Synthesis and Chemistry of Agrochemicals V - ACS Publications

Chapter 25

Downloaded by UNIV OF GUELPH LIBRARY on June 19, 2012 | http://pubs.acs.org Publication Date: May 14, 1998 | doi: 10.1021/bk-1998-0686.ch025

Pyridinylpyrimidine Fungicides: Synthesis, Biological Activity, and Photostability of Conformationally Constrained Derivatives John P. Daub and Donna L. Piotrowski Agricultural Products, Stine-Haskell Research Center, duPont and Company, P.O. Box 30, Newark, DE 19714 A class of pyridinylpyrimidine fungicides represented by compound 1 is presented. Synthetic methods for the preparation of these novel compounds and structure-activity relationships are discussed. These compounds show broad spectrum control of plant pathogens with excellent activity on wheat eyespot (Pseudocercosporella herpotrichoides), wheat leaf blotch (Septoria nodorum) and rice blast (Pyricularia oryzae). The impact of photolability on the commercial viability of this class of fungicides is highlighted.

Our investigation of the class of fungicides represented by compound 1 was directed by the hypothesis that the mode-of-action involves chelation to a metalloenzyme. Molecular modeling suggested that the phenyl ring needs to be twisted out of plane relative to the pyridine for chelation to occur (Kleier, D. Α., DuPont Company, unpublished data). Therefore, our strategy for the preparation of novel fungicides was to incorporate a bridge between the phenyl and pyridine rings to control the dihedral 246 © 1998 American Society angle between these two rings in order to maximize biological activity. Chemical For example, the pyrimidine fungicide 2, which was discovered by Katoh et al (7), is transformed into the fused-tricycle 3 by incorporation of a trimethylene bridge as illustrated below. Analysis of Dreiding models indicated that the dihedral angles with a trimethylene and tetramethylene bridge are about 50° and 100°, respectively. Calculations on bridged

In Synthesis and Chemistry of Agrochemicals V; Baker, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1998.

247


bipyridines by Thummel suggest these angles to be about 45° and 58°, respectively, due to conjugation effects (2). Field efficacy of compound 1 was significantly lower than predicted by greenhouse testing which we attributed to photolability since the half-life observed in laboratory tests was 16 hours under artificial sunlight. Therefore, we also investigated the photostability of this class of fungicides.

Results and Discussion Synthetic Routes. Some methods for the preparation of these bridged compounds have been previously described by Daub et al (3). Below, we provide details for the preparation of several bridged fungicides to illustrate these methods. The sevenmembered ring fluoride 8 was prepared from 8-fluoro-1 -benzosuberone (4) as shown below. The pyridoannulation method of Chelucci et al (4) was used for thefirstthree steps with the exception that we substituted 1,3 -dimethy 1-3,4,5,6-tetrahydro-2( 1H)pyrimidinone (DMPU) for hexamethylphosphoramide. The novel benzoazetine 6



248 was obtained in the alkylation step and its structure was confirmed by hydrolysis to a hydrazine-substituted benzosuberone. Presumably, the mechanism for the formation of this benzoazetine proceeds via a benzyne intermediate. The cyanopyridine 7 was prepared from the intermediate JV-oxide using the highly regioselective method of Fife (5). Finally, the pyrimidine ring was built using standard methods (1,3). The trimethylene- and ethylene-bridged compounds 1 and 51 (see Table I under StructureActivity Relationships) were prepared from 1-benzosuberone and 1-tetralone, respectively, using mis linear sequence. The propenylene-bridged compound 52 (see Table I) was prepared from compound 1 by radical bromination with N-bromosuccinimide followed by hydrobromide elimination using l,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The ethenylene-bridged compound 54 (see Table I) was prepared from 7,8-benzoquinoline using the latter part of the above sequence starting at the oxidation/Fife reaction steps. The halogenated compounds 12-15 were prepared as shown below. The known (3) tricyclic pyridine 9 was chlorinated to provide the 10-chloro and 8-chloro tricyclic pyridines 10a and 10b in 32% and 15% yields, respectively. Similarly, bromination of pyridine 9 afforded the 10-bromo and 8-bromo tricyclic pyridines 11a and lib in 47% and 21% yields, respectively. Individually, these chlorides 10a,b and bromides lla,b were converted to the bridged fungicides 12-15 by the same methods described above for the preparation of the fluoride 8. We found that chlorides 12 and 13 could also be prepared directly from the unsubstituted compound 1 in 32% and 24% yields, respectively, along with a trace (4%) of the 9-chloro isomer 17a using the same chlorination method. 1) MCPBA, C1CH CH C1 2

