This study was conducted to prepare calcium chelate of low-molecular-weight tuna bone collagen peptides (TBCP_LMW) with a high chelation rate and to identify its structural characteristics and stability. The optimum conditions for calcium chelation of TBCP_LMW (TBCP_LMW-Ca) were determined through single-factor experiments and response surface methodology, and the calcium-chelating capacity reached over 90% under the optimal conditions. The amino acid compositions implied that Asp and Glu played important roles in the formation of TBCP_LMW-Ca. Structural characterizations determined via spectroscopic analyses revealed that functional groups such as -COO⁻, N-H, C=O, and C-O were involved in forming TBCP_LMW-Ca. The particle size distributions and scanning electron microscopy results revealed that folding and aggregation of peptides were found in the chelate. Stability studies showed that TBCP_LMW-Ca was relatively stable under thermal processing and more pronounced changes have been observed in simulated gastric digestion, presumably the acidic environment was the main factor causing the dissociation of the TBCP_LMW-Ca. The results of this study provide a scientific basis for the preparation of a novel calcium supplement and is beneficial for comprehensive utilization of tuna bones.

Marine-derived Penicillium fungi are one of the most important sources for the discovery of new bioactive natural products. This study characterized the isolation, structures, and antiglioma activities of twelve compounds, including three novel ones—penipyridinone B (1), 11S-(−)-penilloid A (2), and 11R,14E-(+)-penilloid A (3)—from the marine fungus Penicillium sp. ZZ1750. The structures of the novel compounds were determined via extensive nuclear magnetic resonance (NMR) spectroscopic analyses, high-resolution electrospray ionization mass spectroscopy (HRESIMS) data, Mosher’s method, optical rotation (OR) calculations, and electronic circular dichroism (ECD) calculations. Penipyridinone B represents the first example of its structural type and showed potent antiglioma activity, with IC₅₀ values of 2.45 μM for U87MG cells and 11.40 μM for U251 cells. The known compounds of questiomycin A (9) and xanthocillin X (10) also showed antiproliferative activity against both U87MG and U251 cells, with IC₅₀ values of 13.65 μM to 22.56 μM. The antiglioma activity of questiomycin A and xanthocillin X may be related to the promotion of reactive oxygen species (ROS) production, the reduction of mitochondrial membrane potential (MMP), and the enhancement of caspase-3 enzyme activity.

Marine-derived Streptomyces actinomycetes are one of the most important sources for the discovery of novel bioactive natural products. This study characterized the isolation, structural elucidation and biological activity evaluation of thirty compounds, including twelve previously undescribed compounds, namely hygrocins K–U (5–13, 17 and 18) and streptophenylpropanamide A (23), from the marine-associated actinomycete Streptomyces sp. ZZ1956. Structures of the isolated compounds were determined by a combination of extensive NMR spectroscopic analyses, HRESIMS data, the Mosher’s method, ECD calculations, single crystal X-ray diffraction and comparison with reported data. Hygrocins C (1), D (2), F (4), N (8), Q (11) and R (12), 2-acetamide-6-hydroxy-7-methyl-1,4-naphthoquinone (22), echoside C (27), echoside A (28) and 11,11′-O-dimethylelaiophylin (30) had antiproliferative activity (IC₅₀: 0.16–19.39 μM) against both human glioma U87MG and U251 cells with hygrocin C as the strongest active compound (IC₅₀: 0.16 and 0.35 μM, respectively). The analysis of the structure–activity relationship indicated that a small change in the structures of the naphthalenic ansamycins had significant influence on their antiglioma activities. Hygrocins N (8), O (9), R (12), T (17) and U (18), 2-amino-6-hydroxy-7-methyl-1,4-naphthoquinone (21), 2-acetamide-6-hydroxy-7-methyl-1,4-naphthoquinone (22), 3′-methoxy(1,1′,4′,1″-terphenyl)-2′,6′-diol (26), echoside C (27) and echoside A (28) showed antibacterial activity against methicillin-resistant Staphylococcus aureus and Escherichia coli with MIC values of 3–48 μg/mL.