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Synthesis, biological evaluation and SAR studies of benzimidazole derivatives as H1-antihistamine agents
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Chinese Chemical Letters 23 (2012) 707–710 www.elsevier.com/locate/cclet
Synthesis, biological evaluation and SAR studies of benzimidazole derivatives as H1-antihistamine agents Xiao Jian Wang a, Mei Yang Xi b, Ji Hua Fu b, Fu Rong Zhang a, Gui Fang Cheng a, Da Li Yin a,*, Qi Dong You b,* a
Department of Medicinal Chemistry, Beijing Key Laboratory of Active Substances Discovery and Drugability Evaluation, State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing 100050, China b School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China Received 31 March 2012 Available online 11 May 2012
Abstract A series of benzimidazole derivatives have been designed, synthesized and evaluated for H1 antihistamine activity. Six compounds have showed potent antihistamine H1 activity. The primary SAR analysis indicated that benzyl or benzylidinyl substituted on the exo-nitrogen atom and C2 of the benzimidazole were significant. Further experiments indicated that compound 17d displayed excellent activity to reduce mast cell degranulation, moderate anti-PAF activity and decreased potency on hERG compared to astermizole. Hence compound 17d could serve as anti-allergic agent for further development. # 2012 Da Li Yin. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Benzimidazole derivatives; Antihistamine activity; SAR; Anti-PAF activity; hERG
Histamine has been widely recognized as an intercellular messenger, which plays an important role in several physiological processes [1,2]. Four histamine receptors have been identified (H1–4), characterized as critical members of the G protein coupled receptors (GPCRs) superfamily [3–5]. Among them, H1 receptor protein that has a molecular weight of 53–58 kDa in different animal tissues is regarded as responsible to histamine mediated allergy syndrome and therefore as the target of anti-allergy drugs since it controls the contraction of smooth muscle and is responsible for allergy and immunity courses [2,6,7]. The first generation H1 antagonists such as mepyramine and diphenhydramine were proven to possess significant antihistamine effects. However, most of them also displayed the side effect of sedation. The central depressant effects have been devoid by the second generation H1 antagonists due to the low penetration of the agents into CNS [6,8]. However, the substantial clinical results indicated that some of the second generation agents (astermizole, terfenadine) that cause potentially fatal arrhythmia as side effect have been withdrawn from the market [9]. Astermizole is a potent histamine H1-receptor antagonist (Ki = 2 nmol/L). However, it causes acquired long QT syndrome cardiac arrhythmias including torsades de pointes, and sudden death due to blockage of the rapidly
* Corresponding authors. E-mail addresses: [email protected] (D.L. Yin), [email protected] (Q.D. You). 1001-8417/$ – see front matter # 2012 Da Li Yin. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. http://dx.doi.org/10.1016/j.cclet.2012.04.020
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X.J. Wang et al. / Chinese Chemical Letters 23 (2012) 707–710
Scheme 1. Reagents and condition: (a) KF, K2CO3, 180 8C, 24 h, 85%; (b) Zn, AcOH, rt, 2 h, 98%; (c) Boc2O, 1 mol/L NaOH, THF, 25 8C, 2 h, 97%; (d) ethyl chloroformate, Et3N, CH2Cl2, 0 8C, 30 min; (e) AcOH, reflux, 2 h, 72%.
