ANTHELJIINTICS. IV
January 1970
was treated with excess HC1 and the precipitate was collected by filtration and crystallized from EtOH. 2 - ( ( 3-[Bis(2-hydroxyethyl)amino]propyl)amiiio)-3-chloro-1,4-naphthoquinone hydrochloride (XIXb) was obtained (24.5 g, 72%) as orange crystals, mp 149-151'. 5,8-Isoquinolinedione 8-Oxime (XXXI).-S-Isoquinolinol(i.3 g, 0.05 mole) was dissolved in 50 ml of H20 and 6.5 ml of concentrated HC1 and was treated at 5-10' with a solution of 3.5 g (0.0.; mole) of Ka?rTO2in H2O. The mixture was stirred at 5-10' for 3 hr and the product was collected by filtration and crystallized from DhIF. The product (1.4 g, 16%) was obtained as olive crystals, mp 233" dec. A n a l . (CgHgN202) C, H, N. 2-(Piperidin0methyl)-l-naphthol.-~4 solution of 72.0 g (0.5 mole) of 1-iiaphthol, 43.0 g (0.3 mole) of piperidine, and 38 ml (0.5 mole) of 40% formalin in 500 ml of EtOH was heated under reflrix o n a >team bath for 2.5 hr and chilled. The crystalline precipitate that separated was collected by filtration and dried at 4.5' zn eacuo (70.1 g , mp 120-132'). The crude product was
109
crystallized twice from EtOH, slurried into 500 ml of HzO, and treated with 50 ml of concentrated HC1. The precipitate was collected and heated to 90" in 2 1. of HzO, and the mixture was filtered. The insoluble material was discarded. The filtrate was treated with decolorizing charcoal, chilled, and made strongly alkaline with 50yoNaOH. The precipitate was collected, washed with HnO, and dried at 65' in vacuo. Crystallization from EtOH afforded 33.0 g (27%) of pure product, mp 134-135'. ilnal. (CiGHigXO) C, H, X.
Acknowledgments.-The authors express their appreciation to Dr. Paul E. Thompson and coworkers for the antischistosome testing, Nrs. Maria L. Zamora for chemical assistance, Mr. C. E. Childs and associates for the microanalyses, and Dr. J. 11. Tandenbelt and coworkers for the spectral data.
Novel Anthelmintic Agents. IV. Noncyclic Amidines Related to Pyrantel J. W. MCFARLAXD AXD H. L. HOWES, JR. Pjize, Medical Research Laboratories, Groton, Connecticut 06340 Receiced July 14, 1969 Anthelmintic activity has been discovered among some S,N-disubstituted thiophenepropionamidines and thiopheneacrylamidines. Activity is associated with compounds in which one N substituent is Me and the other Substitution at the N ' position abolishes activity. Synthetic methods and is Me, Et, allyl, MeO, or Me". structure-activity relationships are discussed.
The discovery of a new class of anthelmintic agents was reported in the first papers of this series.'V2 I t was observed that certain compounds of the type represented by 1 are highly effective against the intestinal nematode Nematospiroides dubius when tested in mice; indeed one member of the series, pyrantel (2), has undergone extensive evaluation in domestic animals and in man.
