Inhibitors of Indolamine N-Methyltransferase
Journal of Medicinal Chemistry, 1979, Vol. 22,No. 3 237
For analysis, the product was dissolved in water by the addition of a minimal amount of 1 N KOH, followed by precipitation with HC1 and workup as described above: ‘H NMR (DzO) 6 2.36 (3 H,s,H-2’),3.2 (2H, m, H-P), 4.0 (1H, m, H-a), 4.91 (2H,d, H-5’, slP-lH coupling constant = 10 Hz), 5.77 (1 H, s, H-4’), 6.20 (1 H, S, H-5”),6.69 (1 H,S, H-2”),7.74 (1H,8, H-6);UV A,, (pH 7.0)250 ( 6 6400,s), 292 ( e 4630), 326 nm (c 8780). Anal. (CI7H1gN20gP*H20)C, H, N, P. Acknowledgment. The research was supported by Public Health Service Grant 5429-16-9 (5-23323).
(17) M. Smith, Biochem. Prep., 8, 130 (1961). (18) J. E. Churchich and J. G. Farrelly, J.Biol. Chem., 244,3685 (1969). (19) M. H. O’Leary and J. M. Malik, J. Biol. Chem., 247,7097 (1972). (20) A. E. Braunstein, V. I. Ivanov, and M. Ya Karpeisky in
References and Notes (a) Abbreviations used are: Dopa, 3,4-dihydroxyphenyl-
76,648 (1954). (22) T. 6. French, D. S. Auld, and T. C. Bruice, Biochemistry, 4, 77 (1965). (23) G. Hammes and P. Fasella, J . Am. Chem. Soc., 85,3929 (1963). (24) R. C.Hughes, W. T. Jenkins, and E. H. Fischer, Proc. Nntl. Acad. Sci. U.S.A., 48, 1615 (1962). (25) W. B. Dempsey and E. E. Snell, Biochemistry, 2,1414(1963). (26) A. Relimpio, J. C. Slebe, and M. Martinez-Carrion, Biochem. Riophvs. Res. Commun., 63,625 (1975). ( 2 7 ) J. S.Heller, E. S. Cancllakis, D. L. Bussolotti, and J. K. Coward, Biochim. Biophys. Acta, 403,197 (1975). (28) G.Tunnicliff, T. T. Ngo, and A. Barbeau, Experientia, 33, 20 (1977). (29) C. Rorri-Voltattorni, A. Minelli, and C. Turano, Boll. Soc. Ital. B i d . Sper., 47,700 (1971);Chem. Abstr., 76,137410X
alanine; dopamine, 3,4-dihydroxyphenylethylamine;Boc, tert-butoxycarbonyh OMe, methyl estgr; OEt, ethyl ester: TFA, trifluoroacetic acid; NMR nuclear magnetic resonance. (a) G. A. Lancaster and T. L. Sourkes, Can. J. Biochem., 50,791(1972). (b) N. Kirshner and McC. Goodall, Biochim. Biophys. Acta, 24, 658 (1957). C. Borri-Voltattorni, A. Minelli, and P. Borri, FEBS Lett.,
75,277 (1977). J. G.Christenson, W. Dairman, and S. Udenfriend, Arch. Biochem. Biophys., 141,356 (1970). A. Fiori, C. Turano, C. Borri-Voltattorni, A. Minelli, and M. Codini, FEBS Lett., 54,122 (1975). W. Lovenberg, H. Weissbach, and S.Udenfriend, J. Biol. Chem., 237,89 (1962). J.-C. David, W.Dairman, and S.Udenfriend, Arch. Biochem. Biophys., 160,561 (1974). J. M.Saavedra. Fed. Proc., Fed. Am. SOC. Exp. Biol., 36,
2134 (1977).
0.Hornykiewicz, Pharmacol. Rev., 18,925 (1966). 0.Hornykiewicz, Fed. Proc., Fed. Am. SOC. Exp. Biol., 32, 183 (1973). J. R. Bianchine, F. S.Messiha, and T. J. Preziosi, Adu. Neurol., 2, 101 (1973). R. M. Pinder, R. N. Brogden, P. R. Sawyer, T. M. Speight, and G. S.Avery, Drugs, 11, 329 (1976). M. Ikawa, Arch. Biochem. Biophys., 118,497 (1967). E. S. Severin, N. N. Gulyaev, E. N. Khurs, and R. M. Khomutov, Biochem. Biophys. Res. Commun., 35, 318 (1969). V. Raso and B. D. Stollar, J. Am. Chem. SOC.,95, 1621 (1973). J. W. Thanassi and W. C. Cunningham, unpublished observations.
