Diverse naturally occurring events relevant to proteins, including processing and post-translational modification, provide significant clues enabling advances in peptide/protein chemistry. Our motivation to synthesize large proteins prompted us to seek scientific bases utilized in synthetic experiments on the intein-mediated protein processing system. This account describes peptide/protein thioester-producing protocols whose design is based on acyl transfer reactions observed in the intein system, and the development of the stimulus-responsive amide cleavage and its application to the modulation of peptide function. Finally, several findings derived from nature-inspired research efforts, including peptide mimetic synthesis and S-protected cysteine chemistry, are described.

We developed the addition reaction of α-silyl amines with benzalmalononitriles catalyzed by a Mg²⁺-conjugated pyrene catalyst under visible light irradiation. The catalytic activity of this complex was higher than pyrene alone, a Mg²⁺ Lewis acid alone, and the sum of these two independent catalytic elements. The observed enhancement in catalytic activity was likely due to electrostatic interactions of the Mg²⁺ Lewis acid with the pyrene radical anion, which was generated through photoinduced single electron transfer from α-silyl amines to the catalyst’s pyrene moiety.

A C₁₀CO-NalLeuVal (C10NLV) tripeptide was synthesized and explored as a carrier for paclitaxel (TAX) delivery. Five types of TAX-loaded micelles were produced by loading TAX with different doses of C10NLV. 3-(4,5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay showed that TAX-loaded micelles dramatically reduced TAX IC₅₀ values of TAX-resistant A549 (A549/TAX) and Lewis lung carcinoma (LLC) cells in a C10NLV-dose-dependent manner, with micelles 4 and 5 exhibited comparable inhibitory effects on A549/TAX proliferation. Flow cytometry analysis showed that TAX-loaded micelles 4 promoted lung cancer cell apoptosis in a TAX-dose-dependent manner. Immunofluorescent staining and Western blotting revealed that TAX-loaded micelles 4 dramatically reduced the protein levels of F-actin, p53, Bcl-2, and LC3A/B in A549/TAX cells. Wound healing, cell adhesion, migration, and invasion assays demonstrated that TAX-loaded micelles 4 suppressed the metastatic abilities of lung cancer cells. Furthermore, compared with the same dose of free TAX, TAX-loaded micelles 4 significantly reduced the volumes and weights of A549/TAX-generated tumors as well as the numbers of LLC-generated pulmonary metastatic foci in mice, without affecting the organ/body weight ratios, body weights, and blood cell counts. Histological analysis demonstrated that TAX-loaded micelles 4 administration resulted in tubulin and CD206 downregulation as well as cytoplasm disappearance and nuclear shrinkage in xenograft tumors. These data suggest that TAX-loaded micelles 4 inhibits the proliferative and metastatic capacity of lung cancer cells, despite TAX resistance. TAX-loaded micelles 4 suppresses lung tumor growth and metastasis in vivo without inducing systemic toxicity. Thus, the C10NLV-based TAX delivery is effective and safe to combat TAX resistance and metastasis in lung cancer.

The crystal structures of two methoxyphenylbenzamide isomers are described, (Ph2Br) and (Ph3Br), with the general formula C₁₄H₁₂BrNO₂. This structural study revealed the presence of N–H–O and C–H–O hydrogen bonds, Br–Br halogen bonds, C–H–π, and C–Br–π molecular contacts, showing in both compounds, a central C1–C7(O1)–N1(H1)–C8 amide segment, to be almost linear. The close proximity between the Br1 and O1 in Ph2Br showed that its interatomic distance was less than the sum of their VDW radii, generating an increase in the electrostatic potential in the O1 region, making possible the appearance of the so-called σ and π-holes on bromine. These specific conditions give rise to the formation of the Br–Br halogens bonds, which are united in a very interesting way, allowing the bond to extend by joining halogen atoms between different molecules forming an isosceles triangle with Br–Br distances equal to 3.5403(4) Å and 5.085 Å as its base. The presence of the carbonyl group in Ph2Br, an excellent acceptor of hydrogen and halogen bonds, led to competition between these bonds to organize crystal growth. The analysis of the compounds as pharmacophores showed that the bromine atom plays a key role in interactions with protein residues, reaching good ligand-protein interaction values comparable to the values presented by the parent inhibitor, Asciminib. In contact with the ALA356 residue, the bromine of Ph2Br participates with a higher contact geometry using the σ-hole, whereas the bromine of Ph3Br employs a more efficient contact geometry by taking advantage of its π-hole.

