Bioorganic & Medicinal Chemistry Letters 24 (2014) 480–484
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Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antibacterial activity of a series of novel 9-O-acetyl- 40 -substituted 16-membered macrolides derived from josamycin Zhehui Zhao, Longlong Jin, Yanpeng Xu, Di Zhu, Yi Liu, Chao Liu, Pingsheng Lei ⇑ State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Beijing Key Laboratory of Active Substances Discovery and Drugability Evaluation, Department of Medicinal Chemistry, Institute of Materia Medica, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing 100050, PR China
a r t i c l e
i n f o
Article history: Received 26 September 2013 Revised 25 November 2013 Accepted 10 December 2013 Available online 15 December 2013 Key words: Macrolide Josamycin Antibacterial activity Synthesis
a b s t r a c t A series of novel 9-O-acetyl-40 -substituted 16-membered macrolides derived from josamycin has been designed and synthesized by cleavage of the mycarose of josamycin and subsequent modification of the 40 -hydroxyl group. These derivatives were evaluated for their in vitro antibacterial activities against a panel of Staphylococcus aureus and Staphylococcus epidermidis. 15 (40 -O-(3-Phenylpropanoyl)-9-Oacetyl-desmycarosyl josamycin) and 16 (40 -O-butanoyl-9-O-acetyl-desmycarosyl josamycin) exhibited comparable activities to josamycin against S. aureus (MSSA) and S. epidermidis (MSSE). Ó 2013 Elsevier Ltd. All rights reserved.
Macrolide antibiotics have been widely used to treat bacterial infections for the past 60 years.1 They are considered as the preferred therapeutic agents for the treatment of upper and lower respiratory tract infections because of their safety and efficacy.2 The high-resolution X-ray cocrystal structures of the bacterial ribosome with macrolides have revealed the detailed interaction at atomic level.3 It demonstrated that the macrolides inhibit bacterial protein synthesis by sterically blocking the passage of nascent polypeptides through the exit tunnel of the ribosome.4 The therapeutic utility of the macrolides has been severely compromised by the emergence of resistant pathogens.5 Two of the most important mechanisms of macrolide resistance were ribosomal mutation (erm) and efflux–mediated resistance (mef).6 Recently, several researches7 have been made to overcome macrolide resistance, which resulted in the discovery of ketolides such as telithromycin (Tel)8 and cethromycin (ABT-773)9 (Fig. 1). The 16-membered macrolides, such as josamycin and tylosin (Fig. 1), constitute an important class of useful antibiotics of the macrolide family, which were studied relatively backward compared that with 14-membered macrolides.10 But they offer some advantages over the 14-membered macrolides. These advantages include better gastrointestinal tolerance, lack of drug–drug interactions, and the activity against resistance expressing strains.11 During our efforts to develop novel macrolides active against ⇑ Corresponding author. Tel.: +86 10 63162596; fax: +86 10 63017757. E-mail address: [email protected] (P. Lei). 0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.bmcl.2013.12.029
bacteria, we became interested in josamycin primarily because its activities are not affected by mef-resistance. Josamycin is an important drug used to treat Gram-positive and mycoplasma infections. This macrolide antibiotic is composed of a 16-membered lactone ring and an unusual disaccharide D-mycaminosyl-Lmycarose at C-5 position, which is oriented similarly to the 5-O-desosamine of 14-membered macrolides.4 Furthermore, the mycarose extends toward the peptidyl transferase center (PTC), making additional interactions at G2505 and U2506. The previous work shows that the mycarose of 16-membered macrolide is very important to the antibacterial activity, and removal of it from macrolide will reduce the antibacterial activity one or two orders of magnitude.12 The main reason may be that the sugar substituent contributes significantly to binding-free energy since they contribute 1/2 to 2/3 of the interaction surface.4 Unfortunately the disacchaharide is not stable under acid condition. Much of the early efforts on structural modifications within the 16-membered macrolide have been directed toward modification of the aldehyde group13 or the hydroxyl groups of mycarose.14 In recent years, the modifications on 16-membered macrolide focused on rebuilding the lactone bearing an arylalkyl-type side chain.15 But there were only few reports describing removal of the mycarose and modification of the mycaminose with different side chains to explore the interaction of the sugar of the 16-membered macrolide with the PTC.16,17 Phan et al. removed the mycarose sugar of tylosin and synthesized 4-substituted macrolides.16 The introduced arylalkyl side chain was thought to be important for
Z. Zhao et al. / Bioorg. Med. Chem. Lett. 24 (2014) 480–484
the improvement of the activities against sensitive and resistant bacteria. The author considered that there may be other interactions with ribosome RNA bases, but the works showed little information of structure–activity relationship (SAR) about the interaction between the substitutes and the PTC.
481
Based on that, we intended to find some new molecule entities to improve antibacterial activity and the acid stability of 16-membered macrolide using different substituents to replace the mycarose and study the preliminary SAR. Herein, we reported an efficient procedure for preparing a series of novel 40 -substituted
Figure 1. Chemical structures of telithromycin, cethromycin, josamycin and tylosin.
