Journal of Medicinal Chemistry, 1978, Vol. 21, No. 8 781
2- Nitroimidazole Derivatives
Acknowledgment. We are grateful to Messrs. F. Lund, S. Rachlin, and J. Enemark for encouragement and support and to Mr. K. Nielsen for skillful technical assistance throughout this work. References and Notes (1) (2) (3) (4)
H. J. Petersen, German Patent Offenleg. 2 557 438 (1976).
C. Kaergaard Nielsen, unpublished results. H. J. Petersen, J . Med. Chem., 17, 101 (1974). R. W. Brimblecombe, W. A. Duncan, G. J. Durant, J. C. Emmet, C. R. Ganellin, and M. E. Parsons, J. Znt. Med. Res., 3, 86 (1975). ( 5 ) G. J. Durant, J. C. Emmet, C. R. Ganellin, P. D. Miles, M. E. Parsons, H. D. Pram, and G. R. White, J . Med. Chem., 20, 901 (1977).
(6) S. M. Gadekar, S.Nibi, and E. Cohen, J . Med. Chem., 11, 811 (1968). (7) R. Appel, R. Kleinstuck, and K.-D. Ziehn, Chem. Ber., 104, 1335 (1971). ( 8 ) H . Z. Lecher, R. P. Parker, and R. S.Lang, U S . Patent 2 479 498 (1949). (9) American Cyanamid Co., British Patent 643 012 (1950). (10) C. G. McCarthy, J. E. Parkinson, and D. M. Wieland, J. Org. Chem., 35, 2067 (1970). (11) F. H. S.Curd, J. A. Hendry, T. S.Kenny, A. G. Murphy, and F. L. Rose, J . Chem. Soc., 1630 (1948). (12) L. Ellenbogen, P. S.Chang, and J. R. Cummings, Arch. Znt. Pharmacodyn. Ther., 207, 170 (1974). (13) J. Litchfeld, Jr., and F. Wilcoxon, J. Pharmacol. Exp. Ther., 96, 99 (1949).
Synthesis and Biological Activity of New 2-Nitroimidazole Derivatives Bruno Cavalleri,* Giancarlo Volpe, Vittorio Arioli, Fabio Pizzocheri, and Albert0 Diena Research Laboratories, Gruppo Lepetit S.p.A., 20158 Milano, Italy. Received December 29, 1977 In an earlier paper we described the synthesis and the antitrichomonas activity of 2-nitro-a,a,l-trimethyl-lHimidazole-5-methanol (2). Starting from this compound, several derivatives have been synthesized. Among these, the phenyl carbonate 8 has been shown to possess activity equal to that of 2 and to be less toxic. This compound therefore is interesting in comparison with some antitrichomonas agents currently in use clinically. Before undertaking an in-depth investigation, compound 8 was subjected to some studies to see whether it has any effects on the central nervous system (CNS). Preliminary results show that, at therapeutic doses, it might induce unwanted CNS effects to a lesser degree than metronidazole.
