Pesticide Synthesis Through Rational Approaches - American

acceptable to rats, (i.e. Table II). Table II. (a). Treated Diet. Untreated Diet. Males-. 14g. 17g. Females- l l g. 24g. T o t a l -. 25g. 41g. Diet. ...
0 downloads 0 Views 1MB Size
4 The Discovery and Development of Bromethalin, an Acute Rodenticide with a Unique Mode of Action BARRY A. DREIKORN and GEORGE O. P. O'DOHERTY Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

Lilly Research Laboratories, Eli Lilly and Company, Greenfield, IN 46140 Because rodent populations world-wide were becoming resistant to the widely used Warfarin-type anticoagulant poisons, a search was initiated to find a rodenticide with a different mode of action; one that would be effective against these resistant rodents. This search led to the discovery of the toxic nature of a family of diphenyl amines which act as uncouplers of oxidative phosphorylation. A structure-activity relationship (SAR) study was undertaken to choose a derivative that would be both poisonous to rodents but still readily consumed by them. This approach led to the discovery of bromethalin, N-methyl-2,4-dinitro-N (2,4,6-tribromophenyl)-6-(trifluoromethyl)benzeneamine, which had a l l the desired rodenticidal properties. H i s t o r y . For c e n t u r i e s man has recognized that rodent pests destroy h i s h a b i t a t , consume h i s food, and cause the spread o f v i r u l e n t diseases. Throughout the same c e n t u r i e s man has sought to e l i m i n a t e these pests with a v a r i e t y o f poisons such as s t r y c h n i n e , arsenious oxide, and red s q u i l l - a s t e r o i d a l g l y c o s i d e e x t r a c t e d from the bulb o f a l i l y - l i k e plant, Urginea maritima. These m a t e r i a l s , as w e l l as more recent poisons l i k e z i n c phosphide and f l u o r o a c e t i c a c i d , work as acute r o d e n t i c i d e s and can be e f f e c t i v e when a rodent consumes a l e t h a l quantity o f poison i n a s i n g l e dose i n i t s food or drink. Unfortunately, animals o f t e n consume l e s s than a l e t h a l dose, which produces side e f f e c t s which the animals a s s o c i a t e with the b a i t . The r e s u l t i s that they become " b a i t shy" and are l i k e l y to be wary of the same poison b a i t a second time. The discovery o f the anticoagulant p r o p e r t i e s o f dicoumarin (1) l e d t o the development o f the more potent anticoagulant w a r f a r i n (2), (Structure 1). The subsequent discovery that the a n t i c o a g u l a n t s can be s u c c e s s f u l l y used as m u l t i p l e dose

0097-6156/ 84/ 0255-0045506.00/ 0 © 1984 American Chemical Society

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

PESTICIDE SYNTHESIS THROUGH RATIONAL APPROACHES

46

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

r o d e n t i c i d e s ( 3 ) s i g n a l l e d a s h i f t from the development o f acute r o d e n t i c i d e s t o the chronic, a n t i c o a g u l a n t m a t e r i a l s . These compounds a l l work by suppressing the a c t i v i t i e s o f vitamin-K dependent c l o t t i n g f a c t o r s i n the t a r g e t animal's blood which consequently causes the animal t o bleed t o death. The a n t i ­ coagulants avoid the development of b a i t shyness because they don't produce poisoning symptoms that cause feeding to stop. Because they are e f f e c t i v e a t low dosages(0.005-0.25%) they are r e l a t i v e l y non-toxic to domestic animals and man.

CH

I

CO

I

ο I Warfarin

1 Indandiones

Very r a p i d l y , a number of other a n t i c o a g u l a n t s , i n c l u d i n g the indanediones ( 4 ) , ( S t r u c t u r e 2), were developed as r o d e n t i c i d e s . Warfarin f i r s t came i n t o wide usage as a r o d e n t i c i d e i n 1950 and v i r t u a l l y supplanted a l l other m a t e r i a l s then i n use. In the case o f a l l these e a r l y m a t e r i a l s , m u l t i p l e b a i t a p p l i c a t i o n s were needed to c o n t r o l rodent populations which, while making the m a t e r i a l s s a f e r t o use than the a v a i l a b l e acute poisons, c u r t a i l e d t h e i r use i n underdeveloped and l e s s a f f l u e n t c o u n t r i e s because of the l a r g e q u a n t i t i e s of b a i t that must be placed t o destroy the populations of rodents. Within the f i r s t decade a f t e r i t and the other a n t i ­ coagulants were f i r s t s u c c e s s f u l l y employed, reports(_5) were received that Norway r a t s i n a farming area i n Scotland were "remarkably t o l e r a n t " t o w a r f a r i n and other a n t i c o a g u l a n t s . A d d i t i o n a l cases o f r e s i s t a n c e were reported i n Norway, Denmark, England, Wales, Germany, and the N e t h e r l a n d s . ( 6 ) The f i r s t evidence o f a n t i c o a g u l a n t r e s i s t a n c e i n the United States came from a study of Norway r a t s l i v i n g on a farm near Raleigh, North Carolina.(J7) They have s i n c e been found i n a great number o f other s i t e s i n the U.S.(8) Soon r e s i s t a n t mice populations a l s o began t o be discovered.(9) The a n t i c o a g u l a n t r e s i s t a n t populations were found to be c r o s s r e s i s t a n t to the v a r i o u s , chronic r o d e n t i c i d e s .

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

4.

