Wen-Jun He

Isolation and characterization of cytotoxic cyclotides from Viola tricolor

Many plants of the Violaceae plant family have been used in traditional remedies, and these plants often contain cyclotides, a particular type of plant cyclopeptide that is distinguished by a cyclic cystine knot motif. In general, bioactive plant cyclopeptides are interesting candidates for drug development. In the current study, a suite of 14 cyclotides, which includes seven novel cyclotides [vitri B, C, D, E, F, varv Hm, and He], together with seven known cyclotides [varv A, D, E, F, H, vitri A, and cycloviolacin O2], was isolated from Viola tricolor, a common flower. A chromatography-based method was used to isolate the cyclotides, which were characterized using tandem mass spectrometry and NMR spectroscopy. Several of the cyclotides showed cytotoxic activities against five cancer cell lines, U251, MDA-MB-231, A549, DU145, and BEL-7402. Three cyclotides, vitri A, vitri F, and cycloviolacin O2, were the most cytotoxic. The cytotoxic activity of the cyclotides did not correlate well with their hemolytic activity, indicating that different interactions, most likely with membranes, are involved for cytotoxic and hemolytic activities. Homology modeling of the structures was used in deriving structure-activity relationships.

Isolation and characterization of cytotoxic cyclotides from Viola philippica

Cyclotides are a large family of plant peptides characterized by a macrocyclic backbone and knotted arrangement of three disulfide bonds. This unique structure renders cyclotides exceptionally stable to thermal, chemical and enzymatic treatments. They exhibit a variety of bioactivities, including uterotonic, anti-HIV, cytotoxic and hemolytic activity and it is these properties that make cyclotides an interesting peptide scaffold for drug design. In this study, eight new cyclotides (Viphi A-H), along with eight known cyclotides, were isolated from Viola philippica, a plant from the Violaceae family. In addition, Viba 17 and Mram 8 were isolated for the first time as peptides. The sequences of these cyclotides were elucidated primarily by using a strategy involving reduction, enzymatic digestion and tandem mass spectroscopy sequencing. Several of the cyclotides showed cytotoxic activities against the cancer cell lines MM96L, HeLa and BGC-823. The novel cyclotides reported here: (1) enhance the known sequence variation observed for cyclotides; (2) extend the number of species known to contain cyclotides; (3) provide interesting structure-activity relationships that delineate residues important for cytotoxic activity. In addition, this study provides insights into the potential active ingredients of traditional Chinese medicines.

A new family of cystine knot peptides from the seeds of Momordica cochinchinensis

Momordica cochinchinensis, a Cucurbitaceae plant commonly found in Southeast Asia, has the unusual property of containing both acyclic and backbone-cyclized trypsin inhibitors with inhibitor cystine knot (ICK) motifs. In the current study we have shown that M. cochinchinensis also contains another family of acyclic ICK peptides. We recently reported two novel peptides from M. cochinchinensis but have now discovered four additional peptides (MCo-3-MCo-6) with related sequences. Together these peptides form a novel family of M. cochinchinensis ICK peptides (MCo-ICK) that do not have sequence homology with other known peptides and are not potent trypsin inhibitors. Otherwise these new peptides MCo-3 to MCo-6 were evaluated for antimalarial activity against Plasmodium falciparum, and cytotoxic activity against the cancer cell line MDA-MB-231. But these peptides were not active.

Antimicrobial, Cytotoxic Lignans and Terpenoids from the Twigs of Pseudolarix kaempferi

Seven new compounds, including four lignans, (+)-(8S,8′S)-9,9′-dibenzoylsecoisolariciresinol (1), (+)-(8S*,8′R*)-4,4′-dimethyloxomatairesinol (2), (+)-(7S*,8R*,8′R*,9′S*)-9′-n-butoxytsugacetal (3), and pseudolarkaemin A (4), a pyronane glycoside, pseudolarkaemin B (5), an ent-beyerene glycoside, pseudolarkaemin C (6), and a triterpene, 25-epi-pseudolarolide Q (7), along with 25 known compounds (8–32) were isolated from the twigs of Pseudolarix kaempferi. Their structures were elucidated mainly by the analysis of their NMR and MS data. Pseudolarolide C acid (24) was isolated for the first time as a natural product. All compounds were evaluated for antimicrobial activity against Candida albicans and Staphylococcus aureus, and cytotoxic activity against K562, HT-29, B16, BGC-823, BEL-7402, SGC-7901, U251, and A549 cancer cell lines were assayed. Results indicated that the new compounds 3, 7, and some known compounds showed antimicrobial and cytotoxic activities.

