A Cytochrome P450 Enzyme Catalyses Oxetane Ring Formation in Paclitaxel Biosynthesis.

Oxetane synthase (TmCYP1), a novel cytochrome P450 enzyme from Taxus×media cell cultures, has been functionally characterized to efficiently catalyse the formation of the oxetane ring in tetracyclic taxoids. Transient expression of TmCYP1 in Nicotiana benthamiana using 2α,5α,7ß,9α,10ß,13α-hexaacetoxytaxa-4(20),11(12)-diene (1) as a substrate led to the production of a major oxetane derivative, 1ß-dehydroxybaccatin IV (1 a), and a minor 4ß,20-epoxide derivative, baccatin I (1 b). However, feeding the substrate decinnamoyltaxinine J (2), a 5-deacetylated derivative of 1, yielded only 5α-deacetylbaccatin I (2 b), a 4ß,20-epoxide. A possible reaction mechanism was proposed on the basis of substrate-feeding, 2H and 18O isotope labelling experiments, and density functional theory calculations. This reaction could be an intramolecular oxidation-acetoxyl rearrangement and the construction of the oxetane ring may occur through a concerted process; however, the 4ß,20-epoxide might be a shunt product. In this process, the C5-O-acetyl group in substrate is crucial for the oxetane ring formation but not for the 4(20)-epoxy ring formation by TmCYP1. These findings provide a better understanding of the enzymatic formation of the oxetane ring in paclitaxel biosynthesis.

Functional Characterization and Cyclization Mechanism of a Diterpene Synthase Catalyzing the Skeleton Formation of Cephalotane-Type Diterpenoids.

CsCTS, a new diterpene synthase from Cephalotaxus sinensis responsible for forming cephalotene, the core skeleton of cephalotane-type diterpenoids with a highly rigid 6/6/5/7 tetracyclic ring system, was functionally characterized. The stepwise cyclization mechanism is proposed mainly based on structural investigation of its derailment products, and further demonstrated through isotopic labeling experiments and density functional theory calculations. Homology modeling and molecular dynamics simulation combined with site-directed mutagenesis revealed the critical amino acid residues for the unique carbocation-driven cascade cyclization mechanism of CsCTS. Altogether, this study reports the discovery of the diterpene synthase that catalyzes the first committed step of cephalotane-type diterpenoid biosynthesis and delineates its cyclization mechanism, laying the foundation to decipher and artificially construct the complete biosynthetic pathway of this type diterpenoids.

Chemical constituents from the stems of Dendrobium gratiosissimum and their biological activities.

Eight C6-C3-based bibenzyl derivatives (dengraphenols A-G, K), three mono-bibenzyls (dengraphenols I, L-M), one bis-bibenzyl (dengraphenol H), one oxyneolignane (dengraphenol J), one phenanthrene (dengraphenol N), and one picrotoxane-type sesquiterpene (dengrasusane A) were isolated from the stems of Dendrobium gratiosissimum. The resolution of dengraphenols A-J by chiral HPLC afforded ten pairs of enantiomers [(±)-dengraphenols A-J]. Their structures with absolute configurations were elucidated on the basis of comprehensive spectroscopic analyses, computational calculation methods and single-crystal X-ray diffraction, among which twenty-four [(±)-dengraphenols A-E, (+)-dengraphenol F, (±)-dengraphenols G-J, dengraphenols K-N, dengrasusane A] were undescribed. Ten compounds [(±)-dengraphenol B, (±)-dengraphenols D-E, (±)-dengraphenol H, (-)-dengraphenol I and dengraphenol N)] showed potent cytotoxicity against eight human cancer cell lines (A431, A2780, H460, HCT8, BGC823, SW1990, Daoy, and HGC27) with IC50 values of 3.77-9.75 µM. At a concentration of 10 µM, (-)-dengraphenol C, (±)-dengraphenol F, and (±)-dengraphenol K exhibited remarkable hepatoprotective activity against APAP-induced toxicity with a cell survival rate of 65.8%, 70.6% and 73.5%, respectively; dengraphenol N displayed significant anti-inflammatory effects; and dengraphenol K showed strong inhibitory activity against α-glucosidase with IC50 values of 5.71 µM. These results would provide potential compounds for drug discovery.

New quinones, a sesquiterpene and phenol compounds with cytotoxic activity from the aerial parts of Morinda umbellata L.

Eight previously undescribed compounds, two quinones (1-2), one sesquiterpene (3), and five phenol compounds (4-8), including three enantiomers (6a, 7a, and 8a), along with three corresponding known enantiomers (6b-8b) were isolated from the aerial parts of Morinda umbellata L. Their structures were elucidated by 1D and 2D NMR spectroscopy, X-ray diffraction, and experimental and calculated ECD spectra, respectively. Compound 5 was found to have weak cytotoxity, which inhibited the growth of seven human cancer cell lines (A2780, HeLa, MCF-7, BGC-823, H7420, Ketr3 and SW 1990) with IC50 values from 13.3 to 15.1 µM.

