ACETYLCHOLINE AND HISTAJIIKE hTAGONISTS
March 1970
225
Structure-Activity Relations. I. A Series of Antagonists of Acetylcholine and Histamine a t the Postganglionic Receptors MEITH BOWDEK A N D R. C. YOVNG Department of Chemistry, The Cniversity of Essex, Colchester, Essex, England Recezved September 2, 1969
A series of aniinoester hydrochlorides, which are antagonists of acetylcholine and histamine a t postganglionic receptors, have been synthesized. Their activity has been successfully correlated by Hansch linear free energy relations involving polar, steric, and partition substituent constants. The results are related to receptordrug interactions.
Hansch and his coworkers' have developed linear free energy relat'ions which can correlate biological activity and chemical structure. The relations, 1 and 2 , together with simplified versions, have been proposed to relate t'he molar concentrat'ion, C,, of a substituted compound of a series, which all cause an equivalent biological response, to the hydrophobic log (1/Cx)
= --a
T
*+b~+pu+c
log ( l / C x ) = b.rr
+ pu + c
(1)
(2) bonding or partition constant, T , and the Hammett constant, u. The constants a, b , p , and c are obtained from the regression analysis and define the response of the biological system to structural features. The partition constant, T , is defined from a model system v i t h partition between 1-octanol and HzO.'>* The Hammett substituent constants are measures of the polar effects of ineta- and para-substituted benzene d e r i v a t i ~ e s . ~However, q values could be used to correlate polar effects in aliphatic system^.^ Steric effects can be estimated in these systems by the steric substituent constant, ES.j These two latter parameters have been used very successfully in the Taft-Ingold equation (3) to correlate reactions which depend on both factors.5,6 log ( k j h J
+ 6Ex
(3) Recently, Caniniarata7 has shown that the electronic polarizability, Pe,can be used in correlating biological activities. This parameter could relate either the charge transfer ability or spatial demands of the substituent. Many studies have been made of the structureactivity relations for antagonists of acetylcholine a t the postganglionic receptors.8 These drugs interfere wit'h the transmission of nerve impulses mediated by acet'ylcholine a t the junctions of the postganglionic cholinergic nerves. The best-known antagonist a t these sites of the "muscarine-like" actions of acetyl= pin1
(1) (a) C. Hansch and T. F u j i t a , J . Amer. Chem. Soc., 86, 1616 (1964); (b) C. Hansch, R . R I . Muir, T. Fujita, P. P. Maloney. F. Geiger, a n d M. Streich, ibad., 85, 2817 (1963). (2) la) T. Fujita, J. I v a s a , a n d C. Hansch. ibid., 86, 5175 (1964); (b) J. In-asa. T. Fujita, a n d C. Hansch, J . X e d . Chem., 8 , 150 (1965); (c) C. Hansch a n d S.bl. .4nderson. J . Ore. Chem., 82, 2583 (1967). (3) H . H. JaffB, Chem. Rev., 68, 191 (1953). (4) (a) R . IT. T a f t a n d I. C. Lewis. J . Amer. Chem. Soc., 80, 2436 (1958); 81, 5343 (1959): (b) &I.Charton, J . Org. Chem.. 29, 1222 (1964). ( 5 ) R. IT. T a f t i n "Steric Effects in Organic Chemistry," hl. 9. Ne\vman. E d . , J o h n K l e y & Sons, Inc., Ken. T o r k , S . Y., 1956, Chapter 13. ( 6 ) K . B o w d e n a n d R . C . Young, Can. J . Chem., 47, 2775 (1969). (7) A . C a m m a r a t a , J . .Wed. Chem., 10,525 (1967). (8)(a) A. Behbington a n d R . 1%'. Brimblecombe, Aduan. Drug Res., 2 , 143 (1965); (h) R. B. Barlow, "Introduction t o Chemical Pharmacology," 2nd ed, 4Iethuen and Co. Ltd., London, 1964, Chapter VII.
choline is atropine. A vast number of esters of aminoalcohols have been studied and their activity usually is measured by their ability to antagonize contractions in isolated guinea-pig ileum. Histamine can also stimulate the ileum. It probably has a site of action distinct from that of acetylcholine, but similarities exist.g Many antagonists of acetylcholine also inhibit the action of histamine but to a different degree. I n the present study, a series of aminoester hydrochlorides have been synthesized and their antagonism to acetylcholine and histamine has been measured. These activities have been correlated using structural parameters and the results related to drug-receptor interactions.
