Toxicological Significance of Oxidation and Rearrangement Reactions

5 Toxicological Significance of Oxidation and Rearrangement Reactions of S-Chloroallyl Thio -and Dithiocarbamate Herbicides

1

2

3

INGOLF SCHUPHAN , YOFFI SEGALL , JOSEPH D. ROSEN , and JOHN E. CASIDA 4

Downloaded by UNIV LAVAL on May 16, 2016 | http://pubs.acs.org Publication Date: June 11, 1981 | doi: 10.1021/bk-1981-0158.ch005

Pesticide Chemistry and Toxicology Laboratory, Department of Entomological Sciences, University of California, Berkeley, CA 94720

Many organosulfur compounds undergo biological oxidation at the sulfur atom to yield products which have pronounced physiological activity or serve as intermediates in generating bioactive compounds. Three examples are the lachrymating agent in onions (1) (1), the oxo intermediate (2) in metabolic desulfuration of phosphorothionate insecticides to form potent cholinesterase inhibitors (2), and the sulfoxides (3) produced on metabolism of thiocarbamate herbicides (3).

>

y ^ 0 3 The herbicidal activity of S-alkyl thiocarbamates (3-5) and the mutagenic activity of an S-(2,3-dichloroallyl) thiocarbamate (6) are probably due to the reactivity or decomposition products of their metabolically-formed sulfoxides.

1

Current address: Institut für Pflanzenschutzmittelforschung, Biologische Bundesanstalt, 1 Berlin 33, Federal Republic of Germany. Current address: Israel Institute for Biological Research, Ness-Ziona, P.O.B. 19, Israel. Current address: Department of Food Science, Cook College, Rutgers University, New Brunswick, NJ 08903. To whom correspondence should be addressed. 2

3

4

0097-6156/81/0158-0065$05.00/0

© 1981 American Chemical Society Rosen et al.; Sulfur in Pesticide Action and Metabolism ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SULFUR IN PESTICIDE ACTION AND METABOLISM

66

This review considers the S - c h l o r o a l l y l t h i o - and d i t h i o c a r bamate h e r b i c i d e s with p a r t i c u l a r emphasis on the t o x i c o l o g i c a l s i g n i f i c a n c e o f t h e i r o x i d a t i o n and rearrangement r e a c t i o n s .


Thiocarbamate

Sulfoxides

Synthesis. Oxidation of S - a l k y l o r S-benzyl N , N - d i a l k y l t h i o carbamates with one equivalent of m-chloroperoxybenzoic a c i d (MCPBA) in chloroform or methylene c h l o r i d e a t -25° to 25°C y i e l d s the corresponding carbamoyl s u l f o x i d e (3) i n e s s e n t i a l l y q u a n t i t a t i v e y i e l d (3-5). The S - c h l o r o a l l y l thiocarbamate s u l f o x ides (e.g., 4-7) are obtained in the same manner except that the temperature i s maintained between -20°C and 0°C f o r the o x i d a t i o n and e x t r a c t i o n o f the r e a c t i o n mixture with 5% sodium carbonate aqueous s o l u t i o n (7, 8 ) . 0

0

4 2—chloroallyl thiocarbamate sulfoxide

-< N

?

if ' 0

0 6

2,3-dichloroallyl thiocarbamate sulfoxide (diallate sulfoxide, cfs-frans)

7 2,3,3— tri chloroallyl thiocarbamate sulfoxide (triallate sulfoxide)

S p e c t r a l Features. The IR s p e c t r a o f carbamoyl s u l f o x i d e s (3) of S ^ a l k y l , S-benzyl and S - c h l o r o a l l y l d e r i v a t i v e s show the c h a r a c t e r i s t i c S-*0 absorption band near 1070 cm~l, which i s not present i n the s p e c t r a of the parent compounds (5, 7-9) . The NMR chemical s h i f t s f o r the carbamoyl s u l f o x i d e s (Table I) support t h e i r proposed s t r u c t u r e s . In examining the o x i d a t i o n r e a c t i o n s , i t i s convenient to add MCPBA to a s o l u t i o n of the thiocarbamate i n CDCI3 a t -20°C and take frequent s p e c t r a during o x i d a t i o n as the r e a c t i o n mixture warms up to 40°C. Comparison of these spectra with that o f the parent compound a t -20 to 40°C allows r e c o g n i t i o n of s h o r t - l i v e d intermediates and terminal products. With the parent thiocarbamates f o r compounds 5-7, the methyl group s i g n a l s appear as one doublet a t 40°C but two

Rosen et al.; Sulfur in Pesticide Action and Metabolism ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


3

2

2

1.18 (t)

3.40 (qa)

3.84 (s)

5.26 (d) 5.48 (d)

1

2

3

4/5

Protons

2-Chloroallyl thiocarbamate 12

0

^"Ύ

Cl

(m)

5.55 (s)

3.90 (s)

3.49 (m)

1.26

Sulfoxide 4

3

N

0

(bm)

6.03

(m)

3.51 (d) 3.68 (d)

3.80

1.30 (d)

3-Chloroallyl thiocarbamate

λ

ο

1.30(1.31) (d)

Diallate c i s (trans)

N

6.23

(m)

3.70 (d) 3.84 (d)

6.52(6.23) (t)

3.86(4.06) (d)

6.53(6.54) (t)

3.89(4.10) (d)

3.60(3.60) (-qi) 4.36(4.35) (~qi)

1.29(1.29) (dd) 1.44(1.45) (dd)