1 Ar = C,H& C4H,0, C,H, R = H, CH, n = 2,3 _.-=optional bond
2
In pursuing the structure-activity relationships in this series, we became concerned over the question of whether a cyclic amidine system was essential to good anthelmintic activity. Therefore, a number of noncyclic compounds (3) were prepared and tested. Very early in this work S,S-dimethy1-2-thiophenepropionamidine (10) emerged as an analog active not only
against N . dubius but also against the tapeworm Hymenolepis nana; other active compounds were subsequently discovered. The present work will describe the structure-activity relationships within the noncyclic series of compounds, and will attempt to correlate these findings with those of the cyclic series. Chemistry.-Most of the compounds under discussion were prepared by the action of imidate salts on amines or aminelike substances. However, when an amine was more conveniently available as its HCl salt, an alternate combination n a s employed: the imidate salt was converted to its free base, and the base was then allowed to react nith the amine salt. Three general procedures were used to prepare the requisite imidate salts. Method A followed the technique of Pinner, i.e., the reaction of a nitrile with dry HCI and an alcohol in dry E t 2 0 . This method is useful for preparing S-substituted and S,S-disubstituted amidineb, but is not suitable for the preparation of S'substituted compounds. Intermediates for the latter substances are readily prepared by method B, the formation of ethyl N-alkylimidates by the action of Et30 +BFA- on an IT-alkylamide. Some a,p-unsatuRCONHR,
3
10
(1) W. C. Austin, W.Courtney, J. C. Danilenicz, D. H . Morgan, R . L. Cornwell, L. H. Conover, H . L. Homes, Jr., J. E. Lynch, J . W. McFarland, ' . J . Theodorides, Nature, 212, 1273 (1966). and 1 (2) J. 1%'. RlcFarland, L. H. Conover, H . L. Howes, Jr., J. E. Lynch, D. R . Chisholm. W.C. Austin, R . L. Cornwell, J. C. Danilewioz. 1%'. Courtney, and D. H. Morgan, J. Med. Chem., 12, 1066 (1969).
+
Et,O
EtJO'BF,-
~HR,' RC, BF,-
+
Et,O
rated nitriles tended to react very slowly or not at all in the Pinner reaction; in such instances the reaction of the corresponding amides with 1,3-propane sultone (method C) served to prepare the desired imidate salt.3 (3)
W.Ried and E . Schmidt, Ann.,
616, 114 (1964).
110
ArCH-CHCONH,
\.()I.
+
.4rCH=CHC.
t h v rouiiclu or111 ~~f.iiiatospiioa~l(es dubzus :itid t h i ) tapen orni H ~ j ~ / l o / ~/ / pa /i ms . Different substaiicci \ \ OIT disiolved 01' wqieiidccl i i i :I 14; c a r b o x y m e t h ~ l c c l l ~ i l ~ i ~ ~ ~ wlution at .uch :i coiicc~ntrationthat 0.4 ml delivered :LII ;ippropri:ite c h r t c i :I 20-g niouw. Treated mice u e i ~ dosed oiice cach dn? for 1-3 day:,. Initially, a high do\(. (23-300 mg k p dq)(liidiiig on the compouiid's toxicit) j i t as given to a group of four infected male micr. If atithelmintic activity \va- detected, the compound I\ :i+ tested at \ucces\ively lower dose:, until :t minimum effcctive doye (lIED) TW- caytuhlished. The LIED is con-.itlered to be the lowe-t do-c which c:tuses a t least a 90% rcductiori in t h e -3-, dublu\ worm burden as comp:irc'd t o uritreated infected coiitrols, or the lowest dose whicli will cause 100cc cIe,irmcc~of H . m t i a or AS.obvelatn. Further detail- of thc-e teiting methods are given i j ~ Homes and J , y i i c l ~ ~T h e results of these t
ot
o,s02 .!%
/",+ 'O(CH,),SO,-
The amidoxime 14 way prepared by the ndditioii oi H,NOH to 2-thiopheriepropionitrile (method D). Assignment of the trans configuration to the double bond in 36 war based on the nmr spectrum of the compound in D20. I t has been shown previously* that the coupling conhtuiit JaP fur the olefinic protons of trans-pyrantel (2) is 1.5.7 cph, and that Jaa for the r i s pyrantel isomer i y 12.5 cps. The coupling conbtant Jas for 36 is 13.8 cp-, arid i- therefore consistent with the tmns configurat iori. Biological Evaluation.-Compounds were tested for :tnthelmintic activity in \I orm-infested mice. Each mouse harbored a iiatural infection of the pin\\ orm Syphacia oboelata. and experimentally induced infect i o i i z
I::
' 4 ) H. I,. Ilonr-, .Jr.. a r i d .J. I:. Lynch,
J . Parasitol., 53, 108.5 (1967).
111
ANTHELYINTICS.IV
.January 1970
TABLE 111
NO.