Experimental Section lo Acids, Acid Chlorides, 2-DialkylaminoethanoIs, and 2-Dialkylaminoethyl Chlorides.-These compounds iTere prepared by known method~l1-l~and, after purification, had physical constants in good agreement with literature values, except for the acid described below. 2-Chlorofluorene-9-carboxylic Acid.-This acid was prepared by metalation of 2-chlorofluorene with ethereal n-BuLi, followed by treatment with solid C02.12a After recrystallization from MeOH-H20, the colorless acid had mp 213-215'. Anal. (ClrHiiC1, 0 2 ) C, H, C1,O. Ester Hydrochlorides.-These were prepared by reacting either the acid chloride with the dialkylaminoalcohol in CCHC or the acid with the dialkylaminoethyl chloride in i-PrOH or PhAIe." An exception to this is 2-diet,hylaminoethyl 2-aminofluorene-9carboxylate.HC1, which was prepared by direct reduction of the 2-nitro ester hydrochloride.ll The ester hydrochlorides were purified by recrgstallizat,ion, sometimes after conversion into base and treat,ment with ethereal HC1 (see Table I). pK, Values of the Ester Hydrochlorides.-These were determined in50% v/v EtOH-H20, at, 25 ( & O . l ) ' , at, 0.004 31 concentration using a method described pre~ious1y.l~Those fluorene esters having an unsubstituted 9-position have a second pK, due to formation of the carbanion at higher pH (pK, of diethylaminoethyl fluorene-9-carboxylate is approximately 12 in H?O). The likelihood of interference from this second ionization is considerably reduced in 50% EtOH-H20 due t,o the differential effect (9) 'a) Reference Sb Chapter X ; (b) D . J. Triggle, "Chemical Aspects of t h e Autonomic Xerrous System," Academic Press L t d . , London, 1965, p 120. (10) Melting points were determined on a Kofler hot-stage microscope and are corrected. Where analyses are indicated b y symbols of t h e elements, analytical results mere within +0.4% of t h e theoretical values. (11) R . R . Burtner and J. IT. Cusic, J . Amer. Chem. Soc., 65, 262, 1582 (1943). (12) (a) J. D . Dickenson and C. Eaborn, J. Chem. Soc., 2337 (1959); (b) K. Bowden, N. B. C h a p m a n , a n d J. Shorter, ibid., 5239 (1963). (13) (a) N. Loefgren a n d B. Lundqvist, Svensk. K e m . Tidskr., 58, 206 (1946); (b) J. 1%'. Cusic a n d R . A . Robinson, J . Org. Chem., 16, 1921 (1951); (c) A. L. Jlndzhoyan, G. L. P a p a y a n , and N. JI. Organdzhanyan, Dokl. d k n d . N a u k Brm. SSR, 81, 37 (1960) (see Chem. Abstr., 6 6 , 9446 (1961)); ( d ) H . E. Zaugy a n d E. W. Horrom, J . Amer. Chem. Soc.. 7 2 , 3004 (1950); (e) P. Pi. Craig I. H . Witt, E. Macko, J. G. Dacanoy, E. J. F e l l o w , and G. E . Ullyot, ibid., 78, 1339 (1951). (14) K. B o x d e n , &I. H a r d y , and D . C. Parkin, Can. J . Chem., 46, 2929 (1968).
ACETYLCHOLISE AND
March 1970 TABLE I1
TABLE I11 SUBSTITUEKT CONSTANTS" (NUCLEAR SUBSTITCTIOS )
SUBSTITUEST COsST.WTSa Substituent*
E.
