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Paphiopedilum callosum (Rchb.f.) Stein belongs to the Orchidaceae family. The phytochemistry and bioactivities of this plant have not been reported. In this study, a bioassay-guided isolation with a yeast cellbased assay was performed to isolate topoisomerase I poison compounds from the roots of P. callosum. One new and five known compounds were isolated. According to their spectroscopic data (ESI-MS, NMR, IR and UV), the new compound (1) is 3′-hydroxy-2,6,5′-trimethoxystilbene. The known compounds (2-6) were identified by comparing their spectroscopic data with those in the literature. According to the yeast cell-based assay, all the compounds were topoisomerase Ι poisons based on their ability to inhibit the growth of yeast cells. As further confirmation, the cytotoxic activities of the isolated compounds were evaluated using human cancer cell lines (MCF-7 and NCI-H187). The compounds exhibited varying degrees of cytotoxicity on the representative cell lines. These isolated compounds could serve as new lead compounds in the development of cancer chemotherapeutics.

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In accordance with Thai wisdom, indigenous plant leaves have been used as food packaging to preserve freshness. Many studies have demonstrated that both antioxidant and antimicrobial activities contribute to protecting food from spoilage. Hence, the ethanolic extracts of leaves from selected plants traditionally used as food packaging, including Nelumbo nucifera (1), Cocos nucifera (2), Nypa fruticans (3), Nepenthes mirabilis (4), Dendrocalamus asper (5), Cephalostachyum pergracile (6), Musa balbisiana (7), and Piper sarmentosum (8), were investigated to determine whether they have antioxidant and antimicrobial activities against spoilage microorganisms and foodborne pathogens that might be beneficial for food quality. Extracts 1–4 exhibited high phenolic content at 82.18–115.15 mg GAE/g and high antioxidant capacity on DPPH, FRAP and SRSA assay at 14.71–34.28 μg/mL, 342.92–551.38 μmol Fe2+/g, and 11.19–38.97 μg/mL, respectively, while leaf extracts 5–8 showed lower phenolic content at 34.43–50.08 mg GAE/g and lower antioxidant capacity on DPPH, FRAP, and SRSA at 46.70–142.16 μg/mL, 54.57–191.78 μmol Fe2+/g, and 69.05–>120 μg/mL, respectively. Extracts 1–4 possessed antimicrobial activities against food-relevant bacteria, including Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, and Escherichia coli. Only N. mirabilis extract (4) showed antimicrobial activities against Salmonella enterica subsp. enterica serovar Abony and Candida albicans. Extracts 5–8 showed slight antimicrobial activities against B. cereus and E. coli. As the growth and activity of microorganisms are the main cause of food spoilage, N. fruticans (3) was selected for bioassay-guided isolation to obtain 3-O-caffeoyl shikimic acid (I), isoorientin (II) and isovitexin (III), which are responsible for its antimicrobial activity against foodborne pathogens. N. fruticans was identified as a new source of natural antimicrobial compounds I–III, among which 3-O-caffeoyl shikimic acid was proven to show antimicrobial activity for the first time. These findings support the use of leaves for wrapping food and protecting food against oxidation and foodborne pathogens through their antioxidant and antimicrobial activities, respectively. Thus, leaves could be used as a natural packaging material and natural preservative.