activating delayed rectifier K+ current IKr and the human ether-a go-go related gene (hERG) K+ channels that underlie it (IC50 = 0.9 nmol/L) [10,11]. A systematic structure modification based on astermizole has been made in order to discover the novel H1 receptor antagonists with reduced hERG blockage activity. We reported herein the synthesis and biological evaluation of a series of benzimidazole derivatives. The SAR of the in vitro antihistamine effects of these compounds was discussed. 1. Result and discussion The synthetic route for benzimidazole derivatives 7a, 7b and 17a–17f is summarized in Schemes 1 and 2 respectively. Compounds 3a and 3b were obtained by the amination of 1 with p-fluorine or p-chlorine substituted aniline (2a and 2b). The further reduction of the nitro with Zn/AcOH in CH2Cl2 afforded 4a and 4b. On the other hand, Boc-protected 5 gave compound 6 which could acylate 4a and 4b in the presence of ethyl chloroformate. The further cyclization and deprotection in refluxed acetic acid afforded 7a and 7b (Scheme 1). Compounds 10a and 10b were obtained by the amination of p-fluorine or p-chlorine substituted benzyl chloride. Additionally, compounds 14 and 16 were synthesized from 11 according to previous literature [12]. 17a–17f were generated by the following acylation, cyclization and deprotection procedures (Scheme 2). The antihistamine activity of target compounds 7a, 7b, 17a–17f were assessed by inhibition of histamine-induced contraction in guinea ileum that was performed according to the method of Magnus [13]. 17c, 17d, 17f showed the maximum in vitro antihistamine activity which are more potent than astermizole. The introduction of 4-fluoro or chloro benzyl group onto the exo-nitrogen atom of the benzimidazole system was significantly more active than the 4fluoro or chloro phenyl substituted derivatives, which indicated that the flexibility of the group is required for antihistamine activity. Each compound 17a, 17c, 17e (4-fluoro) was as active as 17b, 17d, 17f (4-chloro), respectively.
NH2 Cl
NH2 8
H2N
a
X
+
HN
9-10a X=F 9-10b X=Cl
9a-b
10a-b
X
O
HN HCl
HO
N
HO
b
N Boc
NH
11 c
5 O
Boc N 12
d
Boc N
e
6 O
EtO f
g
Boc N
Boc N O
O EtO
h, i X
HO
14
15
m
NH or
Boc N
O 13
N
O
O
HO 16
or
17a: X=F, m=0 17b: X=Cl, m=0 17c: X=F, m=1, double bond 17d: X=Cl, m=1, double bond 17e: X=F, m=1 17f: X=Cl, m=1
Scheme 2. Reagents and condition: (a) K2CO3, DMF, 50 8C, 6 h, 78%; (b) Boc2O, 1 mol/L NaOH, THF, 25 8C, 2 h, 97%; (c) Boc2O, 2 mol/L NaHCO3, THF, 25 8C, 6 h, 98%; (d) ethyl diethoxyphosphoryl acetate, K2CO3, DMF, 78 8C, 12 h, 90%; (e) 1 mol/L NaOH, CH3OH, 25 8C, 30 min, 98%; (f) 10% Pd/C, H2, C2H5OH, 25 8C, 7 h, 96%; (g) 1 mol/L NaOH, CH3OH, 25 8C, 30 min, 98%; (h) ethyl chloroformate, Et3N, CH2Cl2, 0 8C, 30 min; (i) AcOH, reflux, 2 h, 74%.
X.J. Wang et al. / Chinese Chemical Letters 23 (2012) 707–710
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Table 1 Antihistamine, receptor binding and anti-PAF activities of benzimidazole derivatives. No.
AntiH1 activity ileum IC50 (mmol/L)a
H1 receptor binding IC50 (mmol/L)a
PAF-induced platelet aggregation IC50 (mmol/L)a
7a 7b 17a 17b 17c 17d 17e 17f Desloratadine Astermizole
4.07 0.661 0.0692 0.0457 0.0191 0.00794 0.0174 0.049 0.0721 0.0453
0.337 0.717 0.0213 0.0221 0.00335 0.000881 0.00268 0.00224 0.00588 0.004
150 130 200 110 100 78 100 140 130 nd b
a The IC50 values were determined from six different concentrations of compounds at twofold dilutions, and were the means of two separate experiments. b Not determined.
