.July, 1963
ASTHELYISTICACTIVITYA N D CHEMICAL STHUCTTJRE
starting material, and no dehydrated compound XIS. substance could be detected.
X o other
Acknowledgment.-The authors extend their gratitude to Dr. E. Schlittler for his interest in this project.
36 1
We also to thank the members of our Microanalytical and Spectral Sections for their cooperation, and Dr. A. J. Plummer and Dr. 1,. Witkin for the biological data.
A n Empirical Relationship between Anthelmintic Activity and Chemical Structure AI. HARFESIST Bimoiigh.y [i7ellcome & Po. ( I’.S.d .) Inc., T h e Wellcome Research Laboratories, Tzickahoe, S e i : I-ork Received Janiiary 30, 1963 The anthelmintic activity against the mouse pinworm Syphacza obnelata is reported for several different types compound, including Y,Y-dialkylnaphthamidinesalts, some highly substituted dihydropyridines \T ith quaternary salt groupings, and some stilbazole and other quaternary salts. Based on these results it was postulated that an association of a ring moiety 15-ith a center which is cationic at physiological pH values might confer anthelmintic properties on molecules. Raqdom selection of four groups of compounds with such structures gave three groups n hinh had active members. [if
In previous publications’,* we have meiitioiied that oiie structural feature found in a high proport’ioii of our compounds with anthelmintic activity against the mouse pinworm S y p h a c i a obvelata was the existence of a center of positive charge near or in a cyclic syst’em. Some of t’he compounds tested, which were not, previously reported, and the results which led t o this empirical observat’ion are given below. This is followed by the results of arbitrary selection of some compounds fitting the same criterion of structure, which previously had been prepared for other purposes, and a description of their activity against S. obcelata in the mouse. Methods The compounds were prepared b>-methods reported in the literature unless otherwise annotated. All alkyl groups are normal unless stat,ed otherwise. Those compounds tested initially u w e selected as representative substances with a high numerical ratio of oral to intraperitoneal L D ~ O in the mouse as deterniined by M r . R. T’. Fanelli of these Laboratories. Testing for pinworm acativity \vas done essentially as described in a previous publication3 using mice infected by exposure to infected “source mice” for 8 days, and dosed by gavage once a day for 2 days thereafter, unless otherwise stated. Results are reported as per cent clearance of worms by autopsy in comparison to the worm count in simultaneously infected but untreated “control” mice. Each result, and each ”cont.ro1” result are averages of 8 mice.
active against S . obvelata in the mouse, undei our test conditions. I n addition to these. a fen- miscellaneous quaternary salts either of substituted anilines (e.g., I) or benzylamines (e.g., TI) had appreciable activity.
A number of other mono- and bis-quaternary salts were prepared or purchased. Those with purely aliphatic substituents were inactive or had only slight activity a t a readily attainable dosage. One alicyclic candidate, methyldodecylpiperidiniuni bromide, had slight activity. As had been reported previously, however, various quaternary piperaziniuni salts had substantial activity. 1-3
Experimental Data hnthelmiiitic activities are given in Table I for representative examples of the 2 types of compounds, 4-methoxyi~apht~hamidines~ and quaternary salts of highly substituted 4-(aminophenyl)-l,4-dihydrop~~idines,~ of which sei-era1 members were found to be reasonably (1) RI. Harfcnist, J . A m . Chem. Soc., 79, 2211 (1957). (2) H. TV. Brown, K. L. Hussey, K. F . C h a n , 11.Harfenist, R. l’, Fanelli, and E. Magnien, Toxicol. A p p l . Pharmacol., 1, 350 (19.59). ( 3 ) ( a ) K. F.Chan, A m . J . H y g i e n e , 56, 22 (19.52): (b) RI. Harfenist, R. V. Fanelli, R. Baltzly, H. JV. Brown, K. L. Hussey, a n d K. F. Chan. J . Pharmacol. E.rp/l. Therap., 121, 347 (19.57). Unless otherwise stated t h e tests reported here were done b y Drs. Brown. Hussey, 2nd Chan. (4) Prepared originally by M r . E. Lorz as potential local nnesthetics. See E . Lorz and R. Baltzly, J . A m . Chrm. S O C .70, , 1904 (1948). These are shown in their symmetrical protonated form, as is reasonable in view of t h e p & values repoi.ted b y E. Lorz a n d R. Baltzly, i b i d . , 71, 3992 (1949), for related compounds. (5) Prepared originally 3s potential curareform substances by Dr. A. P. Phillips. See A . P . Phillips, zbid., 71, 400.1 11949).
