Reactive oxygen species and subsequent oxidative stress are reported to play important roles in chronic metabolic diseases. Plant-derived polyphenols, especially food-derived phenolics, have attracted a lot of attention due to their potential usage against oxidative stress-related diseases. The leaf of Psidium guajava (known as guava) is regarded as a good resource of polyphenols and its products are commercially available in Japan as functional foods against multiple chronic metabolism disorders. In the course of finding novel polyphenols with antioxidative activities from guava leaf, 11 acylated phenolic glycosides (1–11), including 5 new oleuropeic acid-conjugated phenolic glycosides, named guajanosides A–E (1, 2, and 5–7), along with 17 known meroterpenoides (12–28), were isolated and identified. Their structures were determined by spectroscopic data analysis, chemical degradation, and acid hydrolysis. Compounds 1, 2, and 5–11 displayed potent reactive oxygen species-scavenging activity in lipopolysaccharide-stimulated RAW 264.7 macrophage cells. Western blot revealed that compound 6 markedly increased the expression levels of nuclear factor-erythroid 2-related factor 2 (Nrf2), NAD­(P)H quinone dehydrogenase 1 (NQO1), and the glutamate–cysteine ligase catalytic subunit. The current study revealed the presence of oleuropeic acid-derived phenolic glycosides in guava leaf and highlighted the potential usage of this type of phenolics against oxidative stress-related metabolic diseases via activation of the Nrf2 signaling pathway.

Eleven metabolites, six echinosporins (1−6), four dibenzoyls (7−10), and an aromatic compound (11), were isolated from the fermentation broth of lichen-associated Amycolatopsis hippodromi. The structures of the new compounds (1−5, 8−11) were elucidated by comprehensive spectroscopic analysis including data from experimental and calculated ECD spectra. Amycolasporins A−C (1−3) demonstrated antibacterial activities against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli with MIC values of 25 or 100 μg/mL. Amycolasporin C (3) and the known dibenzoyl (7) attenuated the production of NO due to the suppression of the expression of nitric oxide synthase (iNOS) in LPS-induced RAW 264.7 cells in a dose-dependent manner.

Four new barringtogenol C-type triterpenoid saponins, namely acerplatanosides A – D (1–4), along with 22 known compounds (5–26), were isolated from the stem bark of Norway maple (Acer platanoides). Their structures were elucidated on the basis of comprehensive spectroscopic analyses and chemical hydrolysis. This is the first report of triterpenoid saponins isolated from Norway maple. Compounds 1, 3, and 4 showed cytotoxicity against 4 human cancer cell lines with IC50 values ranging from 9.4 to 39.5 µM.

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