2

2) TMSCN, Me2NCOCl CH2C12 3) NaOMe, MeOH

^

4) NH4CI, EtOH, H2O, reflux

x

5) MeC(=O)CH2CH(0Me)2 NaOMe, MeOH, reflux

5% aq. N a O C l , -9:X = Y = H TFA — ,10a:X = H , Y = Cl,32% 10b: X = Cl, Y = H, 15% NBS, ^ l l a : X = H , Y = Br, 47% TFA, RT l l b : X = Br, Y = H,21% -

L

12:X 13:X 14:X 15:X

= H , Y = CI, 28% = C1, Y == H, 11% = H , Y = Br, 58% = B r , Y == H,27%

In order to prepare 9-substituted derivatives, we used the procedure shown below. The previous route required eight steps to convert a benzosuberone to a target pyridmylpyrimidine. In this sequence, we use the effective pyridoannulation method of Jameson and Guise (6) requiring only two steps from a benzosuberone. Although the yields of the 9-substituted compounds 17a-c were rather low, the convergency of the method saved much effort. This pyridoannulation method was also used to prepare the tetramethylene- and methylene-bridged compounds 50 and 53 (see Table I) from 7,8,9,10-tetrahydro-5(6i7)-benzocyclooctenone and 1 -indanone, respectively.


249

16b: R = Br


16c:R = Me

3) NH4OAC

17b: R = Br, 10%

AcOH, reflux

17c: R = Me, 9%

Palladium couplings using the 10- and 8-bromides 14 and 15 provided very efficient access to several other substituents. As shown below, we converted the 10-bromide 14 to the 10-phenyl and 10-naphthalenyl compounds 18 and 19 via Suzuki coupling. Similarly, the 8-bromide 15 was coupled with phenylboronic acid to give the 8-phenyl compound 20. The 10-cyanide 21 and the silylacetylene 22 were also prepared via palladium couplings. The silylacetylene 22 was deprotected to give the desired 10-acetylene 23 by treatment with potassium hydroxide in methanol. Method A PhB(OH)2 or l-naphth-B(OH)2 Pd(PPh )4, PhH 2MNa?(Xh Method Β KCN, THF, reflux Pd(PPh ) Method C TMS-CsC-H 18: R = Pd(OAc)2, P(o-Tol)3 19: R = 20: R = Et3N, reflux 21: R = 22: R = KOH, MeO] 23: R = 3

3

14: 10-Br 15: 8-Br

4

10-Ph, 73% (Method A) lO-(l-naphthyl), 49% (Method A) 8-Ph, 82% (Method A) 10-CN, 75%(MethodB) 10-OC-TMS, 38% (Method C) 10-OC-H, 100%

Our strategy for the preparation of 11-substituted compounds used the pyridine nitrogen to direct chemistry to the ortho position. Compound 1 was cyclopalladated with palladium(II) acetate to give a crude palladium complex. This crude complex was treated with 3-chloroperoxybenzoic acid followed by reduction with sodium borohydride as described by Grigor et al (7) to afford the phenol 24 in 28% yield. This phenol was of high interest since it was designed to increase photostability through a photoenolization process. Bromination of the crude palladium complex under the conditions of Horino et al (8) afforded the 11-bromide 25 in 18% yield. This bromide showed slow interconversion of conformations by NMR due to the steric hindrance between the bromine and the nitrogen lone-pair. In contrast, the phenol 24 showed rapid interconversion of conformations presumably due to hydrogen bonding between the phenolic hydrogen and the pyridine nitrogen.


250

1) Pd(OAc)2,EtOH

f

For 24:

^

1

2) MCPBA, CH2CI2, 0°C N

^ ^

3) NaBH4, MeOH, 0 ° C


For 25: 2) Br2, CCLt, CH2CI2, NaOAc

24: X = OH, 28% Me 25:X = Br, 18%

The following scheme illustrates the preparation of several heterocycle combinations which also possess a 1,4-orientation of two nitrogens for chelation. The bipyridines 27a-c were prepared using the pyridoannulation method of Jameson and Guise (6). The pyridmylpyrimidines 28a-c, wherein the location of the two heterocycles have been reversed relative to compound 1, and the bipyrimidine 29 were