“Pyridoxal Catalysis: Enzymes and Model Systems”, IUB Symposium, Moscow, E. E. Snell, A. E. Braunstein, E. S. Severin, and Yu. M. Torchinsky, Eds., Interscience, New York. N.Y.. 1968. DD 291-302. (21) D. E.’Metzler, M.I!&a. and E. E. Snell, J. Am. Chem. SOC.,
(1972).
(30) M.H. O’Leary and R. L. Baughn, J. Bid. Chrm., 252,7168 (1977). (31) H. C. Dunathan, Adu. Enzymol., 35,79 (1971). (32) S.D.Nelson, J . R. Mitchell, J. A. Timbrell, W. R. Snodgrass, and G. B. Corcoran, Science, 193,901 (1976). (33) S.S.Tate, R. Sweet, F. H. McDowell, and A. Meister, Proc. Natl. Acad. Sci. U.S.A., 68,2121 (1971). (34) Sale of this material has been discontinued by its major supplier owing to its explosive proper tie^.^^ We prepared this material in small-scale quantities by the method of Carpino et (35) P. Feyen, Angew. Chem., Znt. Ed. Engl., 16, 115 (1977). (36) L. A. Carpino, B. A. Carpino, P. J. Crowley, C. A. Giza, and P. H. Terry, Org. Synth., 44,15 (1964);“Organic Synthesis”, Collect. Vol. V, Wiley, New York, N.Y., 1973,p 157. (37) S. N. Banerjee and C. Ressler, J. Org. Chem., 41,3056(1976). (38) H. F. Schott and W. G. Clark, J.Biol. Chem., 196,449(1952). (39) J. €3. Fellman and E. S.Roth, Biochemistry, 10,408(1971).
Cyclic Amidine Inhibitors of Indolamine N-Methyltransferase Joshua Rokach,” Pierre Hamel, N o r m a n R. H u n t e r , Grant Reader, Clarence S. Rooney. Merck Frosst Laboratories, Pointe ClairefDorual, Quebec, Canada H9R 4P8 P a u l S. Anderson,* E d w a r d J. Cragoe, Jr., Merck Sharp and Dohme Research Laboratories, West Point, Pennsylvania 19486
and Lewis R. M a n d e l Merck Sharp and Dohme Research Laboratories, Rahway, New Jersey 07065. Received March 6, 1978 Syntheses of a large number of mono- and bicyclic, as well as a few tricyclic, amidine derivatives related to 2,3,4,6,7,8-hexahydropyrrolo[ 1,2-a]pyrimidine (DBN) are reported. In vitro potencies for inhibition of the enzyme indolamine N-methyltransferase (INMT) from rabbit and human lung are presented. Four bicyclic amidine derivatives and 11 monocyclic derivatives were found to be equal or superior to DBN in in vitro potencies. With the bicyclic amidines, increasing ring size or introduction of substituents reduced activity. Among the monocyclic analogues, the most potent representatives were five- or six-membered systems with an exocyclic imino group, combined with methyl or ethyl substituents on the endocyclic nitrogen. Introduction of additional substituents decreased inhibitory potency. 2,3,5,6-Tetrahydro-8H-imidazo[2,1-c] [ 1,4] thiazine and 3-methyl-2-iminothiazolidine have been shown to cause inhibition of lung INMT when administered orally to rabbits. Although t h e c u r r e n t treatment of schizophrenia involves the use of neuroleptic agents which are dopamine antagonists, interest persits i n o t h e r approaches to t h e
therapy of this disease which are based on t h e theory that the illness is caused by an endogenously produced chemical toxin. T h e r e is considerable evidence that N,N-di-
0022-2623/79/1822-0237$01.00/00 1979 American Chemical Society
238 Journal of Medicinal Chemistry, 1979, Vol. 22, No. 3
Scheme I
Rokach et al.
Scheme I1 H
Method A
C
L
--
N ' H
27
Scheme I11 Method D
I
I CH30SF
li
R
0
z
or R or ~ o + B F ~ - ( R : c Hc~ ~, H ~ )
3 R X ( R z a l k y l , aro!k,l, X=CI, 01,orII
Method E
Z = C1, F, OCH,, or SCH,
I FSOCH~
ii
0 2 R,O+BF~-I R C H 3 , C 2 H 5 J 3 R X iR=alkyl, orylolky!.
