Insecticidal activity of cyanohydrin and monoterpenoid compounds

Article abstract of DOI:10.3390/50400648

The insecticidal activities of several cyanohydrins, cyanohydrin esters and monoterpenoid esters (including three monoterpenoid esters of a cyanohydrin) were evaluated. Topical toxicity to Musca domestica L. adults was examined, and testing of many compounds at 100 μg/fly resulted in 100% mortality. Topical LD₅₀ values of four compounds for M. domestica were calculated. Testing of many of the reported compounds to brine shrimp (Artemia franciscana Kellog) resulted in 100% mortality at 10 ppm, and two compounds caused 100% mortality at 1 ppm. Aquatic LC₅₀ for values were calculated for five compunds for larvae of the yellow fever mosquito (Aedes aegypti (L.)). Monoterpenoid esters were among the most toxic compounds tested in topical and aquatic bioassays.

Full text of DOI:10.3390/50400648

Molecules 2000, 5, 648-654
molecules
ISSN 1420-3049
http://www.mdpi.org
Insecticidal Activity of Cyanohydrin and Monoterpenoid
Compounds
1
2
3
1
Chris J. Peterson , Rong Tsao , Aimee L. Eggler and Joel R. Coats *
1
Department of Entomology, Iowa State University, Ames, IA 50011 USA
Tel.: (515) 294-4776, Fax: (515) 294-4757, E-mail: jcoats@iastate.edu
2
Agriculture Canada, Vineland, ON, Canada
3
Department of Biochemistry, University of Wisconsin - Madison, Madison, WI 53706 USA
*Author to whom correspondence should be addressed.
Received: 29 February 2000 / Accepted: 24 March 2000 / Published: 3 April 2000
Abstract: The insecticidal activities of several cyanohydrins, cyanohydrin esters and mono-
terpenoid esters (including three monoterpenoid esters of a cyanohydrin) were evaluated.
Topical toxicity to Musca domestica L. adults was examined, and testing of many com-
pounds at 100 mg/fly resulted in 100% mortality. Topical LD values of four compounds for
50
M. domestica were calculated. Testing of many of the reported compounds to brine shrimp
Artemia franciscana Kellog) resulted in 100% mortality at 10 ppm, and two compounds
caused 100% mortality at 1 ppm. Aquatic LC values were calculated for five compounds
(
50
for larvae of the yellow fever mosquito (Aedes aegypti (L.)). Monoterpenoid esters were
among the most toxic compounds tested in topical and aquatic bioassays.
Keywords: Cyanohydrin, monoterpenoid, insecticide.
Introduction
There is a growing need for effective, biodegradable pest-control compounds. Nineteen new major
pesticides were introduced from 1961 to 1970, eight from 1971 to 1980, and only three from 1981 to
1985 [1]. Several recent publications from our laboratory have reported insect activity in cyanohydrin
[2] and monoterpenoid compounds [3–5]. Naturally occurring cyanohydrins from flax, cassava, bam-
©
2000 by MDPI (http://www.mdpi.org). Reproduction is permitted for noncommercial purposes.

6
49
Molecules 2000, 5
boo, peach pits and almonds probably serve a chemical defense function in the plants to protect against
insect herbivory [6]. Hundreds of monoterpenoids are produced in plant essential oils, and apparently
serve a defensive function as well [7]. In the current work we report the synthesis and biological ac-
tivities of several new simple cyanohydrins, as well as novel cyanohydrin esters and monoterpenoid
esters. Three compounds were monoterpenoid esters of a potent synthetic cyanohydrin, 1-cyano-1-
hydroxy-2-propene (1; synonyms: CHP, 2-hydroxy-3-butenenitrile, acrolein cyanohydrin). CHP is an
analog of two naturally occurring cyanohydrins in flax. These three cyanohydrins, CHP, methyl ethyl
ketone cyanohydrin and dimethyl ketone cyanohydrin, have been shown to be potent insect fumigants
[2]. We examined the activity in topical application to adult house flies (Musca domestica L.), as well
as in aquatic bioassay to brine shrimp (Artemia franciscana Kellog) and the larvae of the yellow fever
mosquito (Aedes aegypti (L.)).
Results and Discussion
The cyanohydrins synthesized by the methods reported in this study and tested against the inverte-
brates are shown in Figure 1.
CN
CN
CN
OH
OH
OH
Citronellyl Cyanohydrin (2)
Citryl Cyanohydrin (3)
Cyanohydroxypropene
(
CHP) (1)
CN
CN
OH
OH
X
Cinnamyl Cyanohydrin (6)
X=H: Mandelonitrile (4)
X=OH: 4-Hydroxymandelonitrile (5)
Figure 1. Structures of cyanohydrin compounds tested in this study.
Figure 2 shows the structures of cyanohydrin esters synthesized by the reported methods. Note that
compounds 12, 13 and 15 are monoterpenoid esters of the cyanohydrin CHP (1).
CN
CN
O
X=Acetate (7)
X
=
=
=
=
Propionate (8)
Pivalate (9)
Acrylate (10)
Chloropropionate (11)
O
O
CHP-
=Decanoate (12)
=Citronellate (13)
=4-Fluorobenzoate (14)
=Cinnamate (15)
Mandelonitrile Acetate (16)
Figure 2. Structures of cyanohydrin esters.