SI
277
HISTA4h11NEA N T A G O N I S T S
Substituent
n
2.22 PhCHz 0.115 -0.37 PhiCH 0.19 -1.46 2.98 3 PhsChIe 0.1.5 -3.55 3.50 4.75 4 Ph,CCH,CH=CH? 0.17: -4.33 3.04 XaCH 0 315 -1.29 3 6 TxCH 0,255 -1.75 3.38 0.235 -1.29 7 AnCH 3.59 0.22j -1.10 3.61 8 FlCH 4.13 0 . 1.5; -1.73 9 FlCMe 4.61 10 FlCCHJIe 0.13; -1.97 11 F1CCHIIe2 0.12; -3.30 5.04 12 FlC( CH*)3hIe 0.14; -2.09 5.69 13 FlCChIe3 0.08; -4.12 L63 6.31 14 FlCCH2Ph 0,23 -2.16 1.81 1.5 FlCOH 0.4i -0.90 4.60 16 2-Br(FlCH) 0.31 4.44 0.31 17 z-Cl(F1CH) 3.23 0.235 18 2-OH (FlCH ) 19 2-0hIe (FlCH ) 0.26 3.75 3.56 20 2-XOI(FlCH) 0.406 2.36 21 P-NHz(F1CH) 0 . 205 5 U I constants are literature values o r calculated from literature data;6 E, constants are literature values;6 and x constants are from this study (see Experimental Section). See Table I. 1 2
R
UIll
loe pe
H 0.0 0.0 0 . 23 Br 0.391 1 .32 0.97 C1 0.373 1.22 0 s1 OH 0.121 1.24 0.46 OlIe 0.115 2.03 0.89 NO2 0.710 1.81 0.92 NH? 0.040 1.36 0..X u,,, constants are literature values;l7 P , (nil) values (polarizability) were calculated from the literature data:18 and R constants are from this study (see Experimental Section). 1~
Results and Discussion Antagonism to ACh.-Our first attempts to correlate the antagonist activity of the amino ester hydrochlorides involved the complete series of diethylaminoethyl ester hydrochlorides, R C O 2 C H Z C H z S E tHCl 2 ~ ( I ? = 21, Table I, 1 t o 21). All these salts have pk', values which are closely related23 (mean value i.: 7.87 0.06) due to the lack of proximity of the -ubstituent to the SEt, group. Thus, the state of ionization of these aminoesters in any test medium i- rilmojt
*
TABLE 117 CORREL.iTIONS O F .\ST.AGONIS>I
O F .kCETYLCHOLINE BY A L L THE
2-DIETHYLAMINOETHYL ESTERS (?Z = 21)" 1'
a
+0.871x(l.07) +4.495 0.387 O.il4 - 0.114x(0.75) +1.6l501(0.88) f5.851 0.331 0 . i:30 -0.136x2(1.3i J + 0 . 996x(1.21) +1.812u1(1.01) +3.733 0,445 0 . 714 a n = number of compounds: I = correlation coefficient; s = standard deviation and the quantity in parentheses is the Student's t test (lit'. G. W. Snedecor, "Statiatical Methods," 5th ed, Iowa State University Press, Ames, Iowa, 1936) foy the %igiiificaiir*e of the regression variable above. 1 2 3
- 0 , 2 1 8 x ? ( l , 29)
TABLE V CORRELATIOSb O F .kNT.IGONISM O F ACETYLCHOLINE BY THE XOSNUCLEAR SUBSTITUTED 2-~IETHYL.lMISOETHYLESTERS (n 15)'
4
- 0 . 174x2(l,61)
6 7 8 9 a
- 1.16jx(1.30) -0.123x(0.72) - U . 329x(l. 64)
>
-0.317x2(3.73) - 0 . 169x2(1.43)