The racemic trimeric quinone and polycyclic quinones isolated from the aerial parts of Morinda umbellata L.

Four undescribed racemic quinones, umbellatas Q-T, were isolated from the aerial parts of Morinda umbellata L. All enantiomers were separated on a chiral HPLC column, and their structures were elucidated by UV spectroscopy, IR spectroscopy, HR-ESI-MS, 1D and 2D NMR spectroscopy, DP4+ NMR calculations, ECD spectroscopy, and X-ray diffraction. Three of the racemes are polycyclic anthraquinones, and one is a rare racemic trimer of naphthoquinone-bisnaphthohydroquinones. (+)-Umbellata S exhibited potent cytotoxicity (IC50: 6.2-9.3 µM) against the A2780, HeLa, H7420, Ketr3 and SW 1990 human cancer cell lines.

[Advances in studies on structure and pharmacological activities of natural tirucallane-type triterpenoids].

The tirucallane-type triterpenoids, composed of six isoprene units, belong to a group of tetracyclic triterpenoids. Although the naturally-derived tirucallane-type triterpenoids were found in a small amount, the kind of compounds showed various structures, which consist of apo-type, linear said-chain-type and cyclolike said-chain-type and broad bioactivities, such as cytotoxicity, anti-inflammation, antioxidation and anti-plasmin, etc. This paper summarized origins, structures and bioactivities of tirucallane-type triterpenoids in recent ten years. The future research and exploration of tirucallane-type triterpenoids were discussed and prospected.

Inhibition of IL-6 expression by lignans and other constituents isolated from Schefflera rubriflora C. J. Tseng & G. Hoo.

Schefflera rubriflora, a plant native to Yunnan Province in China, is often used to treat ailments such as neuropathic pain, tracheitis, and cough. However, the active components imparting these pharmacological effects are largely unexplored. In this study, five novel lignans and three new derivatives of benzoid or pyran were isolated from the leaves and twigs of S. rubriflora. The structures of these compounds were determined by the comprehensive analyses of the 1D and 2D NMR spectra and ESI mass spectra and a comparison of the obtained data with those of the literature data. All the compounds were tested for the inhibition of IL-6 expression. Three of the isolated compounds could inhibit the expression by 52% to 72%.

[Reviews on natural monocyclic sesquiterpenoids and their bioactivities].

Sesquiterpenes are a class of terpenoids composed of three isoprene units( 15 carbons). Sesquiterpenoids possess a variety of different structures,including acyclic sesquiterpenes,monocyclic sesquiterpenoids,bicyclic sesquiterpenoids,tricyclic sesquiterpenoids,tetracyclic sesquiterpenoids and macrocyclic sesquiterpenoids. Among them,a large number of monocyclic sesquiterpenoids were isolated and display extensive bioactivities,such as cytotoxic,antioxidant,anti-inflammatory,antibacterial and other activities. In this review,we summarized the progress about the phytochemistry and biological activities of monocyclic sesquiterpenoids( a total of161 compounds) reported from 2014 to 2018( 5 years),including megastigmanes,monocyclofarnesol-type,bisabolane-type,germacrane-type,and other types of monocyclic sesquiterpenoids. Furthermore,several future research perspectives and development of sesquiterpenoids as potential therapeutic agents were discussed as well.

Cytotoxic quinones from the aerial parts of Morinda umbellata L.

Although Morinda umbellata L. has been used in numerous folk medicines, there is a lack of phytochemical studies on this plant. Sixteen undescribed quinones, namely, ten anthraquinones (umbellatas A-J), one naphthohydroquinone (umbellata K), one naphthohydroquinone dimer (umbellata L), and four dinaphthofuran quinones (umbellatas M-P), were isolated from the aerial parts of Morinda umbellata L. (Rubiaceae). The structures of all the isolated quinones were elucidated based on spectroscopic methods. Four of the unknown quinones (umbellatas A, H, K and M) showed potent cytotoxic effects against A431, A2780, NCI-H460, HCT116, HepG2, and MCF-7 human cancer cell lines with IC50 values of 1.3-7.1 µM. These results reveal potential lead compounds for the development of new anticancer agents.

Anti-inflammatory terpenes from Schefflera rubriflora C. J. Tseng & G. Hoo with their TNF-α and IL-6 inhibitory activities.

The 95% ethanol extract and its EtOAc and n-BuOH fractions obtained from the leaves and twigs of Schefflera rubriflora C. J. Tseng & G. Hoo showed significant inhibitory activities (33.6%, 35.7% and 40.6%, respectively) against croton oil-induced ear inflammation in mice. Bioactivity-guided isolation and separation gave eight previously undescribed terpenes or terpene glycosides. Structural elucidation was based on UV, IR, and NMR spectroscopy, MS, experimental and calculated ECD data, and Mosher's method. To identify anti-inflammatory components from the extract, all the compounds were evaluated for tumor necrosis factor-α (TNF-α) and interleukine-6 (IL-6) inhibitory activities. Four undescribed compounds inhibited mRNA expression of TNF-α and IL-6 with IC50 values of 15.3-52.4 µM.

