Yongchun Yang

Lignans and Neolignans from Sinocalamus affinis and Their Absolute Configurations

Twenty-two new lignans and neolignans (1-22), together with 14 known analogues, have been isolated from an ethanolic extract of the stem (with skin removed) of Sinocalamus affinis. Their structures were elucidated by spectroscopic and chemical methods. On the basis of systematic NMR and circular dichroism (CD) data analysis, the validity of J7,8 and ΔδC8-C7 values to distinguish threo and erythro aryl glycerol units in different neolignans and the CD data [particularly the Rh2(OCOCF3)4-induced CD data (the E band)] to determine the absolute configurations at C-8 (C-7) of the aryl glycerol units are discussed. At a concentration of 10 μM, compounds 20 and 22 inhibited NO production in mouse peritoneal macrophages 84.2±5.9% and 71.7±1.0%, respectively. Compounds 19, 20, and 22 showed activity against serum deprivation induced PC12 cell damage by increasing the cell viability from 80.7±2.8% to 91.6±6.4%, 107.2±8.0%, and 97.6±8.5%, respectively.

Alkaloids from the Root of Isatis indigotica

Seventeen new alkaloids (1-17) and 14 known analogues have been isolated from an aqueous extract of the root of Isatis indigotica. The structures and absolute configurations of these compounds were determined by extensive spectroscopic data analysis, including 2D NMR, single-crystal X-ray crystallography using anomalous scattering of Cu Kα radiation, and electronic circular dichroism spectra calculations based on the quantum-mechanical time-dependent density functional theory. Compounds 1, 2, and 3 are the first examples of natural products with unique linkages between a molecule of 2-(4-methoxy-1H-indol-3-yl)acetonitrile and 2-(1H-indol-3-yl)acetonitrile, 2-(4-methoxy-1H-indol-3-yl)acetonitrile, and 4-hydroxyphenylethane, respectively. Compounds (-)-4 and (+)-4 represent the first natural products with the pyrrolo[2,3-b]indolo[5,5a,6-b,a]quinazoline skeleton. Some structural assignments for the new alkaloids suggest that the assignments made for certain previously reported alkaloids require revision. Compounds 1-3 and arvelexin (18) show antiviral activity against the influenza virus A/Hanfang/359/95 (H3N2), with IC(50) values of 3.70-12.35 μM, and 17 inhibits Coxsackie virus B3 replication with an IC(50) of 6.87 μM.

A minor diterpenoid with a new 6/5/7/3 fused-ring skeleton from Euphorbia micractina.

A novel diterpenoid with an unprecedented 6/5/7/3 fused-ring skeleton, euphorbactin (1), was isolated from an ethanol extract of the roots of Euphorbia micractina. The structure was determined by extensive spectroscopic studies, especially by 2D NMR and CD data analysis. A proposed biosynthetic pathway and preliminary investigations of the biological activity of compound 1 are also discussed.

Bioactive neolignans and lignans from the bark of Machilus robusta.

Sixteen new neolignans and lignans (1-16), together with 12 known analogues, have been isolated from an ethanol extract of the bark of Machilus robusta. Compounds 1 and 2 showed activity against HIV-1 replication in vitro, with IC(50) values of 2.52 and 2.01 μM, respectively. At 10 μM, 6, 8, and 9 reduced dl-galactosamine-induced hepatocyte (WB-F344 cells) damage, and 9 could additionally attenuate rotenone-induced PC12 cell damage. The known compounds (-)-pinoresinol (17) and (+)-lyoniresinol (18) were active against serum deprivation induced PC12 cell damage.

Highly acylated diterpenoids with a new 3,4-secograyanane skeleton from the flower buds of Rhododendron molle.

Four highly acylated diterpenoids with a new 3,4-secograyanane skeleton, secorhodomollolides A-D (1-4), have been isolated from the flower buds of Rhododendron molle. Their structures including absolute configurations were determined on the basis of spectroscopic data interpretation and single-crystal X-ray crystallography. Compound 4 exhibited significant analgesic and sedative effects at a dose of 5 mg/kg, and compound 2 showed selective cytotoxic activity against human hepatoma carcinoma cell line (Bel-7402) with IC(50) 0.97 microM.

Glucosylated caffeoylquinic acid derivatives from the flower buds of Lonicera japonica.

