Compounds of formula ##STR1## in which R represents hydrogen, formyl or an alkanoyl group of two to twenty-five carbon atoms and R' represents an alkyl group of one to thirty-five carbon atoms are of value as mosquito attractants, mosquitoes being attracted to a location where they and/or their eggs or larvae are then destroyed.

This invention relates to compounds having activity as oviposition 
attractants for mosquitoes and to the use of these compounds in mosquito 
control. 
The eggs of the mosquitoes Culex pipiens fatigans (=quinquefasciatus), 
Culex pipiens pipiens, Culex pipiens molestus and Culex tarsalis have 
previously been studied with a view to identification of the natural 
oviposition attractant which is present therein. The eggs have been found 
to contain a mixture of 1,3-diglycerides of mono- and di-acetoxy fatty 
acids and these glycerides have been identified as being responsible for 
the natural oviposition attractive effect of the eggs. These compounds are 
of interest in mosquito control in view of the involvement of mosquitoes 
of this genus in various parts of the world in the spread of various 
diseases, for example Culex pipiens fatigans acting as a vector for 
filarial disease (Wuchereria bancrofti) known as elephantiasis, Culex 
tarsalis for Western equine encephalitis, the Culex tritaeniorhynchus 
group for Japanese B encephalitis and other viral diseases, and the Culex 
pipiens group for Rift Valley fever. 
We have now isolated from the apical droplets of eggs of Culex pipiens 
fatigans further, non-glyceride, oviposition attractants having a 
structure which is an unusual one among pheromones. These attractants, 
whose existence was previously quite unexpected, are present in the apical 
droplet of the eggs in only small amounts but they are significantly more 
potent as oviposition attractants for mosquitoes of this general type than 
the previously reported glyceride oviposition attractants. These newly 
discovered compounds, together with certain analogues thereof, are 
therefore of considerable interest for use in mosquito control. 
Accordingly, the present invention comprises a compound of formula 
##STR2## 
in which R represents hydrogen, formyl or an alkanoyl (alkyl-CO-) group of 
two to twenty-five carbon atoms and R' represents an alkyl group of one to 
thirty-five carbon atoms. 
The major naturally occurring compound of this type is 
6-acetoxy-5-hexadecanolide but we have also identified the compounds 
6-hydroxy-5-hexadecanolide and 6-acetoxy-5-tetradecanolide as occurring in 
mosquito eggs. However, whilst compounds (I) in which R is hydrogen or 
especially an acetyl group are of particular interest, as are compounds 
(I) in which R' is n-octyl or particularly n-decyl, variations from the 
naturally occurring structures through the presence of a formyl group or 
of other branched or, more preferably, straight chain alkanoyl or alkyl 
groups, for example propionyl in the case of R and n-hexyl or n-dodecyl in 
the case of R', are also of interest. In particular, the presence of a 
smaller alkyl group R', for example of as few as six, four or even less 
carbon atoms, may be of value in some circumstances through the consequent 
increase in volatility of the compound (I). Similarly, the presence of an 
alkyl group R' larger than C.sub.8 -C.sub.10 or an alkanoyl group R larger 
than C.sub.2 may be of value in the preparation of long acting 
compositions through the consequent decrease in volatility. Such higher 
molecular weight compounds may also be advantageous through a consequent 
reduction in water solubility, although 6-acetoxy-5-hexadecanolide itself 
already has only a low water solubility. An increase in the molecular 
weight of the compound through an increase in the size of R' rather than 
of R is preferred in view of the lesser effect upon the oviposition 
attractant activity of the compound. Thus, a molecular weight of about 600 
may conveniently be achieved through an increase in the size of R' by 
about twenty carbon atoms rather than of R or of both R and R' by about 
ten carbon atoms. Accordingly a preferred upper limit of size for an 
alkanoyl group comprising R is less than twenty-five or even twenty carbon 
atoms, an upper limit of ten carbon atoms or more especially only three, 
four or five carbon atoms being preferred, whilst an increase in the size 
of an alkyl group comprising R' not only to fourteen, sixteen or eighteen 
carbon atoms, but also to twenty, twenty-five or thirty carbon atoms, may 
be more readily accepted. 