Sulfoxide 6 c i s (trans)

3"γ*ΊΤ»

3.57 (-qi) 3.82(3.82)(bm) 4.24 (~qi)

1.28 (dd) 1.44 (dd)

Sulfoxide 5

-< Y^N

2

(bm) 4.13 (s)

3.82

1.31 (d)

Triallate

ο

4.16 (d)

3.61 (~qi) 4.37 (-qi)

1.28 (dd) 1.46 (dd)

χ

Sulfoxide

^ΥΤ·«

Chemical S h i f t Data (ppm) f o r S - C h l o r o a l l y l Thiocarbamates and Thiocarbamate S u l f o x i d e s (]_, 8 ) . Solutions i n CDC1- a t 20 -40°C with t e t r a m e t h y l s i l a n e as the i n t e r n a l standard. Proton c o u p l i n g i n Hz: (CH ) -CH, 6.7 i n a i l cases; CH -C=CH,ν -alkyl thiocarbamate s u l f o x i d e s with a 3-hydrogen present (8 and 9) are r e l a t i v e l y unstable, decomposing by a cis-éliminâtion mechanism. Extensive breakdown occurs at 25°C i n the case of the S - t - b u t y l thiocarbamate s u l f o x i d e s and at 80 °C i n the case of the j>-ethyl d e r i v a t i v e s (11). The S-benzyl thiocarbamate s u l f o x i d e s , l a c k i n g the β-hydrogen, are the most s t a b l e compounds of t h i s type (11).

S - ( 2 - C h l o r o a l l y l ) thiocarbamate s u l f o x i d e s C e , are thermally unstable and w i t h i n one hour at 25°C they undergo a spontaneous [2,3] sigmatropic rearrangement to give the j>-0( 2 - c h l o r o a l l y l ) thiocarbamate s u l f e n a t e e s t e r s (10) i n q u a n t i t a t i v e y i e l d (7). This thermal rearrangement i s analogous to the r e v e r s i b l e rearrangement of £-tolyl a l l y l s u l f o x i d e s (12, 13). A s u l f e n a t e e s t e r analogous to 10 but with methyl instead of c h l o r i n e i s formed on MCPBA o x i d a t i o n of the corresponding Sm e t h a l l y l thiocarbamate; t h i s patent report (14) does not mention any intermediates or speculate on the mechanism of the r e a c t i o n . Formation of the s u l f e n a t e e s t e r i s conveniently monitored not only by IR and NMR but a l s o by CI-MS, i n the l a t t e r case because i n contrast to the s u l f o x i d e s (7, 9) the s u l f e n a t e s are s u f f i c i e n t l y s t a b l e to e x h i b i t a strong molecular i o n (7).



5.

SCHUPHAN ET AL.

S-Chloroallyl Thio- and Dithiocarbamate Herbicides 69

S ^ ( 3 - C h l o r o a l l y l ) thiocarbamate s u l f o x i d e s Ce.£., 5-7) undoubtedly rearrange i n an analogous manner but i n t h i s case the s u l f e n a t e q u i c k l y undergoes an a d d i t i o n a l 1,2-éliminâtion r e a c t i o n (7) . The r e s u l t i n g products are the Ν,Ν-dialkylcarbamoyls u l f e n y l c h l o r i d e (11) and the carbonyl compound, i . . ^ . aldehydes from the 3 - c h l o r o a l I y l d e r i v a t i v e s (e.£., 5 and 6) and a c i d c h l o r i d e s i n the case of the 3,3-dichloro analogs (e.&., 7) (7,8). This thermal rearrangement along with the 1,2-elimination r e a c t i o n i s analogous to a sequence p r e v i o u s l y reported f o r a r y l 3 - c h l o r o a l l y l s u l f o x i d e s (15).

11

2-chloroacrolein

Oxidations. The Stalky1 and S^-benzyl thiocarbamate s u l f o x ides are converted almost q u a n t i t a t i v e l y to the corresponding sulfones on MCPBA o x i d a t i o n i n chloroform (3-5). S^(2-Chloroa l l y l ) thiocarbamate 12 or the corresponding s u l f o x i d e (4) w i t h excess oxidant gives the s u l f o n e d e r i v a t i v e (13) which i s i s o meric with the s u l f i n a t e e s t e r (14) obtained from the s u l f e n a t e e s t e r (10) with 1 mole of MCPBA. Compounds 13 and 14 give c h a r a c t e r i s t i c NMR (Table II) and CI-MS spectra (see below). The unusual NMR s p e c t r a l feature of the S ^ ( 2 - c h l o r o a l l y l ) t h i o c a r b a mate s u l f o x i d e (4) i n e x h i b i t i n g a s i n g l e t f o r the two protons of the terminal methylene i s r e t a i n e d on f u r t h e r o x i d a t i o n to the sulfone (13) (Tables I and I I ) . Oxidation of s u l f e n a t e e s t e r 10 r e s u l t s i n the aforementioned s p l i t t i n g of the CH3 and CH2-N proton s i g n a l s due to the c h i r a l center and r e s t r i c t e d r o t a t i o n around the amide C-N bond of the s u l f i n a t e e s t e r (14) (Table I I ) . Both 13 and 14 give a molecular i o n on CI-MS, but sulfone 13 decomposes by l o s s of ethylene and s u l f i n a t e 14 cleaves o f f oxy gen to give the base peak. Further o x i d a t i o n of 14 r e s u l t s i n a new product with completely d i s t i n c t NMR s i g n a l s c o n s i s t e n t with those expected f o r the s u l f o n a t e e s t e r (Table I I ) .



