Jean-Jacques Godfroid

Platelet activating factor (PAF-acether): total synthesis of 1-O-octadecyl 2-O-acetyl sn-glycero-3-phosphoryl choline

Platelet-activating factor (PAF), a mediator of anaphylaxis and inflammation, is released from IgE-sensitized antigen-stimulated basophils [l-3]. PAF is a low molecular weight phospholipid which is sensitive to hydrolysis by phospholipases AZ, C, and D, but not by lipase from Rhizopus arrhizus or sphingomyelinase C [4]. PAF appeared to be a glycerophospholipid with a choline polar head group devoid of an ester function at position 1 [4,5]. The presence of PAF has been demonstrated in cells from several species including man [3,6,7], rabbit [l-3], rat [8] and pig [4]. PAF has been obtained from rat and mouse peritoneal macrophages upon stimulation by the ionophore A23187 or exposure to phagocytable particles [9]. PAF has been shown to induce aggregation of blood platelets from rabbit [1,3],man [lO],rat [ll] andguineapig [12].The structure of the molecule responsible for PAF activity has been elucidated [13,14]. This was obtained by acetylation of 2-lyso plasmalogens possessing a 30phosphoryl choline group [ 131 or a 3-O-phosphoryl ethanolamine group followed by reaction with diazomethane and quaternization with methyl iodide [ 141. This result lead us to propose a 1 -O-alkyl 2-0-acetyl sn-glycero3-phosphoryl choline structure and the terminology ‘PAF-acether’ for this substance. However, total synthesis was necessary to confirm the structure of PAF-acether. Here, we report the total synthesis of l-O-octadecyl20acetyl sn-glycero3-phosphoryl choline, which has the same biological activity as the natural PAF-acether.

Alkyl analogs of diacylglycerol as activators of protein kinase C

Diacylglycerols which activate protein kinase C have the 1,2‐sn configuration. Short‐chain saturated fatty acids or long‐chain unsaturated fatty acids are required for supporting the potency of these lipids. Using alkyl analogs such as 1‐O‐decyl‐2‐O‐decanoylglycerol, 1‐O‐decanoyl‐2‐O‐decylglycerol, 1,2‐O‐didecyl‐glycerol, 1‐O‐hexadecyl‐2‐O‐acetylglycerol and 1‐O‐decyl‐2‐O‐acetylglycerol, we showed that the ether bond was consistently associated with a loss of activity to varying extents. The results suggest that the ester bond in the 1‐position is a major determinant of diacylglycerol‐mediated protein kinase activation.

An Efficient Asymmetric Synthesis of Prostaglandin E1

An asymmetric total synthesis of Prostaglandin E1 (5) has been achieved in a two-component coupling process. The chiral hydroxycyclopentenone 6 was readily available from furan with 96% ee. The key reaction step was a kinetic enzymatic resolution followed by an in situ inversion. A catalytic asymmetric reduction of the γ-iodo vinyl ketone 19 with the Corey CBS catalyst gave the ω-side chain 7 with >96% ee. Conjugate addition using the reaction with dilithiocyanocuprate followed by mild cleavage of the silyl protective groups and enzymatic hydrolysis of the methyl ester 22 gave (–)-PGE15in high yield.

Structure–activity relationships in platelet-activating factor (PAF). 11-From PAF-antagonism to phospholipase A2 inhibition: syntheses and structure–activity relationships in 1-arylsulfamido-2-alkylpiperazines

1-Benzoyl-2-alkyl piperazines are strong inhibitors of Group I and II secreted PLA(2)s. An improvement of their activity was obtained by replacing the amide function by a sulfamide and by introduction of electrodonor substituents on the para position of the benzenesulfonyl moiety. Neither the position on one of the carbon of the piperazine ring nor the absolute configuration of this carbon have an effect on the affinity for one or the other group of PLA(2), but the lipophilicity remains for these series an essential parameter. In addition structure-activity relationships allow new hypothesis on interaction of these piperazine derivatives with the catalytic site of PLA(2)s.