Compounds 17e and 17f with –CH2– between benzimidazole and piperidine were 2–5-fold more active than 17a and 17b in which benzimidazole directly linked to piperidine, whereas 3–10-fold improvement was observed for 17c and 17d with a carbon–carbon double bond between benzimidazole and piperidine. The further receptor binding assay [14] indicated that all tested compounds displaced the radioligand (3Hmepyramine) from H1 receptor with an IC50 ranging from 0.8 to 717 nmol/L (Table 1). In this respect, compounds 17d are more active than astermizole and desloratadine, while compounds (17c, 17e, 17f) showed the same order of magnitude of an affinity for the receptor as the controls. Benzimidazole derivatives were also tested for platelet activating factor receptor (PAF) antagonist activity using in vitro PAF-induced platelet aggregation assay to fully evaluate their anti-allergy activity [15]. PAF is believed to be a potent chemotactic stimulus for eosinophils, and it is involved in mediating allergy and inflammatory disease. The results suggested that only 17d possessed moderate anti-PAF activity. Compound 17d has been further evaluated for its ability to reduce the number of degranulated mast cells (DMC) of Wistar rat [16]. 17d displayed excellent inhibitory effect on the numbers of DMC with a concentration-dependent manner (IC50 = 3.1 nmol/L). The significant protection from mast cell degranulation induced by 17d demonstrated that it possessed good anti-allergy activity. The hERG IC50 value for 17d was corroborated by cellular electrophysiology using a standard whole-cell voltage clamp assay in CHO cells that stably expressed hERG [17]. The results showed that 17d possessed moderate inhibitory activity on hERG (IC50 = 142.2 nmol/L) (Fig. 1). In comparison, astermizole potently blocked the IKr-like current with IC50 values of 36 nmol/L.
Fig. 1. The inhibitory activity of 17d on hERG.
X.J. Wang et al. / Chinese Chemical Letters 23 (2012) 707–710
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2. Conclusion We describe the synthesis and biological activity toward the new benzimidazole derivatives as H1-antihistamine agents. The SAR study reveals that the flexible substitution of 4-fluoro or chloro benzyl group onto the exo-nitrogen atom of the benzimidazole, and carbon–carbon double bonds between benzimidazole and piperidine showed increased antihistamine activity. Compound 17d showed potent histamine H1-receptor antagonistic activity, moderate anti-PAF activity and displayed significant reduction effect on the numbers of DMC. The hERG affinity of 17d is remarkably decreased compared with astermizole. It is therefore believed that compound 17d is a more potent, safer and promising compound for further development. Acknowledgment This project was supported by National Major Scientific and Technological Special Project (No. 2009ZX09301-003). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
S.J. Hill, Pharmacol. Rev. 42 (1990) 45. S.J. Hill, C.R. Ganellin, H. Timmerman, et al. Pharmacol. Rev. 49 (1997) 253. I. Gantz, M. Schaffer, J. DelValle, et al. Proc. Natl. Acad. Sci. U. S. A. 88 (1991) 429. T.W. Lovenberg, B.L. Roland, S.J. Wilson, et al. Mol. Pharmacol. 55 (1999) 1101. Y. Zhu, D. Michalovich, H. Wu, et al. Mol. Pharmacol. 59 (2001) 434. R. Leurs, M.J. Smit, H. Timmerman, Pharmacol. Ther. 66 (1995) 413. D.D. Metcalfe, D. Baram, Y.A. Mekori, Physiol. Rev. 77 (1997) 1033. F.E. Simons, K.J. Simons, N. Engl. J. Med. 330 (1994) 1663. H. Suessbrich, S. Waldegger, F. Lang, et al. FEBS Lett. 385 (1996) 77. Z. Zhou, V.R. Vorperian, Q. Gong, et al. J. Cardiovasc. Electrophysiol. 10 (1999) 836. P.J. Chiu, K.F. Marcoe, S.E. Bounds, et al. J. Pharmacol. Sci. 95 (2004) 311. M.S. Ashwood, A.W. Gibson, P.G. Houghton, et al. J. Chem. Soc., Perkin Trans. 1 (6) (1995) 641. R. Magnus, Pflugers Arch. 102 (1904) 123. M.D. De Backer, W. Gommeren, H. Moereels, et al. Biochem. Biophys. Res. Commun. 197 (1993) 1601. G.V. Born, Nature 194 (1962) 927. H. Behrendt, Int. Arch. Allergy Appl. Immunol. 82 (1987) 283. C.A. Blum, X. Zheng, S. De Lombaert, J. Med. Chem. 47 (2004) 2318.
