Factor Xa (FXa) is a serine protease which plays a critical role in the coagulation cascade, serving as the point of convergence of intrinsic and extrinsic pathways.3-7) It represents an attractive target for anticoagulant drug development. [8][9][10][11][12][13][14] Most nonpeptide FXa inhibitors reported in the literature are dibasic compounds. Nagahara et al. 15,16) have reported the synthesis and evaluation of a series of bis(amidino)-derivatives, and through investigation, DX-9065a (1) [17][18][19][20][21] was found to be a selective FXa inhibitor. Further, YM-60828 (2), [22][23][24][25][26][27] which is closely related to 1 in terms of structure, was found to have a more potent inhibitory effect on FXa.On the other hand, as described in the preceding paper, 1) we have synthesized M55113 (3) as a potent inhibitor of FXa (IC 50 ϭ0.06 mM) with high selectivity for FXa over trypsin and thrombin. Compared with the structure of compound 3, the features of compound 1 and compound 2 include a functional acid group in the linker part of the molecule. According to the Xray structure of the complex of compound 1 in des- GlaFXa,28) it is clear that the nitrogen atom of Gln-192 forms a weak hydrogen bond with the acid function of compound 1.In order to obtain a compound which has powerful inhibitory activity on FXa, it is necessary to introduce a functional group into the position at which compound 3 and Gln-192 of FXa protein are expected to form a hydrogen bond.In this paper, we wish to report the continuing search for potent compounds that have a substituent at the piperazine and piperidine rings of compound 3. Thus, the structure-activity relationships of compound 3 derivatives were examined. ChemistryA key intermediate 7 was prepared from glycine ethyl ester hydrochloride, as illustrated in Chart 1. The compound 5, obtained by the reaction of glycine ethyl ester hydrochloride (4) with bromoacetaldehyde diethyl acetal in the presence of cesium carbonate (Cs 2 CO 3 ) 29,30) and sodium iodide, was treated with 6-chloro-2-naphthalenesulfonyl chloride under basic conditions, and the resulting sulfonamide 6 was hydrolyzed with aqueous trifluoroacetic acid (TFA) to give the formyl compound 7.Synthetic routes of compounds 12 and 17 are shown in Chart 2. Compound 9 was prepared by protection of the primary amino group with di-tert-butyl dicarbonate (Boc 2 O) and subsequent debenzylation of a secondary amino group with H 2 over Pd/C. Condensation of 9 with 4-chloropyridine 1-oxide under basic conditions gave the 4-piperidinopyridine 1-oxide derivative 10. Hydrogenolysis of 10 over Raney Ni 31) in methanol (MeOH), followed by treatment with HClMeOH, yielded compound 11. The final compound 12 was obtained smoothly by reductive condensation of 11 with the intermediate 7. 32)Reaction conditions in the preparation of compound 17 from compound 13 33) were not much different from the conversion of 8 to 12.Synthesis of 4-substituted piperidine derivatives containing another functional group (compound 18-20) in place of the hydroxyl...

