Chemistry Reference
In-Depth Information
O
R
2
R
1
O
O
O
R
1
= methyl
R
2
= CH=CH
2
Pyrethrin I
H
3
C
C
O
R
1
=
R
2
= CH=CH
2
Pyrethrin II
O
R
1
= methyl
R
2
= CH
2
CH
3
Jasmolin I
R
1
=
H
3
C
C
O
R
2
= CH
2
CH
3
Jasmolin II
O
H
3
C
C
O
R
1
= methyl
R
2
= CH
3
Cinerin I
R
1
=
R
2
= CH
3
Cinerin II
Pyrethroids often have two, three or more chiral centers and therefore can
have four, eight, or more stereoisomers. Sometimes they are sold as single
isomers, such as deltamethrin, useful for more than 150 crops including veg-
etables, fruits, cereals, oil seed rape, rice, soybeans, and corn. This pyrethroid
has eight possible stereoisomers. The chiral carbons are designated by an
asterisk in the depicted structure. The commercial product has R configu-
ration at each of the chiral cyclopropyl carbons and S at the cyanobenzylic
carbon. Deltamethrin is highly toxic to insects. Compared with pyrethrin I, it
is 1400 times as toxic to the housefly [29].
O
CN
Br
O
*
O
**
Br
Deltamethrin
Cypermethrin has eight possible stereoisomers; it is used as a mixture of
stereoisomers but only two of the eight are active. Typically the R configura-
tion at the cyclopropyl carbon alpha to the carbonyl of the ester is more active
than the S configuration; for example in permethrin it is 25 times more toxic
to houseflies than the R configuration [30].
R more toxic to houseflies
O
O
CN
Cl
Cl
O
O
O
**
*
O
Cl
**
Cl
Permethrin
Cypermethrin
Most mosquito devices such as coils, mats, or vaporizers contain
pyrethroids because mosquitoes are rapidly paralyzed and cannot suck
Search WWH ::
Custom Search