NMe

2

For 27a-c: 1) f-BuOK, THF, RT Me

°Vy

r2

Il 2) NH4OAC

Rl

AcOH, reflux For 28a-c and 29: Et3N, EtOH, reflux NH HCl-i H ls

26

2

Nx

27a: X

Y = CH,

R l = Me, R =

27b: X

Y = CH,

R l = H , R2 = Me, 8%

27c: X

Y = CH,R1=R2 =Me,30%

28a: X

Ν, Y = CH,

2

H,

R l = Me, R2 =

60%

H,

32%

28b: X = N,

Y

= CH, R l

H , R 2 = Me,61%

28c: X = N,

Y

= CH, R l

R

29:X = Y = N, R l = R 2

2

= Me, 22%

Me, 51%

1) MeMgBr Et20 0°CtoRT pxj 2) acid hydrolysis 3) Me2NCH(OMe)2, 110 °C w

4) Et3N, EtOH, reflux, MeC(=NH)NH HCl 2

30

12%

Et3N, MeCN, RT

N^

HC1« I OMe 75%

Me


^Me

251


prepared by condensation of the vinylogous amide 26 with amidines. The pyridinylpyrimidine 31 where the pyrimidine is attached through the 4-position was prepared from cyanopyridine 30. The pyridinyltriazine 33 was prepared by the condensation of the amidine 32 with methylacetimidate. Next, we turned our attention to optimizing the substitution of the pyrimidine ring of compound 1. Notably, we incorporated alkoxy, alkylthio and alkylamino groups onto the pyrimidine ring to increase the basicity of the pyrimidine electron lone-pairs and presumably increase the chelation ability. As illustrated below, most of these compounds were prepared by standard methods of pyrimidine synthesis. The dimethoxypyrimidine 49 was prepared using the pyridoannulation method of Jameson For 34: (MeO)2CHCH2CH(OMe)2 NaOAc, 120 °C For 35: EtOCH=C(Me)CHO Et3N, EtOH, reflux For 36:

•HC1

MeC(=0)CH C02Et 2

NaOEt, EtOH, reflux For 44:

Et02CCH2C02Et

32

NaOEt, EtOH, reflux POCI3, reflux NaOMe, MeOH, RT NaOEt, EtOH, RT NaSMe, MeCN, reflux NaSEt, MeCN, reflux M e N H H C l , Et3N, THF, reflux 2

M e N H H C l , EQN, THF,reflux 2

POCI3, reflux NaSMe (2.5 eq.), MeCN, RT NaOMe (1 eq.), MeOH, RT NaSMe, MeCN, RT

NMe

2

34: R 35: R • 36: R : 37: R

= R2 = H,24% = R2 = H, with 5-Me, 11% = Me,R2 = OH, 45% = Me, R2 = CI, 98%

•38:R = Me,R2 = OMe, 100%

39: R 40: R 41: R 42: R 43: R 44: R -45:R

2

= Me, R = OEt, 100% = Me,R2 = SMe, 100% = Me,R2 = SEt,82% = Me, R2 = NHMe, 72% = Me,R2=NMe2, 100% = R2 = OH, 16% = R2 = C1, 96%

46: R = R2 = SMe, 100% -47:R

= OMe,R2 = Cl, 92%

48: R = OMe,R2 = SMe,81%

l)i-BuOK, THF, RT Me

N

0Me

°*Sf Y

N.

OMe 2) NH4OAC AcOH, reflux

26

41%


.OMe

252


and Guise (6) in good yield. The di(thio)alkoxypyrimidine compounds 46, 48 and 49 were of interest for the increased basicity of the pyrimidine nitrogens as well as for the possibility of increased photostability since they lack pyrimidine methyl groups which could be involved in radical and other photodegradative processes. Structure-Activity Relationships. Tables I-V below show the preventive control of wheat eyespot, wheat leaf blotch and rice blast observed for the compounds described above. These compounds show broad-spectrum control of plant pathogens (5) but these three pathogens are the strength of this class. In all five tables, the trimethylene bridged compound 1 is shown in the first line as a benchmark since it was overall the most active compound prepared. In addition, these tables show the photolysis half-life ratio relative to compound 1 since we believed that photolysis impacted the field efficacy of this class of fungicides. Table I shows the biological control of compounds with various bridges. The compounds are arranged in descending overall activity. Note that an asterisk in the tables indicates that the compound was tested at 25 g/ha. The two most active compounds are clearly the trimethylene bridged compound 1 and the tetramethylene bridged compound 50. These two are the only ones with the phenyl ring significantly twisted out of planarity relative to the pyridine ring supporting our working hypothesis. Compounds 51-54 have much smaller dihedral angles between the phenyl and pyridine rings which, we believe, lowers activity. Most notably, the ethenylene bridged compound 54 wherein the dihedral angle is constrained to 0° is not active at 100 g/ha on any of the pathogens. Table I. Effect of Ring Size and Conformation

% Control (I = less than 50%) Photolysis Rice Wheat Wheat Leaf Cmpd Blast Blotch Eyespot tl/2 No. W 100 g/ha 100 g/ha 100 g/ha Ratio 1 92 94 100* 1.0 CH CH CH2 50 88 100* 67 0.79 CH CH CH2CH2 51 99 I 0.39 CH CH 521 I 97 I CH=CH-CH 53 0.09 I I 90 CH 54 CH=CH I I I 0.54 Compound is a mixture of two regioisomers. * Compound tested at 25 g/ha. 2

2

2

2

2

2

2

-

2

1


-

253 Table II compares the activity of compounds with the optimal trimethylene bridge versus the Sumitomo fungicides 2 (7), 55 (9) and 56 (70). The bridged compounds generally show higher activity. Most notable is the comparison of the bridged compound 28a to the unbridged compound 55 wherein the central ring is a pyrimidine and the terminalringis a pyridine.