~
H
x :c:, 0 r . o r I ) methyltryptamine (DMT) may be such a causative agent.'t2 The existence of enzymatic pathways for its formation in animals and the fact that it is hallucinogenic in man have been cited in support of this In addition, the I H administration of the amino acid precursors of DMT, methionine and tryptophan, has been found to exacerbate Y = -CHR,CH,-, -SCH=CH-, -SN=CH-, -(CH,),O-, schizophrenic symptornatol~gy.~ Furthermore, the DMT -CH,CH,SCH,-, -CR,=CHSCH,, -CH,CH,CH,S-, -CH=CHCH,S-, -CR,=CR,CR,=CR,-, -CH,CH,CH=CH-, precursor tryptamine is present in human brain4 and has -CH= CHN= CH-. been reported to be elevated in the urine of some schizophrenicse6Thus. the inhibition of DMT biosynthesis as a possible therapeutic approach to schizophrenia is both and then further characterized as crystalline, stable hyrational and attractive to the medicinal chemist. drogen fumarates or other salts. Compounds 5-7 and 16 The availability of indolamine N-methyltransferase were synthesized by different, but straightforward, pro(INMT), a lung enzyme which has been found to catalyze cedures as described under the Experimental Section. the synthesis of DMT by transfer ofthe methyl group from Compound 27 was prepared as shown in Scheme 11. S-adenosylmethionine to N-methyltryptamine (NMT), The two most generally employed routes to the monocyclic amidine analogues of interest in this study are provided the in vitro assay required to search for an appropriate DMT synthesis inhibitor.' This assay has shown in Scheme 111. In method D, a high degree of regioselectivity of alkylation on the ring nitrogen of the been used in our iaboratory as a primary screen and served to identify 2,3,4,6,7,8-hexahydropyrrolo[ a-amino cyclic imine normally was observed. In method 1,2-a]pyrimidine E, alkylation on the ring nitrogen of compounds with Z (DBN) as a potent, specific inhibitor of INMT from rabbit, substituents resulted in a great enhancement of the rate monkey, and human lung t i s ~ u e . This ~ suggested the of displacement of Z by amines. Frequently for method design and synthesis of related structures in a search for E the cyclic amide was available as starting material. The more effective agents. Presented in this paper are the amide could be either chlorinated (with POC1, or PC15)to syntheses and in vitro enzyme inhibitory activities of a give the chloro intermediate (Z = C1) or alternatively variety of bicyclic and monocyclic amidine analogues alkylated using trimethyl- or triethyloxonium fluoroborate related to DBN. Positive results from in vivo experiments in which rabbits were fed 2,3,5,6-tetrahydro-8H-imida- or methyl fluorosulfonate to give the imino ether intermediate (Z = OCH,, OC2H5). As a variation of the latter, z0[2,1-c][ 1,4]thiazine (22) and 3-methyl-2-iminothiaolidine (29) in the drinking water are described. Inhibition of the it was sometimes found necessary to convert the amide to the thioamide using P&, which was alkylated (on sulfur) biosynthesis of DMT from NMT in rabbits by 22 is also with greater ease than the corresponding cyclic amide ( u n reported. oxygen). Chemistry. The bicyclic amidines prepared as ana6-Fluoro-l-methyl-2-imino-1,2-dihydropyridine (74). logues of DBN were prepared. in general, from the apprepared from 2,6-difluoropyridine by method E (l),was propriate lactams using one of the three synthetic methods readily isolated as such. However, exposure to K,C03 in outlined in Scheme I. The lactanis were either cornethanol resulted in the displacement of the fluoride ion niercially available or were prepared by known procedures. by an ethoxy group to give 78. Reaction of 6-fluoro-lThese methods have been described previously and do not methyl-2-fluoropyridinium fluorosulfate with excess NH3 require further c ~ m m e n t . ~In~ each ' ~ case, the intermeor Me", gave the 6-amino-l-methyl-2-imino-1,2-didiates did not require rigorous purification, since the hydropyridine derivatives 76 and 77 directly as the bicyclic amidines could he purified by simple distillation
Journal of Medicinal Chemistry, 1979, Vol. 22, No. 3 239
Inhibitors of Indolamine N-Methyltransferase
Scheme VI
Scheme IV y
"2
3
\C=S /
"2
t
CICH2CH2CH
\OEt
-
P PA ___)
E t 0G A N H 2
86
I
CH3
64
