Anti-inflammatory constituents isolated from the flowers of Hosta plantaginea via suppression of the NF-κB signaling pathway in LPS-stimulated RAW 264.7 macrophages

Hosta plantaginea (Lam.) Aschers flower is traditionally used in China as an important herbal medicine for the treatment of inflammatory disease. The present study isolated one new compound, namely (3R)-dihydrobonducellin (1), and five known ones, p-hydroxycinnamic acid (2), paprazine (3), thymidine (4), bis(2-ethylhexyl) phthalate (5), and dibutyl phthalate (6) from H. plantaginea flowers. These structures were elucidated from spectroscopic data. Among them, compounds 1-4 remarkably suppressed nitric oxide (NO) production in lipopolysaccharide (LPS)-induced RAW 264.7 cells with half maximal inhibitory concentration (IC₅₀) values of 19.88 ± 1.81, 39.80 ± 0.85, 19.03 ± 2.35, and 34.63 ± 2.38 μM, respectively. Furthermore, compounds 1 and 3 (20 μM) significantly decreased levels of tumor necrosis factor α (TNF-α), prostaglandin E2 (PGE2), interleukin 1β (IL-1β), and IL-6. Additionally, compounds 1 and 3 (20 μM) prominently reduced the phosphorylation protein level of nuclear factor kappa-B (NF-κB) p65. The present findings indicated that compounds 1 and 3 may be new candidates against inflammation via blocking the NF-κB signaling pathway.

Synthesis and Structure Revision of Naturally Occurring Homoisoflavane (+)-Dracaeconolide B

Dracaeconolide B (1), a naturally occurring homoisoflavane, was isolated from the red resin of Dracaena cochinchinensis. Efforts have been made to elucidate the exact structure of compound 1 since it was confirmed that dracaeconolide B did not contain a 7-hydroxy-5,8-dimethoxy moiety. The structure of dracaeconolide B was revised by synthesis of three homoisoflavanes containing a 5,6,7-trioxygenated moiety each and analysis by NMR spectroscopy. The revised structure of dracaeconolide B was proposed as 3-(4-hydroxybenzyl)-7-hydroxy-5,6-dimethoxychromane. Noyori's Ru-catalyzed asymmetric transfer hydrogenation was used to synthesize (+)-dracaeconolide B. The absolute configuration of the compound was revised to S based on the results obtained by the electronic circular dichroism calculation. We examined the antiangiogenic activity of (S)- and (R)-dracaeconolide B and of synthetic 5,6,7- and 5,7,8-trioxygenated homoisoflavanes. The results can potentially help in the synthesis of related natural products and support drug discovery to treat neovascular eye diseases.

Enantioselective Synthesis of Homoisoflavanones by Asymmetric Transfer Hydrogenation and Their Biological Evaluation for Antiangiogenic Activity

Neovascular eye diseases are a major cause of blindness. Excessive angiogenesis is a feature of several conditions, including wet age-related macular degeneration, proliferative diabetic retinopathy, and retinopathy of prematurity. Development of novel antiangiogenic small molecules for the treatment of neovascular eye disease is essential to provide new therapeutic leads for these diseases. We have previously reported the therapeutic potential of anti-angiogenic homoisoflavanone derivatives with efficacy in retinal and choroidal neovascularization models, although these are racemic compounds due to the C3-stereogenic center in the molecules. This work presents asymmetric synthesis and structural determination of anti-angiogenic homoisoflavanones and pharmacological characterization of the stereoisomers. We describe an enantioselective synthesis of homoisoflavanones by virtue of ruthenium-catalyzed asymmetric transfer hydrogenation accompanying dynamic kinetic resolution, providing a basis for the further development of these compounds into novel experimental therapeutics for neovascular eye diseases.

Naturally Occurring Homoisoflavonoids: Phytochemistry, Biological Activities, and Synthesis (Part II)

This review documents all the new homoisoflavonoids (HIFs) that have been reported since 2007, whose total number has grown from 159 in 2007 to 295 at the present time. This review contains their structures, biological sources, plant parts they are obtained from, and, if reported, their optical rotations and melting points. The same classification is followed as an earlier review to ease reference to both reviews. This review takes note of the recent revision of plant families that were known to contain HIFs that have now been merged into one big family, Asparagaceae. Homoisoflavonoids also occur in Fabaceae and others. Two taxa, Ophiopogoan japonicus (Asparagaceae) and Caesalpinia sappan (Fabaceae), have been the source of many HIFs. These are briefly summarized. The biological properties of HIFs are also reviewed under the topics such as antioxidant, anti-inflammatory, antimicrobial, antidiabetic, and cytotoxic. The review also surveys the total synthesis of natural HIFs. All new compounds are classified and tabulated following the same style as the previous review.

Dedicated to Professor Andrew Paul Krapcho on the occasion of his 87th Birthday.

Direct Access to Chiral β-Fluoroamines with Quaternary Stereogenic Center through Cooperative Cation-Binding Catalysis

A direct route to chiral β-fluoroamines with tetrasubstituted C-F centers through the organocatalytic Mannich reaction of α-fluoro cyclic ketones and α-amidosulfones by using a chiral oligoethylene glycol as a cation-binding catalyst and KF as a base is reported. For most substrates, nearly perfect enantioselectivities were achieved even at very high temperatures (>80 °C). The salient features of this process include a) a transition-metal-free and operationally simple procedure, b) direct use of α-amidosulfones as bench-stable precursors of sensitive imines, c) direct enolization of racemic α-fluoro cyclic ketones, and d) excellent stereoselectivity up to 99 % enantiomeric excess and >20:1 diastereoselectivity (anti/syn). Thus, this protocol is easily scalable and provides a new approach for the synthesis of biologically relevant products with tetrasubstituted C-F centers. Furthermore, this protocol was also successfully extended to generate C-Cl and C-Br quaternary stereogenic centers.