70

TABLE I I 1. H Chemical S h i f t Data (ppm) f o r S - ( 2 - C h l o r o a l l y l ) N,N-Diethylthiocarbamate and I t s Oxidation Products. S o l u t i o n s i n CDCl^ a t 20°-40°C with t e t r a m e t h y l s i l a n e as the i n t e r n a l standard. Proton c o u p l i n g i n Hz: CH~-CH , 7.1; =CH , 1.1; OCH^ i n compound 14, 13.1. u b l e t , tt==t tr riipplleett,, qa =quartet, m=multiplet. s = s i n g l e t , d = doublet, = quart 2


Compound number and s t r u c t u r e

CH (tj

CH -N (qa)

S-CH (s)

1.18

3.40

3.84

1.26(m)

3.49(m)

3.90

3

^"Y

Nv^S^^X^j

1

2

2

2

0CH (s)

=CH, (d)'

2

5.26 5.48

5.55(s)

0

0

13

J '

1

1.30(m) CI

10

\

N

s

^°v>

1.18

3.46 3.75

5.68(s)

4.39

3.18

4.48

5.45

*CI

14

3s^ | 0v

"^N^

1.23 1.29

3.47 3.58

4.46(d) 5.46 4.73(d) 5.57

1.25 1.30

3.44 3.70

4.92

0 0,

Ν

γ\Χ, S. Jl

U

γο- ^ c .

excess^

~Λ

!

7 ^

_yοY|^ , c

^

ς

N

-*

M+ l

240

[ M

-C H ] 2

4

+

,

2

I

13

.

N

II

N

12 \ / Nf^

5.51 5.66

y

10

/ ° \ 1 MCPBA JL

^ c ,

o \ \ , ^ ° \ ) S^ I N>

-J

M + l

S

A

τ

c

l

M

_

0

240 2

14


2

3

2

5.

SCHUPHAN ET AL.

Dithiocarbamate


Sulfines

Synthesis. Oxidation of S - c h l o r o a l l y l dithiocarbamates with equimolar MCPBA i n chloroform, methylene c h l o r i d e or methanol a t -25°C gives a very exothermic r e a c t i o n l e a d i n g to the correspond ing dithiocarbamate s u l f i n e s (15), i^.e. s u l f a l l a t e s u l f i n e (16) and i t s t r a n s - 2 , 3 - d i c h l o r o analog (17) (16). Cl>.

>Y N S

s

>Y ^c, s

s

ô


15

ô 16

Ζ/ γ^ο, Ν

s

ô 17

Thus, the p r e f e r r e d s i t e of p e r a c i d o x i d a t i o n i s the thiono s u l f u r i n dithiocarbamates (16), as with d i t h i o e s t e r s (17, 18), r a t h e r than the t h i o l o s u l f u r o x i d i z e d i n thiocarbamates. S p e c t r a l Features. Examination of the equimolar s u l f a l l a t e MCPBA r e a c t i o n mixture r e v e a l s a product with a CI-MS peak appropriate f o r s u l f a l l a t e p l u s one oxygen (16). NMR s p e c t r a l data (Table I I I ) e s t a b l i s h that the p e r a c i d monooxygenation products of s u l f a l l a t e and c h l o r o - s u l f a l l a t e a r e s u l f i n e s 16 and Γ7 (16). There i s an u p f i e l d s h i f t of ~0.9 ppm f o r the S-CH protons a t t r i b u t a b l e to "through space" s h i e l d i n g by the negative environment of the s u l f i n e oxygen. Oxidation a t the t h i o l o instead of the thiono s u l f u r would have l e d to a downfield s h i f t f o r the S-CH protons, 3.84 ppm f o r the corresponding thiocarbamate (12) and 3.90 ppm f o r i t s s u l f o x i d e d e r i v a t i v e (4) (Table I I ) . S i m i l a r s p e c t r a l changes occur on conversion of d i t h i o e s t e r s to t h e i r s u l f i n e d e r i v a t i v e s (17). I t appears l i k e l y that s u l f i n e s 1J3 and Γ7 are obtained as i s o m e r i c a l l y - p u r e m a t e r i a l s s i n c e only a s i n g l e S-CH s i g n a l i s evident (Table I I I ) . The l a c k of s i g n i f i c a n t changes i n the chemical s h i f t s of the N-Ct^CH^ protons i n c o n t r a s t to the S-CH^ protons on o x i d a t i o n of s u l f a l l ate and c h l o r o - s u l f a l l a t e (Table I I I ) provides supporting evidence f o r the Z^-sulfines. 2

2

2

Rearrangements. P e r a c i d monooxygenation of dithiocarbamates with 3 - c h l o r o a l l y l s u b s t i t u e n t s (e , chloro-sulfallate), i n c o n t r a s t to the analogous thiocarbamates (e.&., d i a l l a t e ) , does not lead to [2,3] sigmatropic rearrangement followed by 1,2e l i m i n a t i o n r e a c t i o n s , i.e. the equimolar chloro-sulfallate-MCPBA r e a c t i o n gives no products with NMR s i g n a l s f o r =CH protons (16). T h i s lends support to other NMR s p e c t r a l evidence noted above that only the thiono group i s o x i d i z e d . 2

S u l f i n e s 16^ and JL7 a r e r e l a t i v e l y s h o r t - l i v e d i n s o l u t i o n , r e v e r t i n g to the s t a r t i n g m a t e r i a l s w i t h i n a few hours a t 40°C or r a p i d l y on a d d i t i o n of triphenylphosphine or attempted i s o l a t i o n



4.31

5.33 5.60

3 (s)

4/5 (d)

a

Singlet.