Scheme 1. Reagents and conditions: (a) acetic anhydride, pyridine, room temperature, overnight, 98%; (b) 4-methylbenzenesulfonic acid, toluene, reflux, 18 h, 67%; (c) methanol, room temperature, overnight, 99%.
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Z. Zhao et al. / Bioorg. Med. Chem. Lett. 24 (2014) 480–484
16-membered macrolides and their antibacterial activity against Staphylococcus aureus and Staphylococcus epidermidis. Our approach is to find an efficient route to synthesis 40 -substituted josamycin derivatives by removing the mycarose sugar and modifying the 40 -hydroxyl group. Scheme 1 outlines the syntheses of 3, the 9-O-acetyl-desmycarosyl josamycin. Treatment of
josamycin with acetic anhydride (3.5 equiv) in pyridine gave 1 in a yield of 98%. The 400 -hydroxy group of josamycin is a tertiary hydroxyl group which is hard to acylate at this react condition. Hydrolysis of the 40 -mycarose group of 1 by p-toluenesulfonic acid in toluene gave the corresponding 40 -hydroxyl compound 2, then deprotection of the 20 -OH smoothly in the methanol gave 3 as a
Scheme 2. Reagents and conditions: (a) NaOH, THF/H2O, room temperature, overnight, 90%; (b) NaOH, THF/H2O, reflux, overnight, 88%.
Scheme 3. Reagents and conditions: (a) 1-isocyanato-4-(trifluoromethyl)benzene, DCM, room temperature, overnight, 82%; (b) methanol, room temperature, overnight, 99%; (c) NaOH, THF/H2O, room temperature, overnight, 87%; (d) NaOH, THF/H2O, reflux, overnight, 88%.
Scheme 4. Reagents and conditions: (a) benzoic acid, EDCI, TEA, HOBT, chloroform, room temperature, overnight, 78%.
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key intermediate, the structure was confirmed by HR-MS, 1H NMR, and 13C NMR spectra. The signals at 168.9 ppm (C@O) and 21.6 ppm (CH3) disappeared in the 13C NMR of compound 3, compared with that of compound 2. Meanwhile the signals of C-20 in the 13C NMR and H-20 in the 1H NMR moved to high field. In this route aldehyde group was not necessary to be protected, that can shorten our procedures. In Przybylski’s work, hydrolysis of 3-O-acetate of josamycin derivatives gave a,b-unsaturated product.18 The same procedure was used to hydrolyze 3 to obtain two a,b-unsaturated derivatives 4 and 5. Scheme 2 outlines the syntheses of 4 and 5. Compound 3 was hydrolyzed by sodium hydroxide under ambient condition to give 4, and further hydrolysis of 9-O-acetate to give 5. By our knowledge, isocyanates and acids were the facile ways to modify the hydroxyl group of 14-membered macrolide smoothly in high yield.19 So some commercial isocyanates and acids were chosen to react with 3. Schemes 3 and 4 outlines the syntheses of 7–10. Treatment of 2 with 1.0 equiv of 1-isocyanato-4-(trifluoromethyl)benzene in dichloromethane gave 6 in a yield of 82%, and deprotection of 6 in methanol gave final product 7 in a yield of 95%. 8 and 9 were gotten as the procedure similar to 4 and 5. The 13C NMR spectra of 4, 5, 8 and 9 which all have the double bond at C-2, C-3 position showed the new signals of C-2, C-3 were at about 88 ppm and 91 ppm. Meanwhile, the signals of C-6, C-7, C8 and C-22 had a large shift to low field, the signals of C-10, C-11, C-12 and C-13 changed too, that means that the conformation of the whole structure of 16-membered macrolide had a great change. The conjugated double bonds at C-10 and C-13 interacted with the new formed double bond at C-2 and C-3 and made the unusual change of the signal of C-2 and C-3. The final product 10 was prepared by condensation of 3 with the benzoic acid using 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDCI) and triethylamine (TEA)in chloroform, 1-Hydroxybenzotriazole (HOBT) as catalyst, in a yield of 78%. The antibacterial activities of 3–5, 7–10 were showed in the Table 1. From the result of the activities, compared with that of josamycin, the antibacterial activity of 3 declined about one order of magnitude against S. aureus (MSSA) and S. epidermidis (MSSE). Compound 10 remained some antibacterial activity against S. aureus (MSSA) and S. epidermidis (MSSE). So the more acids were chosen to modify the compound 3. The products 11–17 (Fig. 2) were synthesized by the similar procedure of 10 in a yield of 32– 81%. All the compounds were confirmed by HRMS, 1H NMR, and 13 C NMR spectra. The antibacterial activities of the target compounds were assessed against some respiratory pathogens, including macrolide drug sensitive and resistant strains. Josamycin was chosen as the reference compounds. The in vitro antibacterial activity was reported as minimum inhibitory concentrations (MICs), which was determined by the broth microdilution method as recommended by the CLSI.20
ATCC 29213, 15 and 09–06 are methicillin-sensitive Staphylococcus aureus (MSSA). ATCC 33591 and 09–13 are methicillin-resistant Staphylococcus aureus (MRSA). ATCC 12228 and 09–9 are methicillin-sensitive Staphylococcus epidermidis (MSSE). 09–3 is a methicillin-resistant Staphylococcus epidermidis (MRSE). All the MRSA and MRSE strains chosen in this test are constitutively resistant strains supplied by Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College (IMB, China). All of the compounds synthesized, as well as josamycin as references, were tested for in vitro antibacterial activity against five strains of S. aureus and three stains of S. epidermidis The activities are reported in Table 1 and Table 2 as minimum inhibitory concentrations (MICs). The antibacterial activities of 3–5, 7–10 were shown in Table 1. Among of them, 3–5 were unsubstituted derivatives, 7–9 were carbamate derivatives and 10 was ester derivative. The antibacterial activity of compound 3 was one order of magnitude weaker than that of josamycin against S. aureus (MSSA) and S. epidermidis (MSSE). The antibacterial activities of 4 and 5 were none or weaker than that of 3. The antibacterial activities of 7, 8 and 9 were none or weaker than that of the 3. On the other hand, the activity of 10 was stronger than that of the 3 against S. aureus (MSSA) and S. epidermidis (MSSE) In reviewing the data of Table 2, it was noteworthy that the ester analogue had an improved activity against S. aureus and S. epidermidis. The activity of 11, bearing a methoxyl group on the phenyl ring, was same as that of 10. While the activity of 12,
Figure 2. Chemical structures of the products 11–17.
