Xiao-Zhen Chen

Brevianamide J, A New Indole Alkaloid Dimer from Fungus Aspergillus versicolor

Brevianamide J (1), a new indole alkaloid dimer, was isolated together with four new diketopiperazine alkaloids (brevianamide K-N, 2-5) from the solid-state fermented culture of Aspergillus versicolor. Their structures were elucidated on the basis of spectral data. X-ray crystallographic analysis confirmed the structures of 1 and 4.

Lathyrol Diterpenes as Modulators of P-Glycoprotein Dependent Multidrug Resistance: Structure–Activity Relationship Studies on Euphorbia Factor L3 Derivatives

Five series of 37 new acylate and epoxide derivatives (3-39) of Euphorbia factor L3, a lathyrol diterpene isolated from Euphorbia lathyris, were designed by modifying the hydroxyl moiety of C-3, C-5, or C-15. Chemoreversal effects of the acylates on multidrug resistance (MDR) were evaluated in breast cancer multidrug-resistant MCF-7/ADR cells that overexpress P-glycoprotein (P-gp). Eight derivatives exhibited greater chemoreversal ability than verapamil (VRP) against adriamycin (ADR) resistance. Compounds 19 and 25 exhibited 4.8 and 4.0 times, respectively, more effective reversal ability than VRP against ADR resistance. To determine the key characteristics of Euphorbia factor L3 derivatives that contribute to MDR reversal, we conducted a structure-activity relationship study of these compounds. The simulation studies indicated different possible mechanisms and revealed the important influence of hydrophobic interactions and hydrogen bonds in the flexible cavity of P-gp.

Analysis of phenolic glycosides from Ilex litseaefolia using electrospray ionization quadrupole time-of-flight mass spectrometry.

Figure 1. Phenolic glycosides: 3-hydroxy-4-O-b-D-(6-Oacetylglucopyranosyl)benzyl vanilloate (litseaefoloside A (1), Mr 494.1424); 3-hydroxy-4-O-b-Dglucopyranosylbenzyl vanilloate (vanilloylcalleryanin (2), Mr 452.1319); 4-O-b-Dglucopyranosylbenzyl vanilloate (3, Mr 436.1369); 3-hydroxy4-O-b-D-(6-O-caffeoylglucopyranosyl)benzyl vanilloate (litseaefoloside C (4), Mr 614.1636); 3-hydroxy-4-O-b-D-(6-Ovanilloylglucopyranosyl)benzyl vanilloate (litseaefoloside D (5), Mr 602.1636); 4-O-b-D-(6-O-vanilloylglucopyranosyl)vanillic acid (6, Mr 480.1268). Dear Editor,

Analysis of cipadesin limonoids from Cipadessa cinerascens using electrospray ionization quadrupole time-of-flight tandem mass spectrometry and quantum chemical calculations

RATIONALE Limonoids, a class of tetranortriterpenoids, exhibit various biological effects, such as insect antifeedant and growth regulating activities, antimicrobial activity, potent cell adhesion inhibitory effects, antimalarial activity, anticancer activities, and antioxidant activity. The potential application brings the need for reliable, fast and low-cost analysis of this class of compounds. METHODS Six cipadesin limonoids (1-6), including a pairs of isomers, from leaves and barks of Cipadessa cinerascens were investigated by electrospray ionization quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) in positive-ion mode. Characteristic processes were further studied by theoretical calculations. RESULTS 1,3-Hydrogen rearrangement might play a significant role in the cleavage of -O- bridge bond in ring B and further produces some characteristic ions. For [M + Na](+) precursor ions, the product ion at m/z 133 might indicate the structure of ring A and the losses of CO(2) and AcOH occur readily. Interestingly, the radical product ion at m/z 460 from [M + Na](+) ions seems to be the characteristic ion for compound 1. A deuterium-labeling experiment supported the processes forming the radical ion. For [M + NH(4)](+) ions, high-abundance product ions resulting from sequential loss of AcOH can be observed. In addition, a pairs of isomers was unambiguously differentiated based on MS or MS/MS spectra. CONCLUSIONS In summary, sufficient information obtained from fragmentation experiments of [M + Na](+), [M + NH(4)](+) or [M + H](+) precursor ions is especially valuable for rapid identification of these limonoids or their metabolites in complex mixtures. The high-abundance radical product ion is of scientific interest.

Evaluation of relative isotopic abundance measurements in a quadrupole time-of-flight mass spectrometer for elemental composition determination of natural products in traditional Chinese medicine

The relative isotopic abundance (RIA) measurement errors of a quadrupole time-of-flight (Q-ToF) instrument incorporating analog-to-digital converter detectors were systemically evaluated by stochastically collecting about 200 data in positive ion mass spectrometry (MS) mode. Errors varied with peak intensities at definite spectral acquisition rates but were very close, even if peak intensities changed sharply at different spectral acquisition rates with the same concentration. Intensity thresholds were systematically defined at 1 Hz of spectral acquisition rates. RIA measurement errors were also evaluated using peak area. It seemed that peak area was better adapted for the high-intensity ions while peak intensity was suited for very low-intensity ions. Several known compounds were selected for RIA measurements for product ions in tandem mass spectropmetry (MS/MS) mode. An extract of a representative traditional Chinese medicinal, Paederia scandens was analyzed with high-performance liquid chromatography-electrospray ionization-QToF-MS/MS. The unique elemental compositions of some compounds could not be identified even with exact masses and MS/MS spectra of measured and reference compounds. RIA errors, especially of (M + 2)M−1, provided vital information for determining the elemental composition.