Complex obtained on r e a c t i o n of

New (s)

3.87 3.96

3.77 4.03

2 (qa)

10.06

5.46 5.94

4.48

3.76 4.15

1.44 1.48

a

Complex 22

6.31

4.52

3.38 4.00

1.30

b

Chlorosulfallate

1 2

l

6.43

3.69

3.88 3.95

1.29

b

Sulfine 17

S

C

^

Cl

10.03

6.41

4.74

3.79 4.16

b

t f a

1.46

M

Complex 22

s u l f a l l a t e or c h l o r o -• s u l f a l l a t e with 4 molar e q u i v a l e n t s of MCPBA.

5.30 5.54

3.43

1.29

Sulfine 16

H ^ H

1.28

Sulfallate

2

1 (t)

Protons

1

3

*H Chemical S h i f t Data (ppm) f o r S u l f a l l a t e , C h l o r o - S u l f a l l a t e , T h e i r S u l f i n e D e r i v a t i v e s and Further Oxidation Products. S o l u t i o n s i n CDC1 at 20°-40°C with t e t r a m e t h y l s i l a n e as the i n t e r n a l standard. Proton coupling i n Hz: CH^-CH^, 7.1; = CH^, 1.1.s = s i n g l e t , d = doublet, t = t r i p l e t , qa = quartet.

TABLE I I I


Ο

>

w H

> α

W > Ο H δ

Β

H Ο

C/3

w

to

5. SCHUPHAN ET AL.

S-Chlorocillyl Thio- and Dithiocarbamate Herbicides 73

i n v o l v i n g e x t r a c t i o n with aqueous sodium carbonate s o l u t i o n (16). This l o s s of oxygen probably i n v o l v e s an o x a t h i i r a n intermediate 18 which can a l s o extrude s u l f u r . D e s u l f u r a t i o n to form the t h i o carbamate (e.j>. 1 2 ) i s normally a minor pathway but becomes major when p - t o l u e n e s u l f o n i c a c i d i s present i n the r e a c t i o n mixture (16). R

MCPBA

\


15

Y"

-LsJ S 18

Oxidations. Treatment of s u l f a l l a t e or c h l o r o - s u l f a l l a t e with a 3-5-fold molar excess of MCPBA leads to e n t i r e l y d i f f e r e n t products than equimolar MCPBA. This i s evident on comparing the NMR s p e c t r a l features of s u l f a l l a t e , s u l f i n e 16, and complex 22 or of the

MCPBA

2 MCPBA CI S

sulfallate

19

u OvÂ

^0

Τ * u

Ύ 0

V

21

20

22

Γ N N ^ H

Τ

Τ S

+ CI^^ ~

S

v

0

1

Q -^CI

0

+ ArÔÂr

0

23

24



74

analogous products from c h l o r o - s u l f a l l a t e (Table I I I ) . Complex 22^ gives diethylformamide (23), 2 - c h l o r o a l l y l d i s u l f i d e (24) and the anhydride of m-chlorobenzoic a c i d on TLC i s o l a t i o n u s i n g s i l i c a g e l or on treatment with p y r i d i n e , h y d r o c h l o r i c a c i d , sod ium b i s u l f i t e or sodium carbonate. However, complex 22^ gives com pletely different H (Table I I I ) and C NMR s i g n a l s than any one or combination o f a l l of the compounds obtained on TLC i s o l a t i o n (16) . The s t r u c t u r e i n d i c a t e d f o r 22 i s one way to r a t i o n a l i z e i t s s p e c t r a l f e a t u r e s and r e a c t i o n c h a r a c t e r i s t i c s (16). NMR s t u d i e s r e v e a l that the low r e s o n a t i n g proton ( - 10 ppm) i s d i r e c t l y bonded to a carbon (181.2 ppm) which i s s p l i t to two l i n e s i n the l ^ C proton o f f resonance decoupling mode. T h i s o b s e r v a t i o n i s c o n s i s t e n t with a s u l f i n e carbon bearing one proton, which i n d i cates that the dithiocarbamate molecule i s already cleaved i n solution. S u l f i n e s u l f o x i d e JL9 i s a p p r o p r i a t e f o r the cleavage r e a c t i o n due to i t s e x c e l l e n t l e a v i n g group. I s o l a t i o n of d i sulfide i n d i c a t e s that the l e a v i n g group incorporated i n t o the complex i s a s u l f o x i d e r a t h e r than a s u l f o n e . A p o r t i o n of the low temperature NMR spectrum of complex 22 i s very s i m i l a r i n a l l r e s p e c t s y e t not i d e n t i c a l with that of diethylthioformamide s u l f i n e (20) (prepared by MCPBA o x i d a t i o n of the thioformamide a t -30°C). Thioformamide s u l f i n e 2£ decomposes very f a s t above -20°C to give diethylformamide (23) and elemental s u l f u r . Accordingly, s u l f i n e 20 must e x i s t i n s o l u t i o n i n a complexed form. A l l p r o p e r t i e s of complex 22 from s u l f a l l a t e and the analogous complex "22" from c h l o r o - s u l f a l l a t e a r e c o n s i s t e n t with the i n d i c a t e d adduct of diethylthioformamide s u l f i n e (20) and a mixed peroxyanhydride (21).