Table 1 In vitro antibacterial activities of 3–5, 7–10 MIC (lg/mL)
S. aureus
S. epidermidis
ATCC 29213 ATCC 33591 15 09–6 09–13 ATCC 12228 09–3 09–9
MSSA MRSA MSSA MSSA MRSA MSSE MRSE MSSE
3
4
5
7
8
9
10
Josamycin
16 >32 16 16 >32 16 >32 16
>64 >64 >64 >64 >64 64 >64 64
>32 >32 >32 >32 >32 >32 >32 >32
>64 >64 >64 >64 >64 >64 >64 >64
>64 >64 >64 >64 >64 >64 >64 >64
>64 >64 >64 >64 >64 >64 >64 >64
8 >64 8 8 >64 8 >64 8
1 >32 2 1 32 1 >32 2
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Table 2 In vitro antibacterial activities of 3 and 10–17 MIC (lg/mL)
S.aureus
S. epidermidis
ATCC 29213 ATCC 33591 15 09–6 09–13 ATCC 12228 09–3 09–9
MSSA MRSA MSSA MSSA MRSA MSSE MRSE MSSE
3
10
11
12
13
14
15
16
17
Josamycin
16 >32 16 16 >32 16 >32 16
8 >64 8 8 >64 8 >64 8
8 >64 8 8 >64 8 >64 8
32 >64 >64 32 >64 32 >64 32
8 >32 >32 8 >32 4 >32 4
8 >64 16 8 >64 8 >64 8
4 >32 8 4 >32 4 >32 4
4 >64 4 4 >64 4 >64 4
8 >64 8 8 >64 8 >64 8
1 >32 2 1 32 1 >32 2
bearing a nitro group, was decreased remarkably. Compared that with the benzoate ester, the cinnamate ester was slightly improved the activity against S. epidermidis. The quinolyl group substituent did not improve the activities. Compared the activities of 13 and 15, conversion of the carbon–carbon double bond into carbon–carbon single bond can improve the activities. The activity of aliphatic ester was similar as that of the aromatic ester. 15 and 16 exhibited comparable activity against S. aureus and S. epidermidis, which proved that b-substituted acids may be the best substituted group to modify the 40 -hydroxyl of josamycin. All the compounds showed none activities against resistant-pathogens. Next, we would synthesize more b-substituted acids to modify the 40 -hydroxyl of josamycin. In conclusion, a series of novel 40 -substituted 16-membered macrolides were designed and synthesized in an efficient route. Isocyanates and acids were used to replace the unstable mycarose substituent in josamycin and their derivatives were evaluated for the in vitro antibacterial activities against a panel of S. aureus and S. epidermidis. The b-substituted acids may be the best substitutes for modification the 40 -hydroxyl group of 16-membered macrolide. These studies present a considerable opportunity for overcoming the acid instability of 16-membered macrolide and improving their antibacterial activities. Acknowledgments This work was supported by the National S&T Major Special Project on Major New Drug Innovation (Item Number: 2008ZX09401-004 and 2009ZX09301-003) and National Natural Science Foundation of China (81072524). And we are grateful to Professor Xuefu You for the antibacterial activity test. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.bmcl.2013. 12.029. References and notes 1. (a)Macrolides: Chemistry Pharmacology and Clinical Uses; Bryskier, A. J., Butzler, J.-P., Neu, H. C., Tulkens, P. M., Eds.; Arnette Blackwell: Paris, 1993; (b) Henninger, Todd C. Expert Opin. Ther. Patents. 2003, 13, 787; (c) Katz, L.; Ashley, G. W. Chem. Rev. 2005, 105, 499. 2. Zhanel, G. G.; Dueck, M.; Hoba, D. J.; Vercaigene, L. M.; Embil, J. M.; Gin, A. S.; Karlowsky, J. A. Drugs 2001, 61, 443. 3. (a) Schlunzen, F.; Zarivach, R.; Harms, J.; Bashan, A.; Tocilj, A.; Albrecht, R.; Yonath, A.; Franceschi, F. Nature 2001, 413, 814; (b) Schlunzen, F.; Harms, J.; Franceschi, F.; Hansen, H.; Bartels, H.; Zarivach, R.; Yonath, A. Structure 2003, 11, 329; (c) Berisio, R.; Harms, J.; Schlunzen, F.; Zarivach, R.; Hansen, H.; Fucini, P.; Yonath, A. J. Bacteriol. 2003, 185, 4276; (d) Tu, D.; Blaha, G.; Moore, P. B.; Steitz, T. A. Cell 2005, 121, 257. 4. Hanson, J.; Ippolito, J. A.; Ban, N.; Nissen, P.; Moore, P.; Steitz, T. Mol. Cell 2002, 10, 117. 5. Takashima, H. Curr. Top. Med. Chem. 2003, 3, 991.