Potent antihyperglycaemic property of a new imidazoline derivative S-22068 (PMS 847) in a rat model of NIDDM

Recent data suggest that some imidazoline derivatives can lower plasma glucose in experimental animal models of diabetes. We studied the activity of an imidazoline S‐22068, in rat model of non‐insulin‐dependent diabetes mellitus (NIDDM) produced with a low dose of streptozotocin (35 mg kg−1, i.v.) in the adult. The respective increase over basal value in glucose (ΔG) and insulin (ΔI), and the rate of glucose disappearance (K), were measured during a 30 min intravenous glucose tolerance test. After an intraperitoneal injection of S‐22068 (24 mg kg−1), ΔG (mM min −1) was decreased (91.67±5.83 vs 120.5±3.65; P<0.001), whereas K was increased (1.74±0.09 vs 1.18±0.05; P<0.001). Although insulinaemia was increased at time‐point 0 of the test, ΔI was unchanged. During oral glucose tolerance tests (OGTT), S‐22068 (24 mg kg−1, p.o.) improved glucose tolerance, and its efficiency was potentiated after chronic treatment (15 days). Basal glycaemia was unaffected by the treatment. Under the same conditions, a higher dose of S‐22068 (40 mg kg−1) further improved glucose tolerance without causing hypoglycaemia. Binding experiments revealed that S‐22068 displays no affinity for either adrenoceptors or the two imidazoline receptors I1 or I2. These results demonstrate that S‐22068 improves glucose tolerance without causing hypoglycaemia. Thus S‐22068 represents a new potential option in the treatment of NIDDM.

4-Alkoxybenzamidines as new potent phospholipase A2 inhibitors.

A series of 4-alkoxybenzamidines was synthesized, varying the number of carbons of the alkyl chain, and their potency as phospholipase A2 (PLA2) inhibitors was evaluated. The relationship between their capacity to inhibit PLA2 activity and their lipophilicity was examined. The optimum of the inhibitory effect against two extracellular PLA2S from rabbit platelets and bovine pancreas was observed with compounds bearing an alkyl chain of 12 and 14 carbons. These 4-dodecyl and tetradecyloxbenzamidines inhibited bovine pancreatic and rabbit platelet lysate PLA2S with IC50 values of 3 microM and 5-5.8 microM, respectively. The mechanism of inhibition was of the competitive type. In addition, 4-tetradecyloxbenzamidine was shown to exert an antiinflammatory effect in vivo on the carrageenan-induced rat paw oedema. These results show that 4-tetradecyloxybenzamidine will serve as an interesting tool to investigate the physiological role of mammalian-secreted PLA2, both in vitro and in vivo.

PAF receptor structure: a hypothesis.

Different hypotheses of the structure of platelet-activating factor (PAF) receptor based on structure-activity relationships of agonists and antagonists are reviewed. For an agonistic effect, strong hydrophobic interactions and an ether function are required in position-1 of the glycerol backbone; chain length limitations and steric hindrance demand a small group in position-2. The unusual structural properties of non-PAF-like antagonists required 3-D electrostatic potential calculations. This method applied to seven potent antagonists suggests a strong “Cache-oreilles” (ear-muff) effect,i.e., two strong electronegative wells (isocontour at −10 Kcal/mole) are located at 180° to each other and at a relatively constant distance. Initial consideration of the “Cache-oreilles” effect implied the structure of a bipolarized cylinder of 10–12 Å diameter for the receptor. However, very recent results on studies with agonists and antagonists structurally similar to PAF suggest that the receptor may in fact be a multi-polarized cylinder.