DREIKORN AND O'DOHERTY

Bromethalin, an Acute Rodenticide

47

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

Discovery o f bromethalin I n i t i a l search f o r a r o d e n t i c i d e . I n t e r e s t a t L i l l y i n the d i s c o v e r y o f a r o d e n t i c i d e from among our extensive f i l e o f b i o l o g i c a l l y a c t i v e compounds f i r s t began with N. J . A. Gutteridge, a L i l l y chemist working i n England. When he became aware o f the r e s i s t a n c e problem he s t a r t e d a search f o r some r o d e n t i c i d a l l y a c t i v e m a t e r i a l s that would c o n t r o l r e s i s t a n t rodent populations. He appreciated the f a c t that although t o x i c i t y i s an e s s e n t i a l p r e r e q u i s i t e f o r an e f f e c t i v e r o d e n t i c i d e , i t was not the s o l e c r i t e r i o n upon which an i d e a l r o d e n t i c i d e i s based. He o u t l i n e d , i n one o f the most extensive reviews o f r o d e n t i c i d e s to date(10), other features o f an i d e a l r o d e n t i c i d e as f o l l o w s : (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix)

The t o x i c a c t i o n should be slow t o allow animal t o consume a l e t h a l dose, The poison should not be unpalatable, and should p r e f e r a b l y be o d o r l e s s , Symptoms o f acute poisoning should be absent; no b a i t shyness. The manner o f death should not arouse s u s p i c i o n s i n s u r v i v i n g animals, The poison should be s p e c i f i c t o the species t o be controlled. No d i f f e r e n c e i n s u s c e p t i b i l i t y due t o age, sex, o r s t r a i n should be present. There should be no danger o f secondary poisoning through animals e a t i n g poisoned rodents. No immunity o r build-up o f t o l e r a n c e t o the poison should develop. The chemical compound i n the b a i t should be s t a b l e under v a r i e d environmental c o n d i t i o n s .

Although Gutteridge was u n s u c c e s s f u l i n f i n d i n g a compound that would s a t i s f y these c r i t e r i a , h i s work sparked our i n t e r e s t i n t h i s problem. This i n t e r e s t i n r o d e n t i c i d e s was f u r t h e r increased by the d i s c o v e r y o f the a n t i c o a g u l a n t a c t i v i t y o f a s e r i e s of imidazo(4,5b)pyridines ( S t r u c t u r e 3), which were s t r u c t u r a l l y so d i s s i m i l a r t o the known a n t i c o a g u l a n t s that they were f i r s t thought t o have a d i f f e r e n t mode o f a c t i o n . Subsequent s t u d i e s ( l l ) i n d i c a t e d that i n s p i t e o f the t o t a l l y d i f f e r e n t chemical s t r u c t u r e o f the imidazo(4,5b)pyridines, these compounds suppressed the same f o u r v i t a m i n Κ dependent procoagulants that w a r f a r i n supresses. Further, rodents r e s i s t a n t t o the warfarin-type o f a n t i c o a g u l a n t s were a l s o r e s i s t a n t t o these m a t e r i a l s . T h i s continues t o be true f o r a l l the s o - c a l l e d "second g e n e r a t i o n " a n t i c o a g u l a n t s now a v a i l a b l e .

American Chemical Society Library 1155 16th St. N. w. In Pesticide Synthesis Through Rational Approaches; Washington, 0 . C. 20038Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

PESTICIDE SYNTHESIS T H R O U G H RATIONAL APPROACHES

48

Br 3

N0

2

4

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

X = Halogen, Trifluoromethy 1 R = Hydrogen, Hydroxy1, O - a l k y l Ρ = Perfluoroalkyl

Bromethalin

The discovery of the a c t i v i t y of the diphenyl amines. At t h i s point there began a sequence of events that f i n a l l y l e d to the the discovery of the diphenyl amine r o d e n t i c i d e bromethalin (Structure 4). Our i n t e r e s t i n the chemistry of the diphenylamines i n i t i a l l y came about because of the discovery that they had f u n g i c i d a l a c t i v i t y against a number of plant diseases (12). A large number of these compounds were synthesized i n order to develop a f u n g i c i d a l s t r u c t u r e - a c t i v i t y r e l a t i o n s h i p . One of the most promising of these f u n g i c i d e s i n greenhouse t e s t s , was t r i c h l o r o - t r i n i t r o diphenyl amine (Structure 5).

CI

N0

2

5 This compound, targeted as a f o l i a r a p p l i e d f u n g i c i d e , was a c t i v e against diseases of grape, e s p e c i a l l y downy mildew, and so a l a r g e sample was prepared f o r p o s s i b l e e v a l u a t i o n under f i e l d conditions. Before a p o t e n t i a l f u n g i c i d e i s t e s t e d on a l a r g e s c a l e i n a f i e l d t e s t program, an e v a l u a t i o n i s c a r r i e d out t o determine i f there i s any p o t e n t i a l danger to the a p p l i c a t o r . While undergoing t h i s routine t o x i c o l o g i c a l hazard e v a l u a t i o n , i t was noted that t h i s compound had an o r a l L D 5 0 of 3.2 mg/kg i n Harlan r a t s . On the b a s i s of t h i s r e s u l t , we decided that compound _5 was too hazardous to be evaluated as a f o l i a r

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

4.