6. Leclerq, Q.; Courvalin, P. Agents Chemother. 1991, 35, 1267. 7. (a) Bukvic´ Krajacic´, M.; Peric´, M.; Smith, K. S.; Ivezic´ Schönfeld, Z.; Ziher, D.; Fajdetic´, A.; Kujundzic´, N.; Schönfeld, W.; Landek, G.; Padovan, J.; Jelic´, D.; Ager, A.; Milhous, W. K.; Ellis, W.; Spaventi, R.; Ohrt, C. J. Med. Chem. 2011, 54, 3595; (b) Chen, X.-Z.; Xu, P.; Liu, L.; Zheng, D.; Lei, P.-S. Eur. J. Med. Chem. 2011, 46, 208; (c) Cong, C.; Wang, H.; Hu, Y.; Liu, C.; Ma, S.; Li, X.; Cao, J.; Ma, S. Eur. J. Med. Chem. 2011, 46, 3105; (d) Liu, Y.; Carreras, C. W.; Claypool, M.; Myles, D. C.; Shaw, S. J. Bioorg. Med. Chem. Lett. 2011, 21, 3712; (e) Pereira, D.; Fernandes, P. Bioorg. Med. Chem. Lett. 2011, 21, 510; (f) Ma, X.; Zhang, L.; Wang, R.; Cao, J.; Liu, C.; Fang, Y.; Wang, J.; Ma, S. Eur. J. Med. Chem. 2011, 46, 5196; (g) Kumar, R.; Rathy, S.; Hajare, A. K.; Surase, Y. B.; Dullu, J.; Jadhav, J. S.; Venkataramanan, R.; Chakrabarti, A.; Pandya, M.; Bhateja, P.; Ramkumar, G.; Das, B. Bioorg. Med. Chem. Lett. 2012, 22, 476; (h) Liang, J.-H.; Li, X.-L.; Wang, H.; An, K.; Wang, Y.-Y.; Xu, Y.-C.; Yao, G.-W. Eur. J. Med. Chem. 2012, 49, 289; (i) Liang, J.-H.; An, K.; Lv, W.; Cushman, M.; Wang, H.; Xu, Y.-C. Eur. J. Med. Chem. 2013, 59, 54; (j) Jiang, J.W.; Sun, Y.; Nie, Y.; Zhi, H.-J.; Zhang, X.-J.; Li, X.; Sun, H.-P.; You, Q.-D. Bioorg. Med. Chem. Lett. 2013, 23, 3452; (k) Magee, T. V.; Han, S.; McCurdy, S. P.; Nguyen, T.-T.; Granskog, K.; Marr, E. S.; Maguire, B. A.; Huband, M. D.; Chen, J. M.; Subashi, T. A.; Shanmugasundaram, V. Bioorg. Med. Chem. Lett. 2013, 23, 1727. 8. Denis, A.; Agouridas, C.; Auger, J.-M.; Benedetti, Y.; Bonnefoy, A.; Bretin, F.; Chantot, J.-F.; Dussarat, A.; Fromentin, C.; Gouin D’Ambrières, S.; Lachaud, S.; Laurin, P.; Le Martret, O.; Loyau, V.; Tessot, N.; Pejac, J.-M.; Perron, S. Bioorg. Med. Chem. Lett. 1999, 9, 3075. 9. (a) Or, Y. S.; Clark, R. F.; Wang, S.; Chu, D. T. W.; Nilius, A. M.; Flamm, R. K.; Mitten, M.; Ewing, P.; Alder, J.; Ma, Z. J. Med. Chem. 2000, 43, 1045; (b) Ma, Z.; Clark, R. F.; Brazzale, A.; Wang, S.; Rupp, M. J.; Li, L.; Griesgraber, G.; Zhang, S.; Yong, H.; Phan, L. T.; Nemoto, P. A.; Chu, D. T. W.; Plattner, J. J.; Zhang, X.; Zhong, P.; Cao, Z.; Nilius, A. M.; Shortridge, V. D.; Flamm, R.; Mitten, M.; Meulbroek, J.; Ewing, P.; Alder, J.; Or, Y. S. J. Med. Chem. 2001, 44, 4137. 10. Kirst, H. A. Prog. Med. Chem. 1994, 31, 265. 11. Kirst, H. A.; Sides, G. D. Antimicrob. Agents Chemother. 1989, 33, 1413. 12. (a) Mutak, S.; Maršic´, N.; Kramaric´, M. D.; Pavlovic´, D. J. Med. Chem. 2003, 47, 411; (b) Fu, H.; Marquez, S.; Gu, X.; Katz, L.; Myles, D. C. Bioorg. Med. Chem. Lett. 2006, 16, 1259; (c) Miura, T.; Kanemoto, K.; Natsume, S.; Atsumi, K.; Fushimi, H.; Yoshida, T.; Ajito, K. Bioorg. Med. Chem. 2008, 16, 10129. 13. Poras, H.; Kunesch, G.; Barrière, J. C.; Berthaud, N.; Andremont, A. J. Antibiot. (Tokyo) 1998, 51, 786. 