Doi:10.1016/j.bmcl.2006.11.09

Bioorganic & Medicinal Chemistry Letters xxx (2007) xxx–xxx Synthesis and antitubercular activity of quaternized promazine Aaron B. Bate,a,  Jay H. Kalin,a,  Eric M. Fooksman,b Erica L. Amorose,a Cristofer M. Price,a Heather M. Williams,a Michael J. Rodig,a Miguel O. Mitchell,a,* Sang Hyun Cho,c Yuehong Wangc aDepartment of Chemistry, Salisbury University, Salisbury, MD 21801, USA bDepartment of Biological Sciences, Salisbury University, Salisbury, MD 21801, USA cInstitute for Tuberculosis Research, College of Pharmacy, University of Illinois-Chicago, Chicago, IL 60612, USA Received 5 November 2006; revised 29 November 2006; accepted 30 November 2006 Abstract—Quaternized chlorpromazine, triflupromazine, and promethazine derivatives were synthesized and examined as antituber-cular agents against both actively growing and non-replicating Mycobacterium tuberculosis H37Rv. Impressively, several com-pounds inhibited non-replicating M. tuberculosis at concentrations equal to or double their MICs against the actively growingstrain. All active compounds were non-toxic toward Vero cells (IC50 > 128 lM). N-Allylchlorpromazinium bromide was only weak-ly antitubercular, but replacing allyl with benzyl or substituted benzyl improved potency. An electron-withdrawing substituent onthe phenothiazine ring was also essential. Branching at the carbon chain decreased antitubercular activity. The optimum antituber-cular structures possessed N-(4- or 3-chlorobenzyl) substitution on triflupromazine.
Ó 2006 Elsevier Ltd. All rights reserved.
Tuberculosis (TB), the disease caused by Mycobacterium chain in Mtb becomes blocked and shuts down. Ndh-2 tuberculosis (Mtb), infects approximately two billion is the only NADH dehydrogenase enzyme expressed in people. The World Health Organization estimates that Mtb and is thus vital to its surviNdh-2 is also found about two million people die each year from TB due in a number of other bacteria such as Staphylococcus to the lack of and inability to afford proper health care.
aureus and Enterococcus faecalis but is not expressed Overcrowding and ill-nourishment of poor people living in large cities leads to a high incidence of the disease dueto the ease at which the infection can be transferred.
Humans rely only on type I NADH dehydrogenase This situation contributes to the accelerated speed at (ndh-1) and thus minimal toxicity in humans is predict- which TB spreads in underdeveloped countries. There ed with ndh-2 inhibitors. In the 1950s and 1960s psychi- is also an alarming increase in cases of TB caused by atrists noticed a more pronounced inhibition of Mtb multidrug-resistant strains of M. tuberculosis (Mtb), occurring in TB-infected, schizophrenic patients taking due in part to inadequate drug therapy as a result of higher doses of an antipsychotic drug, chlorpromazine, incorrectly selected medications or suboptimal drug dos- as opposed to patients who were taking lower doses of ing.Thus, there is a need for new drugs targeting en- this drug.Later, Weinstein et al. discovered that zymes essential to mycobacterial survival. One such N-(benzyl)-chlorpromazinium inhibited Mtb in vitro at target is type II NADH-menaquinone dehydrogenase an even lower concentration than chlorpromazine it- (ndh-2). By inhibiting ndh-2, the electron transport self.This was the first quaternized promazine derivative(QPD) discovered to be an antibacterial agent againstMtb. Chlorpromazine and its QPD were both found toselectively inhibit ndh-2; there was no inhibition of Keywords: Antitubercular; Promazine; Promethazine; Chlorproma- ndh-1.Other phenothiazines were also described to zine; Triflupromazine; Quaternized.
* Corresponding author. E-mail: have antitubercular activity.In order to establish a   These authors equally contributed to manuscript preparation.
preliminary SAR for QPDs, we decided to synthesize 0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.11.091 Please cite this article in press as: Bate, A. B. et al., Bioorg. Med. Chem. Lett. (2007), doi:10.1016/j.bmcl.2006.11.091 A. B. Bate et al. / Bioorg. Med. Chem. Lett. xxx (2007) xxx–xxx chlorpromazine HCl: R1 = Cl
1: R1 = Cl;
a: R2 = H, X = Br
b: R2 = 4-Cl, X = Cl
4: R1 = CF3
c: R2 = 3-Cl, X = Cl
d: R2 = 2-Cl, X =Cl
e: R2 = 4-F, X = Cl
f: R2 = 4-CH3, X = Cl
g: R2 = 4-OCH3, X = Cl
h: R2 = 4-NO2, X = Cl
Scheme 1. Reagents: (a) potassium carbonate, water, ethyl acetate; (b) benzyl or allyl halide, acetone.
quaternized derivatives of promazine, chlorpromazine, The syntheses of the quaternized promazine and pro- and triflupromazine, and to measure their MICs against methazine derivatives were based on the procedure de- both actively growing and non-replicating Mtb.
1.00 gram of promazine, chlorpromazine, or triflupro- mazine hydrochloride was dissolved in water and then potassium carbonate was added to raise the pH to 10.