DREIKORN AND O'DOHERTY

Bromethalin, an Acute Rodenticide

49

fungicide. Instead we submitted the compound to a r o d e n t i c i d e feeding study. I t proved to be t o x i c to r a t s i n t h e i r d i e t at 25 ppm and i t appeared that the onset of t o x i c i t y was delayed. With a t e s t i n g system a l r e a d y i n place from our work with the a n t i c o a g u l a n t s , we began a search f o r other r o d e n t i c i d a l diphenyl amines from among the diphenyl amines synthesized f o r t h e i r fungicidal activity. Since the r e l a t i v e t o x i c i t y of the other analogs made f o r the f u n g i c i d e program was unknown, we set out t o determine what aspects of the s t r u c t u r e of diphenyl amines made the compounds t o x i c . To accomplish t h i s we u t i l i z e d a screen o r i g i n a l l y e s t a b l i s h e d to determine the t o x i c i t y of drug candidates. The t e s t used was one to determine the t o x i c i t y of compounds to mice, i n which groups of three mice were i n j e c t e d i n t r a p e r i t o n e a l l y (I.P.) with an a c a c i a suspension of the t e s t compound u n t i l a l e v e l was reached where no t o x i c i t y was observed. This screen avoids many of the p i t f a l l s of f e e d i n g s t u d i e s s i n c e the t e s t compounds cannot be r e j e c t e d . By means of t h i s t e s t , we were a b l e to semi-quantify the t o x i c i t y of a l a r g e number of diphenyl amines very r a p i d l y . Some of the r e s u l t s obtained can be seen i n Appendix I. Once we determined the t o x i c i t y by t h i s I.P. route, we then t e s t e d the most a c t i v e compounds i n a non-choice f e e d i n g t e s t i n which the t e s t compounds were incorporated i n t o a r a t d i e t and fed to weanling and a d u l t Sprague-Dawley r a t s f o r ten days. This t e s t required f i v e r a t s per dose l e v e l and the l e v e l s were from 200 ppm to 10 ppm. D a i l y feed consumption data as w e l l as necropsy data on the dead and moribund r a t s were c o l l e c t e d . There appeared to be a good c o r r e l a t i o n between the mouse t o x i c i t y data from an I.P. route and the r a t feeding study (Appendix I I ) . With the r e s u l t s from these t e s t s we were a b l e to d e f i n e the "A" r i n g s u b s t i t u t i o n requirements r e q u i r e d to make the t r i n i t r o diphenyl amines t o x i c to r a t s . Since t o x i c i t y i s a necessary but not s u f f i c i e n t q u a l i t y of a r o d e n t i c i d e , the next phase of the t e s t i n g was conducted to determine the a c c e p t a b i l i t y of the t r e a t e d d i e t to r a t s and mice. The t e s t c o n s i s t e d of twenty r a t s per treatment l e v e l with at l e a s t twenty c o n t r o l animals. The t e s t s were run from three to ten days, with the feed consumption data and necropsy data recorded f o r each animal. The d e s i r a b l e candidate compounds should comprise at l e a s t 30% of the t o t a l d i e t of the r a t s and should have a m o r t a l i t y of 90% or more. The most a c t i v e r o d e n t i c i d a l compound turned out to be our i n i t i a l l e a d , 2 , 4 , 6 - t r i c h l o r o - 2 * , 4 , 6 ' - t r i n i t r o d i p h e n y l amine (Structure 5). This was t e s t e d under a v a r i e t y of c o n d i t i o n s with white laboratory r a t s and mice. We were able to determine from these t e s t s that, even g i v e n a choice, l a b o r a t o r y r a t s and mice would consume enough of the t o x i c a n t to cause 80% l e t h a l i t y . To determine how a c t i v i t y against l a b o r a t o r y rodents t r a n s l a t e d i n t o a c t i v i t y against w i l d rodents, we asked Dr. W i l l i a m B. Jackson at the Center f o r Environmental Research f