14. (a) Kurihara, K.; Ajito, K.; Shibahara, S.; Ishizuka, T.; Hara, O.; Araake, M.; Omoto, S. J. Antibiot. (Tokyo) 1996, 49, 582; (b) Ajito, K.; Kurihara, K.; Shibahara, S.; Hara, O.; Shimizu, A.; Araake, M.; Omoto, S. J. Antibiot. (Tokyo) 1997, 50, 92; (c) Kurihara, K.; Kikuchi, N.; Ajito, K. J. Antibiot. (Tokyo) 1997, 50, 32; (d) Ajito, K.; Kurihara, K.; Shibahara, S.; Hara, O.; Okonogi, T.; Kikuchi, N.; Araake, M.; Suzuki, H.; Omoto, S.; Inouye, S. J. Antibiot. (Tokyo) 1997, 50, 150; (e) Ajito, K.; Shimizu, A.; Shibahara, S.; Hara, O.; Kurihara, K.; Araake, M.; Tohyama, K.; Miyadoh, S.; Omoto, S.; Inouye, S. J. Antibiot. (Tokyo) 1997, 50, 366; (f) Kurihara, K. I.; Ajito, K.; Shibahara, S.; Hara, O.; Araake, M.; Omoto, S.; Inouye, S. J. Antibiot. (Tokyo) 1998, 51, 771. 15. (a) Miura, T.; Kurihara, K.-I.; Furuuchi, T.; Yoshida, T.; Ajito, K. Bioorg. Med. Chem. 2008, 16, 3985; (b) Furuuchi, T.; Miura, T.; Kurihara, K.-I.; Yoshida, T.; Watanabe, T.; Ajito, K. Bioorg. Med. Chem. 2008, 16, 4401; (c) Miura, T.; Natsume, S.; Kanemoto, K.; Shitara, E.; Fushimi, H.; Yoshida, T.; Ajito, K. Bioorg. Med. Chem. 2010, 18, 2735. 16. Phan, L. T.; Jian, T.; Chen, Z.; Qiu, Y.-L.; Wang, Z.; Beach, T.; Polemeropoulos, A.; Or, Y. S. J. Med. Chem. 2004, 47, 2965. 17. Wang, Z.; Jian, T.; Phan, L. T.; Or, Y. S. Bioorg. Med. Chem. Lett. 2004, 14, 519. 18. Przybylski, P.; Pyta, K.; Brzezinski, B. Tetrahedron Lett. 2009, 50, 6203. 19. (a) Xu, Y.; Chen, X.; Zhu, D.; Liu, Y.; Zhao, Z.; Jin, L.; Liu, C.; Lei, P. Eur. J. Med. Chem. 2013, 69, 174; (b) Li, X.; Ma, S.; Yan, M.; Wang, Y.; Ma, S. Eur. J. Med. Chem. 2013, 59, 209; (c) Kumar, R.; Rathy, S.; Hajare, A. K.; Surase, Y. B.; Dullu, J.; Jadhav, J. S.; Venkataramanan, R.; Chakrabarti, A.; Pandya, M.; Bhateja, P.; Ramkumar, G.; Das, B. Bioorg. Med. Chem. Lett. 2012, 22, 476; (d) Kapic´, S.; ˇ ipcˇic´ Paljetak, H.; Palej Jakopovic´, I.; Fajdetic´, A.; Ilijaš, M.; Štimac, V.; Brajša, C K.; Holmes, D. 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Bioorganic & Medicinal Chemistry Letters journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antibacterial activity of a series of novel 9-O-acetyl- 40 -substituted 16-membered macrolides derived from josamycin Zhehui Zhao, Longlong Jin, Yanpeng Xu, Di Zhu, Yi Liu, Chao Liu, Pingsheng Lei ⇑ State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Beijing Key Laboratory of Active Substances Discovery and Drugability Evaluation, Department of Medicinal Chemistry, Institute of Materia Medica, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing 100050, PR China
a r t i c l e
i n f o
Article history: Received 26 September 2013 Revised 25 November 2013 Accepted 10 December 2013 Available online 15 December 2013 Key words: Macrolide Josamycin Antibacterial activity Synthesis
a b s t r a c t A series of novel 9-O-acetyl-40 -substituted 16-membered macrolides derived from josamycin has been designed and synthesized by cleavage of the mycarose of josamycin and subsequent modification of the 40 -hydroxyl group. These derivatives were evaluated for their in vitro antibacterial activities against a panel of Staphylococcus aureus and Staphylococcus epidermidis. 15 (40 -O-(3-Phenylpropanoyl)-9-Oacetyl-desmycarosyl josamycin) and 16 (40 -O-butanoyl-9-O-acetyl-desmycarosyl josamycin) exhibited comparable activities to josamycin against S. aureus (MSSA) and S. epidermidis (MSSE). Ó 2013 Elsevier Ltd. All rights reserved.