Factor Xa (FXa), a trypsin-like serine protease, holds the central position that links the intrinsic and extrinsic mechanisms in the blood coagulation cascade. FXa is known to activate prothrombin to thrombin. Thrombin has several procoagulant functions that include the activation of platelets, feedback activation of other coagulation factors, and conversion of fibrinogen to insoluble fibrin clots. [4][5][6][7][8] Comparison of hirudin 9-13) (a thrombin inhibitor) and tick anticoagulant peptide [14][15][16][17][18][19][20] (a FXa inhibitor) suggests that inhibition of FXa may result in less bleeding risk, leading to a more favorable safety/efficacy ratio. [21][22][23][24] Direct inhibition to FXa has therefore emerged as an attractive strategy for the discovery of novel antithrombotic agents. [25][26][27][28][29][30][31] In preceding papers, 1,2) we reported the synthesis and evaluation of compounds in a series of 1-arylsulfonyl-3-piperazinone derivatives, of which M55113 (1) 4--2-piperazinecarboxylic acid were found to be potent inhibitors of FXa (IC 50 ϭ60 nM, 31 nM, 6 nM, respectively) with high selectivity for FXa over trypsin and thrombin.In more recent investigations, fixation of the conformation of testing compounds is believed to affect the strength of interaction between such compounds and the target enzyme. Accordingly, in the next stage of investigation our interest was focused on the synthesis of compounds containing a rigid structure in the central part of the compound (2, 3), and on comparison of the inhibitory activities of the compounds thus synthesized for FXa with those of previously reported compounds. A molecule with a spiro structure in between the piperidine moiety and piperazine moiety was therefore designed as the next candidate for further development of FXa inhibitor. The present paper concerns the synthesis of a series of compounds 4 with a spiro[5H-oxazolo[3,2-a]pyrazine-2(3H),4Ј-piperidin]-5-one skeleton, together with the FXa inhibitory activities of these new compounds. ChemistryFirst, acyclic precursor 9 was prepared as shown in Chart 1. Sulfonylamidation of glycine ethyl ester hydrochloride (5) with 6-chloro-2-naphthalenesulfonyl chloride (6) under traditional conditions yielded the corresponding naphthalenesulfonylamide 7. When 7 was treated with 1-acetoxy-3-chloroacetone (8) in DMF in the presence of potassium carbonate, 9 was obtained in good yield as expected.When 4-(aminomethyl)-1-benzyl-4-piperidinol (10) was allowed to react with acyclic precursor 9 under acidic conditions, a product 11 containing a spiro N,O-acetal structure on the piperazinone ring was obtained, as expected.The reaction pathway of the formation of the spiro skeleton from 9 and 10 is illustrated in Chart 2. In the first step, a Schiff base was formed by dehydration between a carbonyl group in 9 and a primary amino group in 10. Subsequent nucleophilic addition of a hydroxyl group to an azomethine Discovery Research Center, Mochida Pharmaceutical Co., Ltd.; 722 Jimba-aza-uenohara, Gotemba, Shizuoka 412-852...

Factor Xa (FXa), a trypsin-like serine protease, occupies the central position that links the intrinsic and extrinsic mechanisms in the blood coagulation cascade. FXa is known to activate prothrombin to thrombin. Thrombin has several procoagulant functions, including the activation of platelets, feedback activation of other coagulation factors, and conversion of fibrinogen to insoluble fibrin clots.6-10) Comparison of hirudin 11-15) (a thrombin inhibitor) and tick anticoagulant peptide [16][17][18][19][20][21][22] (a FXa inhibitor) suggests that inhibition of FXa may result in less risk of bleeding, leading to a more favorable safety/efficacy ratio. [23][24][25][26] Direct inhibition of FXa has therefore emerged as an attractive strategy for the discovery of novel antithrombotic agents. [27][28][29][30][31][32][33] In a previous paper, 4) we reported the synthesis and evaluation of compounds in a series of spiro [5H-oxazolo[3,2-a] (Table 1).These differences will affect the overall conformation of the compound, and differences in conformation between N,N-spiro acetal and N,O-spiro acetal might affect FXa inhibitory activity. In addition, differences in basicity between N,N-spiro acetal and N,O-spiro acetal might work on FXa inhibitory activity. ChemistryFirst, the keto-ester 5, an acyclic precursor, was prepared as shown in Chart 1.Ethyl glycinate 1 was converted by ring opening glycidyl methyl ether 2 to the corresponding amino-alcohol. The amino-alcohol was treated with benzyl chloroformate in THF-H 2 O in the presence of sodium carbonate with an Nprotected amino-alcohol 3 obtained in good yield. In the next step, the amino-alcohol 3 was oxidized to the keto-ester 5 by the 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl benzoate 4-NaClO oxidation method. was allowed to react with keto-ester 5 in toluene, the key intermediate 7 containing a N,N-spiro acetal structure on the Pharmaceutical Research Center, Mochida Pharmaceutical Co., Ltd.; 722 Jimba-aza-Uenohara, Gotemba, Shizuoka 412-8524, Japan. Received June 10, 2006; accepted September 2, 2006; published online September 5, 2006 We have already reported unique compounds containing a N,O-spiro acetal structure as an orally active factor Xa (FXa) inhibitor. This time, we described a N,N-spiro acetal structure as an analogue of the N,O-spiro acetal structure for an orally active FXa inhibitor. The synthesis of these analogues could be achieved in a similar fashion to the N,O-spiro acetal synthesis. Consequently, FXa inhibitory activity was increased and more active compounds could be found (M58163: IC 50 ‫16.0؍‬ nM, M58169: IC 50 ‫85.0؍‬ nM). Additionally, the absolute configuration could be determined by X-ray crystallography analysis (M58169: (R)-config.).