Eight new glycosides with hepatoprotective activity isolated from the aerial parts of Morinda parvifolia.

Eight new glycosides, morindaparvins P-W, were isolated from the butanol extract of the aerial parts of Morinda parvifolia. These new structures were elucidated by comprehensive spectroscopic analysis and by comparing the experimental and calculated electronic circular dichroism spectra. The butanol extract was observed to significantly reduce the levels of alanine aminotransferase, aspartate transaminase, and lactate dehydrogenase in the sera of mice with concanavalin A-induced hepatitis. At a concentration of 10 µM, five compounds (1, and 4-7) isolated from the butanol extract possessed hepatoprotective activities against the damage induced by acetaminophen in human HepG2 liver cancer cells.

[Reviews on natural naphthoquinones and their bioactivities].

The naphthaquinones are widely distributed in plants. They are usually in higher plants, but a few of them were also found in microorganisms. There is a lot of research showing that they had multiple pharmaco-activities such as cytotoxic, antioxidant, anti-inflammatory and antibacterial activities, etc. In recent years, they have attracted extensive attention at home and abroad especially in terms of the anti-tumor activity. For further research, 69 new natural naphthoquinones reported in the last five years (2013-2017) were reviewed. They were divided into five major types: simple 1,4-naphthoquinones, furan and pyran naphthoquinones, 1,2-naphthoquinones, naphthohydroquinones and naphthoquinone polymers, which showed cytotoxic, antioxidative, anti-inflammatory and antibacterial biological activities, et al. The research of these compounds in the future was also proposed.

Glycosides of naphthohydroquinones and anthraquinones isolated from the aerial parts of Morinda parvifolia Bartl. ex DC (Rubiaceae) increase p53 mRNA expression in A2780 cells.

Eight previously undescribed naphthohydroquinone glycosides, namely morindaparvins H-O, together with four known anthraquinone glycosides were isolated from the n-BuOH extract of the aerial parts of Morinda parvifolia Bartl. ex DC (Rubiaceae). The structures of morindaparvins H-O were elucidated on the basis of spectroscopic analysis. To our knowledge, this is the first isolation of quinone glycosides from the plant M. parvifolia. The results showed that all 12 compounds at the concentration of 50 µM significantly increased p53 mRNA expression in A2780 cells compared with the blank control group.

[Constituents isolated from n-butanol extract of leaves of Moringa oleifera].

Seventeen compounds were isolated from n-butanol extract of the leaves of Moringa oleifera, using column chromatography over macroporous resin HP-20,Sephadex LH-20, and ODS. Their structures were identified as two carboline,tangutorid E(1) and tangutorid F(2); three phenolic glycosides,niazirin(3)，benzaldehyde 4-O-α-L-rhamnopyranoside(4) and 4-O-ß-D-glucopyranosidebenzoic acid(5); four chlorogenic acid and derivatives,4-caffeoylquinic acid(6),methyl 4-caffeoylquinate(7),caffeoylquinic acid(8) and methyl caffeoylquinate(9); two nucleosids,uridine(10) and adenosine(11); one flavone,quercetin 3-O-ß-D-glucopyranoside(12); five other types of compounds,phthalimidineacetic acid(13),3-pyridinecarboxamide(14),3,4-dihydroxy-benzoic acid(15),5-hydroxymethyl-2-furancarboxylic acid(16) and 5-hydroxymethyl-2-furaldehyde(17) by the spectral data of ¹H, ¹³C-NMR and MS. Among them,compounds 1-2,7,9-10,16 and 17 were isolated from M. oleifera for the first time.

A New Nortriterpenoid, a Sesquiterpene and Hepatoprotective Lignans Isolated from the Fruit of Schisandra chinensis.

A new nortriterpenoid, 19(R)-hydroxyl-wuweizidilactone H (1), and a sesquiterpene, (6R)-ß-chamigrenic acid (2), together with one known nortriterpenoid, wuweizidilactone H (3), and three known hepatoprotective lignans, micrantherin A (4), gomisin M2 (5) and schizandrin (6) were isolated from the fruit of Schisandra chinensis. Their structures were elucidated by UV, IR, HRESIMS, NMR spectra and X-ray analysis. Among them, the absolute configuration of 2 was confirmed for the first time. In vitro assays, compounds 4-6 (10 µM) exhibited hepatoprotective activities (survival rate: 44%, 43% and 44%) against damage induced by N-acetyl-p-aminophenol (APAP) in human liver carcinoma (HepG2) cells.