Macrolide antibiotics have been widely used to treat bacterial infections for the past 60 years.1 They are considered as the preferred therapeutic agents for the treatment of upper and lower respiratory tract infections because of their safety and efficacy.2 The high-resolution X-ray cocrystal structures of the bacterial ribosome with macrolides have revealed the detailed interaction at atomic level.3 It demonstrated that the macrolides inhibit bacterial protein synthesis by sterically blocking the passage of nascent polypeptides through the exit tunnel of the ribosome.4 The therapeutic utility of the macrolides has been severely compromised by the emergence of resistant pathogens.5 Two of the most important mechanisms of macrolide resistance were ribosomal mutation (erm) and efflux–mediated resistance (mef).6 Recently, several researches7 have been made to overcome macrolide resistance, which resulted in the discovery of ketolides such as telithromycin (Tel)8 and cethromycin (ABT-773)9 (Fig. 1). The 16-membered macrolides, such as josamycin and tylosin (Fig. 1), constitute an important class of useful antibiotics of the macrolide family, which were studied relatively backward compared that with 14-membered macrolides.10 But they offer some advantages over the 14-membered macrolides. These advantages include better gastrointestinal tolerance, lack of drug–drug interactions, and the activity against resistance expressing strains.11 During our efforts to develop novel macrolides active against ⇑ Corresponding author. Tel.: +86 10 63162596; fax: +86 10 63017757. E-mail address: [email protected] (P. Lei). 0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.bmcl.2013.12.029
bacteria, we became interested in josamycin primarily because its activities are not affected by mef-resistance. Josamycin is an important drug used to treat Gram-positive and mycoplasma infections. This macrolide antibiotic is composed of a 16-membered lactone ring and an unusual disaccharide D-mycaminosyl-Lmycarose at C-5 position, which is oriented similarly to the 5-O-desosamine of 14-membered macrolides.4 Furthermore, the mycarose extends toward the peptidyl transferase center (PTC), making additional interactions at G2505 and U2506. The previous work shows that the mycarose of 16-membered macrolide is very important to the antibacterial activity, and removal of it from macrolide will reduce the antibacterial activity one or two orders of magnitude.12 The main reason may be that the sugar substituent contributes significantly to binding-free energy since they contribute 1/2 to 2/3 of the interaction surface.4 Unfortunately the disacchaharide is not stable under acid condition. Much of the early efforts on structural modifications within the 16-membered macrolide have been directed toward modification of the aldehyde group13 or the hydroxyl groups of mycarose.14 In recent years, the modifications on 16-membered macrolide focused on rebuilding the lactone bearing an arylalkyl-type side chain.15 But there were only few reports describing removal of the mycarose and modification of the mycaminose with different side chains to explore the interaction of the sugar of the 16-membered macrolide with the PTC.16,17 Phan et al. removed the mycarose sugar of tylosin and synthesized 4-substituted macrolides.16 The introduced arylalkyl side chain was thought to be important for
Z. Zhao et al. / Bioorg. Med. Chem. Lett. 24 (2014) 480–484
the improvement of the activities against sensitive and resistant bacteria. The author considered that there may be other interactions with ribosome RNA bases, but the works showed little information of structure–activity relationship (SAR) about the interaction between the substitutes and the PTC.
481
Based on that, we intended to find some new molecule entities to improve antibacterial activity and the acid stability of 16-membered macrolide using different substituents to replace the mycarose and study the preliminary SAR. Herein, we reported an efficient procedure for preparing a series of novel 40 -substituted
Figure 1. Chemical structures of telithromycin, cethromycin, josamycin and tylosin.
Scheme 1. Reagents and conditions: (a) acetic anhydride, pyridine, room temperature, overnight, 98%; (b) 4-methylbenzenesulfonic acid, toluene, reflux, 18 h, 67%; (c) methanol, room temperature, overnight, 99%.
482
Z. Zhao et al. / Bioorg. Med. Chem. Lett. 24 (2014) 480–484
16-membered macrolides and their antibacterial activity against Staphylococcus aureus and Staphylococcus epidermidis. Our approach is to find an efficient route to synthesis 40 -substituted josamycin derivatives by removing the mycarose sugar and modifying the 40 -hydroxyl group. Scheme 1 outlines the syntheses of 3, the 9-O-acetyl-desmycarosyl josamycin. Treatment of
josamycin with acetic anhydride (3.5 equiv) in pyridine gave 1 in a yield of 98%. The 400 -hydroxy group of josamycin is a tertiary hydroxyl group which is hard to acylate at this react condition. Hydrolysis of the 40 -mycarose group of 1 by p-toluenesulfonic acid in toluene gave the corresponding 40 -hydroxyl compound 2, then deprotection of the 20 -OH smoothly in the methanol gave 3 as a
Scheme 2. Reagents and conditions: (a) NaOH, THF/H2O, room temperature, overnight, 90%; (b) NaOH, THF/H2O, reflux, overnight, 88%.
