Ginkgolide Derivatives for Photolabeling Studies:  Preparation and Pharmacological Evaluation

Abstract

The terpene trilactones (TTLs), ginkgolides and bilobalide, are structurally unique constituents of Ginkgo biloba extracts, which exhibit various neuromodulatory properties. Although the TTLs are believed to be responsible for some of these effects, the specific interactions with targets in the central nervous system remain to be elucidated on a molecular level. Ginkgolides are known antagonists of the platelet-activating factor (PAF) receptor. Herein, we describe the first examination of the binding of native TTLs and their derivatives to the cloned PAF receptor, confirming that of the TTLs, ginkgolide B is the most potent PAF receptor antagonist. Ginkgolide derivatives carrying photoactivatable and fluorescent groups for the purpose of performing photolabeling have been prepared and evaluated using the cloned PAF receptor. These studies have shown that ginkgolide derivatives with aromatic photoactivatable substituents are potent PAF receptor antagonists with K i values of 0.09-0.79 µM and hence excellent ligands for clarifying the binding of ginkgolides to PAF receptor by photolabeling studies. Ginkgolide derivatives incorporating both fluorescent and photoactivatable groups still retained binding affinity to the PAF receptor and hence should be promising ligands for photolabeling and subsequent sequencing studies.

A Study of the Crystal Structure and Hydrogen Bonding of 3-Trifluoroacetyloxime Substituted 7-Acetamido-2-aryl-5-bromoindoles

“…The accurate calculated m/z values for these compounds, nevertheless, represent in each case a closet fit consistent with the assigned molecular structures. Whereas the 2-arylindole-3-acetoximes undergo acid-mediated Beckmann rearrangement into 3-acetamido-2-arylindoles with ease [21], the analogous oximes derived from the trifluoroacetyl derivatives are generally stable towards rearrangement into amides [22]. With this literature precedent in mind, we subjected compounds 2a-d to trifluoroacetic acid-mediated Beckmann rearrangement under reflux for 2 h following the literature precedent [11].…”

“…Aqueous work-up and purification of the crude products by silica gel column chromatography afforded compounds characterized by means of NMR, IR, and mass spectrometric methods as the corresponding 3-trifluoroacetyloxime substituted 7-acetamido-2-aryl-5-bromoindole derivatives 3a-d. The latter are interesting because the α-trifluoromethylated ketoximes can be tosylated or mesylated and then cyclized into the corresponding diaziridines [22][23][24]. Diaziridines, on the other hand, have been found to readily undergo oxidation into diazirines, which are important in photoaffinity labelling experiments in vivo and in vitro due to their propensity to undergo photochemical reactions to generate carbenes [23,24].…”

Chemistry and Biology of Terpene Trilactones fromGinkgo Biloba

“…DMSO may cause problems in certain assay systems, [140] although such effects are not uniformly observed. [141] To increase the water solubility of ginkgolides, Weber and Vasella synthesized glycosylated ginkgolide analogues. [142,143] Glycosidation was carried out by reaction of ginkgolides with a glycosylidene-derived diazirine to give a large number of glycosylated analogues.…”

“…[177] Clarification of the interactions between ginkgolides and PAFR at the molecular level can be carried out with photolabeling techniques. Therefore, we recently prepared photoactivatable derivatives of GB (2) and GC (3) [141] and generated highly potent analogues with 4-(bromomethyl)-benzophenone (81), trifluoromethyldiazirine (82), and tetrafluorophenyl azide (83) groups at the 10-OH position of GB (Figure 8) as the most active (K i = 90-150 nm). These derivatives are promising tools for characterizing the PAFRginkgolide interaction.…”

Influence of lipophilicity and stereochemistry at the C7 position on the cardioprotective and antioxidant effect of ginkgolides during rat heart ischemia and reperfusion

“…1) is essential for PAF antagonism [Corey and Srinivas Rao, 1991], it may be anticipated that any structural modification around the C 8 (e.g., change in local lipophilicity or steric crowding) may result in a modulation of anti-PAF activity of ginkgolides. A large series of C 1 and/or C 10 derivatives of GkB were tested as anti-PAF agents, and significant improvements in this property have been reported [Corey and Gavai, 1989;Chen et al, 1998;Hu et al, 1999Hu et al, , 2000Stromgaard et al, 2002]. The importance of the nature of the substituents at the C 7 position of ginkgolides on their pharmacological properties has been highlighted in myocardial ischemia/reperfusion studies [Pietri et al, 2001], showing that the weak PAF inhibitor 1, which should be less lipophilic than GkA and GkB owing to the increased number of hydroxyl substituents ( Fig.…”