Targeted profiling of polyphenols in trees may reveal valuable sources of natural compounds with major applications in pharmacology and disease control. The current study targeted the profiling of polyphenols using HPLC-DAD in Quercus robur, Q. macrocarpa and Q. acutissima bark extracts. Free radical scavenging of each extract was investigated using antioxidant assays. Antimicrobial activities against a wide spectrum of bacteria and fungi were explored, as well as anticancer activities against different cancer cell lines. The HPLC-DAD analyses revealed the availability of several polyphenols in high amounts, including ellagic acid (in Q. robur) and caffeic acid (in Q. macrocarpa) in all three species. The bioactivity assay revealed high antioxidant activity in Q. robur compared to that of the other species, as well as phenolic standards. The three oak bark extracts showed clear antibacterial activities against most bacteria tested, with the highest antibacterial activities in the extracts of Q. robur. In addition, the three extracts showed higher antibacterial activities against Pseudomonas aeruginosa, Micrococcus flavus, and Escherichia coli compared to that of other bacteria. There were strong antifungal activities against some fungi, such as Aspergillus flavus, Penicillium funiculosum, and Penicillium ochrochloron. There were also noticeable anticancer activities against MCF-7, HeLa, Jurkat, and HT-29 cell lines, with the highest anticancer activity in the extracts of Q. robur. This is the first study that reveals not only novel sources of important polyphenols (e.g., ellagic acid) in Q. robur, Q. macrocarpa and Q. acutissima bark but also their anticancer activities against diverse cancer cell lines.

In traditional folklore, medicinal herbs play a vital role in the prevention and treatment of microbial diseases. In the present study, the phenolic profiles of the medicinal plants Asparagus aethiopicus L., Citrullus colocynthis L., Senna alexandrina L., Kalanchoe delagoensis L., Gasteria pillansii L., Cymbopogon citratus, Brassica juncea, and Curcuma longa L. were determined by high-performance liquid chromatography with a diode-array detector method. The results revealed rich sources of important compounds such as robinin in the fruits and leaves of A. aethiopicus; caffeic acid in the tubers of A. aethiopicus and quercitrin in the leaves of G. pillansii. Further, relatively high antioxidant, antibacterial, and antifungal activities were observed in C. colocynthis fruit coat, S. alexandrina pods, and A. aethiopicus leaves, respectively. The relatively higher the bioactivities of plants extracts associated with the phenols in these plants, in particular, the more abundant the phenols. Therefore, it was concluded that the fruit coat of C. colocynthis, pods of S. alexandrina, and leaves of A. aethiopicus might be excellent sources of natural products. These plant extracts also have a wide spectrum of antimicrobial activities that could be used in the pharmaceutical industries and to control diseases.

Natural populations of Ruta graveolens L. and Artemisia abrotanum L. in northern Saudi Arabia may be a rich source of natural polyphenols with potential biological activities. Therefore, tentative high-performance liquid chromatography–diode array detection was used to analyze the polyphenol contents of leaf extracts. R. graveolens mainly contained the phenolic acids chlorogenic acid and p-coumaric acid and the flavonoids rutoside and quercetin, whereas those of A. abrotanum mainly contained the phenolic acids isochlorogenic acid and rosmarinic acid and the flavonoid quercetin. Leaf extracts of both species showed antioxidant activities due to the presence of quercetin, chlorogenic acid, and p-coumaric acid as well as antiproliferative and cytotoxic activities against cancer cells, which may be attributed to necrotic cell accumulation during the early and late apoptotic periods. Both species also exhibited antibacterial activity, although the activity was higher in R. graveolens due to the high contents of quercetin and other polyphenols. Finally, both species exhibited antifungal activities, which were associated with specific polyphenols. This is the first study to confirm the richness of polyphenols and wide spectrum of biological activities in natural populations of R. graveolens and A. abrotanum in northern Saudi Arabia.