Table II. Comparison with Sumitomo Fungicides

Cmpd No.

W X = CH,Y = N,R = Me (Pyr-Pyrim) 2 H,H 3 CH CH CH X = N,Y = CH,R = H (Pyrim-Pyr) 55 H, H 28a CH CH CH X = Y = CH,R = H (Pyr-Pyr) 56 H,H 27a CH CH CH * Compound tested at 25 g/ha. 2

2

% Control (I = less than 50%) Wheat Leaf Rice Wheat Blast Blotch Eyespot 100 g/ha 100 g/ha 100 g/ha —

2

83 I

100*

79 93

97 95*

I 80

97*

-

92 94

2

2

2

I 75

2

2

2

53 89

Table III shows various heterocycle combinations with the optimal trimethylene bridge. The comparison of bipyridines 27a-c shows the importance of a methyl group at the 6-position of the terminal pyridine ring for activity. Similarly, the pyridmylpyrimidine 28a with a methyl group at the 6-position of the terminal pyridine ring is clearly more active than the 4-methyl (28b) and 4,6-dimethyl (28c) analogs. The heterocycle combinations are arranged in descending activity based on the most active compounds prepared within each set. Pyridinyltriazine 33 has dimethyl substitution so a more appropriate comparison may be with compounds 3 (Table V), 27c and 28c which would move this heterocycle combination above the bipyridines in relative activity. Compound 31, where the pyrimidine ring is connected through the 4-position, is much less active than its isomer, compound 1. Bipyrimidine 29 was not


254 active at 100 g/ha on any of the three pathogens. All of the heterocycle combinations tested for photostability showed lower stability than pyridmylpyrimidine 1.


Table III. Effect of Heterocycle Combinations

Cmpd No.

Rl R2 X = CH, Υ = Ν, Ζ = CH (Pyr-Pyrim) 1 Me Η X = Υ = Ζ = CH (Pyr-Pyr) 27a Me Η 27b H Me 27c Me Me X = Ν, Y = CH, Ζ = CH (Pyrim-Pyr) 28a Me Η 28b H Me 28c Me Me X = CH, Y = Z = N (Pyr-Triaz) 33 Me Me X = Y = CH, Ζ = Ν (Pyr-4-Pyrim) 31 Me Η Χ = Y = Ν, Ζ = CH (Pyrim-Pyrim) 29 Me Me * Compound tested at 25 g/ha.

% Control (I = less than 50%) Rice Photolysis Wheat Wheat Leaf Blast Blotch Eyespot tl/2 Ratio 100 g/ha 100 g/ha 100 g/ha

94

100*

92

1.0

89 64 93

97* I 99

94 I 71

0.53

75 I I

95* I 99

80 I 57

0.87

I

98*

60

0.81

I

88

71

—

I

I

I

-

-

Table IV shows the activity for compounds with the optimal bridge and optimal heterocycle combination wherein the phenyl ring is substituted. Compounds with small substituents (halogen, methyl and ethynyl) show comparable activity to compound 1 but were slightly less photostable. Surprisingly, the 10-cyano compound


255 21 is an exception with much lower activity. The larger phenyl group is acceptable at the 10-position (compound 18) though it loses activity on wheat eyespot. A phenyl group in the 8-position (compound 20) greatly reduces activity. Phenol 24, which was designed to be more photostable, showed exceptional photostability but, unfortunately, showed much lower activity than compound 1. The hydrochloride salt 57 and the copper(II) chloride complex 58 derived from compound 1 have equal activity to compound 1 but much lower photostability.


Table IV. Effect of Substitution on Phenyl Ring

Cmpd No. R 1 H 13 8-C1 15 8-Br 17a 9-C1 17b 9-Br 17c 9-Me 8 10-F 12 10-C1 14 10-Br 25 11-Br 57 H(HC1 Salt) 58 H (CuCl2 Complex) 23 10-C=CH 22 10-OC-TMS 18 10-Ph 19 lO-(l-Naphth) 20 8-Ph 21 10-CN 24 11-OH * Compound tested at 25 g/ha.

% Control (I = less than 50%) Wheat Wheat Leaf Rice Photolysis Blotch Blast Eyespot *l/2 100 g/ha 100 g/ha 100 g/ha Ratio 1.0 92 94 100* 0.52 89 98 98* 0.75 100* 75 I 94 0.65 93 99* 0.50 I 98* 98 0.44 97* 98 I 94 0.49 76 100* 98* 0.58 98 93 0.65 92 100* 96 0.82 77 99* 53 84 0.15 100* 91

Synthesis and Chemistry of Agrochemicals V - ACS Publications

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