Chinese Chemical Letters 23 (2012) 707–710 www.elsevier.com/locate/cclet
Synthesis, biological evaluation and SAR studies of benzimidazole derivatives as H1-antihistamine agents Xiao Jian Wang a, Mei Yang Xi b, Ji Hua Fu b, Fu Rong Zhang a, Gui Fang Cheng a, Da Li Yin a,*, Qi Dong You b,* a
Department of Medicinal Chemistry, Beijing Key Laboratory of Active Substances Discovery and Drugability Evaluation, State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia Medica, Peking Union Medical College and Chinese Academy of Medical Sciences, Beijing 100050, China b School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China Received 31 March 2012 Available online 11 May 2012
Abstract A series of benzimidazole derivatives have been designed, synthesized and evaluated for H1 antihistamine activity. Six compounds have showed potent antihistamine H1 activity. The primary SAR analysis indicated that benzyl or benzylidinyl substituted on the exo-nitrogen atom and C2 of the benzimidazole were significant. Further experiments indicated that compound 17d displayed excellent activity to reduce mast cell degranulation, moderate anti-PAF activity and decreased potency on hERG compared to astermizole. Hence compound 17d could serve as anti-allergic agent for further development. # 2012 Da Li Yin. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Benzimidazole derivatives; Antihistamine activity; SAR; Anti-PAF activity; hERG
Histamine has been widely recognized as an intercellular messenger, which plays an important role in several physiological processes [1,2]. Four histamine receptors have been identified (H1–4), characterized as critical members of the G protein coupled receptors (GPCRs) superfamily [3–5]. Among them, H1 receptor protein that has a molecular weight of 53–58 kDa in different animal tissues is regarded as responsible to histamine mediated allergy syndrome and therefore as the target of anti-allergy drugs since it controls the contraction of smooth muscle and is responsible for allergy and immunity courses [2,6,7]. The first generation H1 antagonists such as mepyramine and diphenhydramine were proven to possess significant antihistamine effects. However, most of them also displayed the side effect of sedation. The central depressant effects have been devoid by the second generation H1 antagonists due to the low penetration of the agents into CNS [6,8]. However, the substantial clinical results indicated that some of the second generation agents (astermizole, terfenadine) that cause potentially fatal arrhythmia as side effect have been withdrawn from the market [9]. Astermizole is a potent histamine H1-receptor antagonist (Ki = 2 nmol/L). However, it causes acquired long QT syndrome cardiac arrhythmias including torsades de pointes, and sudden death due to blockage of the rapidly
* Corresponding authors. E-mail addresses: [email protected] (D.L. Yin), [email protected] (Q.D. You). 1001-8417/$ – see front matter # 2012 Da Li Yin. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. http://dx.doi.org/10.1016/j.cclet.2012.04.020
708
X.J. Wang et al. / Chinese Chemical Letters 23 (2012) 707–710
Scheme 1. Reagents and condition: (a) KF, K2CO3, 180 8C, 24 h, 85%; (b) Zn, AcOH, rt, 2 h, 98%; (c) Boc2O, 1 mol/L NaOH, THF, 25 8C, 2 h, 97%; (d) ethyl chloroformate, Et3N, CH2Cl2, 0 8C, 30 min; (e) AcOH, reflux, 2 h, 72%.