New sources of polyphenols with anticancer, antioxidant, and antimicrobial properties in arid environments are critical for the development of alternative medicines and natural remedies. This study explored the polyphenol profiles and biological activities of methanolic leaf extracts from natural Mentha × piperita and Mentha longifolia populations in northern Saudi Arabia. Chromatographic analyses identified several polyphenols in M. × piperita including phenolic acids: rosmarinic acid (1547.6 mg/100 g DW (dry weight)), cryptochlorogenic acid (91.7 mg/100 g DW), and chlorogenic acid (69.4 mg/100 g DW), as well as flavonoids: naringin (328.8 mg/100 g DW) and cynaroside (162.8 mg/100 g DW). The major polyphenols in M. longifolia were: rosmarinic acid (781.6 mg/100 g DW), cryptochlorogenic acid (191.1 mg/100 g DW), p-coumaric acid (113.0 mg/100 g DW), m-coumaric acid (112.2 mg/100 g DW), and chlorogenic acid (63.8 mg/100 g DW). M. × piperita and M. longifolia leaf extracts had high antioxidant activities due to the major polyphenols (cynaroside, rosmarinic and cryptochlorogenic acids). M. × piperita had higher activities against different cancer cells than M. longifolia. Naringin, cryptochlorogenic acid, and rosmarinic acid had the highest activities against cancer cells. The leaf extracts had antibacterial effects against most bacteria species (Pseudomonas aeruginosa was most sensitive), which was attributed to the polyphenols. Antifungal activities were similarly broad (Aspergillus flavus was most sensitive) and attributed to naringin, cryptochlorogenic acid, and caffeic acid. Populations of M. × piperita and M. longifolia in Northern Riyadh may be a valuable source of natural biologically active compounds.

Discovering new natural resources of polyphenols is the aim of many recent studies in the field of natural product research. This study tentatively investigated the polyphenols profile of the stems of seven Mammillaria species (M. rhodantha, M. spinosissima, M. hahniana, M. crucigera, M. candida, M. albilanata, and M. muehlenpfordtii) using high performance liquid chromatography with DAD detector (HPLC-DAD) method. Furthermore, the anti-cancer, anti-oxidant, and anti-bacterial potentials of these extracts as well as major identified phenols were explored. The HPLC-DAD study confirmed the availability of six phenolic acids, including gentisic acid, chlorogenic acid, caffeic acid, protocatechuic acid, sinapic acid, and p-hydroxybenzoic acid. The dominant compounds were: gentisic acid in M. rhodantha and M. spinosissima; chlorogenic acid in M. muehlenpfordtii, M. crucigera, and M. rhodantha; and caffeic acid in M. rhodantha, M. crucigera, and M. spinosissima. Stems of Mammillaria sp. showed antiproliferative effects against HeLa, MCF-7, and Jurkat cells. In HeLa and MCF-7 cells, the best antiproliferative activities were found in the treatments with M. rhodantha, M. spinosissima, and M. muehlenpfordtii. The apoptotic assay of M. rhodantha, M. spinosissima, and M. muehlenpfordtii showed accumulation of necrotic cells in the early and late apoptotic phase. M. rhodantha, M. spinosissima, and M. muehlenpfordtii showed the highest anti-oxidant activities using 2,2-diphenyl-1-picrylhydrazyl (DPPH), β-carotene bleaching, and ferric reducing anti-oxidant power (FRAP) assays. M. rhodantha was the best source of antioxidants. Mammillaria sp. showed moderate anti-bacterial effects against bacteria and the highest effects were found using the extracts of M. rhodantha, M. spinosissima, M. crucigera and M. muehlenpfordtii against most bacteria. The anti-bacterial activities were attributed to other phenolic compounds (e.g., chlorogenic acid) than gentisic acid, which was not active against most bacteria. Mammillaria sp. could be considered to be an important natural source of phenolic acids with anti-cancer, anti-bacterial, and anti-oxidant activities.