R1
Rz
R3
Salt
Preparatix e method"
Recrystn solvent
RIP, o C
A1 177-179 HC1 H 29 H H A1 164- 166 HC1 CH3 H 30 CH, B1 137-139 HBF, 31 CHa CH, H B1 153-155 HBF, 32 CzHs CH3 H B1 209-211 HBFi CHJ 33 CHa CH, a The symbols used in this column are e.\;plained a t the beginning of the S.dzibius. See Table I, footnote j .
FormulaC
mg/kg
CgHtaC1X-L >300 i-PrOH-Et20 CnHiiClXi > 100 lleCN-Me2C0 CllHliBFiNl >2.50 lIeOH-i-Pr?O CIlH19BFIKI >230 lle2C0 CleHlsBFIXl >230 H20-MeOH Minimum effectlve dose Experimental Section.
Days given
3 2 3 3 3 against
TABLE IV
NO.
S
Salt
Preparatii e method"
hlp,
Recrystn solvent
oc
NED? FormulaC
mg/kg
CSH13ClXj,S > 100 d 50 ;z1 168- 171 i-PrOH CioH17ClNrS > 100 h1 234-257 bIeOH- i-PrOH C 9H13Clx~S 23 * llinimum effective dose a The symbols used in this column are explained a t the beginning of the Experimental Section. See Table I, footnote 9. A-. dubius. See Table I, footnote f . 34 10 35 36
CHz (CHzh (CH2)3 ~RZTLS-CH=CH
A1
HC1 HC1 HC1 HC1
204-206
i-PrOH
Days given
3 3 1 1 against
TABLE V
KO.
RI
Salt
PreparatiT e methodb
Mp,
Recrystn solvent
oc
Formulae
mukg
Days given
2 (Pyrantel) Tartaric 12.5 36 CHs HC1 A1 2 54-2 37 XIeOH-i-PrOH CpH&lK2S 23 37 C& HC1 A1 193-193 bIeOH-hIe2CO CtOH15ClK2S 50 35 C3H7 SSLQ A3 183-1 86 lIeOH-i-PrOH C I ~ H Z ~ X Z O & >250 39 CiHs SSA(< A3 162-164 lleOH-tPrOH CI~HZ,K;,O~S-L >250 40 NHCHS HPFB A44 144-146 EtOH CsHuF6NaPS 250 The symbol. uied in this column are explained a t the beginning of the Experimental Section. a SSA = sulfosalicylic acid. calcd, 50.7; found, 51.2. d PIIininiuni effective dobe against S.dzibius. e See Table I, footnotef.
1 1
3 3 3 3 C:
TABLE 1-1
HXH
AICH~CH~C
\
NO.
-4r
Salt
Preparati\ e method"
M p , OC
N(CH& Recrystn sol\ ent
Formulad
MED,~ mg/kg
Days given
(Pyrantel) Tartaric 9 12 5 1 2-Thienyl HC1 9 50 3 41 3-Methyl-2-thienyl HC1 A1 180-181 i-PrOH C,oHiiClN,S 100 1 30 Phenyl HC1 9 > 100 2 42 O-Tolyl H C1 A1 165-166 i-PrOH Ci2HIgClN2 >lo0 1 4:: 2-Fury1 HCl 11 1.50-152 lleOH-Me&O CsH&lX;,O >250c 3 Xinimum effective dose against The symbols used in this column are explained at the beginning of the Experimental Section. S.dubius. c The minimum effective dose against H . nanu is, hon-ever, 125 mg'kg. d See Table I, footnotef. e See Table I, footnoteg. 2 10
noncyclic amidines are reported in the last columns of Tables I-VII. Structure-Activity Relationships.-Except ~there noted, all discussions of anthelmintic activity in this section refer to activity against N . dubius. The noncyclic amidines described in this paper all bear gross structural resemblances to pyrantel. Each
compound possesses (i) a simple aromatic system, (ii) an amidine function, and (iii) a chain of atoms connecting the aromatic ring with the amidine moiety (compare 1 and 3). Because of this, many similarities in the structure-activity relationships between the cyclic and noncgclic amidines should be expected and are indeed found. Differences exist as well.
