Sovcmber 1967
1003
P Y R I D I S E C a R H O X A h l I D E S AND CHOLISERTER.4SES
The Effect of Piperidinecarboxamide Derivatives on Isolated Cholinesterase Systems. Substituted N1-Benzyl-3-(N,N-cliethylcarbanioy1)piperidines' JAMES 6. BEASLEY,
SANUEL
'r. C H R I S T I A S , w.R O N A L D S M I T H F I E L D ,
L.
A N ) LIND.4
WILLIFORD
D ~ p n ~ t i n e noft .2lrclicinnl Chcmzstry, Tnzversity of Tennessee College of Pharmacy, J f P m p h i s , TPnnmsw
J8103
Received September 19, 1966 Rewsed JIanitscript Rereiced June 5 , 1969
.4 series of sitbstituted N1-benzyl-3-(N,N-diethylcarbamoyl)piperidine hydrobromides containing methyl, met hoxyl, chloro, and nitro substituents in the meta and para position? were evaluated for inhibi i n isolated hiimaii plasma cholinesterase and horse serum cholinesterase systems. The derivative t ( I inhibit competitively both enzyme preparations. For each isomeric pair of inhibit,ors, the meta-substituted analog was always more potent than the corresponding para-substituted isomer. N1-(m-l\lethylbenzyl)-3-(N,Ndiethylcarbamoy1)piperidine hydrobromide was the most potent of the inhibitors studied and X'-(p-nitrohenzyl)-3-(S,X-diethylcarbamoyl)piperidinehydrobromide the least potent, in bot,h enzyme systems, although the order of inhibitory potency for the ot'her derivatives was not identical. The data suggest that differences in the specificities of human plasma cholinesterase and horse serum cholinesterase may he attrihiited to variations in striictrire at or near the anionic site.
The presence of an anionic site2 in cholinesterases appears t o be the distinguishing feature between this class of enzymes3 and other esterases. Differences in the restrictive nature of the anionic sites of serum vholinesterase4 (acylcholine acylhydrolase, E.C. 3.1.1.8) and of ac'etylcholinesterasej (acetylcholine hydrolase, E.C. 3.1.1.7) may be responsible for specificity and activity differences observed for these two enzyme systems. Current indications are that an additional binding site may be present in BuChE.6 Wilson and Quan,' in a study on the complementariiiess of AChE8 inhibitors, observed that the position and nature of substituent groups in substituted phenyltrimethylammonium ions \\ ere important in determining their effectiveness as .lChE inhibitors. I n an earlier investigation9 we also noted that the position of the carbarno) 1 constituent in piperidiriecarboxamide inhibitors of 1 T h E affected their potencies. Recently, Quintana and Smithfield'o prepared a series of meta- and para-substituted S1-benzyl-3-(S,S-diethylcarbamoS-l)piperidirie hydrobromides (Table I) t o study the effect, on the electron density around the heterocyclic nitrogen, which substituent variation would induce. They were also interested in determining the influence which such structural variations would exert on the lipophilic-lipophobic characteristics of the subject moieties. I n accord with our interests concerning the influence of physicochemical parameters" on cholinesterase(1) This investigation was supported by Grants GU-2381 and GB-4453 from t h e National Science Foundation and a grant from Marion Laboratories, Inc., Kansas City, M o . Computer facilities were provided through U. S. Public Health Service Grant H.E. 09495. (2) K. B. Augustinsson in "Handhuch der Experimentellen Pharmakolopie," Val. XI', G . 13. Koelle. Subed., Springer-Verlag, Berlin, 1963, p 101. (3) R. A. Oosterbaan in "Comprehensive Biochemistry," Vol. XVI, hf. Florkin and E. H . Stotz, Ed., Elsevier Publishing Co., Kew T o r k , N . Y., 1965, Chapter 5 . (4) I. B. Kilson, J . B i d . Chem.. 908, 123 (1951). (5) J. C. Kellett and C. \T. Hite. J . Pharm. Sci., 6 4 , 883 (1965). (6) K. B. Augustinsson, Biochim. Biophys. Acta, 198, 35 (1966). (7) I. B. Wilson and C. Quan, Arch. Biochem. Biophys., 75, 131 (1958). (8) Abbreviations used in this paper are: AChE, acetylcholinesterase; PChE. human plasma cholinesterase; BuChE, butsrylcholinesterase; AC h, acetylcholine. (9) J. G. Beasley, R. P. Quintana, and G. G. Nelms, J. M e d . Chem., 7 , 698 (1961). (10) R. P. Quintana and \V. R. Smithfield, ibid., 10, 1178 (1967). (11) W. P. Purcell, J. G. Beasley, R. P. Quintana, and J. A. Singer, ibid., 9, 297 (1966).
,-K~ Compd
I IT V I1
R
H CHI CHa OCK, OCH,
m
x
105b,cp
rd
2.16 2.11
0 0.52 1.02 0.57 7.81 0.18 I11 1.42 0.31 VI C1 1 .56 0.54 TI1 1.52 C1 0.61 T'III NO, 9.32 -0.39 IX so* 5.14 -0.36 a Although t,he subject molecules have not been specifically analyzed conformationally, sufficient evidence is available on the relative stability of the various conformers of piperidine and carbamoylpiperidine analogs [cf. W. Barbieri and L. Bernardi, Tetrahedron, 21, 2453 (1965); E. L. Eliel, "Stereochemist,ry of Carbon Compounds," 3lcGraw-Hill Book Co., Inc., New York, S . Y., 1962,p 246; W. P. Piircell and J. A. Singer, J . Cheni. Soc., 1431 (1966)l to justify showing them in the chair conformation. b Inhibition studies were conducted titrimetrically a t 26" using the procedure described in the text. A Ki value of 2.16 x 10-9 III was found for physostigmine sulfate. This agrees well with previously published values (J. P. Long in "Handbuch der Experimentellen Pharmakologie," G. B. Koelle, Subed., SpringerVerlag, Berlin, 1963, p 377). T values from partition coefficients (octanol-water) of substituted nitrobenzenes.**
inhibitor interactions, it seemed appropriate to investigate the cholinesterase-inhibitory properties of this series of derivatives (Tables I and 11). Experimental Section All reagents and derivatives iised in this study were of analytically piire grade or the equivalent. AChCI, physostigmine sulfate, and PChE (Type 11, pseudo)'* were ohtained from
(12) T h e specific activity of this preparation was found t o be approximately 3 units/mg where activity is expressed a s pmole of ACh hydrolyze(l/ min per mg of protein a t 26' and p H 7.4.
100 I
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