10 For footnotes see Table I\-.
+3.471~1(1.50)
+2.686~(3.51)
+4.837u1(2.14) +6.6460-1(3.68)
-0.217x(1.09)
+:3.955u1(l, 66)
+ 1.109x(1.08)
met.ric met,hod and were corrected fur ionization of the acids.2a to lo-' Jf in aqueous phase. The partition Acids were constant,, x, is defined, in t,hii; study, as log P , - log Pnre so that x for Me equals 0.0. A value for PhCH? on this scale can be calculated as 2.22.2a The paramet,erh for the other acids were then calculated from t,heir log P , values relative to that of phenylacet,ic acid. The T vallies of the very insoluble carboxylic acids (Table 11, subst,ituent,s4,9-14> 16-21) were estimated from values for the substituents calculated from our and from literature d a t a . 1 ~ 2 * The 2 2 lack of additivity of effects of the phenyl group6 (Table 11, substituents 1, 2 ) k considered to arise from mutual shielding of these groups reducing their effective hydrophobicity. The parameters are considered to be certain to 4=5yc. Regression Analysis.-Regres.ion analyses xere made using multiple regression analysis (least squares). ( 2 2 ) (a) C. Hansch, E. W.Deutsch. and R. 3 . S m i t h , J . Amev. Chem. Soc., 87,2738 (1965); (b) C. Hansch, J. E. Quinlan, a n d G. L. Lawrence, J . Ow. Chem., 33, 347 (1968).
-0. 124Ee(0.57) -0.084E,(0.46)
-0.030E8(0. 14) -0.198E,(0.95)
$4.300 +i.69.i +6.960 $4.750 -0.197 $4.379 $5.562
0 0 0 0 0 0 0
702 ill
764 720 491 733 714
the same and nearly independent of the nature of the group R . Attempts have been made to correlate the antagonist activity with the polar and partition constants in Hansch-type relations in Table IT. The .ingle parameter correlations have been omitted from this and later tsbles as no useful or wccewful relations were observed. Unfortunately none of the attempted correlstions (1-3) shown has a high enough Student's t test or correlation coefficient, ie., r < 0.7, to warrant discussion. Steric parameters cannot be usefully applied, as E , values for the 2-substituted fluorene esters will be almost the same as the unsubstituted fluorene ester. (23) T h e p value for t h e 2-substituted fluorene-9-carlioxylic diethylaminoethyl esters (using r,) is only 0.24 (pKaa = 7.86,r = 0.960,n = 6).
March 1970
-\CETTLCHOLIKE AND
HISTAMINE -kVT.4GONISTS
.? i
b? d
9
TABLE VI1 CORRELATIOSS OF ANTAGOSISM OF ACETYLCHLORINE BY THE KCCLEAR SUBSTITUTED ~ - D I E T H Y L . ~ J I I ~ESTERS O E T H( ~ nL = 7 J,& r
11 12 1:3 14 1t5 16 17 a
+0.001*2(0.00)
+0.226s(0.07) +0.387~(0.98) +0.279~(3.69) +0 ,64943.49)
+0.195r(0.25) +0.300~(3.19)
$5.634 $4 75.5
0.289 0 481 0 982 0 918
0,708 0,649 0 , 139 0 ,294
+6.603 t3.775 + 3 . ,572
0 926 0 982 0.984
0,279 0.160 0.134
+4 4.52
-1.019~,(0.88) -0.754R(10. 01) -2.194 log P , (4.38) -0.770B(4.77) -0.735R(8.69) -0.739R(8.25)
+0.281~,(0.59) +0.0127ry0. 11)
-0, 147um(O.50)
For footnotes see Table IV.
CORRELITIOXS O F AhT.iGOSIShl O F
a
+4 771
18 - 0 , 2081r2(2,0 2 ) 19 20 -0.213s2(2.01) For footnotes see Table IV.