I I:!
\r
tPyrant el) 2-Thieti yl :j-Thietiyl :!-lIet hyl-2-thieiiyl ,j-lIet hy1-2-t hieiiyl Phenyl ~-T(~lyl ~ - F U 1K > 'The *yirihols iiseci i n this column are explained at the beginning of the I~sperimei~tal Se(*tioti. .\-. rli/bicts. Pee Table I, footnotef. See Table I, footnote g.
.\tnong the himilarities the following should he noted. (1) 111 each serie-, 2-thienyl is the aromatic mo-t favorable for anthelmintic activity; the 3 tem IS also effective, but the corresponding 2-thienvl compounds are more potent. ( 2 ) Activity is found i n compounds in which the aromatic and amidiiie sj stem. are contiected hy ethylene (CH,CH,) or tram-vinyleiie (CH=CH) bridges; extending the bridge to trimethyIpiie ((CHJ?) or shortening it to CH, leadb to a decren\e i n :ictivity ( w Table IT.'). (:3) Only a narrow r w g e of 5tructurd change- may be made in the :mitiiiic tern without lo., of activity. In order t o inve.tigate this latter point, n e tcrnittically prepired and tested the coinpouiids drccribed in Table, I. 11, mid y. The r e d t - show that (:I) buh5titution of the amidine YJ >tern 1. 1iecessai.J for activity, (h) ;I single zub-tituent 1. not ,uficient, (c) S' substitution is unfavorable for activity, and (d) S,S dibiib\titution leads to activity, hut one wb-tituent must he .\IC, aiid the second may he AIe, I:t, N e O , I l e S H , or all1 1. Iri keeping n-ith ohm-vatioiiz made iri the cyclic \erie-, there appear5 to be :in optimum value of lipophilicity associated with the mor^ potent members of this acyclic yeriei. Thu. conipouiida iiidficiently subctituted o i l S arc' too hydrophilic t o active [conditions :i aiid b above], while compoundwith subhtitueiits larger than the Ale allyl comhiriatio~l ;ire too lipophilic to bc actiw (see example, iii T:iblc 11). Other factorh, possibly steric, must iilw p h i ii role, bccauw it is difficult to hee why the :illy1 compound 21 is active, and why the related Pr (18),7-Pr (19), atid propargyl (22) analogs are not. Similarl! , the 111:tctivity of the S-F:t-S'-AIe compound 12 I- difficult to rc~solvc~with lipophilicity :irgumeiit. alone (cornpaw n i t h 17). The principal difference to be found betn eeii t h e c j clic and noncyclic series is that ttmorig the CJ clic ainidiries several phenyl analogs are active, and boiiie are even highly potent ; the corresponding compoundz in the noncyclic series are not active a t subtoxic h e (sce Table YII), Other arid more subtle differences txtn'ccn the two series exist, but discussion of thete :it thi. time does not seem profitable. ~ h i e r d l y ,the noncyclic amidines do not exhihit yignificant activity against S. obvelata. Only 10 aiid i t \ ftirj.1 ~ i a l o g43 are active againqt H . ,/ana, hut 43 1iiinctive again-t N. ilubius.