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

50

PESTICIDE SYNTHESIS THROUGH RATIONAL APPROACHES

and S e r v i c e s , Bowling Green U n i v e r s i t y , to conduct a study using compound 5 on some o f h i s w i l d rodent populations. The t r i a l s he ran on w i l d r a t s and mice p a r a l l e l l e d our own s t u d i e s on laboratory r a t s and mice, but h i s r e s u l t s were q u i t e d i f f e r e n t from ours. In h i s studies with w i l d Norway r a t s (Rattus norvegicus), the r a t s t o t a l l y r e j e c t e d the treated d i e t , a c t u a l l y choosing not t o eat rather than eat the t o x i c a n t . The r e s u l t s with house mouse (Mus musculus) proved e q u a l l y u n s a t i s f a c t o r y . What we had was a very t o x i c m a t e r i a l that was not r e a d i l y acceptable t o w i l d rodents, even i n a non-choice t e s t . We r e a l i z e d that i n order to develop one of these diphenylamines as a r o d e n t i c i d e , we had t o f i n d a way t o get rodents t o eat a t o x i c amount of the t o x i c a n t . We were convinced that the novel r o d e n t i c i d a l mode o f a c t i o n o f these m a t e r i a l s ( i . e . non-anticoagulant) would be v a l u a b l e i f we could f i n d a way to get rodents t o consume them, so we approached the problem as one of e i t h e r f i n d i n g a analog of 5^ that would be more t o x i c o r more acceptable. I f t h i s approach f a i l e d , as a l a s t r e s o r t we could look at ways to make formulations more acceptable. The search f o r a more a c t i v e diphenyl amine concentrated on the s u b s t i t u e n t s on the "B r i n g , s i n c e we were confident that we had d e f i n e d the s u b s t i t u t i o n patterns on the "A" r i n g . A s t r u c t u r e - a c t i v i t y r e l a t i o n s h i p study (SAR) was c a r r i e d out with the r e s u l t s seen i n Appendix I I I . Only one s u b s t i t u t i o n seemed to be s u p e r i o r to the t r i n i t r o ; the s u b s t i t u t i o n of one o f the ortho n i t r o groups with a trifluoromethy 1. A new SAR u s i n g the Mouse T o x i c i t y Test as a screen was conducted, holding "B" r i n g constant with 2 - t r i f luorome thy 1-4, 6 - d i n i t r o phenyl and s u b s t i t u t i n g the "A" r i n g . The r e s u l t i n d i c a t e d that the same s u b s t i t u t i o n pattern that l e d t o the most a c t i v e t r i n i t r o compounds h e l d f o r the 2 , 4 - d i n i t r o - 6 - t r i f l u o r o m e t h y 1 compounds, except that the l a t t e r compounds were more a c t i v e (Appendix I V ) . However, even these more t o x i c compounds were d i s c r i m i n a t e d against i n our c h o i c e - e f f i c a c y s t u d i e s . Before we got involved i n the extensive delays and expense i n c u r r e d i n screening a l a r g e number o f these compounds i n free choice e f f i c a c y t e s t s , t e s t s which might not t r a n s l a t e i n t o e f f i c a c y against w i l d rodents, a means was sought t o generate a more acceptable compound by choosing the most "rodent-acceptable atoms" i n the "A" r i n g from among the most a c t i v e s u b s t i t u e n t s and by s u b s t i t u t i n g on the amine n i t r o g e n . We i n i t i a t e d a l i t e r a t u r e search t o determine the kinds o f f u n c t i o n a l groups that a t t r a c t rodents. The object o f the search was t o t r y t o d e f i n e the aromatic s u b s t i t u e n t s on r i n g "A" that have been shown to have a t t r a c t a n t p r o p e r t i e s . This e f f o r t met w i t h no success. Much has been published on the types o f feed g r a i n s and mixtures thereof that are p r e f e r r e d by rodents but l i t t l e on the types of chemicals. While searching the l i t e r a t u r e f o r such p o s i t i v e information, M

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

4.

Bromethalin, an Acute Rodenticide

DREIKORN A N D O'DOHERTY

51

i t became evident that while the work on chemical a t t r a c t a n t s had been very q u a l i t a t i v e , the search f o r r e p e l l e n t s had been put on a rather formal s c i e n t i f i c b a s i s . Working f o r the F i s h and W i l d l i f e S e r v i c e , U.S. Dept. o f the I n t e r i o r , B e l l a c k and DeWitt(13) developed an equation f o r a r e p e l l e n c y Index, K, whose f i n a l form was: K=100-1/100W(8T +4T +2T +T4)(U +U +2U3+4U4+8X)

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

1

2

3

1

2

where T^....T4 represents the d a i l y consumption o f t r e a t e d food; U^...U4 represents the d a i l y consumption o f untreated food, X the r e s i d u a l untreated food and W the kilogram body weight of the animals. Many compounds were t e s t e d using t h i s equation a t both the F i s h and W i l d l i f e Service and a t the Army's Natick Laboratory, and the i t s u s e f u l n e s s i n determining r e p e l l e n c y was v e r i f i e d . On examining t h e i r r e s u l t s , we were s t r u c k by the f a c t that, p e r i o d i c a l l y , negative Κ values occurred. Examination o f the equation shows that t h i s can o n l y happen when l a r g e amounts o f the t r e a t e d d i e t were eaten e a r l y and/or untreated m a t e r i a l was untouched. We i n t e r p r e t e d the f a c t that compounds had l a r g e negative Κ values as an i n d i c a t i o n that they might a c t u a l l y a c t as a t t r a c t a n t s . Although a v a r i e t y of s t r u c t u r e s were represented by these negative Κ v a l u e s , among the s u b s t i t u t e d aromatic compounds a p a t t e r n was observed. Whereas p o l y c h l o r i n a t i o n o f t e n was a s s o c i a t e d with the r e p e l l e n c y o f compounds, polybromination appeared t o confer " a n t i r e p e l l e n c y " e f f e c t s . The K-values shown i n Table I i l l u s t r a t e t h i s p o i n t . Although " a n t i r e p e l l e n c y " i s n ' t n e c e s s a r i l y a d i r e c t measure o f a t t r a c t i v e n e s s o f compounds, i t gave us a r a t i o n a l e f o r our choice o f s u b s t i t u e n t s on the "A" r i n g .

Table I Structures w i t h a negative r e p e l l e n c y index (K = negative v a l u e ) COMPOUND Κ Value A c e t i c a c i d , 1,3,6-tribromo-2-naphthalenyl e s t e r -63 2,4-Dibromo-l-(2,4-dibromophenoxy)benzene -213 1,3,5-Tribromo-2-(2,4,6-tribromophenoxy)benzene -137 2-Amino-l,3-dibromo-4-methy1-9,1O-anthracenedione.... -88 9-Bromoanthracene. · · -77 4-Amino-2, 6-dibromopheno 1 -134 We a l s o recognized that compound _5 possessed a very a c i d i c proton on the amine n i t r o g e n and that many known compounds that e x h i b i t odor and t a s t e c o n t a i n a c i d i c SH, OH, o r NH protons. We thought i t d e s i r a b l e t o replace the proton on the amine with an

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

PESTICIDE SYNTHESIS THROUGH RATIONAL APPROACHES

52

a l k y l group to mask the a c i d i t y . We hoped to r e t a i n the t o x i c i t y of the compound while a v o i d i n g the t a s t e and/or odor c h a r a c t e r i s t i c s that we suspected rodents a s s o c i a t e d with these compounds. Because the most a c t i v e diphenyl amines are s u b s t i t u t e d i n the 2,6- and 2 6 p o s i t i o n s , causing a s t e r i c b a r r i e r to replacement of the amine proton, the methylation could not be c a r r i e d out on the already s u b s t i t u t e d diphenyl amine. The synthesis of these m a t e r i a l s required new, stepwise chemical approaches (Scheme I ) . I

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

I

il SCHEME I

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

4.