Cyclosporin A (CsA) is a common immunosuppressant wildly used in patients with organ transplant and autoimmune diseases; however, it can cause several adverse effects, such as nephrotoxicity and hypertension. The detailed mechanisms have not been completely understood. Atrial natriuretic factor (ANF) and its receptor (mGC-A) have been shown to play a crucial role in the regulation of blood pressure. Here, we investigated the effects of CsA on the activation of mGC-A in ANF-treated LLC-PK1 cells. In our study, ANF-induced mGC-A activities and superoxide generation in LLC-PK1 cells were measured by guanosine 3′,5′-cyclic monophosphate (cGMP) radioimmunoassay and lucigenin-dependent chemiluminescence, respectively. We found that CsA can reduce about 60% of mGC-A activities in ANF-treated LLC-PK1 cells. CsA is known to induce superoxide. Addition of superoxide generators menadione and diamide mimicked the effects of CsA, whereas DPI (a reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase inhibitor) and Tiron (a superoxide quencher) blocked the suppressive effects of CsA on ANF-induced mGC-A activities. We previously showed that the catalytic domain of GC-A (GC-c) expresses guanylate cyclase activities. Addition of menadione, diamide, or peroxynitrite or transfection of Nox-4 NAD(P)H oxidase abolished GC-c activities. In conclusion, CsA inhibits ANF-stimulated mGC-A activities through superoxide and/or peroxynitrite generated by an NAD(P)H oxidase by interacting with the catalytic domain of mGC-A.

We have developed a simple and accurate method for quantifying sugars in herbal medicines, which have hitherto been difficult to quantify. Using ultra performance liquid chromatography-quadrupole-time-of-flight (UPLC-Q-TOF)-MS and two types of columns with different chemical properties, we determined the optimum conditions for separating nine sugars (fructose, galactose, glucose, mannitol, sucrose, melibiose, raffinose, manninotriose, and stachyose) commonly found in herbal medicines. Separation was completed within 10 min when an apHera NH₂ HPLC column was used, although galactose and glucose could not be separated. On the other hand, the nine sugars were completely separated within 16 min when a hydrophilic interaction chromatography (HILIC)pak VG-50 2D column was used. The calibration curves obtained using those two columns gave good linearity for the sugar standards, and the coefficient of determination was 0.995 or higher. Both columns showed excellent performance with short analysis time and high sensitivity. Using our developed method, we were able to quantify sugars in galactose-free herbal medicines within 10 min and in herbal medicines containing galactose within 16 min. We revealed that our method could be used for the analysis of sugars in Angelica acutiloba and Rehmannia glutinosa roots.

The protective effect of phloridzin (PHL) and its potential mechanism were examined in mice with liver injury induced by isoniazid (INH) and rifampicin (RFP). The mice were randomly divided into normal control group, model group, low (80 mg/kg), medium (160 mg/kg) and high (320 mg/kg) phloridzin-treated groups. After 28 d treatment, blood and liver tissue were collected and analysed. The results revealed that PHL regulated liver function related indicators and reduced the pathological tissue damage, indicating that PHL significantly alleviated the liver injury. Furthermore, the level of CYP450 enzyme, the expression of CYP3A4, CYP2E1, heme oxygenase-1 (HO-1) and nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA and protein were inhibited by PHL. These results indicated that PHL exerts a protecting effect against liver injury induced by combination of RFP and INH. The potential mechanisms may be concerned with the activation of Nrf2/HO-1 signaling pathway containing its key antioxidant enzymes and regulation of CYP3A4 and CYP2E1.

Amphipathic cell-penetrating peptides based on the pep-1 sequence were synthesized by replacing the three hydrophilic glutamic acid residues with disubstituted, non-proteinogenic, hydrophobic amino acids. These substitutions facilitated maintenance of the peptides’ secondary structure in a helical conformation, even in aqueous solution. Stability against enzymatic degradation was improved through the use of disubstituted amino acids. The resultant peptides exhibited high membrane permeability that remained relatively stable during prolonged incubation times. The results of this study indicate that the use of non-proteinogenic amino acids may be an effective approach to improve the cell membrane permeability for existing amphiphilic peptides.

LC-MS and molecular networking analyses of the extract of the marine sponge Psammocinia sp. indicated the presence of two new compounds with multiple halogens. LC-MS-guided isolation yielded cyclic peptides, cyclopsammocinamides A (1) and B (2), in an enantiomeric relationship to cyclocinamide A (3). Planar structures of 1 and 2 were elucidated by NMR and mass spectroscopic analyses and the absolute configurations of the amino acid residues were determined using Marfey’s method with their acid hydrolysates. The sponge extract exhibited cytotoxicity and the bioassay-guided isolation afforded a dimeric dilactone macrolide, swinholide A, as the cytotoxic compound.

Here, we synthesized three acetogenin analogs containing pyrimidine moieties linked by amine bonds, which represent the skeleton structure of pyrimidifen, a mitochondrial complex I-inhibiting insecticide. Replacing the pyrimidine moiety linked by the amine bond remarkably enhanced growth-inhibitory activity of the analogs against several human cancer cell lines. Moreover, these analogs selectively and potently inhibited the growth of these human cancer cell lines regardless of the pyrimidine substituents. Furthermore, COMPARE analyses suggested that these analogs inhibited cancer growth by inhibiting mitochondrial complex I. Our study provides insights into the design of acetogenin analogs as novel antitumor agents.