1 3

Other o x i d a t i o n products of s u l f a l l a t e a r e formed v i a t h i o carbamate 12^ as d i s c u s s e d b e f o r e . Metabolism of T h i o - and

Dithiocarbamates

Oxidations and Rearrangements. S - A l k y l and S-benzyl N,Nd i a l k y l t h i o c a r b a m a t e s a r e converted to t h e i r s u l f o x i d e d e r i v a t i v e s (3) both i n v i v o i n r a t s and on i n c u b a t i o n with l i v e r microsomes and NADPH (3-5, 19-21). Studies with EPTC (25) r e v e a l that they may a l s o undergo h y d r o x y l a t i o n a t each a l k y l carbon (designated by arrows) and that carbon h y d r o x y l a t i o n a t the S-CI^ moiety gives an unstable intermediate which y i e l d s acetaldehyde on decomposi t i o n (19).

EPTC (25)

S - α —hydroxy compound

Although d i a l l a t e s u l f o x i d e (6) i s too unstable f o r p o s s i b l e i s o l a t i o n as a metabolite, i t i s e s t a b l i s h e d as an i n v i t r o and


5.

SCHUPHAN ET AL.

S-Chloroalîyî Thio- and Dithiocarbamate Herbicides 75


i n v i v o intermediate i n mammals by the d e t e c t i o n of two of i t s d e r i v a t i v e s , 1.e., the g l u t a t h i o n e (GSH) conjugate and i t s f u r t h e r metabolites formed by an i n i t i a l carbamylation r e a c t i o n (10) (see below) and 2 - c h l o r o a c r o l e i n detected i n the microsome-NADPH system and d e r i v e d from the rearrangement-elimination r e a c t i o n sequence discussed above (6). S u l f a l l a t e a l s o y i e l d s 2 - c h l o r o a c r o l e i n i n the microsome-NADPH system, presumably by JS-C^ h y d r o x y l a t i o n (22) on analogy with the metabolism of EPTC shown p r e v i o u s l y . Carbamylation Reactions. S - A l k y l , ^ - b e n z y l and S - c h l o r o a l l y l thiocarbamates do not r e a d i l y r e a c t with GSH. In c o n t r a s t , t h e i r s u l f o x i d e d e r i v a t i v e s Q and 6) are very e f f e c t i v e carbamylating agents f o r many t h i o l s i n c l u d i n g GSH (19, 21). The GSH conjugates formed i n v i v o v i a 3^ and j> are q u i c k l y cleaved, a c e t y l a t e d and f u r t h e r metabolized as f o l l o w s (19-21, 23, 24).

The s u l f e n i c a c i d l i b e r a t e d on carbamylation i s o x i d i z e d i n p a r t to the corresponding s u l f o n i c a c i d based on s t u d i e s with d i a l l a t e (6, 8 ) . T o x i c o l o g i c a l S i g n i f i c a n c e of O x i d a t i o n and Rearrangement Reactions P r o h e r b i c i d e s . Thio- and dithiocarbamates probably r e q u i r e metabolic a c t i v a t i o n p r i o r to e x e r t i n g t h e i r h e r b i c i d a l e f f e c t s . S u l f o x i d e metabolites of t h e S - a l k y l thiocarbamates are g e n e r a l l y more potent h e r b i c i d e s than the parent compounds (.3-5) . The h e r b i c i d a l a c t i o n of these s u l f o x i d e s probably r e s u l t s from t h e i r carbamylating a c t i o n f o r t h i o l s , although the s p e c i f i c t a r g e t s i t e or receptor i s not defined (23, 24). I t i s conceivable that the S - c h l o r o a l l y l thiocarbamate h e r b i c i d e s may a c t i n the same way, s i n c e t h e i r s u l f o x i d e s are a l s o potent carbamylating agents



76

(8, 10). As an a l t e r n a t i v e , d i a l l a t e might be a p r o h e r b i c i d e and 2 - c h l o r o a c r o l e i n the u l t i m a t e h e r b i c i d e r e l e a s e d on decomposi t i o n of d i a l l a t e s u l f o x i d e (8). Promutagens. S - ( 2 - C h l o r o a l l y l ) t h i o - and dithiocarbamate h e r b i c i d e s , i n c o n t r a s t to the ^ - a l k y l thiocarbamates, show muta genic a c t i v i t y i n the Salmonella typhimurium "Ames assay; however, they are only mutagenic on metabolic a c t i v a t i o n , jL.e^, with the S9 mix (25-27). The requirement f o r the l i v e r microso mal mixed-function oxidase system f o r mutagenic a c t i v i t y l e d to the hypothesis that the S - c h l o r o a l l y l t h i o - and dithiocarbamates are promutagens and that an o x i d a t i o n process i s involved i n formation of the u l t i m a t e mutagens (6). I t was t h e r e f o r e of great i n t e r e s t to note that 2 - c h l o r o a c r o l e i n , an o x i d a t i v e metabolite of both d i a l l a t e and s u l f a l l a t e , and i t s 2,3-dichloro and 2,3,3t r i c h l o r o analogs a r e extremely potent mutagens (6-8, 22, 28). Various c h l o r o a c r o l e i n metabolites a r e l i k e l y to be the u l t i m a t e mutagens formed from d i a l l a t e , t r i a l l a t e and s u l f a l l a t e as discussed l a t e r . Polymer formation occurs on r e a c t i o n of deoxyadenosine with the d i f u n c t i o n a l 2 - c h l o r o a c r o l e i n , probably due to cross l i n k i n g v i a S c h i f f base formation a t the carbonyl group and Michael a d d i t i o n at the double bond (28).