6
50
Molecules 2000, 5
Figure 3 shows the structures of esters of two monoterpenoids, cinnamic acid and cironellic acid.
O
O
X
Y
O
O
Cinnamate
Citronellate
X=Methyl (17)
Y=Methyl (21)
=Propyl (22)
=Allyl (23)
=
=
=
Propyl (18)
Allyl (19)
Propargyl (20)
=Propargyl (24)
Figure 3. Monoterpenoid esters.
Topical testing on M. domestica showed that most of the cyanohydrins and their analogs had LD50
values between 10 and 100 mg/fly (Table 1). Monoterpenoid esters containing the alcoholic moieties
CHP (12, 13 and 15), propargyl (20 and 24) and allyl (19 and 23), all three of which are unsaturated,
were the most effective. The presence of the CHP moiety was not always associated with high toxicity,
and esterification of CHP with acetate, propionate or pivalate moieties produced less effective com-
pounds than esterification of CHP with monoterpenoid moieties (compare 7–9 to 12, 13 and 15 in Ta-
ble 1). More studies need to be conducted in order to determine the nature of toxicity in relation to
structure.
Table 1. Results of topical toxicity testing on M. domestica (percentage mortality).
N°
1
Compound
CHP
100 mg/fly 10 mg/fly 1 mg/fly
100
100
100
80
0
0
5
0
7
CHP acetate
8
CHP propionate
CHP pivalate
CHP decanoate
CHP citronellate
CHP cinnamate
Methyl cinnamate
Propyl cinnamate
Allyl cinnamate
0
0
9
0
0
1
1
1
1
1
1
2
2
2
2
2
2
3
5
7
8
9
100
100
87
64
91
50
0
0
0
0
50
10
0
38
0
100
100
57
40
35
5
4
0 Propargyl cinnamate
0
1
2
3
Methyl citronellate
Propyl citronellate
Allyl citronellate
4
41
0
0
100
100
0
17
15
5
4 Propargyl citronellate
0
Control (acetone blank)

6
51
Molecules 2000, 5
The three cyanohydrin-monoterpenoid esters were among the most toxic compounds tested, with
CHP citronellate (13) being the most toxic, showing 91% mortality at 10 mg/fly. CHP decanoate (12),
CHP cinnamate (15), allyl cinnamate (19) and propargyl cinnamate (20) showed appreciable mortality
at 10 mg/fly as well. Topical LD values on M. domestica (95% fiducial limit) were calculated by us-
5
0
ing SAS [8] and are reported in Table 2.
Table 2. Topical LD values to Musca domestica (expressed in mg/fly) and 95% fiducial limits.
5
0
N°
2
3
4
5
Compound
LD50
> 50
> 50
7.06
33.1
12.7
14.5
95% FL
Citronellyl cyanohydrin
Citryl cyanohydrin
Mandelonitrile
5.45, 8.54
25.5, 47.5
10.2, 15.7
11.8, 17.8
4-Hydroxy mandelonitrile
Cinnamyl cyanohydrin
Mandelonitrile acetate
6
1
6
Aquatic testing with A. franciscana resulted in 100% mortality at 100 ppm for nearly all compounds
tested (Table 3).
Table 3. Results of acute (24-hr) toxicity testing on Artemia franciscana (percentage mortality).
N°
1
3
6
7
Compound
CHP
Citryl cyanohydrin
Cinnamyl cyanohydrin
CHP acetate
100 ppm 10 ppm 1 ppm
100
87
63
0
20
0
100
0
15
0
25
0
9
CHP pivalate
CHP acrylate
100
100
100
100
100
20
100
100
100
100
100
100
100
100
100
4
30
43
43
95
23
30
33
15
40
13
95
35
65
95
90
45
100
100
25
1
1
1
1
1
1
1
1
1
2
2
2
2
2
0
1 CHP chloropropionate
2
3
CHP decanoate
CHP citronellate
100
27
100
80
100
100
100
100
100
100
64
4 CHP 4-fluorobenzoate
5
7
8
9
CHP cinnamate
Methyl cinnamate
Propyl cinnamate
Allyl cinnamate
0 Propargyl cinnamate
1
2
3
Methyl citronellate
Propyl citronellate
Allyl citronellate
4 Propargyl citronellate
Control