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A small group of cinnamamidine salts6 (111) were found to contain one member, 2-chloro-N,X-dibutylcinnamaniidine, R = C1, R’ = C4H9,which cleared an (6) M. Hsrfenist and 4 . P. Phillips, Ibzd. 80. 6261 (1958)
.July, 19K3
AAYTHEL311YTIC ACTIVITY .&Yl)CHERIICAL
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coiiipom1db were selected from those at liaiid i n a laboratory devoted to making potential drugs, and so some selection is implied by the origin of the group from which the selection was made. However, the conipounds selected were not synthesized originally for use against intestinal parasites. This i b not to say that all compouiids with these structural features are active aiithelmintics. Lack of space precludes our listing most of the compounds which were found i n our screening tests to have little or 110 activity against 5'.obidata, which have these structural i'catures. Also, one caiiiiot say that these structural features are necessary for anthelmintic activity. Exaniplcs of antibiotics, phenolic compounds, presumed folic acid antagonists, etc., with activity against 5'. u h e l a t a and against the human pinworm Enterobius elermicitlaris are well known. Several mechanisms may n.ell he operating even in the case of the positively charged compoimds known to have anthelmintic activity. l o r example 3,3'-diethylthiadicarbocyanine iodide (dithiazanine) (YIII), x-hich formally fits our sclieme, i b 1)elievPd to affect respiratory enzyme systems
of nematodes" while piperazine apparently affects the iieuromiisciilar junction a t the site of action of acetylcholiiie in the nematode ilscaris lumbricozdes, and S-carbethoxy-SI-methyl-S'-tetradecylpiperaziiiium salts and various bisyuaternary salts of piperazine cause a rigid paralysis of the same nematode,12analogous to that caused by succinyl choline chloride. l 3 We may speculate that compounds with a cationic center are likely to have activity a t the neuromuscular junction in these aiid that the ring structures may be necessary either to prevent destruction of the compound or to cover a large fixed area on some enzyme onto which the compounds are held by their positive charge. Presumably a quaternary non-cyclic carbon could accomplish both of these objectives as well as a cyclic structure does, but we have not investigated compoiiiids having such groups. Since useful anthelmintic activity depends 011 differential effects such as relative non-absorption by the host but absorption by the parasite, action 011 enzyme systems which differ between host and parasite, or the swamping of the entire parasite by an irritaiit drug which merely is brieilv disturbing to the host, further speculation unsupported by studies of the precise modes of action of our varioiis compoiiiids seems 1111profitable. Acknowledgments.-The author wishes t o thank Drs. H. W. Brown, K. I;. Chan, and K. L. Hussey of the School of Public Health and Administrative -liedicine of Columbia Vniversity, and Dr. R. B. Burrows and hlr. R. Fanelli of these Laboratories for permission to use their previously unpublished results, Dr. R. Baltzly of these Laboratories and Dr. S. Sorton of the Department of Pharmacologv, 1-niversity of Kansas Medical Center, for their helpful comments aiid suggestions, and the various chemists n-ho supplied compounds as indicated. (11) E. Bueiliiig and C . S w a r t i n e l d e r , I'hmmarol. Rei.., 9, 329, esprcially ,337 (lY.57), ~f seq. ( 1 2 ) S. Norton, iin~)riblisIiedohserrations. (13) S. S o r t o n and E. .I. de Beer, .4m.J . T i o p . .ilpd. H ? / g . . 6 , 898 (lY57l. (11) Compare C. .J. Cavallito a n d A . P. G i a y , P r o g r . Drug R e s . . 2 , 136 (1960), et s e q . , in u-l~iclisimilai ideas a s t o t h e n a t u r e of t h e interactions of q u a t e r n a r y salts and animals are presented and e s t r n s i v ~ l ydorurnenteti.