activating delayed rectifier K+ current IKr and the human ether-a go-go related gene (hERG) K+ channels that underlie it (IC50 = 0.9 nmol/L) [10,11]. A systematic structure modification based on astermizole has been made in order to discover the novel H1 receptor antagonists with reduced hERG blockage activity. We reported herein the synthesis and biological evaluation of a series of benzimidazole derivatives. The SAR of the in vitro antihistamine effects of these compounds was discussed. 1. Result and discussion The synthetic route for benzimidazole derivatives 7a, 7b and 17a–17f is summarized in Schemes 1 and 2 respectively. Compounds 3a and 3b were obtained by the amination of 1 with p-fluorine or p-chlorine substituted aniline (2a and 2b). The further reduction of the nitro with Zn/AcOH in CH2Cl2 afforded 4a and 4b. On the other hand, Boc-protected 5 gave compound 6 which could acylate 4a and 4b in the presence of ethyl chloroformate. The further cyclization and deprotection in refluxed acetic acid afforded 7a and 7b (Scheme 1). Compounds 10a and 10b were obtained by the amination of p-fluorine or p-chlorine substituted benzyl chloride. Additionally, compounds 14 and 16 were synthesized from 11 according to previous literature [12]. 17a–17f were generated by the following acylation, cyclization and deprotection procedures (Scheme 2). The antihistamine activity of target compounds 7a, 7b, 17a–17f were assessed by inhibition of histamine-induced contraction in guinea ileum that was performed according to the method of Magnus [13]. 17c, 17d, 17f showed the maximum in vitro antihistamine activity which are more potent than astermizole. The introduction of 4-fluoro or chloro benzyl group onto the exo-nitrogen atom of the benzimidazole system was significantly more active than the 4fluoro or chloro phenyl substituted derivatives, which indicated that the flexibility of the group is required for antihistamine activity. Each compound 17a, 17c, 17e (4-fluoro) was as active as 17b, 17d, 17f (4-chloro), respectively.
NH2 Cl
NH2 8
H2N
a
X
+
HN
9-10a X=F 9-10b X=Cl
9a-b
10a-b
X
O
HN HCl
HO
N
HO
b
N Boc
NH
11 c
5 O
Boc N 12
d
Boc N
e
6 O
EtO f
g
Boc N
Boc N O
O EtO
h, i X
HO
14
15
m
NH or
Boc N
O 13
N
O
O
HO 16
or
17a: X=F, m=0 17b: X=Cl, m=0 17c: X=F, m=1, double bond 17d: X=Cl, m=1, double bond 17e: X=F, m=1 17f: X=Cl, m=1
Scheme 2. Reagents and condition: (a) K2CO3, DMF, 50 8C, 6 h, 78%; (b) Boc2O, 1 mol/L NaOH, THF, 25 8C, 2 h, 97%; (c) Boc2O, 2 mol/L NaHCO3, THF, 25 8C, 6 h, 98%; (d) ethyl diethoxyphosphoryl acetate, K2CO3, DMF, 78 8C, 12 h, 90%; (e) 1 mol/L NaOH, CH3OH, 25 8C, 30 min, 98%; (f) 10% Pd/C, H2, C2H5OH, 25 8C, 7 h, 96%; (g) 1 mol/L NaOH, CH3OH, 25 8C, 30 min, 98%; (h) ethyl chloroformate, Et3N, CH2Cl2, 0 8C, 30 min; (i) AcOH, reflux, 2 h, 74%.
X.J. Wang et al. / Chinese Chemical Letters 23 (2012) 707–710
709
Table 1 Antihistamine, receptor binding and anti-PAF activities of benzimidazole derivatives. No.
AntiH1 activity ileum IC50 (mmol/L)a
H1 receptor binding IC50 (mmol/L)a
PAF-induced platelet aggregation IC50 (mmol/L)a
7a 7b 17a 17b 17c 17d 17e 17f Desloratadine Astermizole
4.07 0.661 0.0692 0.0457 0.0191 0.00794 0.0174 0.049 0.0721 0.0453
0.337 0.717 0.0213 0.0221 0.00335 0.000881 0.00268 0.00224 0.00588 0.004
150 130 200 110 100 78 100 140 130 nd b
a The IC50 values were determined from six different concentrations of compounds at twofold dilutions, and were the means of two separate experiments. b Not determined.