6-Acetoxy-5-hexadecanolide occurs naturally in the erythro form and 
accordingly compounds (I) having an erythro configuration are of rather 
greater interest than those of the threo configuration. It will be 
appreciated that compounds of both the erythro and the threo configuration 
may exist in optically active forms and that one of the d(+) or l(-) 
isomers may be of particular interest by virtue of its possession of an 
enhanced property, particularly biological activity, as compared with the 
other or with the racemic, dl, mixture. However it is of interest that, 
somewhat unusually, the racemic mixture itself shows a high level of 
activity. 
Specific compounds according to the present invention, in increasing order 
of interest, are 6-hydroxy-5-tetradecanolide, 6-acetoxy-5-tetradecanolide, 
6-hydroxy-5-hexadecanolide and 6-acetoxy-5-hexadecanolide. The d- and 
1-erythro isomers of the last mentioned compound have the structures shown 
below (Ac representing acetyl) 
##STR3## 
Although certain of the compounds (I) occur naturally, it is preferred to 
prepare the compounds synthetically for use as oviposition attractants. 
Compounds in which R is hydrogen and those in which R is a formyl or other 
acyl group may each conveniently be prepared from a compound of formula 
EQU HO.sub.2 C--(CH.sub.2).sub.3 --CH(OH)--CH(OH)--R' (II) 
as a precursor. When R is hydrogen such a precursor may be treated with a 
strong inorganic acid such as hydrochloric acid, and then extracted into 
an organic solvent, to effect formation of the .delta.-lactone having a 
hydroxy group adjacent to the ring. Compounds having R.dbd.H may, however, 
be obtained in admixture with the corresponding open chain dihydroxy 
compound (II). When R is acyl, the appropriate anhydride (RCO).sub.2 O or 
acid chloride RCOCl may be used, for example in the presence of an organic 
base such as dry pyridine in the case of the anhydride, to effect 
formation of the .delta.-lactone having an acyloxy group adjacent to the 
ring, or, where R is a higher acyl group than acetyl, acetic anhydride may 
be used initially and acidolysis may then be employed to modify the 
resulting acetoxy group. Such acidolysis may conveniently be effected by 
heating the acetoxy compound with a higher molecular weight acid, an 
appropriate catalyst such as p-toluene sulphonic acid being used where 
desirable. Alternatively, compounds (I) in which R is acyl may be prepared 
by the esterifiction of the corresponding compound in which R is hydrogen 
and compounds (I) in which R is hydrogen may be prepared by the hydrolysis 
of the corresponding compound in which R is acyl, the lactone ring being 
re-formed, if opened by hydrolysis under basic conditions, through 
treatment with strong acid. 
A compound (I) of the erythro or threo configuration may be prepared by the 
use of a precursor having the appropriate configuration. For instance, the 
erythro or threo dihydroxy acid (II) may be used, this conveniently being 
obtained by hydroxylation under suitable conditions of the appropriate (Z) 
or (E) unsaturated acid. Thus, the erythro isomer may be obtained by the 
cis hydroxylation, for example with potassium permanganate, of the (Z) 
unsaturated acid or by the trans hydroxylation, for example with hydrogen 
peroxide, of the (E) unsaturated acid. If a d or l isomer is required, 
substantially free from the other of these isomers, a resolution step must 
be introduced into the synthesis and conveniently such a resolution may be 
effected using a compound of formula (I) rather than a precursor such as a 
compound of formula (II). One convenient approach involves the preparation 
of a diastereoisomeric mixture from the substantially pure erythro or 
threo form of the compound (I) in which the appropriate group R' is 
present but which has a group R which is hydrogen. Such a mixture may be 
readily obtained by treatment of this compound (I) with a pure isomer of 
an optically active esterifying agent such as l- or particularly 
d-.alpha.-methoxy-.alpha.-trifluoromethylphenylacetyl chloride. The 
diastereoisomers may then be separated, for example by thin layer 
chromatography or high pressure liquid chromatography, and the appropriate 
isomer then hydrolysed to yield the required d or l compound (I) in which 
R is hydrogen and which may then be esterified where the desired compound 
(I) has a group R which is acyl. An alternative approach involves the 
acidolysis of a compound (I) in which R is acetyl by treatment with a pure 
isomer of an optically active acid such as l- or particularly 
d-.alpha.-methoxy-.alpha.-trifluoromethylphenylacetic acid to give a 
diastereoisomeric mixture which may be similarly separated. Acidolysis 
will then yield the required d or l optically pure compound (I) in which R 
is acyl. 