.\liniiniini effective dose :ig:titi.t
Experimental Section Boiliiig poitits are iiiicoi,rect ed; iiieltitig points were determitied i111 a Xel-Temp melting p i n t apparatiis (Laboratory llevicrs, Cambridge, Mass.) :mi are corrected. The nitriles used its iiit,ermediates have beeii dewihed el.>ervhere.2 \Gth one e s c e y tion, the amines iiseti wew commercially available; 2,2,2-trifliioio-ru'-niethylethylaniitiewas prepared by a riiodific~atioit5of the method of Hissell and Fiitger.0 \$'here analyse. are indicated only 11)- symbols ut' the eleriirtits, aiialytical results obtaiiied for thiise elemelits were wit hiti 10.4":. of the theoretical valite.. The nieairitig of the syniliol wed i i i d e r the heading "Preparative IIethod" iii the variow tihles is xs follow. The alphabetic charavter referi to the geueral syiitlietic methods illustrated i t i the Esperinreiital Sectioii : t lit: iit,aliic iiiimeral refers t o o i i e of the followitig routines i i d to isolate or piitify the filial prot1iic.t: ( I) isolate the salt directly f i n i i i ttie imction mistw ,talliar; ( 2 ) isolate the pr(idiic~i21.- ii free base and re ( 3 ) isolate the prodiict :IS it f i w lmse, votivert it to a11 ralt, atid recrystallize: i 4 I iirecipitate O I I + SO1Li~~~lli (Jf the CrLl(if? Ijc:1 tirated poltionwi.e a i t h 11.4 g (0.06 r n o l t ~ io f 6 )11. C . Brown and 1'. Iirirn. J . dn.Chern. S o c . , 86, 3566 cl9ti-l). 6 )E. R. Hissell a n d A I . Finger, J . O i g . Chem., 94, 1256 (1959). 7 ) J. Sam a n d A . (', Thurni)sim, J. Pliarm. Sei., 52, 898 (1963).
ASTHELMINTICS.V
January 1970
EtaO+ BF,-.8 After 1 hr at O", the reaction mixture was allowed to warm to room temperature and stirring was continued for 4 hr. The solvent was evaporated under reduced pressure, and the residue was taken up in a minimum of RIeOH and treated with 40 ml of 2.5 Me&H in MeOH. Colorless crystals precipitated after 40 min, and after 3 hr the desired product was filtered: yield 2.17 g, mp 190-196'. One recrystallization from RIeOH afforded 1.31 g of 13, mp 200-202". A second crop was obtained: yield 0.15 g, nip 199-201'; total yield 1.46 g (10%). Method C. N,N-Dimethyl-2-furanacrylamidine Hydrochloride (49).-A stirred, ice-cooled solution of 2 Ar hIe&H in hIeOH (50 nil) was treated portionwise with 13.0 g (0.05 moles) of crude 3-(2-furanacrylimidoyloxy)propanesulfonic acid,* prepared from 2-furanacrylaniide and lJ3-propane ~ u l t o n e .The ~ resulting solution was allovied to warm to room temperature, and to stand for 2 d a j 3. The volatiles were evaporated under reduced pressure, and the reaidue was taken up in H20 and poured into a rapidly stirred mixture of 100 ml of loc: KaOH and 100 ml of Et2O. The ether pha>e was dried, filtered, and evaporated to furnibh 3.1 g of the crude base. The base was dissolved with 20 ml of 1 A- HC1 in NeOH, and the resiilting solution n-as treated with Et?O to precipitate the desired 49 as an oil. The solvents were evaporated and the product crystallized on standing. One recrj stallization from ?IIeOH-AIe2C0 afforded the pure product, ( 8 ) H. Rleerwein, Org. Sun.,46, 113 (1966).
113
yield 1.93 g (19%)) mp 219-221". One more recrystallization from RIeOH-Xe2C0 gave an analytical sample, mp 219-221". Method D. 2-Thiophenepropionamidoxime (14).--4 stirred mixture of 8.3 g (0.12 mole) of HOSH?.HCI and 50 ml of NeOH was treated with 48 ml (0.12 mole) of 2.5 9 XaOMe in nIeOH. E t 2 0 (100 ml) was added and the insoluble matter wa5 filtered. The filtrate was concentrated to about 100 ml and 13.7 g (0.1 mole) of 2-thiophenepropionitrile was added. The resultiiig soliition was heated under reflux for 2 days, and then allowed to cool. The solvents were evaporated under reduced pressure to afford a mixture of oil and crystals. The mixture was triturated with EtgO, and filtered. On Concentrating the filtrate a yellow crystalline solid was obtained, yield 15.7 g. The product was recrystallized from PhH to afford colorless prisms of the desired amidoxime (14), yield 6.03 g (35%), mp 67-72". One further recrystallization afforded analytically pure material, mp 70-72".
