation of bioactive alkaloids (e.g. liensinine, isoliensinine, neferine, dauricine, nuciferine, **Figure 3**) from *Lotus plumule*. The optimal extraction conditions required a 65% aqueous methanol as a solvent and irradiation at 200 W for 260 seconds [42]. Another interesting example, reported by Zhou et al., is the microwave-assisted aqueous two-phase extraction, useful for rapid and simultaneous extraction and separation of alkaloids. This technique was applied to *Radix Sophorae tonkinensis*. The optimum conditions were summarized as follows: ethanol/Na2HPO4 as the extraction solvent, 100 mesh as particle size, 1:75 of S/L ratio, irradiating at 90°C for 5 min [43]. Matrine, sophocarpine, oxymatrine, oxysophocarpine, 5α-hydroxysophocarpine, sophoranol, cytisine, N-methylcytisine, and sophoridine were efficiently extracted.

Recently, Belwal et al. reported an optimized MASE protocol, defined by multicomponent analysis, for the extraction of berberine (**Figure 3**) and polyphenols from diverse species of *Berberis*. The medical properties of berberine (anti-diabetic, hepato-protectant, anti-arthritic, antioxidants, anti-microbial, neuro-protective, and hypo-lipidemic activity) are widely recognized, and it is used in pharmaceuticals and nutraceuticals preparation. In this study, multi-component analysis (MCA) has been used to extract berberine and polyphenols from *B. jaeschkeana* roots under microwave-assisted extraction (MAE) conditions. All the variables, above described, were considered under 42 experiments and the results of the model showed significant model fitness. Under optimized MAE condition, (i.e. 100% methanol, pH 2.0, 598 W, 2 min of irradiation time), the berberine and palmatine (**Figure 3**) contents were recorded in 4.6% and 2.0%, respectively. Under the optimized condition, the yield of alkaloids was found closer to the models' predicted value [34].

Regarding the alkaloids employed as drugs, or of interest for the toxicological use and/or abuse, few extractive procedures by MASE are reported in the literature. As an example, Brachet et al. extracted cocaine and benzoylecgonine from

the leaves of *Erythroxylum coca* by MASE. Different solvents, particle size, time, and power were evaluated. Since MeOH is a high absorbing microwave solvent, and cocaine is highly soluble in it, it was found to be the best extraction solvent [36]. Interestingly, MASE found application in the forensic field as a rapid and cleanup-free method for the extraction and quantification of drugs of abuse and the respective metabolites from human fluids and tissues. Fernandez et al. reported the simultaneous extraction of cocaine, benzoylecgonine, cocaethylene, morphine, 6-monoacethylmorphine, and codeine from human urine [44], hair [45], and vitreous humor samples [46]. The MASE procedure reduces the extraction time, avoids the cleanup steps, and allows a quantitative recovery of the drugs.