Stimulation of insulin release from the MIN6 cell line by a new imidazoline compound, S‐21663: evidence for the existence of a novel imidazoline site in β cells

1 The MIN6 cell line derived from in vivo immortalized insulin‐secreting pancreatic β cells was used to study the insulin‐releasing capacity and the cellular mode of action of S‐21663, a newly synthesized imadizoline compound known for its antidiabetic effect in vivo and its ability to release insulin from perfused pancreas. 2 S‐21663, at concentrations ranging from 10−5 M to 10−3 M was able to release insulin from MIN6 cells; its activity peaked at 10−4 M, a drop in the stimulant factor being noted between 10−4 and 10−3 M. Its efficacy, which did not differ whatever the glucose concentration (stimulant or not), was higher than that of the other secretagogues tested, glucose, sulphonylureas or the peptide tGLP‐1. 3 In contrast to tGLP‐1, S‐21663 did not change the cyclic AMP content, whereas it increased Ca2+ influx via verapamil‐ and nifedipine‐sensitive voltage‐dependent calcium channels, the insulin release being a direct consequence of this Ca2+ entry. The S‐21663‐induced Ca2+ influx appears to be essentially the consequence of closure of K+ channels which differ from the ATP‐dependent K+ (K‐ATP) channels as determined by measurement of 86Rb efflux and use of a K‐ATP channel opener. 4 Comparison of the effects of S‐21663 to that of efaroxan, another imidazoline compound shown to act on insulin release in a glucose‐dependent way via binding sites distinct from the imidazoline I1 and I2 sites, suggested that S‐21663 acts through a novel site which displays a remarkably stable expression along the cell culture. 5 It is concluded that S‐21663 is a very efficient, glucose‐independent insulin secretagogue acting through a novel imidazoline site, linked to K+ channels, distinct from the I1, I2 and ‘efaroxan’ binding sites. In vitro and in vivo features of S‐21663 indicate that this compound, or new drugs drived from it, might be the basis for a new pharmacological approach to the mangement of type II (non insulin‐dependent) diabetes.

In vitro mechanism of action on insulin release of S-22068, a new putative antidiabetic compound.

The MIN6 cell line derived from in vivo immortalized insulin‐secreting pancreatic β cells was used to study the insulin‐releasing capacity and the cellular mode of action of S‐22068, a newly synthesized imidazoline compound known for its antidiabetic effect in vivo. S‐22068, was able to release insulin from MIN6 cells in a dose‐dependent manner with a half‐maximal stimulation at 100 μM. Its efficacy (8 fold over the basal value), which did not differ whatever the glucose concentration (stimulatory or not), was intermediate between that of sulphonylurea and that of efaroxan. Similarly to sulphonylureas and classical imidazolines, S‐22068 blocked KATP channels and, in turn, opened nifedipine‐sensitive voltage‐dependent Ca2+ channels, triggering Ca2+ entry. Similarly to other imidazolines, S‐22068 induced a closure of cloned KATP channels injected to Xenopus oocytes by interacting with the pore‐forming Kir6.2 moiety. S‐22068 did not interact with the sulphonylurea binding site nor with the non‐I1 and non‐I2 imidazoline site evidenced in the β cells that is recognized by the imidazoline compounds efaroxan, phentolamine and RX821002. We conclude that S‐22068 is a novel imidazoline compound which stimulates insulin release via interaction with an original site present on the Kir6.2 moiety of the β cell KATP channels.

Total synthesis of leukotrienes from butadiene

The total synthesis of leukotrienes has been achieved starting from butadiene by a palladium-catalyzed telomerization at room temperature. A Sharpless catalytic asymmetric epoxidation generated the asymmetric centers with >94% ee. Simple transformations of the key intermediate 15 produced the leukotrienes LTA4 methyl ester (4), LTC4 (1), LTD4 (2) and LTE4 (3), as well as (14S,15S)-LTA4 methyl ester (24) and the novel [2H2]-LTA4 methyl ester (28). The use of the opposite chiral director in the Sharpless catalytic asymmetric epoxidation gave the key intermediate 15a that has been used in the synthesis of the double epimers of the leukotrienes as well as LTB4.