Acknowledgments.-Thanks are due to N r . R. B. James for valuable assistance in preparing the compounds mentioned in this article, to 11r. G. F. Smith for his help in evaluating their anthelmintic activity, and to Drs. L. H. Conover and J. E. Lynch for their encouragement and advice during the course of this investigation.
Novel Anthelmintic Agents. V. Thiazoline and Dihydrothiazine Analogs of Pyrantel J. W.J I C F A R L A N D , H. L. HOWES, JR.,L. H. CONOVER, J. E. LYNCH, Pfizer Sferlical Research Laboratories, Gr d o n , Connecticut 06340
\I7. C. AUSTIN,ASD D. H. ~ I O R G S S Pjzar L t d . Research Laboratories, Sandwich, K e n t , Cnited Kingdom Received A u g u s t 1 , 1969 Some 2-thiazoline and .jj6-dihydro-4H-1,3-thiazineanalogi of pyrantel exhibit highly significant activity against the round worm .Yematospiroides dubizis. Only a few members of the thiazoline group are active, and then oiily at high doses; the dihydrothiazine group, however, has many highly potent members. I n the latter, the striictural requirements for activity are less restricted than in the tetrahydropyrimidine (pyrantel) series. The structure-activity relationships within the tetrahydropyrimidine and dihydrothiazine serieb are similar, but certain relationbhips found in the former series are inverted or are absent in the latter. One compound, 5,6dihydro-2-[2-(2-thienyl)ethyl]-4H-l,3-thiazine (6), has been shown to be active against not only dubius, but also agaiiist, Sippustrongylus muris, Syphacia obvclata, Trichinella spiralis, Ascaris s u u m , Ancylostoma caninum, and Toxocara canis. Other highly potent compounds in this seriei are 5,6-dihydro-2-[2-(3-methyl-2-thienyl)ethyl]-4H-lj3-thiaziiie ( 9 ) , 6,6-dihydro-2-pheiiethyl-4H-1,3-thiazine (IO), and 2-[2-(2-furyl)ethy1]-5,6-dihydro4H-1,3-thiaziiie (21).
Nernatospiroicles dubius. Later, the dihydrot hiazine The recent discovery of the broad spectrum anthelhomolog 6 was found to be not only effective but also mintic agent pyrantel has opened new fields of inquiry for those seeking novel agents to treat worm-caused highly potent : the N . d u b i u s burden in mice is reduced diseases. Other amidines, both cyclic and acyclic, greater than 90% by a single dose of only 3.1 mg 'kg. closely similar in structure to pyrantel possess anthelmintic activity with varying degrees of p o t e n ~ y . ~I n, ~ t'he course of investigating the structure-activity relationships among these compounds, we became interested in finding alternatives t o the amidine m ~ i e t y . ~ pyrantel Very early in our studies we observed that the thiazoline 1, when administered at 250 mgikg orally to a mouse, is highly effective agaiiist the round worm A large number of compounds were prepared in thih new series of cyclic thiomidates and were tested in our (11 W. C. Austin, W.Courtney, .I. C. Danilewicz, D. H. Morgan, L. € I . primary screen. The present report will discuss the Conover, H. L. Howes, Jr.. J. E. Lynch, J. VV. McFarland. R. L. Cornmelt. structure-activity relationships which emerged within and V. .I. Theodorides, N u t w e , 212, 1273 (1966). (2) J. W. McFarland, L. H. Conover, H . L. Howes, Jr.. J. E. Lynch, the series, and will compare and contrast these with 1). R. Chisholm, W.C. Austin, R. L. Cornwell, J. C . Danilewicz, W,Courtthe corresponding relationships found in the cyclic ney, and D. H . Morgan, J. M e d . Chem., 12, 1066 (1969). (3) .J. I\'. McFarland and H. L. Honres, J r . , ibid., 13, 109 (1970). amidine series. (4) One such alternative is the 1-substituted pyridine system, e.g., 1-(2Chemistry.-The synthetic methods used to prepare (~-thienyl)vinyllp~ridinium bromide: see J . W. McFarland and H. L the thiazoliries and dihydrothirzirie. followed standard Howes. J r . , ibad.. 12, 1079 (1969).