11

Balance of A c t i v a t i o n / D e t o x i f i c a t i o n Reactions. The a c t i v a t ed intermediates or r e a c t i v e fragments appear to be carbamoyl s u l f o x i d e s or mono-, d i - and t r i c h l o r o a c r o l e i n s , a l l of which a r e r e l a t i v e l y unstable compounds. The carbamoyl s u l f o x i d e s a r e r a p i d l y d e t o x i f i e d by r e a c t i o n with GSH, i n v o l v i n g c a t a l y s i s by a GSH S-transferase i n the case of S - a l k y l and S-benzyl t h i o c a r b a mate s u l f o x i d e s (3-5, 21, 23, 24) but probably not with S-chloro a l l y l thiocarbamate s u l f o x i d e s (6, 8^, 10). 2 - C h l o r o a c r o l e i n i s unstable i n metabolic systems i n c l u d i n g i n the presence of GSH (28). Highly r e a c t i v e a c t i v a t e d intermediates must a c t i n the same c e l l or even c e l l u l a r o r g a n e l l e i n which they a r e formed. Thus, compartmentalization phenomena may be important i n the a c t i o n of the m e t a b o l i c a l l y - a c t i v a t e d t h i o - and dithiocarbamates. Some Reactions of D i a l l a t e , T r i a l l a t e and S u l f a l l a t e of P o s s i b l e Importance to T h e i r Mutagenic and/or Carcinogenic P r o p e r t i e s . Current knowledge of the o x i d a t i o n and rearrangement r e a c t i o n s of S - ( 2 - c h l o r o a l l y l ) t h i o - and dithiocarbamate h e r b i cides i n r e l a t i o n to t h e i r mutagenic a c t i v i t i e s i s i l l u s t r a t e d i n Figures 1 and 2. The mutagenesis data (6, 22, 28) i s from the Ames assay procedure (29) (Figure 3 ) . D i a l l a t e has been examined i n g r e a t e s t d e t a i l (Figure 1), i n part because i t gives the most potent mutagen(s) a f t e r a c t i v a t i o n [_ί·β.· a c t i v a t e d c i s - d i a l l a t e gives 40 revertants/nmole and a c t i v a t e d t r a n s - d i a l l a t e gives 25 revertants/nmole (Figure 3); t h i s potency i s s i m i l a r to that of the carcinogen benzo[a]pyrene 9



5.

SCHUPHAN ET AL.

S - a - h y d r o x y compound proximate mutagen


2,3-dichloroacrolein

(0/-)

ultimate mutagen (104/-)

S — a — h y d r o x y compound p r o x i m a t e mutagen

2,3,3—trichloroacrolein

(0/-)

ultimate mutagen (224/-)

Figure 1. Oxidation and other reactions of diallate and triallate indicating genic activities of the products in the S. typhimurium TA 100 assay (revenants/ nanomole; without activation/with activation; / designates no data availab 2-Chloroacrolein is a diallate metabolite in the mouse liver microsome-NADP system. Dichloroallylsulfonic acid is a urinary metabolite of diallate. The o compounds are potential metabolites of the respective thiocarbamates. The carbamate sulfoxides are unstable at 25°C.



S

OH

mutagen

compound

Η

(113/74)

2-chloroacrolein ultimate mutagen y

OH (0/-)

10

CI

(0.03/0.11)

\

(0/0.45)

0

S/

YY °^

N

0·

13

0

/

N

S/0

I

14

^Y ^

0

_CI

(Ο/-)

H O - i ^ C I Ο

Figure 2. Oxidation and other reactions of sulfallate indicating mutagenic activities of the products in the S. typhimurium TA 100 assay (revertants/nmole; without activation/with activation; / desig nates no data available). All thio- and dithiocarbamates are formed from oxidations with MCPBA except for the α-hydroxy compound. 2-Chloroacrolein is a metabolite in the mouse liver microsomeNADPH system. The other compounds are potential metabolites. Several of the oxidized thio- and dithiocarbamates are unstable at 25°C.

proximate

S—α—hydroxy

12 (0/1.5)

Ο

4 (0/0.39)

ο


5.

SCHUPHAN ET AL.



2500

20

40

60

80

nMoles

Figure 3. Mutagenic activities of the promutagens cis- and trans-diallate sulfallate, the proximate mutagen cis-diallate sulfoxide, and the ultimate mu 2-chloroacrolein, assayed with S. typhimurium strain TA 100 sensitive to base-pai substitution mutagens. The diallate isomers and sulfallate are not mutagenic w the S9 mix. S9 mix refers to a microsomal oxidase system prepared from ra and appropriate cofactors. The methodology is detailed in Refs. 6, 22, and