DREIKORN AND O'DOHERTY

Bromethalin, an Acute Rodenticide

53

In the case o f the p i c r y l d e r i v a t i v e s , the coupling o f 2,4,6trichloro-N-methyl a n i l i n e , 6, with p i c r y l c h l o r i d e , ( F i g u r e 7), gave the d e s i r e d N-methyldiphenyl amine i n the t r i n i t r o s e r i e s (Figure 8). However, the same methylated a n i l i n e , when reacted with 2 - c h l o r o - 3 , 5 - d i n i t r o b e n z o t r i f l u o r i d e , (Figure 9) , c o n s i s t e n t l y demethylated t o the N-H m a t e r i a l , (Figure 10), instead o f g i v i n g the d e s i r e d product, (Figure 11). This was true regardless o f the bases, s o l v e n t s , and c o n d i t i o n s used. Attempts t o use other N-alkylated a n i l i n e s , i n c l u d i n g N-methy1 a n i l i n e i t s e l f a l s o l e d to the d e a l k y l a t e d m a t e r i a l . F i n a l l y an approach was developed whereby 11 could be generated by f i r s t r e a c t i n g 6 with the d e s - n i t r o compound 12 t o form the d e s - n i t r o diphenyl amine JJ3, and then n i t r a t i n g under mild c o n d i t i o n s with ammonium n i t r a t e i n t r i f l u o r o a c e t i c a c i d . Side-by-side comparisons o f the a c c e p t a b i l i t y o f the N-methyl m a t e r i a l 1Λ, versus i t s N-H analog TO, i n d i c a t e d that by b l o c k i n g the f r e e amine we could make the diphenyl amine f a r more acceptable t o r a t s , ( i . e . Table I I ) . Table I I

(a) Treated Diet Males14g Females- l l g Total25g Diet

Untreated Diet 17g 24g 41g

37.9%

62.1%

15g 29$ 44g 62.9%

5g 21g 26g 37.1%

10

CR

.CI

O" "w' C f c H

c

CI

N o

NO,

11

10

5 Males 5 Females Total % o f Diet

vs

11

(b) lOppm 11 lOppm 10 i n Diet i n Diet 63g 30g 5 Males 62g 5 Females 38§ 125g 68g Total 65.4% % o f Diet 35.( >%

(a) Toxicant l e v e l 100 ppm i n treated d i e t (b) The animals were given a choice o f t o x i c a n t s

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

54

PESTICIDE SYNTHESIS THROUGH RATIONAL APPROACHES

On the b a s i s of the i n f o r m a t i o n we had developed, i t appeared that the compound o f choice should be polybrominated i n the "A r i n g , be s u b s t i t u t e d with a 2-trifluoromethy1-4,6-dinitrophenyl group i n r i n g "B", and have a methyl group on the amine nitrogen. S y n t h e t i c a l l y t h i s was a problem since the a p p r o p r i a t e l y s u b s t i t u t e d N-H diphenyl amine cannot be d i r e c t l y converted t o the N-methy1 analog, and the routes used i n the case of the trichloro-N-methyl m a t e r i a l l e d t o poor r e s u l t s . A s y n t h e t i c route was f i n a l l y developed which resolved most of the problems (Scheme I I ) . A diphenyl amine u n s u b s t i t u t e d i n the A r i n g was synthesized from 2 - c h l o r o - 3 , 5 - d i n i t r o b e n z o t r i f l u o r i d e , 9_ and a n i l i n e , and t h i s was methylated u s i n g very m i l d methylating c o n d i t i o n s ; i . e . dimethyl s u l f a t e and sodium carbonate i n acetone t o form the des-brominated compound, (Structure 15). The bromination of JL5 took place i n two steps. The f i r s t two bromines added r e a d i l y while the t h i r d bromine required the use of N-bromosuccinimide (NBS) i n s u l f u r i c a c i d , t o a f f o r d the d e s i r e d m a t e r i a l 4 i n high y i e l d . ,f

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

fl

Br

N0

2

4 SCHEME I I

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

M

4. DREIKORN AND O'DOHERTY

Bromethalin, an Acute Rodenticide

55

F i n a l l y , choice t e s t s were i n i t i a t e d both at L i l l y and at Bowling Green on the a c c e p t a b i l i t y and e f f i c a c y o f t h i s m a t e r i a l as a r o d e n t i c i d e ( J A ) . A l l laboratory t e s t s i n d i c a t e d that compound 4 was r e a d i l y accepted by r a t s and mice (Appendix V ) . In some cases rodents a c t u a l l y seemed to p r e f e r the t r e a t e d d i e t over the b a s a l d i e t . Compound 4 was assigned the L i l l y code EL-614, and, somewhat l a t e r , the generic name bromethalin.

