PAF receptor and "Cache-oreilles" effect. Simple PAF antagonists

Structure-activity relationships in platelet-activating factor. Part 13: synthesis and biological evaluation of piperazine derivatives with dual anti-PAF and anti-HIV-1 or pure antiretroviral activity

HIV-1 infection of the brain and PAF neurotoxicity are implicated in AIDS dementia complex. We previously reported that a trisubstituted piperazine derivative is able to diminish both HIV-1 replication in monocyte-derived macrophages and PAF-induced platelet aggregation. We report in this work new compounds obtained by modifying its piperazine substituents. The structure-activity relationship study shows that a better dual activity or even pure antiretroviral compounds can be obtained in this series.

Enantioselective synthesis of the oxadecalin core of phomactin A via a highly stereoselective Diels-Alder reaction

Phomactin A (1) is a selective antagonist of platelet activating factor (PAF). Herein, we report our progress toward the construction of the oxadecalin core of 1. This route is based on the Diels-Alder cycloaddition of an appropriately functionalized vinyl pyran and a complementary dienophile. A model of this reaction involving 2 and maleic anhydride was conducted. Adduct 3 contains the correct stereochemical arrangements between functional groups necessary for gaining access to phomactin A. Reaction: see text.

A Nozaki-Hiyama-Kishi Ni(II)/Cr(II) coupling approach to the phomactins

[reaction: see text] Through a unified synthetic strategy, appropriately functionalized bicyclic starting materials can be elaborated via Ni(II)/Cr(II) macrocylization to [9.3.1] bicycles. Elaboration of these core structures allows access to phomactin C/D analogues and establishes the first synthetic approach to phomactin A affording an intact octahydrochromene/macrocyclic ring system.

Structure-activity relationships in platelet-activating factor (PAF). 10. From PAF antagonism to inhibition of HIV-1 replication

Excessive levels of PAF and cells of macrophage lineage appear to play an important role in neuronal cell injury, inflammatory syndrome, and HIV replication in CNS resulting in AIDS dementia complex (ADC). The beneficial effects of PAF receptor antagonists are evident and give rise to expected therapeutic strategies for neurotrauma. Piperazine derivatives bearing a "cache-oreilles" (ear-muff) electronic distribution are able to inhibit in vitro PAF effects and, thus, could be used in pathologies where this mediator is involved. Therefore, their potential anti-HIV activity was investigated, and we find that (i) these PAF antagonists are effectively active in HIV-infected monocyte-derived macrophages (MDM) but there is no correlation between both anti-HIV and anti-PAF activities; (ii) the presence of a carbamate function (compounds 1a-d) is favorable to the antiviral activity; (iii) the lipophilicity of the substituent on the piperazinic cycle seems to be less important for the anti-PAF activity than for the antiviral one. Our leading compound, PMS 601 (compound 1a), presents a dual activity with IC(50) of 8 and 11 microM for anti-PAF and anti-HIV activity, respectively, without cytotoxic events at 1000 microM in MDM. Although its mode of action is not clearly defined, these data suggest that PMS 601, which displays no effect on acellular reverse transcriptase or protease tests, deserves further investigation in the treatment of HIV-1-associated dementia.

A pharmacophore for high affinity PAF antagonists. II. Hydrophobicity study using the molecular lipophilicity potential