Three new glucosylated caffeoylquinic acid isomers (1–3), along with six known compounds, have been isolated from an aqueous extract of the flower buds of Lonicera japonica. Structures of the new compounds were determined by spectroscopic and chemical methods as (−)-4-O-(4-O-β-d-glucopyranosylcaffeoyl)quinic acid (1), (−)-3-O-(4-O-β-d-glucopyranosylcaffeoyl)quinic acid (2), and (−)-5-O-(4-O-β-d-glucopyranosylcaffeoyl)quinic acid (3), respectively. In the preliminary in vitro assays, two known compounds methyl caffeate and 2ʹ-O-methyladenosine showed inhibitory activity against Coxsackie virus B3 with IC50 values of 3.70 μmol/L and 6.41 μmol/L and SI values of 7.8 and 12.1, respectively.

Diterpenoid alkaloids from the lateral root of Aconitum carmichaelii.

Twenty-six new diterpenoid alkaloids, 1-26 (1-4: hetisan-type C(20)-diterpenoid alkaloids; 5-26: aconitane C(19)-diterpenoid alkaloids), and two known analogues, hypaconitine 27 and benzoylmesaconine 28, have been isolated from a water extract of the lateral root of Aconitum carmichaelii. Compounds 7 and 8 are rare examples of conformational isomers obtained from the same material. The conformation and conformational transformation of ring A in the C(19)-diterpenoid alkaloids are discussed on the basis of NMR data analysis in combination with single-crystal X-ray crystallography of 6 and 27 by anomalous scattering of Cu Kα radiation. In preliminary analgesic and toxicity assays, the isomer with ring A in the chair conformation (8 or 27) was found to be more active than that with ring A in the boat conformation (7 or 27a). In addition, 15, 16, and 19 showed neuroprotective activity.

C14-Polyacetylene glucosides from Codonopsis pilosula

Seven new C14-polyacetylene glucosides codonopilodiynosides A–G (1–7) were isolated from an aqueous extract of the Codonopsis pilosula roots. Their structures were determined by spectroscopic and chemical methods as (–)-(5S,6E,12E)-tetradeca-6,12-dien-8,10-diyn-1,5,14-triol 5-O-β-d-glucopyranoside (1), (–)-(5S,6E,12E)-tetradeca-6,12-dien-8,10-diyn-1,5,14-triol 5-O-β-d-glucopyranosyl-(1″ → 2′)-β-d-glucopyranoside (2), (–)-(5S,6E,12E)-tetradeca-6,12-dien-8,10-diyn-1,5,14-triol 5,14-di-O-β-d-glucopyranoside (3), (–)-(5S,6E)-tetradeca-6-en-8,10-diyn-1,5,14-triol 5-O-β-d-glucopyranoside (4), (–)-(5S,6E,12E)-tetradeca-6,12-dien-8,10-diyn-1,5-diol 5-O-β-d-glucopyranosyl-(1″ → 2′)-β-d-glucopyranoside (5), (–)-(6S,4E,12E)-tetradeca-4,12-dien-8,10-diyn-1,6-diol 6-O-β-d-glucopyranosyl-(1″ → 2′)-β-d-glucopyranoside (6), and (–)-(5S,6E)-tetradeca-6-en-1,5-epoxy-8,10-diyn-14-ol 14-O-β-d-glucopyranosyl-(1″ → 2′)-β-d-glucopyranoside (7), respectively. The absolute configurations of 1–7 were assigned by enzymatic hydrolysis followed by isolation of glucose and aglycones (1a and 4a–7a), and subsequent comparison of specific rotation, TLC, and 1H NMR data of the glucose with an authentic sugar sample and application of modified Moshers method based on the MPA determination rule of ΔδRS values for 1a and 4a, and ΔδS values for 6a. The configuration of 7 was assigned by electronic circular dichroism calculations based on the quantum-mechanical time-dependent density functional theory.

Acetylenes and fatty acids from Codonopsis pilosula

Four new acetylenes (1–4) and one new unsaturated ω-hydroxy fatty acid (5), together with 5 known analogues, were isolated from an aqueous extract of Codonopsis pilosula roots. Their structures were determined by spectroscopic and chemical methods. The new acetylenes are categorized as an unusual cyclotetradecatrienynone (1), tetradecenynetriol (2), and rare octenynoic acids (3 and 4), respectively, and 3 and 4 are possibly derived from oxidative metabolic degradation of 1 and/or 2. The absolute configuration of 1 was assigned by comparison of the experimental circular dichroism (CD) spectrum with the calculated electronic circular dichroism (ECD) spectra of stereoisomers based on the quantum-mechanical time-dependent density functional theory, while the configuration of 2 was assigned by using modified Mosher׳s method based on the MPA determination rule of ΔδRS values for diols.

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.