TABLE VI11 HISTAMINE BY A L L THE
+1 . 6 9 9 ~ ( 2 . 0 1 ) +0.037~(0,22) +l,7667r(2,02)
2 - D I E T H Y L . k ~ i I ~ O E T H r ESTERS L (n =
+0. 659u1(0.32) 0.966u1(0.51)
+
$2,703 5 . 39.5 + 2 . 296
+
21)"
r
8
0.430 0.079
0.739 0.816 0 , 73.5
0,444
TABLE IX CORRI:L.4TIOS O F .&ST.iGOSISM O F HISTA>lI.UF; BY THE ?iOXXCCLEIR SUBSTITUTED 2-DIETHYL.iMIXOETHYL ESTERS
(n = r
21 .>'> --
-0.283~~12.58)
23 24 25 -0.411~~(4.47) 26 -0.298~~12.50) 27 For footnotes see Table IT'.
+2.236~f2.46) +0.017~(0.08) -0.116~(0.30) +3.527r(4.43) +2.417~(2.35) +O.O4Ox(O. 16)
-2.110 + 3 , 53.5 +6.402 -3.231 -2.046 +1.857 +5.434
$2.3900i(0.85) +3.0.53~~(1.13) +6.200~1(3.19) + 2 . 68401(0.90)
-0.070ES(0.28) - 0.117E,(O. 5 3 ) +O.096Es(0.43) -0.120E,10.46)
TABLEX HISTAJIINE BY THE S U C L E . l R ~-DIETHYLAMISOETHYI, ESTERS (n = 7 ) "
CORREL.k'TIOSS O F *kN'r.kGOKISM O F
0 0 0 0 0 0 0
60.5 26.5 144 310 819 61.3 297
5
0,713 0.863 0.886 0.831 0 , ,537 0.739 0.893
sCBXTITUTED
r
28 29 30 31
-O.0681r2(O.33)
+0.821~(0.57) +0.423r(2.63) + O . 36144.28) +0.508n(4.86)
+O, 3 4 4 4 0 . 5 7 )
32
33 0.064x2(0.55) 34 F o r footnotes see Table IV.
+0.521~,(1.10)
+ O . 810n(0.98) +0.393~(3.85)
-0.2170,(0.68)
evidence.31 This probably indicates one of the reasons for the scatter in the previous series (Table V, regression 8), where it was not possible to allow for the different peripheral spatial demands of the compounds. The fluorene-9-carboxylate aminoesters studied having variation in the side chain (Table I, 8, 22-25) are not sufficient t o enable an attempt at a quantitative separation. This would be more difficult, in any case, for those tertiary amines whose pK, values vary widely (7.11-8.74). Antagonism to Histamine.-The analysis of the antagonist activity of the aminoester hydrochlorides is shown in Tables VIII-X. A very similar pattern of behavior as that noted for antagonism to ACh is observed. S o statistically significant correlation of all the esters occurs (Table VIII). The successful correlation of the nonnuclear substituted diethyl(31) A. RI. Lands, J . Pharmncol. E x p . Ther., 102, 219 (1951).