At the present time, human genital trichomoniasis can be listed among the more important sexually transmitted diseases. However, it is a completely curable and controllable condition. The WHO is collecting data and organizing prevention and treatment centers as part of a worldwide plan for its eradication.’ For this purpose the nitroimidazoles are the most efficient drugs for systemic treatment. However, there are still some as yet unobtained goals (lowering of dosage, shortening treatment time, getting rid of adverse reactions and cross resistance, etc.) which make it worthwhile to continue research in this field.2 Earlier studies of the metabolism of a 2-nitroimidazole derivative 1 (I, R = H; R’ = CH,), shown to be particularly active as an oral antitrichomonas agent,, led to the isolation4 of its principal metabolite 2 (I, R = OH; R’ = CHJ from urines of treated animals. This last compound has been synthesized5 and shown to possess in vivo activity against T r i c h o m o n a s similar to that of the parent compound, while a t the same time it is less toxic.5 On the basis of these findings we have undertaken a limited project consisting of (a) synthesis of the isomer 7 (Table I), in which the hydroxyl is moved to the primary carbon; (b) the synthesis of some functional derivatives of 2; and (c) comparison of 2 with its 5-nitro isomer 14. As a result of this program we have found a derivative, 8, which has activity equal in vivo to that of 2 but is definitely less toxic (Table 11) and has a therapeutic index which is even better than those of some antiprotozoan nitroimidazoles in clinical use. Chemistry. Compound 7 was obtained by the general procedure previously published for the synthesis of 2nitroimidazoles, outlined in Scheme I. The preparation of the intermediate 2-aminoimidazole 6, and the transformation of the latter into the corresponding 2-nitroimidazole 7, proceeded with rather low yields. No attempts were made to improve the yields, since the product showed an activity lower than that of 2. 0022-2623/78/ 1821-0781$01.00/0
H3cc,ar Scheme I
CH~NHZ
HOHzCCH-CHCOOH
I
(C2“1 HCI
I
CH3 NHCH,
3
4 r
1
The syntheses of some derivatives on the tert-hydroxyl group of compound 2 presented some difficulties due t o the tendency to dehydrate with formation of the 5-(1methylethenyl) derivative (I, R, R’ = CH2Is5 Among different reagents employed, phenyl chloroformate gave the phenyl carbonate 8, which was also a useful intermediate for the preparation of compounds 9 and 10. Compound 8 is quite stable in crystalline form and in ethanol or chloroform solution. It led to the hydroxylic starting compound 2 or the methoxy derivative (I, R = OCH,; R’ = CHJ5 by treating it either with water-ethanol or with methanol. Aqueous suspensions of compound 8, prepared under suitable conditions for use in experimental tests, were stable. Treatment of 2 with phenyl isocyanate furnished the phenyl carbamate 11. The benzoate 12 was obtained in low yields, while attempts under various conditions to prepare the acetate led to production of the previously mentioned 5-(l-methylethenyl) derivative. 0 1978 American Chemical Society
782 Journal of Medicinal Chemistry, 1978, Vol. 21, No. 8 Table Ia
Caualleri et al.
R'
I
R'
recrystn soh e n t
yield,
R
%
TLC, Rf
mP, " C
formula
H OCOOC,H, OCONHNH, OCONH, OCONHC,H, OCOC,H,
CH,OH CH, CH, CH, CH, CH
Et,O EtOH i-PrOH EtOH PhH i-Pr 0
0.5 52.1 83.7 76.5 63.0 6.0
0.14 0.65 0.10 0.17 0.47 0.64
88-90 119 (DSC) 166 (DSC) 143-146 155-158 125-128
C,H, 1 ~ 3 ~ , C,,HIiN,O~ C,H,,N,04 C,H,,N,O, c,4H1J 4 0 4 C13,P 3 0 4
CH 3
EtOH
45.8
0.00
160- 163
CI&, J 4 O 5s
compd
7 8
9 10 11 12 13
,.)
>t +1/
a
See the introduction to the Experimental Section,
b
Molecular weight confirmed by the M' peak in the mass spectrum.
Table I1 in vitro act. against selected organisms,O MIC, pg/mL S.a.
compd 2 I
Toure
s.p.
C.p. ISS
C203
30543
>300 200 100 100 100 > 100 100
25 0.8 10 3.1 10 3.1 3.1 > 100
M.g. S6 Weybridge
in vivo act.b re1 ED,,^ against T . u . , (metroT . u . ~ ED,,, mgikg nidazole)
LD,,, mg/k$
T.I.