Cyclopeptide Alkaloids from Ziziphus apetala

Six novel Ia₃-type cyclopeptide alkaloids (1-6) were isolated from stems of Ziziphus apetala. Compound 5 and the known compounds mauritine A (7) and mauritine F (8) were isolated from the roots. Their structures were determined by spectroscopic analyses and chemical methods. The total alkaloids from the roots and the isolated cyclopeptide alkaloids were tested for antidepressant behavior on mice, cytotoxicity, and 11β-hydroxysteroid dehydrogenase (11β-HSD) inhibition in vitro. Only mauritine A (7) showed inhibitory activity on 11β-HSD1, with IC₅₀ values of 52.0 (human) and 31.2 μg/mL (mouse).

Zizimauritic acids A–C, three novel nortriterpenes from Ziziphus mauritiana

Zizimauritic acids A-C (1-3), three novel nortriterpenes with a unique A-nor-E-seco spiro-lactone ceanothane-type triterpene skeleton, together with 3 known triterpenes ceanothenic acid (4), betulinic acid (5), and ceanothic acid (6), were isolated from the roots of Ziziphus mauritiana. Compounds 1-4 showed cytotoxicities with the IC(50) values ranging from 5.05 to 11.94 μg/ml, and compounds 1 and 3 showed an inhibitory effect on the growth of Staphylococcus aureus with the IC(50) values 2.17 and 12.79 μg/ml. A plausible biosynthetic pathway of compounds 1-3 was proposed.

Novel Inhibitor Cystine Knot Peptides from Momordica charantia

Two new peptides, MCh-1 and MCh-2, along with three known trypsin inhibitors (MCTI-I, MCTI-II and MCTI-III), were isolated from the seeds of the tropical vine Momordica charantia. The sequences of the peptides were determined using mass spectrometry and NMR spectroscopy. Using a strategy involving partial reduction and stepwise alkylation of the peptides, followed by enzymatic digestion and tandem mass spectrometry sequencing, the disulfide connectivity of MCh-1 was elucidated to be CysI-CysIV, CysII-CysV and CysIII-CysVI. The three-dimensional structures of MCh-1 and MCh-2 were determined using NMR spectroscopy and found to contain the inhibitor cystine knot (ICK) motif. The sequences of the novel peptides differ significantly from peptides previously isolated from this plant. Therefore, this study expands the known peptide diversity in M. charantia and the range of sequences that can be accommodated by the ICK motif. Furthermore, we show that a stable two-disulfide intermediate is involved in the oxidative folding of MCh-1. This disulfide intermediate is structurally homologous to the proposed ancestral fold of ICK peptides, and provides a possible pathway for the evolution of this structural motif, which is highly prevalent in nature.

Cyclopentapeptides from Dianthus chinensis

A new cyclopentapeptide dianthin I (1), together with two known ones pseudostellarin A (2) and heterophyllin J (3), was isolated from the aerial parts of Dianthus chinensis. The structure of 1 was elucidated as cyclo‐(Gly1– l–Phe2– l–Pro3– l–Ser4– l–Phe5) on the basis of extensive spectroscopic analyses and chemical methods. Copyright

Three new triterpenoids from Rubia schumanniana

Three new triterpenoids, 3β-hydroxy-urs-30-p-Z-hydroxycinnamoyl-12-en-28-oic-acid (1), 3β-hydroxy-olean-30-p-Ehydroxycinnamoyl-12-en-28-oic-acid (2) and 3β,6α-dihydroxy-urs-14-en-12-one (3), together with seven known triterpenoids, were isolated from the roots of Rubia schumanniana. Their structures were established by means of spectroscopic analysis. All compounds were evaluated for cytotoxic activity, and compounds 2–6 showed cytotoxicity with the IC50 values of 10.75∼18.87 µg/mL.

Astershionones A-F, six new anti-HBV shionane-type triterpenes from Aster tataricus

Six new shionane-type triterpenes, astershionones A-F (1-6), were obtained from the roots and rhizomes of Aster tataricus. Their structures were elucidated on the basis of spectroscopic data, mainly NMR and MS data. The absolute configuration of 1 was determined by single crystal X-ray diffraction analysis and CD analysis. 3 showed inhibitory activity against HBsAg and HBeAg secretion with IC50 values of 23.0 and 23.1 μM, and cytotoxicity against HepG 2.2.15 cells with a CC50 value of 170.5 μM. 3 also exhibited inhibitory activity against HBV DNA replication with an IC50 value of 22.4 μM.