-0.281R(3.35) - 0.86110gP~ 13.06) - 0,30OR(l.47) -0.281B(3.03) -0.258R(2.66)
+:3.424 +4,073 +4.557 +4.229
0 0 0 0
732 796 933 926
0.298 0.265 0.155 0.165
t5.815 +3.799 +4.464
0 594 0 941 0 944
0.352 0.171 0.167
aminoethyl esters is shown beloT7 (eq G) (Table IX, regression 2 5 ) . log (1/Cjo)
=
+
+
- 0 . 4 1 1 ~ ~ 3 . 5 2 7 ~ 6.200~1- 2.046 (6)
The calculated and observed values of log (I Cj0) agree to a mean value of k0.406. This correlation is less well-defined than that for the antagonism tolyard acetylcholine. However, the optimum partition constant of K O for this series is 4.29, which compares closely with that found for the previous series. If the receptors for both actions occur in the same or very closely related environment, as is suspected,sb the optimum partition factors would be expected to be very similar. The dependence on polar factors also closely compares with the previous analysis. The nuclear substituted series also give a satisfactory correlation with partition and steric factors, as shown below (eq 7 ) . The calculated and observed values
Antimalarials. 8-Chloro-2-(2'-N,~~--dibu tylaniino- 1'-hpdroxye thyl) benzo[h ] 1,6-11apht h y rid ine"'
-
8-Chloro-i-["'-.\.,-~-dib~itylamino-l'-hydrosyethyl )benzo[ h ]- I ,6-naphthyridiiie (17) w:ia >yilthe,.ized f r o m 4-amino-i-chloroquinoline. While a number of electrophiles failed to react with the weakly iiucleophilic 4-amino function of the 4-aminoyuinoline, utilization of diethyl ethosymethylenemalonate, a relatively strong electrophile, provided a route to the tricyclic heteroaroniatic. c o m p a n d . Whereas eight of its intermediate.. lacked antimalarial wtivity, 8-(~hloro-4-(2'-S,S-dibiitylaniiiio-l'-hydro~yeth~l)ben~n[h]-l,6-iiaphthyridiiie wii. active against PIasrriodiuin bcrghei in mice. This coniporind, however, possessed only slight a(-tiviry agai1i.t 1'. gallinactuiii in chicks arid waa ineffective sg.ainst this organism in niosclriitoe-.
Initially, it ma- our de.ire to prepare :!-nieth> 14 - i S , N - dialkylaminomethyl) benzo [ h ] - 1.6-1i:iphthj 1'1(lines The nucleu- and general Yubstitution patterii ot thi. molecule are derived by the "paper cyclization'' ot the chloroquiIie (I) 4de chain (a. indicated hy t h r :crron.), along with xromatization of t8heformed thirci nllg
CH I
I
I1
C ciii,ideratiori of the antimalarial activitj found 111 thci 4-quinolinemethariol serieq a? ne11 :la in that ut thc Iihenttrithrenemethanols? led to the refinement of I cylacing the iornied dialkj laminomethyl group h\ :I 2 '-dialkylainino-l '-hydrox;-eth> 1 species at thc 4 110.it i o i i of the herizo [h]-I,B-naphth~~idine (11). SJ iithesis of tlie candidate nntimalaristl recluiretl thc ~ ~ ~ c v of n ca eusable functional group at the 4-poaitiori o t tlir tricyclic heteroaromatic nucleus. Since '1 benzo[ i , 1-1,(i-rinphtl~j.ridin---ol (9) pos5eYsd :I requiyite fiiiirtion:dit\r, we bought n reaction which n-ould proviclc t h i - t > p e intermediate in high J ielda T h e :tcidC , I t a l ) zed Conrad-Limpach reaction between 4-:iminoc jrurioline arid acetoacetic e-ter h a been reported to 411 e high j ield, of 2-methylbenzo [h]-1.G-iiaphthyridin4-ol -Ippljing this p r o c e d ~ r e ,n~e were uiisble to i-ohte the desired benzo [II ]-1,6-1iaphtliyridiii---olsor t h ~ po,-ible r quinolylcrotonate intermediate- from the i I (a) 'rll~,n-ork described i n this palier u a s uerforined under C o n t r a c t S , , 1).\1~.\1~.6i-C-7060 with the U. S. Army Medical Research a n d De\ + Io) n i r n t C'ommand. This is Contriliution S o . 665 from t h e .\rmy Ke- r u r c h P r o p a i n on malaria. 11,) To n.liom inquiries should be addressed. , ? ) 1:. \-, \Viseloule. Ed. "h Sur\-ey of .\ntimalarial D r u m , 1941-1945,'' I \ V E:d\\ards, .Inn .irlior, >Iich., 1446. ii G. R . C-oatney. "Survey of .intimalarial Agents," I'iil~lic Heal111
l l u n o p r a p h S o . 9, Federal Security Agency, 1952. K. klaririer and G . .\. R ~ ~ n u i .I.d ~Org. , Cheni.. 1 5 , 1224 (14.50)