1.65 0.28 698.0 4 23 >10 >0.7 n.d. 8 >loo 2 1.65 1969 0.28 3250.0 9 >loo 25 100 660.0 4.67 0.33 141 10 >loo >loo 10 5.74 0.40 900 156 11 .loo 25 100 2.88 28.83 n.d. 12 100 > 100 50 n.d. 1.62 16.2 13 > 100 >loo > 100 >I00 >40 n.d. >4 14 >loo 5 > 100 >loo 5 0.81 8.12 805.0 99 me tronidazoleg > 300 >300 0.6 > 300 5 5.77 1 3800.0 6 58 tinidazoleg 300 >300 0.3 >300 3200.0 1280 2.5 3.1 0.43 nimorazoleg > 300 >300 0.6 >300 1530.0 40 37.9 12.5 4.66 MIC values for S. aureus (S.0.) and S. pyogenes ( S . P . )were determined by a microtiter method" and for C. perfringens (C.P.), M . gallisepticum (M.g.),and T. uaginalis ( T . u . )by a broth dilution m e t h ~ d . ' ~ Subcutaneous infection in mice, oral administration. Details are given in ref 3. Compounds 2, 8, 10,and 12 were suspended in an aqueous solution of 0.75% sodium carboxymethylcellulose, - 5000 (SIPA); compound 7 was dissolved in DMF-H,O; compounds 9 and 1 1 in DMF-phos. phate buffer, pH 7.38; compounds 13, 14,metronidazole, tinidazole, and nimorazole in H,O. The values found for metronidazole under the experimental conditions used varied from 5.77 to 14.1 mgikg. The figures express the ratio between the ED,, (test compound) and ED,, (metronidazole) run in parallel. Acute toxicityz4in mice, oral administration. The compounds were suspended in an aqueous solution of 0 . 5 %Methocel 90-HG Dow. ' The values were unaffected by the addition of 30% bovine serum. Cidal concentration. Spe ref 11-13. n.d. not determined 100 25 100
40
50
25 25
7
Finally, when 2 was allowed to react with methanesulfonyl chloride, an undesired side reaction6 took place, and the pyridinium quaternary salt 13 was obtained. The preparation of compound 14 (the 5-nitro isomer of 2) starting from a-hydroxyisobutyraldehydehas been described.' We found it more convenient to prepare 14 by acetic acid-concentrated sulfuric acid hydrolysis of the corresponding methoxy derivative, obtained from CYmethoxyisobutyraldehyde as reported by the same authors.: 'H NMR and IR data were in accordance with the assigned structures. Biological Results. Table I1 lists the minimal inhibitory concentrations (MIC) for the compounds, tested against selected organisms. In some cases the products showed only minimal activity against the gram-positive bacteria in the test and against Mycoplasma, but almost all of them had definite activity against Clostridium perfringens and Trichomonas uaginalis, except compound 12, which had a trichomonastatic MIC of 100 pg/mL, and compound 13 which, although soluble in water, had no activity against any of the microorganisms in the test. It has been hypothesized8 that the ability of the microorganism to reduce the nitroimidazoles, which is related to the reduction potential (expressed as E , 2), is correlated
with the activity of the 2-nitroimidazoles. Therefore, we measured'" the E,,? values for compounds 2 (-0.65 V), 8 ( 4 . 5 6 V), 14 ( 4.67 V), and metronidazole" (-0.50V). The values found explain the very minor activity against Staphylococcus aureus and Streptococcus pyogenes, since it is probable that values of of the order of -0.30 V would be needed for these compounds to be metabolized by these microorgani~rns.~ However, they do not explain the greater activity in vitro of 2 as compared to the other compounds. It is obvious that other parameters, such as lyo- or lipophilia and steric hindrance, must also enter into the picture. Table I1 contains the ED,, values for oral treatment of 7'. vaginalis infection in the mouse. The relative EDs0, which is the ratio between the ED,, of the test compound and that of metronidazole, used as standard of reference in the same experiment, is useful for rapid comparison. Although we did not obtain an absolute value, we can still see that compound 7 is about half as active as compound 2, which has the tert-hydroxyl. Formation of the phenyl carbonate derivative 8 or the hydrazine carboxylate derivative 9 did not cause any change in activity, while other substitutions generally resulted in less active compounds. However, it is remarkable how drastically the toxicity of compound 8 is
Journal of Medicinal Chemistry, 1978, Vol. 21, No. 8 783
2-Nitroimidazole Derivatives
Table IV. Antagonism of Death Induced by Strychnine or Pentetrazole (Mice)
Table 111. Sleeping Time of Mice Given Hexobarbital Sodium, 75 mg/kg ip, T = 25-26 C
~~
compd 8
metronidazole chlorpromazine hydrochlorideb physiological salineC
dose, mdkg PO
250 500 300 600 1 0.2 mL
m e a n * SE 39.2+ 40.0 * 43.9 t 53.0 f 53.6 i 34.0
*
3.32 2.54 3.79 3.51 3.93
change,%
pQ
+15.5 +18.1 +29.2 +55.9 t57.7
N.S. N.S.
