Mingtao Liu

Pyridinium Alkaloid-Coupled Secoiridoids from the Flower Buds of Lonicera japonica

Three pyridinium inner salt alkaloids, lonijaposides A-C (1-3), based on an unprecedented skeleton of an N-substituted nicotinic acid nucleus coupled through C-5 with C-7 of a secoiridoid, together with seven known iridoids, have been isolated from the flower buds of Lonicera japonica. Their structures were elucidated by spectroscopic and chemical analyses. Lonijaposide C (3) showed activity against the release of glucuronidase in rat polymorphonuclear leukocytes induced by the platelet-activating factor.

Yaoshanenolides A and B: New Spirolactones from the Bark of Machilus yaoshansis

Two novel tricyclic spirolactones bearing long linear alkyl chains, yaoshanenolides A (1) and B (2), formed by Diels-Alder[4 + 2] cycloaddition of a molecule of each butenolide with β-phellandrene, were isolated from the bark of Machilus yaoshansis. Their structures and absolute configurations were determined by extensive spectroscopic methods, especially 2D NMR and ECD data analysis. The proposed biosynthetic pathway is discussed. Both compounds exhibited nonselective cytotoxic activities against several human cancer cell lines.

Dammarane Glycosides from the Root of Machilus yaoshansis

Nine new dammarane triterpene glycosides (1-3 and 8-13) and 12 known analogues have been isolated from an ethanol extract of the roots of Machilus yaoshansis. Compounds 1-7 have an uncommon 20,23-dihydroxydammar-24-en-21-oic acid-21,23-lactone moiety that was previously reported in compounds isolated from Gynostemma pentaphyllum. The configurations of the lactone moieties in 1-3 were determined by comparison of the experimental ECD spectra of 1-3 and the hydrolysates, 1a and 1b, with the corresponding calculated ECD spectra. On the basis of NMR and ECD data analysis of 1-7, the previously reported C-20 and C-23 configurations of 4-7 and related derivatives from Gynostemma pentaphyllum were revised. In addition, the application of NMR data and Cotton effects to the determination of the relative and absolute configurations of the γ-lactone moiety in 3β,20,23-trihydroxydammar-24-en-21-oic acid-21,23-lactone derivatives is discussed.

Abietane and C20-norabietane diterpenes from the stem bark of Fraxinus sieboldiana and their biological activities.

Fourteen new abietane (1-14) and seven new C(20)-norabietane (15-21) diterpenes, together with five known analogues, have been isolated from the stem bark of Fraxinus sieboldiana. Their structures were elucidated by spectroscopic data analysis. In the in vitro assays, at 10(-5) M, compounds 8, 16, and 22 showed inhibitory activity against the release of β-glucuronidase in rat polymorphonuclear leukocytes induced by platelet-activating factor, with 59.7 ± 4.8%, 56.1 ± 5.6%, and 65.9 ± 3.1% inhibition, respectively. Compound 23 was active against H5N1 avian influenza virus with an IC(50) value of 4.8 μM. Compounds 3 and 5 exhibited selective cytotoxic activities against A2780 (IC(50) 1.7 μM) and A549 (IC(50) 6.0 μM), respectively.

Glycosidic Constituents of the Tubers of Gymnadenia conopsea

Ten minor new glycosidic constituents (1- 10), together with 10 known compounds, have been isolated from a neuroprotective fraction of an ethanolic extract of the tubers of Gymnadenia conopsea. The structures of 1-10 were determined using spectroscopic and chemical methods. The compounds isolated were evaluated for activity in in vitro assays for acetylcholine esterase and monoamine oxidase inhibitory activities.

Glycosides from the bark of Adina polycephala.

Four new dimeric phenolic glycosides (1- 4), a new iridoid diglycoside (5), and 15 known glycosides have been isolated from an ethanolic extract of the bark of Adina polycephala. Their structures were determined by spectroscopic and chemical methods. Compounds 1, 3, and 5 showed in vitro inhibitory activity against the release of beta-glucuronidase in rat polymorphonuclear leukocytes induced by platelet-activating factor.

Machilusides A and B: Structurally Unprecedented Homocucurbitane Glycosides from the Stem Bark of Machilus yaoshansis

Two structurally novel homocucurbitane triterpenoid glycosides, machilusides A (1) and B (2), possessing an unprecedented C(36) skeleton with a D-fructose moiety incorporated into a cucurbitane nucleus forming unique cage-like tricyclic ring moieties, were isolated from the stem bark of Machilus yaoshansis. Their structures were determined by spectroscopic methods. Both compounds exhibited nonselective cytotoxic activities against several human cancer cell lines. The biosynthetic pathway of 1 and 2 was postulated.

Cucurbitane Glucosides from the Root of Machilus yaoshansis

Seven new cucurbitane triterpene glucosides (1-5, 8, and 9) and five known analogues (6, 7, 10, cucurbitacin I 2-O-β-d-glucopyranoside, and khekadaengoside K) have been isolated from an ethanol extract of roots of Machilus yaoshansis. Compounds 1 and 2 have an unusual 16,23:22,25-diepoxy unit, 4 is an uncommon cucurbitane 25-carbamate with the carbamoyl amino group attached at C-24 to form an oxazolidinone ring in the side chain, and 8 is the first example of a trinorcucurbitane derivative. The configurations in several pairs of C-24 epimeric cucurbitacins with 24,25-dihydroxy-22-one side chains were assigned, and the validity of J(23a,24) and J(23b,24) values to differentiate the configuration at C-24 in these cucurbitane derivatives is discussed. Compounds 2-4 showed in vitro activity against protein tyrosine phosphatase 1B with IC50 values of 8.63, 2.81, and 4.26 μM, respectively. Cucurbitacin E 2-O-β-d-glucopyranoside (10) showed selective cytotoxicity against BGC-823 and A549 cancer cells with IC50 values of 4.98 and 3.20 μM, respectively.

Butanolide derivatives from the bark of Machilus yaoshansis

Six new butanolide derivatives with long aliphatic side chains (1–6), together with 23 known lipophilic constituents, were isolated from the bark of Machilus yaoshansis. Their structures were elucidated by spectroscopic and chemical methods. All the isolates were evaluated for cytotoxic and anti-inflammatory activities.

Methoxylated fatty acids from the bark of Fraxinus sieboldiana

Nine new fatty acid derivatives, including seven methoxylated (1, 2, and 4–8) and two hydroxylated (3 and 9) fatty acids, have been isolated from the ethanol extract of the stem bark of Fraxinus sieboldiana. Their structures were determined by spectroscopic methods including IR, MS, 1D, and 2D NMR experiments. The 3- or 9-methoxylated fatty acids are reported for the first time in nature.