80



(29)]. D i a l l a t e s u l f o x i d e (6) i s a very potent mutagen without metabolic a c t i v a t i o n and i t decomposes q u i c k l y i n t o 2-chloroa c r o l e i n , found to have the same mutagenic a c t i v i t y of 113 revertants/nmole i n assays without the S9 mix. D i a l l a t e metabo l i s m i n v o l v e s both d i a l l a t e s u l f o x i d e and 2 - c h l o r o a c r o l e i n as intermediates, as discussed above. Thus, d i a l l a t e gives a p r o x i mate mutagen, the carbamoyl s u l f o x i d e , and an u l t i m a t e mutagen, 2 - c h l o r o a c r o l e i n , with about t h r e e - f o l d higher mutagenic a c t i v i t y than the b i o a c t i v a t e d c i s - d i a l l a t e . D i a l l a t e might a l s o y i e l d a second u l t i m a t e mutagen, the very potent 2 , 3 - d i c h l o r o a c r o l e i n , l i b e r a t e d f o l l o w i n g carbon h y d r o x y l a t i o n at the SJ-CI^ s i t e . T r i a l l a t e and s u l f a l l a t e are probably a c t i v a t e d to mutagenic metabolites from the c h l o r o a l l y l moieties without the involvement of t h e i r s u l f o x i d e s as the proximate mutagens (Figures 1-3). T r i a l l a t e s u l f o x i d e (T) i s mutagenic without the S9 mix (6). Somewhat l e s s a c t i v e i s 2 - c h l o r o a c r y l y l c h l o r i d e obtained from t r i a l l a t e s u l f o x i d e on i t s rearrangement and e l i m i n a t i o n reac t i o n s . Hydroxylation of t r i a l l a t e at the carbon α to the s u l f u r p o t e n t i a l l y gives the h i g h l y potent mutagen 2 , 3 , 3 - t r i c h l o r o a c r o l e i n on decomposition of the ^-α-hydroxy proximate mutagen. S u l f a l l a t e o x i d a t i o n with MCPBA does not y i e l d s u l f a l l a t e s u l f o x i d e or 2 - c h l o r o a c r o l e i n . Instead, i t gives a v a r i e t y of s u l f i n e s , s u l f o x i d e s , sulfones, S-O-sulfenate e s t e r s and r e l a t e d products discussed above. Compound 12^ and i t s o x i d a t i o n products are much weaker mutagens than a c t i v a t e d s u l f a l l a t e . The mutagenic a c t i v i t y of s u l f a l l a t e i s most e a s i l y explained by S-methylene h y d r o x y l a t i o n to give a proximate mutagen c l e a v i n g to 2-chloro a c r o l e i n , the u l t i m a t e mutagen and a microsomal oxidase metabo l i t e of s u l f a l l a t e . This hypothesis i m p l i e s , but does not depend, on the greater ease of S-CHL h y d r o x y l a t i o n of s u l f a l l a t e than of i t s thiocarbamate analog t l 2 ) . D i a l l a t e i s reported to be carcinogenic i n mice (30) and s u l f a l l a t e i n mice and r a t s (31). These h e r b i c i d e s are metaboliz ed to give 2 - c h l o r o a c r o l e i n , a potent mutagen. S-Methylene h y d r o x y l a t i o n may a l s o c o n t r i b u t e to the mutagenic a c t i v i t i e s of d i a l l a t e and t r i a l l a t e with 2,3-dichloro- and 2 , 3 , 3 - t r i c h l o r o a c r o l e i n s as the u l t i m a t e mutagens. These c h l o r o a c r o l e i n s may be the u l t i m a t e carcinogens as w e l l as the u l t i m a t e mutagens. Summary Ν,Ν-Dialkylthio- and dithiocarbamate h e r b i c i d e s i n c l u d e s e v e r a l S - a l k y l and S-benzyl compounds without mutagenic a c t i v i t y and three ^ - c h l o r o a l l y l d e r i v a t i v e s which are promutagens, j > - ( 2 , 3 - d i c h l o r o a l l y l ) Ν,Ν-diisopropylthiocarbamate ( d i a l l a t e ) , S - ( 2 , 3 , 3 - t r i c h l o r o a l l y l ) Ν,Ν-diisopropylthiocarbamate ( t r i a l l a t e ) and S - ( 2 - c h l o r o a l l y l ) Ν,Ν-diethyldithiocarbamate ( s u l f a l l a t e ) . D i a l l a t e and s u l f a l l a t e are a l s o carcinogens. A l a r g e number of



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SCHUPHAN ET AL.


products are i d e n t i f i e d from the p e r a c i d o x i d a t i o n of d i a l l a t e , t r i a l l a t e and s u l f a l l a t e . The i n i t i a l o x i d a t i o n products a r e s u l f o x i d e s with d i a l l a t e and t r i a l l a t e and a s u l f i n e with s u l fallate. Sulfoxides of the S - a l k y l , S-benzyl and S - c h l o r o a l l y l thiocarbamates d i f f e r g r e a t l y i n t h e i r s t a b i l i t y , r e a c t i o n s and biological activities. The ^-benzyl and S - a l k y l s u l f o x i d e s are moderately s t a b l e a t room temperature. The l a t t e r compounds with a β-hydrogen pyrolyze a t elevated temperatures by a c i s - e l i m i n a t i o n mechanism. Under p h y s i o l o g i c a l c o n d i t i o n s they r e a d i l y carbamylate t i s s u e t h i o l s such as g l u t a t h i o n e . Sulfoxides of SÎ-(3-chloroallyl), S - ( 2 , 3 - d i c h l o r o a l l y l ) and S - ( 2 , 3 , 3 - t r i c h l o r o a l l y l ) thiocarbamates are thermally unstable and q u i c k l y undergo [2,3] sigmatropic rearrangement followed by 1,2-elimination react i o n s to y i e l d the corresponding Ν,Ν-dialkylcarbamoylsulfenyl c h l o r i d e and a c r o l e i n , 2 - c h l o r o a c r o l e i n and 2 - c h l o r o a c r y l y l c h l o r i d e , r e s p e c t i v e l y . 2 - C h l o r o a c r o l e i n i s a metabolite of enzymatic s u l f o x i d a t i o n of d i a l l a t e and S-methylene h y d r o x y l a t i o n of s u l f a l l a t e . D i a l l a t e and t r i a l l a t e might a l s o y i e l d 2,3-dichloroa c r o l e i n and 2 , 3 , 3 - t r i c h l o r o a c r o l e i n on enzymatic ^-methylene hydroxylation. These h a l o a c r o l e i n s are very potent b a c t e r i a l mutagens. The h e r b i c i d a l a c t i v i t y of the S - a l k y l thiocarbamates i s probably associated with the carbamylating a c t i v i t i e s of t h e i r s u l f o x i d e metabolites, whereas the h e r b i c i d a l and mutagenic a c t i v i t i e s of the S - c h l o r o a l l y l t h i o - and dithiocarbamates may be due a t l e a s t i n part to the generation of potent c h l o r o a c r o l e i n mutagens and h e r b i c i d e s v i a s u l f o x i d e or S-hydroxymethylene intermediates. Acknowledgment Supported i n part by Grant 5 P01 ES 00049 from the N a t i o n a l I n s t i t u t e s of Health. Acknowledgement i s made to the ACS Petroleum Research Fund f o r p a r t i a l support of t r a v e l costs f o r I . Schuphan to p a r t i c i pate i n t h i s Symposium.