The aqueous mixture was subsequently extracted with ethyl acetate. The combined organic extracts were dried with sodium sulfate, gravity filtered, and the solvent was removed in vacuo. The products obtained from these reactions were viscous oils. The viscous oils were dissolved in acetone and reacted with 1 equiv of each al- kyl halide. The reaction vials were sealed and left to run overnight. Ethyl ether was then used to precipitate our final products out of solution. Those QPDs creating gums were triturated with hexanes. The purified products of these reactions were generally white crystal- line solids, with the exception of 1h and 5h, which were slightly yellow. Yields ranged from 40% to 94%.
1H NMR, 13C NMR, and HMBC spectra, along with elemental analysis, confirmed the structures and purity The minimum inhibitory concentration (MIC) of H37Rv was determined using the microplate alamar blue assay (MAand was defined as the lowest concentration effecting a reduction in fluorescence of P90% relative to drug-free controls. Compounds for Please cite this article in press as: Bate, A. B. et al., Bioorg. Med. Chem. Lett. (2007), doi:10.1016/j.bmcl.2006.11.091 A. B. Bate et al. / Bioorg. Med. Chem. Lett. xxx (2007) xxx–xxx which an initial screening revealed an MIC of 10 lM or less were subsequently tested in triplicate. Activityagainst non-replicating M. tuberculosis was determined The authors are grateful for the financial support of by a 10-day anaerobic exposure of a low oxygen- Henson Student Research Grants and the 2005 Guerri- adapted culture containing the Vibrio harveyii lucifer- ase gene to QPDs. After a subsequent 28-h aerobic‘‘recovery’’, the ability to make a luminescent signalwas determined following the addition of the n-deca- nal substrThe LORA MIC was defined asthe lowest concentration effecting a reduction of 1. Maher, D.; Raviglionem, M. C. In Tuberculosis and P90% luminescence relative to drug-free controls.
Nontuberculous, Mycobacterial Infections; Schlossberg, The activities of three compounds (1c, 3c, and 4c) D., Ed., fourth ed.; Saunders: Philadelphia, 1999; p 104.
were confirmed for both MABA and LORA using a 2. Lowell, A. M. In Tuberculosis and Nontuberculous Myco- bacterial Infections; Schlossberg, D., Ed., fourth ed.; colony-forming unit determination by subculturing from the microplate onto drug-free 7H11 agar. MICs 3. Bearing, S. E.; Peloquin, C. A.; Patel, K. B. In Tubercu- for actively growing M. tuberculosis were 1.9-, 2.1-, losis and Nontuberculous Mycobacterial Infections; Sch- and 2.9-fold higher than the MABA MICs, and 1.7-, lossberg, D., Ed., Fourth ed.; Saunders: Philadelphia, 1.9-, and 2.1-fold higher than the corresponding 4. Weinstein, E. A.; Yano, T.; Li, L. S.; Avarbock, D.; Avarbock, A.; Helm, D.; McColm, A. A.; Duncan, K.; The in vitro cytotoxicity for VERO cells was deter- Lonsdale, J. T.; Rubin, H. Proc. Natl. Acad. Sci. U.S.A.
mined for all compounds with a MABA MIC of less than 10 lM using a dye reduction assay following 3 5. Melo, A. M. P.; Bandeiras, T. M.; Teixeira, M. Microbiol.
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QPDs is a requirement for significant antitubercular 9. Gadre, D. V.; Talwar, V. J. Chemother. 1999, 11, 203.
activity (1a vs. 2). Alkyl chain branching (5a, 5f–h) 10. Khan, O. F.; Austin, S. E.; Chan, C.; Yin, H.; Marks, D.; decreases potency. Three of the QPDs having MICs both Vaghjiani, S. N.; Kendrick, H.; Yardley, V.; Croft, S. L.; <4 lM against actively growing Mtb and <8 lM against Douglas, K. T. J. Med. Chem. 2000, 43, 3148.
11. Collins, L.; Franzblau, S. G. Antimicrob. Agents Chemo- non-replicating Mtb possess N-(4- or 3-chlorobenzyl) groups and electron-withdrawing substituents on the 12. Falzari, K.; Zhu, Z.; Pan, D.; Liu, H.; Hongmanee, P.; phenothiazine ring (1c, 4b–c). Based on this MIC data Franzblau, S. G. Antimicrob. Agents Chemother. 2005, 49, and the lack of in vitro mammalian cell toxicity, we will attempt to improve these leads by studying the antitu- 13. Cho, S. H.; Warit, F.; Wan, B.; Di, W.; Hwang, C. H.; bercular potency of other electron-withdrawing substit- Franzblau, S. G. 2005. Presented at the Keystone Sym- uents on the phenothiazine ring and various halogen posium: Tuberculosis: Integrating Host and Pathogen substitutions on the benzyl group. If these improved Biology, Whistler, British Columbia, Canada.
leads also lack mammalian cell toxicity, animal studies 14. Jayaprakash, S.; Yasuyoshi, I.; Wan, B.; Franzblau, S. G.; Kozikowski, A. P. Chem. Med. Chem. 2006, 1, 593.
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