Scheme 3. Reagents and conditions: (a) 1-isocyanato-4-(trifluoromethyl)benzene, DCM, room temperature, overnight, 82%; (b) methanol, room temperature, overnight, 99%; (c) NaOH, THF/H2O, room temperature, overnight, 87%; (d) NaOH, THF/H2O, reflux, overnight, 88%.
Scheme 4. Reagents and conditions: (a) benzoic acid, EDCI, TEA, HOBT, chloroform, room temperature, overnight, 78%.
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key intermediate, the structure was confirmed by HR-MS, 1H NMR, and 13C NMR spectra. The signals at 168.9 ppm (C@O) and 21.6 ppm (CH3) disappeared in the 13C NMR of compound 3, compared with that of compound 2. Meanwhile the signals of C-20 in the 13C NMR and H-20 in the 1H NMR moved to high field. In this route aldehyde group was not necessary to be protected, that can shorten our procedures. In Przybylski’s work, hydrolysis of 3-O-acetate of josamycin derivatives gave a,b-unsaturated product.18 The same procedure was used to hydrolyze 3 to obtain two a,b-unsaturated derivatives 4 and 5. Scheme 2 outlines the syntheses of 4 and 5. Compound 3 was hydrolyzed by sodium hydroxide under ambient condition to give 4, and further hydrolysis of 9-O-acetate to give 5. By our knowledge, isocyanates and acids were the facile ways to modify the hydroxyl group of 14-membered macrolide smoothly in high yield.19 So some commercial isocyanates and acids were chosen to react with 3. Schemes 3 and 4 outlines the syntheses of 7–10. Treatment of 2 with 1.0 equiv of 1-isocyanato-4-(trifluoromethyl)benzene in dichloromethane gave 6 in a yield of 82%, and deprotection of 6 in methanol gave final product 7 in a yield of 95%. 8 and 9 were gotten as the procedure similar to 4 and 5. The 13C NMR spectra of 4, 5, 8 and 9 which all have the double bond at C-2, C-3 position showed the new signals of C-2, C-3 were at about 88 ppm and 91 ppm. Meanwhile, the signals of C-6, C-7, C8 and C-22 had a large shift to low field, the signals of C-10, C-11, C-12 and C-13 changed too, that means that the conformation of the whole structure of 16-membered macrolide had a great change. The conjugated double bonds at C-10 and C-13 interacted with the new formed double bond at C-2 and C-3 and made the unusual change of the signal of C-2 and C-3. The final product 10 was prepared by condensation of 3 with the benzoic acid using 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride (EDCI) and triethylamine (TEA)in chloroform, 1-Hydroxybenzotriazole (HOBT) as catalyst, in a yield of 78%. The antibacterial activities of 3–5, 7–10 were showed in the Table 1. From the result of the activities, compared with that of josamycin, the antibacterial activity of 3 declined about one order of magnitude against S. aureus (MSSA) and S. epidermidis (MSSE). Compound 10 remained some antibacterial activity against S. aureus (MSSA) and S. epidermidis (MSSE). So the more acids were chosen to modify the compound 3. The products 11–17 (Fig. 2) were synthesized by the similar procedure of 10 in a yield of 32– 81%. All the compounds were confirmed by HRMS, 1H NMR, and 13 C NMR spectra. The antibacterial activities of the target compounds were assessed against some respiratory pathogens, including macrolide drug sensitive and resistant strains. Josamycin was chosen as the reference compounds. The in vitro antibacterial activity was reported as minimum inhibitory concentrations (MICs), which was determined by the broth microdilution method as recommended by the CLSI.20
ATCC 29213, 15 and 09–06 are methicillin-sensitive Staphylococcus aureus (MSSA). ATCC 33591 and 09–13 are methicillin-resistant Staphylococcus aureus (MRSA). ATCC 12228 and 09–9 are methicillin-sensitive Staphylococcus epidermidis (MSSE). 09–3 is a methicillin-resistant Staphylococcus epidermidis (MRSE). All the MRSA and MRSE strains chosen in this test are constitutively resistant strains supplied by Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College (IMB, China). All of the compounds synthesized, as well as josamycin as references, were tested for in vitro antibacterial activity against five strains of S. aureus and three stains of S. epidermidis The activities are reported in Table 1 and Table 2 as minimum inhibitory concentrations (MICs). The antibacterial activities of 3–5, 7–10 were shown in Table 1. Among of them, 3–5 were unsubstituted derivatives, 7–9 were carbamate derivatives and 10 was ester derivative. The antibacterial activity of compound 3 was one order of magnitude weaker than that of josamycin against S. aureus (MSSA) and S. epidermidis (MSSE). The antibacterial activities of 4 and 5 were none or weaker than that of 3. The antibacterial activities of 7, 8 and 9 were none or weaker than that of the 3. On the other hand, the activity of 10 was stronger than that of the 3 against S. aureus (MSSA) and S. epidermidis (MSSE) In reviewing the data of Table 2, it was noteworthy that the ester analogue had an improved activity against S. aureus and S. epidermidis. The activity of 11, bearing a methoxyl group on the phenyl ring, was same as that of 10. While the activity of 12,
Figure 2. Chemical structures of the products 11–17.