It will be appreciated that whether the compounds (I) are obtained by 
isolation from nature or, more preferably, synthetically, they are 
conveniently prepared in substantially pure form, i.e. substantially free 
from by-products of manufacture not having the formula (I) shown 
hereinbefore. Although the compounds (I) may be used in the present 
invention in the form of a composition containing more than one such 
compound in which R and/or R' may differ, for example as a mixture of two 
or more of the three naturally occurring compounds (I) referred to 
hereinbefore, it is in practice preferable for the compounds (I) initially 
to be prepared substantially free even from by-products of manufacture of 
a different formula (I) and for any mixture which is used to be produced 
by the deliberate mixing of selected proportions of different compounds 
(I). The use of a mixture of stereoisomers of a compound of a particular 
formula (I) will often be acceptable, although as indicated previously, it 
may in some circumstances be worthwhile preparing the compound in its 
erythro or threo form, which may conveniently be substantially free from 
the other such form, or even as the optically active d or l isomer of one 
of such forms, which may conveniently be substantially free from the other 
such optically active isomer. The words "substantially free from" have 
been used herein particularly to indicate a purity of 90% or more by 
weight. 
Alternative approaches which may be considered for the preparation of a 
synthetic compound (I) for use as an oviposition attractant are the in 
situ preparation of the compound from a precursor thereof, for example the 
use of a dihydroxy acid (II), an ester thereof formed at the carboxyl 
group, or a diglyceride of such compounds, which compound is cyclised in 
situ, conveniently by microbiological action or chemical, including 
enzymic, action. The deliberate preparation of the compounds by 
microbiological action does of course constitute synthetic preparation 
equally with chemical synthesis. 
Moreover, it will be appreciated that the compounds described herein may 
also be prepared by other procedures than those described, particularly by 
other procedures described in the art for the preparation of related 
compounds of a similar type. 
The value of compounds according to the present invention lies in their use 
in the attraction of mosquitoes of the genus Culex, particularly gravid 
female mosquitoes, and also of certain other genera, especially those 
related genera of egg raft laying mosquitoes. Such mosquitoes are 
conveniently attracted to particular sites which are further treated 
either concommitantly or subsequently to kill the young mosquitoes in the 
egg or larval form and/or, more particularly, to kill the adult, 
particularly adult female, mosquitoes. Mosquitoes genrally lay their eggs 
on water and the compounds are therefore conveniently applied in the 
vicinity of or preferably directly on the surface of areas of water where 
the mosquitoes may be expected to breed naturally, for example water in 
proximity to human habitation such as is present in artificial containers, 
tanks, drains, cess pits etc., or alternatively to artificially created 
areas of water, for example water contained in conveniently positioned 
receptacles. This method may be applied with particular advantage to 
domestic habitats where there is close association between the disease 
vector and man. The invention thus includes a method for use in mosquito 
control which comprises applying a compound (I) as defined above to a 
location for the purpose of attracting mosquitoes to that location, 
mosquitoes attracted thereto by the compound (I) and/or their eggs or 
larvae then being destroyed. 
For use as described above, the compounds (I) may be formulated in various 
ways and the invention includes a mosquito attractant composition 
comprising a compound (I) as defined above together with a suitable 
diluent or carrier. Such compositions may consist of an oil based 
formulation or an aqueous formulation, which latter may conveniently 
contain a suitable amount, for example up to about 20%, particularly about 
10%, by volume of an emulsifying agent, especially a non-ionic surface 
active agent which may conveniently be one based on a polyether structure, 
for example polyoxyethylene stearate or nonylphenylpolyethoxyethanol. The 
use of a surface active agent will promote contact of the composition with 
the site to which it is applied but care should be taken to avoid unduly 
solubilising the compound (I). Other components may also be included in 
the composition and, although many of the compounds (I) have a very low 
solubility in water, it may be advantageous to include an agent such as a 
silicone oil in the composition to further prevent mixing of the 
composition with the water usually present at the location to which it is 
applied. Techniques such as electrostatic spraying may of course be used 
for applying the composition, where appropriate, and may even enable the 
compound (I) to be applied without the addition of a diluent or carrier. 
