Five new quinone derivatives, rubiasins D-F (1-3), rubialatones A and B (4 and 5), have been isolated from the roots and rhizomes of three Rubia species, Rubia alata, R. wallichiana and R. schumanniana, together with 26 known quinones (6-31). Their structures have been elucidated on the basis of NMR, MS spectra and computational methods. The compounds have been evaluated for their toxicity to the saprophytic nematode Caenorhabditis elegans and the root-knot nematode Meloidogyne incognita. Compounds 1, 6 and 7 showed toxicity to C. elegans with the LC50 values at 8.50, 9.44 and 44.82 mu g/mL, respectively; and 6 showed toxicity to M. incognita with the LC50 value at 35.22 mu g/mL. Meanwhile, compounds 1 and 6 showed inhibitory effect on egg hatch of C. elegans with the LC50 values at 5.60 and 48.95 mu g/ml. (C) 2018 Elsevier Ltd. All rights reserved.

Three new cyclic hexapeptides, designated as rubischumanins A–C (1–3), together with three known ones (4–6) were isolated from the roots and rhizomes of Rubia schumanniana. The structures were elucidated on the basis of extensive spectroscopic analysis. Cytotoxicity of these compounds was evaluated and compounds 1, 2, 4, and 5 showed cytotoxicity against A549, BGC-823, and Hela cell lines.

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.

Plant cyclopeptides, cyclic compounds formed mainly by the peptidic bonds of 237 protein and non-protein amino acids (mainly L-amino acids) and found in higher plants, have been attractive for their extensive bioactivities and distinctive molecular architectures. During the last half century's study, about 500 cyclopeptides divided into eight types have been isolated from over 120 species, which belong to over 20 families and 60 genera. Some cyclopeptides showed potential anti-tumor, sedative, immunosuppressive, and uterotonic activities. In the Chinese Pharmacopoeia (CP, 2010 Version), 23 species (14 families, 18 genera) containing cyclopeptides have been recorded in the origins of 24 traditional Chinese medicines (TCMs). Heterophyllin B (64), first reported by us from Pseudostellaria heterophylla in 1993 was cited for the first time in CP as the standard substance of cyclopeptides for quality control. In this review, we highlight the progress in the chemical studies of these cyclopeptide-containing TCMs, in particular recent results in our group's publications.

OBJECTIVETo separate and identify cyclopeptides of tubers of Rubia schumanniana.METHODThe 70% methanol extracts from tubers of Rubia schumanniana were separated and purified by silica gel, RP-18, Sephedax LH-20 and HPLC. Their structures were identified by spectral analysis.RESULTNine cyclopeptides were separated and identified as RA- II (1), RA-V (2), RA-VIII (3), rubiyunnanin C (4), RA-X (5), RY-II (6), RA- I (7), RA-XIII (8) and RA-XIII-OMe (9), respectively.CONCLUSIONAll of nine cyclopeptides were separated from R. schumanniana for the first time.

Twelve new arborinane-type triterpenoids (1-12) and four new anthraquinones (13-16), together with 50 known compounds, were isolated from the roots of Rubia yunnanensis. The structures of 1-16 were elucidated by spectroscopic data analysis and chemical methods. All compounds were evaluated for their cytotoxic, antibacterial, and antifungal activities. Rubiyunnanol C (5) is the first example of an arborinane-type triterpenoid with a double bond at C-8-C-9.

Rubiaceae-type cyclopeptides (RAs), cyclic hexapeptides from Rubia plants, have shown potential antitumor activity in vitro and in vivo. Based on the review about plant cyclopeptides (Chem. Rev., 2006, 106: 840), this mini-review will highlight new progress on the discovery, synthesis, and mechanism of RAs isolated during 2005 to 2011, covering recent work in our group.