Platelet-activating factor (PAF) is a powerful phospholipid-derived autacoid involved in many physiopathological mechanisms. Many PAF antagonists have been synthesized and evaluated as therapeutic candidates. In a previous report, we have described an electronic pharmacophore of PAF antagonists using the molecular electrostatic potential. In the present study, a molecular lipophilicity potential is used to compare the hydrophobic properties of 49 "heterocyclic sp2 nitrogen' highly potent PAF antagonists, belonging to six structurally different series (nine hetrazepines, five pyrrolo[1,2-c]thiazoles, 14 carboxamides, nine dihydropyridines, nine pyridinyl-thiazolidines and three imidazo[4,5-c]pyridines). Their common features consist of three hydrophilic (HYD2, HY14(3)B and HYD3) and two lipophilic zones (LIP3 and LIP4), defining the lipophilic pharmacophore of the antagonists. This pharmacophore is also characterized by several zone-to-zone distances: HYD3-HYD2 = 1.3 +/- 1.0 A, HY3B-HYD2 = 7.8 +/- 1.1, HYD3-HY3B = 5.1 +/- 1.1 A, LIP4-LIP3 = 5.4 +/- 1.1 A, LIP3-HYD2 = 11.3 +/- 1.6 A, LIP3-HY3B = 5.9 +/- 1.0 A, LIP3-HYD3 = 4.3 +/- 0.9 A, LIP4-HYD2 = 14.7 +/- 1.6 A, LIP4-HY3B = 8.1 +/- 1.2 A and LIP4-HYD3 = 3.9 +/- 1.1 A. These results represent a new step in the determination of a global pharmacophore for PAF antagonists.

Design and modeling of new platelet-activating factor antagonists. 2. Synthesis and biological activity of 1,4-bis-(3',4',5'-trimethoxybenzoyl)-2-alkyl and 2-alkyloxymethylpiperazines

In the continuation of our investigations on the structure of platelet-activating factor (PAF)-receptor, 25 additional 2-substituted 1,4-bis-(poly- and mono methoxybenzoyl)-piperazines were synthesized and their in vitro biological activities measured. Substituent at position 2 is representative of the classical balance lipophilicity/hydrophilicity, i.e. alkyl, phenylalkyl, alkoxy and polyalkoxy groups. A potent PAF-induced platelet aggregation inhibitory activity measured in PRP medium is obtained with 5c, IC50 = 6 x 10(-8) M, which displaces the [3H]PAF from platelet membrane with an EC50 = 6 x 10(-8) M, and compound 4 presents an EC50 of 3 x 10(-8) M. Examination of structure-activity relationships shows that molecules bearing a hydrophilic or slightly hydrophobic appendix in position-2 are still potent; their IC50 being included between 10(-6) and 10(-7) M. After quantitative analysis, it seems that in PRP medium, the role of serum albumin must be taken into account instead of a pure hydrophobic interaction of the appendix Z into the receptor. The role of the methoxy groups in producing a potent antagonistic activity is demonstrated by syntheses of several 2-octylpiperazine analogs. These specific features will be quantitatively analysed in the following related publication (part 3).

A pharmacophore for high affinity PAF antagonists. I. Electronic model using molecular electrostatic potential

PAF is a powerful phospholipid-derived autacoid involved in many physio-pathological mechanisms. Many PAF antagonists have been synthesized and assayed for therapeutic purposes. In this study, molecular electrostatic potential is used to compare the electronic properties of 48 'heterocyclic sp2 nitrogen' highly potent PAF antagonists, belonging to six series (nine hetrazepines, five pyrrolo[1,2-c]thiazoles, 14 carboxamides, nine dihydropyridines, nine pyridinylthiazolidines and two imidazo[4,5-c]pyridines). Their common features consist of three main electronegative zones (A, B1 and B2) describing the electronic pharmacophore of these ligands. The high affinity of these PAF antagonists seems to be related to this electronegative system A-B(x), which is characterized by three distances A-B1 (9.3 +/- 1.0 A), A-B2 (13.4 +/- 0.7 A) and B1-B2 (4.9 +/- 0.9 A). Moreover, B1 and B2 may surround a common anchorage point in the binding site of the receptor.

A Monte Carlo pharmacophore generation procedure: application to the human PAF receptor

A novel pharmacophore definition procedure is described, which uses a Monte Carlo method to superimpose molecules. Pharmacophore space is searched by a technique similar to high temperature annealing. Subsequent refinement of candidate pharmacophores by energy minimization produces low-energy conformations that may be involved in receptor binding. The method has been applied to compounds that bind to the human platelet-activating factor (PAF) receptor. Alternative binding site models for the PAF receptor are presented and discussed.