Compounds 17e and 17f with –CH2– between benzimidazole and piperidine were 2–5-fold more active than 17a and 17b in which benzimidazole directly linked to piperidine, whereas 3–10-fold improvement was observed for 17c and 17d with a carbon–carbon double bond between benzimidazole and piperidine. The further receptor binding assay [14] indicated that all tested compounds displaced the radioligand (3Hmepyramine) from H1 receptor with an IC50 ranging from 0.8 to 717 nmol/L (Table 1). In this respect, compounds 17d are more active than astermizole and desloratadine, while compounds (17c, 17e, 17f) showed the same order of magnitude of an affinity for the receptor as the controls. Benzimidazole derivatives were also tested for platelet activating factor receptor (PAF) antagonist activity using in vitro PAF-induced platelet aggregation assay to fully evaluate their anti-allergy activity [15]. PAF is believed to be a potent chemotactic stimulus for eosinophils, and it is involved in mediating allergy and inflammatory disease. The results suggested that only 17d possessed moderate anti-PAF activity. Compound 17d has been further evaluated for its ability to reduce the number of degranulated mast cells (DMC) of Wistar rat [16]. 17d displayed excellent inhibitory effect on the numbers of DMC with a concentration-dependent manner (IC50 = 3.1 nmol/L). The significant protection from mast cell degranulation induced by 17d demonstrated that it possessed good anti-allergy activity. The hERG IC50 value for 17d was corroborated by cellular electrophysiology using a standard whole-cell voltage clamp assay in CHO cells that stably expressed hERG [17]. The results showed that 17d possessed moderate inhibitory activity on hERG (IC50 = 142.2 nmol/L) (Fig. 1). In comparison, astermizole potently blocked the IKr-like current with IC50 values of 36 nmol/L.
Fig. 1. The inhibitory activity of 17d on hERG.
X.J. Wang et al. / Chinese Chemical Letters 23 (2012) 707–710
710
2. Conclusion We describe the synthesis and biological activity toward the new benzimidazole derivatives as H1-antihistamine agents. The SAR study reveals that the flexible substitution of 4-fluoro or chloro benzyl group onto the exo-nitrogen atom of the benzimidazole, and carbon–carbon double bonds between benzimidazole and piperidine showed increased antihistamine activity. Compound 17d showed potent histamine H1-receptor antagonistic activity, moderate anti-PAF activity and displayed significant reduction effect on the numbers of DMC. The hERG affinity of 17d is remarkably decreased compared with astermizole. It is therefore believed that compound 17d is a more potent, safer and promising compound for further development. Acknowledgment This project was supported by National Major Scientific and Technological Special Project (No. 2009ZX09301-003). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
S.J. Hill, Pharmacol. Rev. 42 (1990) 45. S.J. Hill, C.R. Ganellin, H. Timmerman, et al. Pharmacol. Rev. 49 (1997) 253. I. Gantz, M. Schaffer, J. DelValle, et al. Proc. Natl. Acad. Sci. U. S. A. 88 (1991) 429. T.W. Lovenberg, B.L. Roland, S.J. Wilson, et al. Mol. Pharmacol. 55 (1999) 1101. Y. Zhu, D. Michalovich, H. Wu, et al. Mol. Pharmacol. 59 (2001) 434. R. Leurs, M.J. Smit, H. Timmerman, Pharmacol. Ther. 66 (1995) 413. D.D. Metcalfe, D. Baram, Y.A. Mekori, Physiol. Rev. 77 (1997) 1033. F.E. Simons, K.J. Simons, N. Engl. J. Med. 330 (1994) 1663. H. Suessbrich, S. Waldegger, F. Lang, et al. FEBS Lett. 385 (1996) 77. Z. Zhou, V.R. Vorperian, Q. Gong, et al. J. Cardiovasc. Electrophysiol. 10 (1999) 836. P.J. Chiu, K.F. Marcoe, S.E. Bounds, et al. J. Pharmacol. Sci. 95 (2004) 311. M.S. Ashwood, A.W. Gibson, P.G. Houghton, et al. J. Chem. Soc., Perkin Trans. 1 (6) (1995) 641. R. Magnus, Pflugers Arch. 102 (1904) 123. M.D. De Backer, W. Gommeren, H. Moereels, et al. Biochem. Biophys. Res. Commun. 197 (1993) 1601. G.V. Born, Nature 194 (1962) 927. H. Behrendt, Int. Arch. Allergy Appl. Immunol. 82 (1987) 283. C.A. Blum, X. Zheng, S. De Lombaert, J. Med. Chem. 47 (2004) 2318.