A new bergenin derivative from Corylopsis willmottiae

A new bergenin derivative, 11-O-(3′-O-methylgalloyl)-bergenin, was isolated from the whole plants of Corylopsis willmottiae Rehd. et Wils, along with 11-O-galloylbergenin, 11-O-syringylbergenin, bergenin, 4-O-galloylbergenin, and 4,11-di-O-galloylbergenin. They were identified on the basis of spectral evidence.

Chemical constituents of Nouelia insignis Franch.

Two new diterpenes and ent-15α-hydroxykaur-16-en-19-oic acid 11,12-acetonide (3), together with 23 known compounds were isolated from the dried aerial parts of Nouelia insignis Franch. The structures of new compounds were determined to be ent-14β,15α-dihydroxykaur-16-en-19-oic acid (1), ent-14β-hydroxy-15-oxokaur-16-en-19-oic acid (2) on the basis of spectral and chemical evidence. The structure of ent-11α,16α-epoxy-15α-hydroxy-16S-kaur-19-oic acid (4) was confirmed by X-ray crystallographic analysis.

A new alternariol glucoside from fungus Alternaria alternate cib-137

A new secondary metabolite, 2-O-methylalternariol 4-O-β-[4-methoxyl-glucopyranoside] (1), together with four known compounds alternariol methyl ether (2), altenuene (3), isoaltenuene (4) and 2-(2′S-hydroxypropyl)-5-methyl-7-hydroxychromone (5), was isolated from the fungus Alternaria alternate cib-137. Its structure was elucidated on the basis of spectroscopic data. Compounds 3 and 4 demonstrated moderate activity against Staphylococcus aureus.

Efficient algorithms for the prize collecting Steiner tree problems with interval data

Given a graph G = (V,E) with a cost on each edge in E and a prize at each vertex in V, and a target set V′ ⊆ V, the Prize Collecting Steiner Tree (PCST) problem is to find a tree T interconnecting vertices in V′ that has minimum total costs on edges and maximum total prizes at vertices in T. This problem is NP-hard in general, and it is polynomial-time solvable when graphs G are restricted to 2-trees. In this paper, we study how to deal with PCST problem with uncertain costs and prizes. We assume that edge e could be included in T by paying cost xe ∈ [ce-, ce+] while taking risk ce+ - xe/ce+ - ce- losing e, and vertex v could be awarded prize pv ∈ [pv-,pv+] while taking risk yv-pv- / pv+ - pv- of losing the prize. We establish two risk models for the PCST problem, one minimizing the maximum risk over edges and vertices in T and the other minimizing the sum of risks. Both models are subject to upper bounds on the budget for constructing a tree. We propose two polynomial-time algorithms for these problems on 2-trees, respectively. Our study shows that the risk models have advantages over the tradional robust optimization model, which yields NP-hard problems even if the original optimization problems are polynomial-time solvable.

Analysis of sesterterpenoids from Aspergillus terreus using ESI-QTOF and ESI-IT.

INTRODUCTION Biosynthesis of terretonin was studied due to the interesting skeleton of this series of sesterterpenoids. Very recently, López-Gresa reported two new sesterterpenoids (terretonins E and F) which are inhibitors of the mammalian mitochondrial respiratory chain. Mass spectrometry (MS), especially tandem mass spectrometry, has been one of the most important physicochemical methods for the identification of trace natural products due to it rapidity, sensitivity and low levels of sample consumption. The potential application prospect and unique skeleton prompted us to study structural characterisation using MS. OBJECTIVE To obtain sufficient information for rapid structural elucidation of this class of compounds using MS. METHODOLOGY The elemental composition of the product ions was confirmed by low-energy ESI-CID-QTOF-MS/MS analyses. The fragmentation pathways were postulated on the basis of ESI-QTOF-MS/MS/MS and ESI-IT-MS(n) spectra. Common features and major differences between ESI-QTOF-MS/MS and IT-MS(n) spectra were compared. For ESI-QTOF-MS/MS/MS experiments, capillary exit voltage was raised to induce in-source dissociation. Ammonium acetate or acetic acid were added into solutions to improve the intensity of [M + H]+. The collision energy was optimised to achieve sufficient fragmentation. Some fragmentation pathways were unambiguously proposed by the variety of abundance of fragment ions at different collision energies even without MS(n) spectra. RESULTS Fragmentation pathways of five representative sesterterpenoids were elucidated using ESI-QTOF-MS/MS/MS and ESI-IT-MS(n) in both positive- and negative-ion mode. The key group of characterising fragmentation profiles was ring B, and these fragmentation patterns are helpful to identify different types of sestertepenoids. CONCLUSION Complementary information obtained from fragmentation experiments of [M + H]+ (or [M + NH4]+ and [M-H](-) precursor ions is especially valuable for rapid identification of this kind of sesterterpenoid.