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

Development o f bromethalin as a r o d e n t i c i d e Once bromethalin had been i d e n t i f i e d as a compound that was both t o x i c t o rodents a t low dose l e v e l s and acceptable to them i n b a i t , i t was necessary to develop information on i t s performance under f i e l d c o n d i t i o n s and t o l e a r n more about the mode o f a c t i o n . F i e l d e v a l u a t i o n of bromethalin. Both indoor and outdoor f i e l d t r i a l s a g a i n s t Norway r a t and house mouse populations were conducted under an EPA experimental use permit i n a number o f geographical l o c a t i o n s i n the U.S.( 1_5,_16) In a l l cases 0.005% bromethalin was used i n a b a i t c o n t a i n i n g 65% corn meal, 25% r o l l e d o a t s , 5% sugar and 5% c o r n o i l ( E . P . A . d i e t ) . Three census techniques were used before and a f t e r bromethalin treatment i n order to estimate c o n t r o l o f the rodent population, followed by snap t r a p p i n g at the end o f the t e s t as an a d d i t i o n a l measure of c o n t r o l . F i e l d r e s u l t s i n d i c a t e that bromethalin b a i t was e x c e p t i o n a l l y e f f e c t i v e against both Norway r a t s and house mouse populations. B a i t acceptance was e x c e l l e n t with no signs o f bait-shyness observed. It was a l s o e s s e n t i a l to determine how e f f e c t i v e bromethalin was a g a i n s t w a r f a r i n - r e s i s t a n t r a t s and mice. Such animals, whose r e s i s t a n c e t o a n t i c o a g u l a n t s had been determined by World Health O r g a n i z a t i o n tests,(l_7) were subjected to a standard EPA choice feeding e f f i c a c y t e s t with bromethalin at 0.005% i n the treated d i e t . The r e s u l t s i n d i c a t e (Appendix 6) that 90% o f the animals were k i l l e d and that consumption patterns were s i m i l a r to those observed i n other choice t e s t s . A f i e l d t r i a l was conducted using 0.005% bromethalin b a i t against a r e s i s t a n t p o p u l a t i o n o f house mice i n a p o u l t r y house. Resistance had been v e r i f i e d by using the standard WHO l a b o r a t o r y procedure. About two-thirds o f the mice t e s t e d were r e s i s t a n t t o warfarin. C o n t r o l was achieved under extremely d i f f i c u l t c o n d i t i o n s ( i . e . , extremely l a r g e p o p u l a t i o n w i t h an abundant food supply i n a complex p h y s i c a l environment). Toxicology o f bromethalin Acute t o x i c i t y of bromethalin. Acute LD5QS were determined i n v a r i o u s t a r g e t and non-target species by gavage a d m i n i s t r a t i o n o f bromethalin s o l u b l i z e d i n p o l y e t h y l e n e - g l y c o l 200. These data

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

PESTICIDE SYNTHESIS T H R O U G H RATIONAL APPROACHES

56

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

i n d i c a t e that s i m i l a r doses were r e q u i r e d to produce l e t h a l i t y i n a l l species t e s t e d . Nevertheless, species s e l e c t i v i t y i s obtained with bromethalin b a i t s s i n c e rodents w i l l consume l a r g e r q u a n t i t i e s of food per u n i t body weight than l a r g e r animals. Secondary t o x i c i t y . In a study run to determine i f bromethalin treated r a t s pose any threat to animals that happen to eat the t r e a t e d carcass, r a t s that had been fed bromethalin b a i t f o r 16 hours at a l e v e l of 0.005% i n t h e i r d i e t s u f f i c i e n t to k i l l 95%, were k i l l e d , ground i n t o "ratburger", and fed to dogs c o n d i t i o n e d to e a t i n g r a t meat. The dogs were fed t h i s d i e t f o r two weeks. At the end of t h i s time, none of the dogs showed any signs of t o x i c i t y . It was concluded that dogs consuming r a t s that had consumed a l e t h a l dose of bromethalin d i d not r e c e i v e enough t o x i c a n t to produce any signs of t o x i c i t y . Mode of a c t i o n of bromethalin. Signs of t o x i c i t y observed i n l a b o r a t o r y or f i e l d e f f i c a c y s t u d i e s u s i n g l a r g e , s i n g l e doses i n c l u d e tremors, one or two episodes of c l o n i c convulsions, and p r o s t r a t i o n , with death u s u a l l y o c c u r r i n g w i t h i n 36 hours. In c o n t r a s t , s u b l e t h a l doses from i n g e s t i o n of repeated small q u a n t i t i e s of b a i t or from doses l e s s than the L D 5 0 can produce l e t h a r g y , h i n d - l e g weakness, loss of muscle tone and paralysis.(18) These e f f e c t s have been observed i n laboratory s t u d i e s and have been shown to be r e v e r s i b l e . Experiments on the p h y s i o l o g i c a l and biochemical mechanisms of a c t i o n suggest that bromethalin uncouples o x i d a t i v e phosphorylation i n c e n t r a l nervous system mitocondria(19). This could lead to a decreased production o f ATP, a diminished a c t i v i t y of Na /K ATPase, and a subsequent f l u i d b u i l d up manifested by f l u i d - f i l l e d vacuoles between the myelin sheaths. T h i s vacuole formation i n t u r n leads to an increased c e r e b r o s p i n a l f l u i d pressure and increased pressure on the nerve axons, y i e l d i n g a decrease i n nerve impulse, p a r a l y s i s , and death. At present i t i s not c l e a r whether the same sequence o f a c t i o n i s r e s p o n s i b l e f o r b r o m e t h a l i n s convulsive and p a r a l y t i c a c t i o n s observed at d i f f e r e n t doses; however, i t i s l i k e l y that some areas of the b r a i n would be more s e n s i t i v e to ATP d e p l e t i o n and f l u i d imbalance than o t h e r s . The c e r e b r a l edema produced by s u b l e t h a l doses of bromethalin can be ameliorated by treatment with an osmotic d i u r e t i c and corticosteroids. Pathology from s u b l e t h a l doses, even without treatment have been shown to be r e v e r s i b l e . +