The compounds may also be applied in monolayers or by the use of various 
other techniques known in the art, for example in microencapsulated form. 
Formulations for domestic use, for example as aerosols, are also of some 
interest. 
Although the mosquitoes, once attracted, may be destroyed by physical 
means, for example by trapping at the location to which the compound (I) 
is applied, it is often more convenient to use some form of insecticidal 
agent to destroy the eggs, larvae or adult mosquitoes. A wide variety of 
agents may be used for this purpose either in the bulk of water at the 
site of application or on the surface thereof, including inorganic poisons 
and even the production of a high salt level in the water. Organic 
pesticides are, however, of especial interest, particularly pyrethroid 
pesticides, for example permethrin, organophosphorus pesticides, for 
example malathion or fenitrothion and some carbamates, for example 
carbaryl, etc. Compounds of particular value as ovicides or larvicides, 
such as chlorpyrifos, temephos, diflubenzuran, chlorodimeform, growth 
regulators such as methoprene and dimilin, pathogenic organisms, such as 
Bacillus thuringensis, or their toxins, larvicidal pellets, dusts and oils 
may be utilized alone or together with insecticides such as those 
described above which are of particular value for use against adult 
mosquitoes. The insecticides may be applied subsequently to the attractant 
compound (I) in a separate procedure but it is particularly convenient for 
the insecticide or insecticides to be applied together with this compound. 
An especially convenient aspect of the present invention consists of a 
mosquito control composition comprising as active components thereof a 
compound (I) as defined above together with an insecticide. 
Whilst quantitative details of the use of the compounds (I) will depend on 
various factors, not least the particular compound (I) employed, it is an 
indication of the level of activity of these compounds that in laboratory 
tests synthetic 6-acetoxy-5-hexadecanolide has been shown to act as an 
attractant for gravid Culex mosquitoes at levels as low as the equivalent 
of one sixteenth of an egg raft (i.e. at a level of 0.02 .mu.g, each Culex 
pipiens fatigans egg raft containing only about 0.3 .mu.g of 
6-acetoxy-5-hexadecanolide) and such activity has been found to be 
maintained over a range of up to about four hundred times this level. Such 
a wide range indicates considerable latitude with regard to the critical 
dosage required in the field. In practice, however, although activity at 
very low levels has been observed in the laboratory, it may be desirable 
to use a larger amount of 6-acetoxy-5-hexadecanolide, or of the equivalent 
amount of another compound (I), for example an amount of as much as 25, 50 
or 100 micrograms or even more being applied per week to a particular site 
with due attention being given to the size of a site, so that a natural 
site containing a large surface area of water will require more compound 
than a smaller artificial receptacle. 
The invention is illustrated by the following examples.

EXAMPLE 1 
Isolation from the Apical Droplets of Mosquito Eggs of 
6-Acetoxy-5-hexadecanolide, 6-Hydroxy-5-hexadecanolide and 
6-Acetoxy-5-tetradecanolide 
Apical droplets are removed on fine glass rods from eggs of Culex pipiens 
fatigans and are dissolved in hexane. Examination of the volatile 
components present in this extract using gas chromatography/mass 
spectrometry [Flexsil capillary column, 25 m.times.0.2 mm, OV101, 
50.degree. C. (10 minutes) 4.degree. C./minute 200.degree. C., He 1 
ml/min, directly coupled to m.s. electron impact, 70 eV, 200.degree. C.] 
shows a major peak (R.sub.t 64 minutes, relative ion current 100) together 
with other peaks including a peak of R.sub.t 59 minutes with a relative 
ion current of 25 and a peak of R.sub.t 53 minutes with a relative ion 
current of 20. The compounds of R.sub.t 64, 59 and 53 minutes are, 
respectively, 6-acetoxy-5hexadecanolide, 6-hydroxy-5-hexadecanolide and 
6-acetoxy-5-tetradecanolide. 