6
52
Molecules 2000, 5
Several compounds showed 100% mortality at 10 ppm, and two compounds, propyl citronellate
(
22) and allyl citronellate (23), displayed 100% mortality at 1 ppm. The most toxic compounds tested
on A. franciscana were esters of cinnamic acid or citronellic acid. Esterification of CHP with monoter-
penoid moieties produced more effective compounds than esterification with the smaller moieties
(
compare 12, 13 and 15 to 7 and 9–11 in Table 3). The cyanohydrins and cyanohydrin esters were of
lower toxicity than monoterpenoid esters (17–24), except for CHP citronellate (13) and CHP cin-
namate (15).
Aquatic LC values (95% fiducial limit) for A. aegypti larvae were calculated by using SAS [8] and
50
are reported in Table 4.
Table 4. LD values (expressed in ppm) to Aedes aegypti larvae and 95% fiducial limits.
5
0
N°
1
Compound
CHP
LC50
2.75
8.22
5.19
14.0
3.77
95% FL
1.94, 3.80
4.59, 17.8
3.55, 7.72
9.68, 23.9
1.78, 7.78
9
CHP pivalate
1
1
1
0
1
4
CHP acrylate
CHP chloropropionate
CHP 4-fluorobenzoate
For all tests, it appeared that esterification of CHP (1) with a nonmonoterpenoid moiety resulted in
equal or lower activity in relation to CHP itself, and this was possibly related to moiety size and polar-
ity. This result was also seen in the comparison of mandelonitrile (4) to mandelonitrile acetate (16) in
topical LD values for M. domestica. Esterification of CHP with a monoterpenoid moiety, however,
50
resulted in equal or higher activity in relation to CHP in topical and aquatic testing. Only three CHP-
monoterpenoid esters were tested in this study; therefore, any conclusions regarding comparative ef-
fectiveness due to the properties of the monoterpenoid moieties are speculative. It is possible that their
hydrolysis in vivo results in two insecticidal moieties, CHP and a monoterpenoid acid.
The limited series presented here indicates that alcoholic moieties containing double or triple bonds
may be more effective than saturated ones, as methyl and propyl monoterpenoid esters were less ef-
fective than CHP, allyl or propargyl esters. Monoterpenoid esters were in most cases more toxic than
monoterpenoid cyanohydrins. Esterification of some monoterpenoids has been demonstrated previ-
ously to enhance insecticidal activity [4,5].
Experimental
The structures of compounds 1–6 are shown in Figure 1, and the numerical designations used in this
paper are as follows: 1-cyano-1-hydroxy-2-propene (CHP) (1), citronellyl cyanohydrin (i. e., the cya-
nohydrin synthesized from citronellal) (2), citryl cyanohydrin (3), mandelonitrile (4), 4-hydroxy-
mandelonitrile (5) and cinnamyl cyanohydrin (6).