+

1

Conclusion Bromethalin i s a unique, h i g h l y potent r o d e n t i c i d e which s a t i s f i e s most of the c r i t e r i a of an i d e a l r o d e n t i c i d e . I t o f f e r s a d i s t i n c t advantage over c u r r e n t l y used acute and anticoagulant r o d e n t i c i d e s because of i t s unique mode of a c t i o n . Bromethalin

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

4. DREIKORN AND O'DOHERTY

Bromethalin, an Acute Rodenticide

57

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

provides a l e t h a l dose t o rodents i n a s i n g l e feeding with death g e n e r a l l y delayed two or three days. Rodents do not d i s c r i m i n a t e against bromethalin b a i t , t h e r e f o r e e x c e l l e n t b a i t acceptance i s achieved. I t has been shown t o have a mode o f a c t i o n d i f f e r e n t from the a n t i c o a g u l a n t s and i s very e f f e c t i v e against a n t i c o a g u l a n t - r e s i s t a n t r a t s and mice. Properly used i t poses no danger t o non-target s p e c i e s . The d i s c o v e r y and development o f bromethalin was the r e s u l t of both s e r e n d i p i t y and the t i m e l y a p p l i c a t i o n o f the s c i e n t i f i c method. The c o n t r i b u t i o n s o f s c i e n t i s t s from many d i s c i p l i n e s were necessary f o r i t s success. Acknowledgments We would l i k e t o thank our L i l l y c o l l e a g u e s Kenneth E. Kramer A l b e r t J . C l i n t o n , Dr. A l v i n M e l l i e r e , Dr. Robert van L i e r , and Steven Spaulding f o r t h e i r many c o n t r i b u t i o n s to the development of bromethalin. We would a l s o l i k e t o recognize the important advisory r o l e played by Dr. W i l l i a m B. Jackson (Bowling Green State U n i v e r s i t y ) .

References 1. 2.

3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Stahmann, M. A.; Huebner, C. F . ; Link, K. P. J . Biol. Chem., 1941, 138, 513 Overman, R. S.; Stahman, Μ. Α.; Huebner, W. R.; Sullivan, W. R.; Spero, L . ; Doherty, D. G.; Ikawa, M.; Graf, L . ; Roseman, S.; Link, K. P. J . Biol. Chem.,1944, 153, 5. O'Connor, J . A. Research, 1:334-336, 1948 Kabat, H.; Stohlman, E. F . ; Smith, M. I. J . Pharmacol, 1944, 80, 160 Boyle, M. Nature 4749:519, 1960 Drummond, D. C. Symp. Zool. Soc. Lond., 26:351-367 Jackson, W. B.; Kaukeinen, D. E. Science, 176 1343-1344, 1972 Jackson, W. B.; Ashton, A. D. 8th Steenbock Symp., Vitamin Κ metabolism and Vitamin K-dependent proteins, University of Wisconsin, Madison, 1979 Rowe, F. P.; Redfern, R. J . Hygiene, 63, 417-425, 1965 Gutteridge, N. J . A. Chemical Society Reviews, vol 1(3) 1972 Bang, N. U.; O'Doherty, G. O. P.; Barton, R. D. Clinical Research, 23 no.4, 251 (1975) Dreikorn, Β. Α.; Kramer, Κ. E. U.S.Patent 4,381,312 Bellack, E . ; DeWitt, J . B. Journal of the American Pharmaceutical Association, ν 38, pp 109-112, 1949

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

58 14. 15. 16. 17.

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

18. 19.

PESTICIDE SYNTHESIS THROUGH RATIONAL APPROACHES Dreikorn, Β. Α.; O'Doherty, G. O. P.; Clinton, A. J.; Kramer, Κ. E. Proceedings Brit. Crop Protection Conf., 1979 491-498 Jackson, W. B.; Spaulding. S. R.; Dreikorn, Β. Α.; van Lier, R. B. L. Proc. Tenth Vert. Pest. Conf., (R.E. Marsh, Ed.), Univ. of Calif.Press, Davis, Calif. Spaulding, S. R.; Jackson, W. B. Vertebrate Pest and Management Materials (in press) World Health Organization Technical Report Series 443: 140-147, 1970 van Lier, R. B. L., Ottosen, L. D., Hanasono, G. Κ., and Carter, J . L . ; Proceedings of the 19th Annual Meeting of the Society of Toxicology, 1980 van Lier, R. B. L., and Ottinger, L. D. The Toxicologist 1(1), 114, (1981)

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

4.

DREIKORN A N D O'DOHERTY

59

Bromethalin, an Acute Rodenticide

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

Appendix I

PPM

S u b s t i t u t i o n on Ring "A"

(a) < > Dose L e v e l s i n Mouse T o x i c i t y

Mono s u b s t i t u t e d C l , Br, F, CN, 1000 300 methyl, e t h y l , n i t r o , methoxy.