inhibition of human lung INMT. The latter was less readily available and of a lower state of purity, which may account for the ICm values being consistently higher than 80 with the rabbit enzyme. The data for the bicyclic and Scheme V monocyclic amidine derivatives are presented in Tables I and 11, respectively. The detailed assay procedure is CICH2CH2CH2CN t NH2R CNCCH~CH~CHZNHRI described under the Experimental Section. In the early stage of this investigation, the effect of ring size on enzyme inhibition by bicyclic amidine derivatives was examined. A comparison of the IC5,, values obtained k for DBN, 2,3,4,6,7,8,9,10-octahydropyrimido[ 1,2-a]azepine (DBU), 1 , 2 , 9 , 19, and 20 indicated that increasing the ring R * -CH2CH size decreased the capacity of such compounds to inhibit 'OEt 52 indolamine N-methyltransferase. Thus, only 2,3,5,654 tetrahydro-7H-pyrrolo[l,2-a]imidazole (9) and 2,3,5,6,7,8-hexahydroimidazo[ 1,2-a]pyridine (20), bicyclic amiproducts. 5,6-Dihydropyridiniminesof the type 79 have dines with both nitrogens in the five-membered ring, were not been described previously. The intermediate 1selected for further structural modification. It was found methy1-2-0~0-1,2,5,6-tetrahydropyridine was prepared with these structures that increasing the size of the using the literature conditions reported for the corremolecule either by addition of large bulky alkyl groups (1 1 sponding 1,6-dimethyl compound." and 13) or aromatic rings (14, 15, 17, and 18) markedly When l-methyl-1,2-dihydropyrazin-2-one was allowed decreased enzyme inhibitory activity. While the placement to react with methyl fluorosulfate, reaction occured on the of a methyl group on the five-membered ring (10 and 12) second nitrogen in preference to the carbonyl oxygen.'* only moderately affected biological activity, as was the case Replacement of oxygen by sulfur13permitted methylation with DBN (compare 3 and 4), the placement of substitto occur as desired, giving an intermediate suitable for uents on the six-membered ring of these structures or DBN conversion t o the desired imine 80 (Scheme IV). (compare 8 and 6) appeared to lower significantly INMT Pyrrolidine derivatives with an N substituent not readily inhibitory activity. Quaternization of the nitrogen (7) in introduced by the general procedure could be prepared DBN also lowered inhibitory activity. starting from 4-~hlorobutyronitrile,by the general proThe consequences of making an isosteric substitution cedure of Kwok and Pranc (Scheme V).14 for C-7 in 20 was also examined. The results in Table I Preparation of the intermediate thione 87 required for the syntheses of 4-methyl-3,4-dihydro-3-imino-2H-1,4-for 21-24 clearly indicated that only the thio analogue 22 was comparable to DBN and 20 in relative potency. thiazines 62 and 63 was accomplished by the method of Increasing the degree of unsaturation (25 and 26), adding Johnson and T h a n a ~ a l l a ,except '~ that chloroacetaldehyde dimethyl acetal was employed. The same intermediate an aromatic ring (28), and changing the location of the sulfur atom (27) appeared to be undesirable modifications. served for the preparation of bicyclic compound 25. The synthesis of 3-methyl-3,4-dihydro-2-imino-6H-1,3-thiazine Although tricyclic analogues of DBN were essentially (64) was accomplished by a different route (see Scheme inactive (see Table I), the monocyclic analogue 49, in which VI). two carbon atoms are excised from the tetrahydroSyntheses of 3-amino- and 3-methylamino-2-iminopyrimidine moiety of DBN, was more potent than DBN as an inhibitor against both rabbit and human INMT. thiazolidines 37 and 38 were accomplished using 2,4,6trimethylphenylsulfonyloxyamine'6 and its N-methyl This finding prompted an examination of the variety of five- and six-membered monocyclic amidine derivatives, derivative, respectively. Methylation of both 3- and 5aminoisothiazoles resulted in methylation exclusively on bearing an exocyclic imine group, shown in Table 11. With the ring nitrogen (compounds 43, 44, 84, and 85.) In the exception of pyrazine 80, monocyclic amidine derivcontrast, when methyl fluorosulfonate was reacted with atives from all other five- and six-membered ring systems, 3-amino-1,2,5-thiadiazole, a mixture of exo- and endowhich possessed methyl groups on the endocyclic N and N-methylated products resulted. 2-Methyl-3-(methylno substituents on the exocyclic N, showed significant in imino)-1,2,5-thiadiazole(45) was prepared by a novel vitro enzyme inhibitory activity. While the corresponding procedure which will be detailed in another p~b1ication.l~ compounds lacking a substituent on the ring N (in which The 2-alkyl-3-iminothiadiazole and isothiazole derivatives the double bond was endocyclic) showed measurable acproved unstable on conversion to the free base forms. tivity, the level was consistently lower. Increases in the Biological Results and Discussion. The primary in size of the alkyl substituent on the ring nitrogen beyond vitro assay to which compounds were submitted was inunsubstituted ethyl resulted in considerable loss of activity, hibition of INMT enzyme from rabbit lung.8 Many of the with large or polar substituents rendering the compounds active compounds from this assay were then tested for essentially inactive. Compounds with a methyl substituent I
CH3
I
CH3
CH3
-
240 Journal of Medicinal Chemistry, 1979, Vol. 22, No. 3
Rokach et al.
9
ri
0
m
m A
0"