Literature Cited

1. Block, E. Amer. Chem. Soc. Symp. Ser., 1981,158 , 3 . 2. Neal, R. A. Amer. Chem. Soc. Symp. Ser., 1981,158,19 . 3. Casida, J. E.; Gray, R. Α.; Tilles, H. Science, 1974, 184, 573. 4. Casida, J. E.; Kimmel, E. C.; Ohkawa, H; Ohkawa, R. Pestic. Biochem, Physiol., 1975, 5, 1. 5. Casida, J. E.; Kimmel, E. C.; Lay, M.; Ohkawa, H.; Rodebush, J. E.; Gray, R. Α.; Tseng, C. K.; Tilles, H. Environ. Quai. Safety, Suppl. 1975, Vol. 3, 675. 6. Schuphan, I.; Rosen, J. D.; Casida, J. E. Science, 1979 205, 1013.




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7. Schuphan, I.; Casida, J. E. Tetrahedron Lett., 1979, 841. 8. Schuphan, I.; Casida, J. E. J. Agric. Food Chem., 1979, 27, 1060. 9. Tseng, C. K.; Below, J. F., J. Agric. Food Chem., 1977, 25, 1383. 10. Chen, Y. S.; Schuphan, I.; Casida, J. E. Agric. Food Chem., 1979, 27, 709. 11. Gozzo, F.; Masoero, M.; Santi, R.; Galluzzi, G.; Barton, D. H. R. Chem. & Ind., 1975, 221. 12. Mislow, K. Rec. Chem. Progr., 1967, 28, 217. 13. Bickart, P.; Carson, F. W.; Jacobus, J.; Miller, E. G.; Mislow, K. J. Am. Chem. Soc., 1968, 90, 4869. 14. Walker, F. H.; Gaughan, E. J. Deutsches Bundespatent Offenlegungsschrift, 1975, 2518544. 15. Lansbury, P. T.; Britt, R. W. J. Am. Chem. Soc., 1976, 98, 4577. 16. Segall, Y.; Schuphan, I.; Casida, J. E., Manuscript in preparation. 17. Zwanenburg, B.; Thys, L.; Strating, J. Tetrahedron Lett., 1967, 3453. 18. Zwanenburg, B.; Kielbasinski, P. Tetrahedron, 1979, 169. 19. Chen, Y. S.; Casida, J. E. J. Agric. Food Chem., 1978, 26, 263. 20. DeBaun, J. R.; Bova, D. L.; Tseng, C. K.; Menn, J. J. J. Agric. Food Chem., 1978, 26, 1098. 21. Hubbell, J. P.; Casida, J. E. J. Agric. Food Chem., 1977, 25, 404. 22. Rosen, J. D.; Schuphan, I.; Segall, Y.; Casida, J. E. J. Agric. Food Chem., 1980, 28, 880. 23. Lay, M.-M.; Hubbell, J. P.; Casida, J. E. Science, 1975, 189, 287. 24. Lay, M.-M.; Casida, J. E. Pestic. Biochem. Physiol., 1976, 6, 442. 25. Carere, Α.; Ortali, V. Α.; Cardamone, G.; Morpurgo, G. Chem.-Biol. Interact., 1978, 22, 297. 26. Sikka, H. C.; Florczyk, P. J. Agric. Food Chem., 1978, 26, 146. 27. De Lorenzo, F.; Staiano, N.; Silengo, L.; Cortese, R. Cancer Res., 1978, 38, 13. 28. Rosen, J. D.; Segall, Y.; Casida, J. E. Mutat. Res., 1980, 78, 113. 29. Ames, Β. N.; McCann, J.; Yamasaki, E. Mutat. Res., 1975, 31, 347. 30. Innes, J. R. M. et al. J. Natl. Cancer Inst., 1969, 42, 1101. 31. "Bioassay of sulfallate for possible carcinogenicity", Natl. Cancer Inst. Carcinogenesis Tech. Rep. Ser., 115, DHEW Publ. (NIH) 78-1370, 1978. RECEIVED February 17, 1981.


Toxicological Significance of Oxidation and Rearrangement Reactions

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