3/3

100

30

10

2/3 3/3 1/3 2/3 2/3

0/3 0/3 0/3 0/3 0/3

3/3

3/3

3/3

0/3

3/3

3/3

3/3

3/3

3/3 3/3 3/3 3/3

3/3 0/3 3/3 0/3

3/3

0/3

3/3

0/3

3/3 3/3 3/3 3/3

0/3 3/3 3/3 3/3

3/3 2/3 3/3

0/3 0/3 3/3

Test 3

2,3-, 2,4-,

3/3 3/3

(a).The Mouse t o x i c i t y data i s expressed as the r a t i o o f the number o f dead mice over the t o t a l t e s t e d a t each l e v e l

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

60

PESTICIDE SYNTHESIS THROUGH RATIONAL APPROACHES

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

Appendix I I

Substituents on Ring "A"

MTT(mg/kg) Feeding Study(PPM) (300) (300) (1000) (3) (3) (1000) (30) (300) (10) (300) (1000) 1/3 (100) (30)

0/5 0/5 0/5 5/5 5/5 0/5 5/5 0/5 5/5 0/5 0/5 0/5 5/5

(200) (200) (200) (15) (15) (200) (100) (200) (30) (200) (200) (200) (100)

(a)Mouse T o x i c i t y Test expressed as a r a t i o o f the number o f dead mice over the t o t a l t e s t e d at the lowest l e v e l t o x i c i t y was observed. (b)Norway r a t feeding study expressed as a r a t i o o f the number o f dead r a t s over the number t e s t e d a t lowest l e v e l t o x i c i t y was observed.

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

4.

DREIKORN AND O'DOHERTY

Bromethalin, an Acute Rodenticide

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

Appendix I I I

MTT(a)( g/ g) M

N0 N0 CF N0 N0 N0 H N0 N0 CH N0 i -Propyl N0 t-Butyl N0 CN N0 S0 NH S0 K N0 CH N0 S0 NH N0 C0 H N0 C0 Et N0 N0 CI CI N0 CF N0 2

2

2

3

2

2

2

2

3

2

2

2

2

2

2

2

3

3

2

2

2

2

2

2

2

2

2

2

3

2

N0 N0 H H N0 N0 N0 N0 N0 N0 N0 N0 N0 N0 N0 N0 N0

2

2

2

2

2

2

2

2

2

2

2

2

2

2

2

3/3 2/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 0/3 3/3

(3) (1000) (1000) (1000) (1000) (1000) (1000) (1000) (1000) (1000) (1000) (1000) (1000) (1000) (1000) (1000) (3)

K

FEEDING^) (ppm)

5/5 (15) 0/5 (200)

5/5 (10 ppm)

(a)Mouse T o x i c i t y Test expressed as the r a t i o of the number o f dead mice over the t o t a l number of animals at the lowest l e v e l t o x i c i t y was observed. (b)Norway r a t feeding study expressed as d e a d / t o t a l a t the lowest l e v e l i n feed that t o x i c i t y was observed.

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

61

PESTICIDE SYNTHESIS THROUGH RATIONAL APPROACHES

Appendix IV

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

N0

a

SUBSTITUENTS ON "A"

3.5- D i c h l o r o 3,4-Dichloro 2,4-Dibromo 2.6-Dibromo 2,4-Difluoro 2.4- D i n i t r o 2.5- D i f l u o r o 3, 5-Di t r i f luorome thy 1 3.4- Dimethyl 2.5-Dimethoxy 2,4,6-Trichloro 2,4,6-Tribromo 2,4,6-Trifluoro 2.6-Dichloro-4-bromo 2-Chloro-4,6-dibromo 2,4,6-Trimethyl 3,4,5-Trimethoxy 2,6-Dibromo-4-trif luorome thy 1

2

MTT< ) (mg/kg)



1/3 3/3 2/3 1/3 2/3 2/3 2/3 3/3 0/3 0/3 3/3 1/3 3/3 2/3 2/3 1/3 0/3 2/3

(3) (10) (3) (30) (30) (30) (30) (3) (1000) (1000) (10) (3) (10) (10) (1) (1000) (1000) (10)

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

4.

DREIKORN AND O'DOHERTY

Bromethalin, an Acute Rodenticide

63

Appendix V Choice E f f i c a c y Studies with 0.005% Bromethalin

Downloaded by GEORGETOWN UNIV on August 25, 2015 | http://pubs.acs.org Publication Date: June 26, 1984 | doi: 10.1021/bk-1984-0255.ch004

Rattus norvegicus Rattus norvegicus Rattus norvegicus Mus musculus Mus musculus Mus musculus Rattus r a t t u s

£/ £/

Dead Total

Test

Strain

Species

3-day 3-day 1-day 3-day 3-day 1-day 3-day

Wistar Wild Wild ICR Wild Wild Wild

136/140 19/20 20/20 19/20 20/20 19/20 20/20

1/ 3.4 2.8 3.6 3.1 3.3 3.4 2.5

Bait

*/

£/

51.2 48.9 56.2 54.4 45.5 47.5 46.0

3.04 1.79 2.65 7.47 5.10 3.47 2.27

Average days u n t i l death; ]>/ Percent acceptable; Bromethalin consumed mg/kg.

Appendix VI E f f i c a c y of 0.005% Bromethalin Against Warfin-Resistant Rodents Laboratory 3-Day Choice Test With Warfarin-Resistant Wild Norway Roats and House Mice a/ Species Rattus norvegicus Mus Musculus

Bromethalin Consumed Mortality (mg/kg)

EPA Placebo

±1 Bromethalin

10 M 10 F

8.2 21.3

7.0 7.7

10/10 9/10

1.0 1.5

10 M 10 F

3.4 1.6

3.3 1.3

8/10 10/10

5.9 2.6

No. Sex

£/ Average 3-Day Consumption (g) RECEIVED December 23,

1983

In Pesticide Synthesis Through Rational Approaches; Magee, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.