Thin layer chromatography of the hexane solution on silica gel 60 (0.25 mm) 
with ether gives a series of spots detectable in control with iodine 
vapour. The material from the R.sub.f 0.39 region of the plate is removed 
and the silica gel extracted with ether. Evaporation of the solution gives 
a residue of erythro-6-acetoxy-5-hexadecanolide together with some lower 
R.sub.t components including 6-acetoxy-5-tetradecanolide. 
In order to obtain the three compounds in substantially pure form 
preparative thin layer chromatography is used to separate the two acetoxy 
compounds from the hydroxy compound and/or preparative gas liquid 
chromatography is used to separate the two acetoxy compounds (and also the 
hydroxy compound). The yield of erythro-6-acetoxy-5-hexadecanolide 
obtained is about 0.3 micrograms per egg raft. The compound isolated from 
the natural source has similar n.m.r. and m.s. spectra and t.l.c. 
behaviour to be synthetic compound of Example 2. 
EXAMPLE 2 
Preparation of 6-Acetoxy-5-hexadecanolide 
(1A) 1-Bromoundecane 
Undecanol (14 g), 48% aqueous hydrobromic acid (30 g) and concentrated 
sulphuric acid (5 ml) are heated together under reflux for 51/2 hours. 
After cooling, water is added and the organic layer is separated, washed 
with concentrated sulphuric acid (20 ml), brine (50 ml) and dilute aqueous 
sodium carbonate (50 ml), and is then dried over calcium chloride. 
Distillaion under vacuum gives 1-bromoundecane (12 g) as a yellow oil, 
b.p. 60.degree.-70.degree. C./0.1 mm. 
(1B) Ethyl 5-oxopentanoate 
Ethyl 5-bromopentanoate (42 g), sodium bicarbonate (34 g) and pyridine 
N-oxide (38 g) in toluene (250 ml) are heated together under reflux in an 
atmosphere of nitrogen with vigorous stirring for 9 hours. After cooling, 
the product is partitioned with water (400 ml). The toluene layer is 
separated and the aqueous layer is extracted with a further amount of 
toluene (100 ml). The combined toluene extracts are dried over magnesium 
sulphate and the toluene removed by fractional distillation. The residue 
is distilled under vacuum to give ethyl 5-oxopentanoate as a colourless 
oil (14.1 g), m.s. M.sup.+ 144. 
(2) (Z)-Hexadec-5-enoic Acid 
Undecyltriphenylphosphonium bromide (16.3 g, prepared by heating 
1-bromoundecane and triphenylphosphine together in refluxing xylene) is 
suspended in dry ether (400 ml) and the mixture is stirred under nitrogen 
whilst 1.7M butyllithium in hexane (47.5 ml) is added from a syringe. The 
resulting bright red solution is cooled to 10.degree. C. and treated 
dropwise with ethyl 5-oxopentanoate (7.25 g) in dry ether (50 ml). After 
10 minutes, water (200 ml) is added and when the solid product has 
dissolved the ether layer is separated and the aqueous layer is washed 
with ether (3.times.100 ml). The combined ethereal solutions are dried 
over magnesium sulphate and the ether is evaporated. The residue is shaken 
with hexane (200 ml), and the mixture is cooled and filtered. The filtrate 
is concentrated to a volume of 100 ml and then cooled to allow 
crystallisation of the triphenylphosphine oxide. When this is complete, 
the mixture is filtered and the filtrate is evaporated to yield ethyl 
(Z)-hexadec-5-enoate in crude form as a yellow oil (10.1 g). 
The above oil is mixed with 10% w/v aqueous sodium hydroxide solution (120 
ml), tetrahydrofuran (120 ml) and methanol (120 ml) and the mixture is 
heated under reflux in an atmosphere of nitrogen for 45 minutes. After 
cooling and filtering, the filtrate is acidified to litmus with 14% w/v 
hydrochloric acid. The product is extracted with ether (2.times.100 ml), 
and the extract is dried (MgSO.sub.4) and evaporated to yield 
(Z)-5-hexadecenoic acid as a straw coloured oil (6.8 g), m.s. M.sup.+ 254, 
.sup.13 C n.m.r. (CDCl.sub.3 /TMS) -26.6 (4C) and -27.3 (7C) p.p.m. 