Table 1 In vitro antibacterial activities of 3–5, 7–10 MIC (lg/mL)
S. aureus
S. epidermidis
ATCC 29213 ATCC 33591 15 09–6 09–13 ATCC 12228 09–3 09–9
MSSA MRSA MSSA MSSA MRSA MSSE MRSE MSSE
3
4
5
7
8
9
10
Josamycin
16 >32 16 16 >32 16 >32 16
>64 >64 >64 >64 >64 64 >64 64
>32 >32 >32 >32 >32 >32 >32 >32
>64 >64 >64 >64 >64 >64 >64 >64
>64 >64 >64 >64 >64 >64 >64 >64
>64 >64 >64 >64 >64 >64 >64 >64
8 >64 8 8 >64 8 >64 8
1 >32 2 1 32 1 >32 2
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Table 2 In vitro antibacterial activities of 3 and 10–17 MIC (lg/mL)
S.aureus
S. epidermidis
ATCC 29213 ATCC 33591 15 09–6 09–13 ATCC 12228 09–3 09–9
MSSA MRSA MSSA MSSA MRSA MSSE MRSE MSSE
3
10
11
12
13
14
15
16
17
Josamycin
16 >32 16 16 >32 16 >32 16
8 >64 8 8 >64 8 >64 8
8 >64 8 8 >64 8 >64 8
32 >64 >64 32 >64 32 >64 32
8 >32 >32 8 >32 4 >32 4
8 >64 16 8 >64 8 >64 8
4 >32 8 4 >32 4 >32 4
4 >64 4 4 >64 4 >64 4
8 >64 8 8 >64 8 >64 8
1 >32 2 1 32 1 >32 2
bearing a nitro group, was decreased remarkably. Compared that with the benzoate ester, the cinnamate ester was slightly improved the activity against S. epidermidis. The quinolyl group substituent did not improve the activities. Compared the activities of 13 and 15, conversion of the carbon–carbon double bond into carbon–carbon single bond can improve the activities. The activity of aliphatic ester was similar as that of the aromatic ester. 15 and 16 exhibited comparable activity against S. aureus and S. epidermidis, which proved that b-substituted acids may be the best substituted group to modify the 40 -hydroxyl of josamycin. All the compounds showed none activities against resistant-pathogens. Next, we would synthesize more b-substituted acids to modify the 40 -hydroxyl of josamycin. In conclusion, a series of novel 40 -substituted 16-membered macrolides were designed and synthesized in an efficient route. Isocyanates and acids were used to replace the unstable mycarose substituent in josamycin and their derivatives were evaluated for the in vitro antibacterial activities against a panel of S. aureus and S. epidermidis. The b-substituted acids may be the best substitutes for modification the 40 -hydroxyl group of 16-membered macrolide. These studies present a considerable opportunity for overcoming the acid instability of 16-membered macrolide and improving their antibacterial activities. Acknowledgments This work was supported by the National S&T Major Special Project on Major New Drug Innovation (Item Number: 2008ZX09401-004 and 2009ZX09301-003) and National Natural Science Foundation of China (81072524). And we are grateful to Professor Xuefu You for the antibacterial activity test. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.bmcl.2013. 12.029. References and notes 1. (a)Macrolides: Chemistry Pharmacology and Clinical Uses; Bryskier, A. J., Butzler, J.-P., Neu, H. C., Tulkens, P. M., Eds.; Arnette Blackwell: Paris, 1993; (b) Henninger, Todd C. Expert Opin. Ther. Patents. 2003, 13, 787; (c) Katz, L.; Ashley, G. W. Chem. Rev. 2005, 105, 499. 2. Zhanel, G. G.; Dueck, M.; Hoba, D. J.; Vercaigene, L. M.; Embil, J. M.; Gin, A. S.; Karlowsky, J. A. Drugs 2001, 61, 443. 3. (a) Schlunzen, F.; Zarivach, R.; Harms, J.; Bashan, A.; Tocilj, A.; Albrecht, R.; Yonath, A.; Franceschi, F. Nature 2001, 413, 814; (b) Schlunzen, F.; Harms, J.; Franceschi, F.; Hansen, H.; Bartels, H.; Zarivach, R.; Yonath, A. Structure 2003, 11, 329; (c) Berisio, R.; Harms, J.; Schlunzen, F.; Zarivach, R.; Hansen, H.; Fucini, P.; Yonath, A. J. Bacteriol. 2003, 185, 4276; (d) Tu, D.; Blaha, G.; Moore, P. B.; Steitz, T. A. Cell 2005, 121, 257. 4. Hanson, J.; Ippolito, J. A.; Ban, N.; Nissen, P.; Moore, P.; Steitz, T. Mol. Cell 2002, 10, 117. 5. Takashima, H. Curr. Top. Med. Chem. 2003, 3, 991.
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