Synthesis and biological activity of amide derivatives of ginkgolide A

Amide Derivatives of Ginkgolide B and Their Inhibitory Effects on PAF-Induced Platelet Aggregation

Ginkgolides are the most important components of Ginkgo biloba extracts, whose lactone can be hydrolyzed in the aqueous environment. Although the hydrolyzed products have complex structures and their functions are not well-understood, opening the lactone ring is an important strategy in producing novel derivatives of ginkgolide. The preparation of a single pure aminolyzed ginkgolide for the study of its bioactivity and understanding of the process of aminolysis are challenging. To obtain stable aminolyzed products, four amide derivatives (2-5) of ginkgolide B (GB, 1) were prepared via the ring-opening reaction of its lactone with propylamine. These products were purified and fully identified by high-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) spectroscopy and were further evaluated for their ability to inhibit the PAF-induced platelet aggregation of rabbit platelets in vitro. Compound 2, which was obtained by selective aminolysis of the lactone ring C of GB, showed a much better inhibitory activity of platelet aggregation (IC₅₀, 15 nM) than the parent compound GB (IC₅₀, 442 nM). The other three products (3-5), which were obtained by the aminolysis of lactone rings C and F of GB, did not show platelet aggregation inhibitory activity. The results greatly extended our understanding of the chemistry of GB and provided important structural information for the exploration and development of new drugs based on ginkgolides in G. biloba.

Lactols in an asymmetric aldol-desymmetrization sequence: access to tetrahydro-4H-furo[2,3-b]pyran-2-one and tetrahydro-4H-furo[2,3-b]furan-2-one derivatives

An asymmetric aldol-desymmetrization sequence was developed which provided highly efficient access to important bicyclic oxygen-containing scaffolds with multiple chiral centers and one is a quaternary stereogenic center containing a free hydroxy group. Moreover, starting from racemic precursors, the final products were obtained as two separable diastereomers by flash chromatography. Several other heterocycles could also be easily generated with this strategy.

Understanding the regulation mechanisms of PAF receptor by agonists and antagonists: Molecular modeling and molecular dynamics simulation studies

Platelet-activating factor receptor (PAFR) is a member of G-protein coupled receptor (GPCR) superfamily. Understanding the regulation mechanisms of PAFR by its agonists and antagonists at the atomic level is essential for designing PAFR antagonists as drug candidates for treating PAF-mediated diseases. In this study, a 3D model of PAFR was constructed by a hierarchical approach integrating homology modeling, molecular docking and molecular dynamics (MD) simulations. Based on the 3D model, regulation mechanisms of PAFR by agonists and antagonists were investigated via three 8-ns MD simulations on the systems of apo-PAFR, PAFR-PAF and PAFR-GB. The simulations revealed that binding of PAF to PAFR triggers the straightening process of the kinked helix VI, leading to its activated state. In contrast, binding of GB to PAFR locks PAFR in its inactive state.

Inhibitory effect of the Korean herbal medicine, Dae-Jo-Whan, on platelet-activating factor-induced platelet aggregation

The anti-thrombic properties of the Korean herbal medicine, Dae-Jo-Hwan (DJW) were investigated. Water extracts, a 70% methanol (MeOH) extract and an ethyl acetate (EtOAc) soluble fraction (III) from DJW inhibited platelet-activating factor (PAF)-induced platelet aggregation in vitro and in vivo assays. The extracts of DJW and eleven herbs from which it is derived, except for Panax ginseng Meyer, Angelica sinensis (OLIV.) DIELS and Schisandra chinensis Baill., inhibited AA-induced blood platelet aggregation to various extents. The effects observed with total DJW was synergistic over-additive rather that additive since the sum of single contributions was lower than the effect of the total extract. Fraction III was specially protected against the lethality of PAF, while verapamil did not afford any protection. Exogenously applied arachidonic acid (AA) (100 microM) led to a 89% platelet aggregation, the release of 14 pmol of ATP, and the formation of either 225 pg of thromboxane A2 (TXA2) or 45 pg of prostaglandin E2 (PGE2), each parameter being related to 10(6) platelets. An application of DJW 5 min before AA, dose-dependently diminished aggregation, ATP-re lease, and the synthesis of TXA2 and PGE2, with IC(50) values of 70, 87, 65 and 72 microg/ml, respectively. The similarity of the IC(50) values suggests the inhibition of cyclooxygenase (COX) by DJW as the primary target, thus suppressing the generation of TXA2, which induces platelet aggregation and the exocytosis of ATP by its binding on TXA2-receptors. These results indicate that DJW shows anti-thrombotic action on human platelets and inhibits the action of PAF in vivo by an antagonistic effect on PAF. Therefore, it may be useful in treating disorders caused by PAF.

QSAR analyses on ginkgolides and their analogues using CoMFA, CoMSIA, and HQSAR

Ginkgolides, isolated from ginkgo balba leaves, were found to be powerful as natural antagonists of human platelet activating factor (PAF) in treatment of some diseases such as acute inflammation, tissue rejection, asthma, and ischemic injury. Ginkgolides have a cage skeleton consisting of six five-membered rings, therefore, are very tough to be synthesized. For finding new powerful substitutes of the natural ginkgolides for treating those diseases, three methods, viz. CoMFA, CoMSIA, and HQSAR, were used to investigate the relationship between 117 ginkgolide analogues with great structural diversity and their bioactivities against PAF receptor. The high q2 released from the different QSAR methods, ranging from 0.583 to 0.684, suggests that three rational and predictive QSAR models were successfully built. These models also show clearly how steric, electrostatic, hydrophobicity, and individual atom affect molecular bioactivity as antagonists of PAF. These results could also be used to account for the unusually higher bioactivity of ginkgolide B than other ginkgolides. The possible binding mechanism between ginkgolides and human PAF receptor was also deduced based on the QSAR models. Therefore, this study should be very helpful in discovering new drugs as PAF antagonists in fighting against various diseases related to PAF and PAF receptor.