6
53
Molecules 2000, 5
Structures of cyanohydrin esters are shown in Figure 2, and are named as follows: CHP acetate (7),
CHP propionate (8), CHP pivalate (9), CHP acrylate (10), CHP 3-chloropropionate (11), CHP de-
canoate (12), CHP citronellate (13), CHP 4-fluorobenzoate (14), CHP cinnamate (15) and mandeloni-
trile acetate (16).
Monoterpenoid esters tested are shown in Figure 3: methyl cinnamate (17), propyl cinnamate (18),
allyl cinnamate (19), propargyl cinnamate (20), methyl citronellate (21), propyl citronellate (22), allyl
citronellate (23) and propargyl citronellate (24).
Compounds 1–3 and 6 were synthesized from potassium cyanide and their corresponding aldehyde.
Stoichiometric amounts of potassium cyanide, the reactant aldehyde and glacial acetic acid were re-
quired. Potassium cyanide (KCN) was added to anhydrous diethyl ether and stirred with a magnetic
stir bar. The aldehyde corresponding to the desired cyanohydrin was added slowly to the reaction
mixture. Glacial acetic acid was added, and the reaction proceeded until the reactant aldehyde was no
longer detected by thin-layer chromatography. The ethereal reaction mixture was washed three times
with a saturated aqueous NaHCO solution, and the aqueous portion was back-extracted with three
3
volumes of diethyl ether and the water layer discarded. The diethyl ether was removed by rotary
evaporation, and the product purified by using column chromotography as necessary. Compounds 4
and 5 were purchased from Sigma Chemical (St. Louis, MO, USA).
Cyanohydrin esters 8–11, 14 and 16 were synthesized from their corresponding cyanohydrins and
acid chlorides, following the method of Rice and Coats [4]. A method more suitable for synthesizing
esters from cyanohydrins and carboxylic acids, utilizing dimethylaminopyridine (DMAP) and dicyclo-
hexylcarboxiimide (DCC), was used for esters 12–13 and 15 [5]. This method was also used for the
synthesis of monoterpenoid esters 17–24. Compound 7 (also known as 2-acetoxy butenenitrile) was
purchased from Aldrich Chemical (Milwaukee, WI, USA).
Topical bioassays to M. domestica (Orlando regular strain) were conducted after Rice and Coats [4]
using a 1-ml volume of acetone to deliver the chemical to the thoracic venters of house flies. The mos-
quito larvae (A. aegypti) and brine shrimp (A. franciscana) were tested by adding the chemical to water
according to the method of Tsao et al. [9]. The mosquito larvae were provided by Dr. W. A. Rowley,
Medical Entomology Laboratory at Iowa State University, Ames, IA. The brine shrimp were pur-
chased from Carolina Biological Supply (Burlington, NC).
Acknowledgments: We thank the Program for Women in Science and Engineering at Iowa State Uni-
versity, Ames, IA. We also thank the Iowa Soybean Promotion Board for partial funding of this proj-
ect. This is journal paper J-18803 of the Iowa Agriculture and Home Economics Experiment Station,
Iowa State University, Ames, IA, project number 3187.

6
54
Molecules 2000, 5
References and Notes
1
.
Ku, H. S. Potential industrial applications of allelochemicals and their problems. In Allelochemi-
cals: Role in Agriculture and Forestry; ACS Symposium Series #330, American Chemical Soci-
ety: Washington, DC, 1987; pp 449–454.
2
3
.
.
Peterson, C. J.; Tsao, R.; Coats, J. R. Naturally occurring cyanohydrins, analogues and derivatives
as potential fumigants. Pest Management Science (in press).
Lee, S.; Tsao, R.; Coats, J. R. Influence of dietary applied monoterpenoids and derivatives on sur-
vival and growth of the European corn borer (Lepidoptera: Pyralidae). J. Econ. Entomol. 1999,
9
2, 56–67.
Rice, P. J.; Coats, J. R. Insecticidal properties of monoterpenoid derivatives to the house fly
Diptera: Muscidae) and the red flour beetle (Coleoptera: Tenebrionidae). Pestic. Sci. 1994, 41,
95–202.
4
5
.
.
(
1
Tsao, R.; Lee, S.; Rice, P. J.; Jensen, C.; Coats, J. R. Monoterpenoids and their synthetic deriva-
tives as leads for new insect-control agents. In Synthesis and Chemistry of Agrochemicals IV;
Feynes, J. G.; Basarab, G. S., Eds.; ACS Symposium Series, American Chemical Society: Wash-
ington, DC, 1995; pp 312–324.
6
7
.
.
Tewe, O. O.; Iyayi, E. A. Cyanogenic glycosides. In Toxicants of Plant Origin, vol. II; Cheeke, P.
R., Ed.; CRC Press: Boca Raton, FL, 1989; pp 43–60.
Wise, M. L.; Croteau, R. Monoterpene biosynthesis. In Comprehensive Natural Products Chem-
istry, Vol. 2; Barton, D.; Nakanishi, K.; Meth-Cohn, O., Eds.; Elsevier: Amsterdam, 1999; pp 97–
1
53.
8
9
.
.
SAS Institute, Ultrix SAS, Version 6.09 SAS User’s Guide. SAS Institute, Cary, NC, 1991.
Tsao, R.; Reuber, M.; Johnson, L.; Coats, J. R. Insecticidal toxicities of glucosinolate–containing
extracts from crambe seeds. J. Agric. Entomol. 1996, 13, 109–120.
Samples Availability: Available from the authors.
©
2000 by MDPI (http://www.mdpi.org). Reproduction is permitted for noncommercial purposes.