Regarding the prevention of blood coagulation, most research in the past decade has been focused on thrombin inhibition.1,2) More recently, inhibition of factor Xa (FXa), which is directly responsible for prothrombin activation, has emerged as an attractive target.FXa, which converts prothrombin to thrombin, holds a central position in the coagulation cascade.3) One molecule of FXa generates over 100 molecules of thrombin. Therefore, inhibition of FXa may be more effective than inhibition of thrombin for the prevention of blood coagulation. 4,5) In addition, a recent study by Harker et al. 6) in a balloon model of thrombosis showed that FXa inhibitors might have less bleeding risk than thrombin inhibitors. 7)Most of the nonpeptide FXa inhibitors reported in the literature are dibasic compounds. Nagahara et al. 8,9) have reported synthesis and evaluation of a series of bis(amidino)-derivatives, and through investigation compound DX-9065a (1) [10][11][12][13][14] was found to be a selective FXa inhibitor. Further, a compound YM-60828 (2) [15][16][17][18][19][20] which is closely related to 1 in terms of structure was found to have a more potent inhibitory effect on FXa.A characteristic common to compounds 1 and 2 is having two amidino groups in their molecules, and is considered the presence of more than one such strongly basic group is seen as an unfavorable element for adequate oral absorption and the good pharmacokinetics necessary for oral antithrombotic agents.Based on these considerations, a compound (3) recently reported by ZENECA Co. 21) is of great interest in the following points:i) The pK a value of 4-(piperidino)pyridine is about 12 and is nearly equal to that of amidinonaphthalene.ii) The basicity of two nitrogen atoms in the piperazine ring is reduced by the adjacent acyl and sulfonyl groups.iii) Due to a resonance structure of 4-dialkylaminopyridines, a 4-(piperidino)pyridine moiety in compound 3 is thought to have a plane structure as well as the naphthalene moiety in compounds 1 and 2.To analyze the role of the carbonyl group in compound 3, the following compounds were synthesized and the inhibitory activity of FXa in vitro was evaluated in our laboratory.In compound 4 the carbonyl group is removed and in compounds 5 and 6 the carbonyl group is replaced by a methylene group. In the present paper we wish to report the process of the above investigation. Chemistry Laboratory, Research Center, Mochida Pharmaceutical Co., Ltd., 722, Jimba-aza-Uenohara, Gotemba, Shizuoka 412-8524, Japan. Received January 25, 2001; accepted June 11, 2001 Intravascular clot formation is an important factor in a number of cardiovascular diseases. Therefore, the prevention of blood coagulation has become a major target for new therapeutic agents. One attractive approach is the inhibition of factor Xa (FXa), which is a key enzyme in coagulation cascade responsible for the generation of thrombin by limited proteolysis of its zymogen, prothrombin. We have investigated 1-arylsulfonyl-3-piperazinone derivatives, containi...

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The first asymmetric synthesis of antithrombotic agent M55529 is reported, wherein the first enantioselective cyclic N,O-acetal formation is clarified.

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