(3) dl-erythro-5,6-Dihydroxyhexadecanoic Acid 
(Z)-5-Hexadecenoic acid (6 g) is dissolved in 0.3M aqueous potassium 
hydroxide (120 ml) and the stirred solution is cooled to 0.degree. C. and 
treated with 0.5M aqueous potassium permanganate (32 ml). The resulting 
product is centrifuged and the supernatant liquid is removed. The 
remaining residue is resuspended in 0.3M aqueous potassium hydroxide (120 
ml) and the product again centrifuged and the supernatant liquid removed. 
The combined supernatants are acidified with 25% v/v acetic acid and the 
resultant precipitate is filtered off and washed with ether to give 
dl-erythro-5,6-dihydroxyhexadecanoic acid as a white powder (1.5 g), m.p. 
122.degree.-123.degree. C., .nu..sub.max (nujal) 1700 cm.sup.-1. On 
recrytallisation from ethanol traces of the threo isomer are removed to 
give pure dl-erythro-5,6-dihydroxyhexadecanoic acid as colourless crystals 
(190 mg from 200 mg), m.p. 125.degree. C. 
4(a) dl-erythro-6-Acetoxy-5-hexadecanolide 
dl-erythro-5,6-Dihydroxyhexadecanoic acid (4 mg) is treated with acetic 
anhydride (20 .mu.l) in dry pyridine (50 .mu.l) for 12 hours. Water (200 
.mu.l) is then added and the resultant mixture is extracted with ether 
(200 .mu.l). After washing with water (3.times.200 .mu.l) the ether 
extract is dried over magnesium sulphate and the ether is evaporated to 
give dl-erythro-6-acetoxy-5-hexadecanolide as a colourless oil (3 mg), 
.delta.(.sup.1 H n.m.r. in CDCl.sub.3 /TMS) 0.88 (tr, CH.sub.3), 1.26 (m, 
8.times.CH.sub.2), 1.69-2.00 (m, 3CH.sub.2, 4CH.sub.2 and 7CH.sub.2), 2.08 
(s, CH.sub.3 CO), 2.53 (m, CH.sub.2 CO), 4.35 (m, 6CH or 5CH), 4.98 (m, 
5CH or 6CH); t.l.c. (silica gel 60, 0.25 mm, with ether) single spot of 
R.sub.f 0.39; g.c.m.s. (under conditions indicated in Example 1) single 
peak of R.sub.t 64 minutes with M.sup.+ 312 and other e.i. mass spectrum 
peaks including m269 (1.0%) and m252 (3.3%). 
4(b) dl-erythro-6-Acetoxy-5-hexadecanolide 
dl-erythro-5,6-Dihydroxyhexadecanoic acid (2 g) is dissolved in acetyl 
chloride (7 ml) and the solution allowed to stand overnight at room 
temperature. Ether (30 ml) and water (30 ml) are then added with cooling. 
The organic phase is washed with water (30 ml), aqueous sodium bicarbonate 
(3.times.30 ml) and brine (30 ml), and then dried (MgSO.sub.4.H.sub.2 O). 
The dried solution is evaporated to give 
dl-erythro-6-acetoxy-5-hexadecanolide as a straw coloured oil (1.5 mg) 
with physical properties identical to those of the product obtained under 
4(a). 
NOTE: The compound dl-threo-6-acetoxy-5-hexadecanolide is prepared by an 
exactly similar procedure from (E)-hexadec-5-enoic acid. The properties of 
this compound differ in that it has an R.sub.t value on g.c.m.s. of 66 
minutes and gives more intense ions at m269 (3.8%) and m252 (6.2%). 
EXAMPLE 3 
Preparation of dl-erythro-6-Acetoxy-5-dodecanolide 
(1) (Z)-Dodec-5-enoic Acid 
Heptyltriphenylphosphonium bromide (16.8 g), prepared from 1-bromoheptane 
and triphenylphosphine analogously to undecyltriphenylphosphonium bromide 
as described in Example 2(2), is suspended in dry ether (300 ml) and the 
mixture is treated whilst stirring under nitrogen with 1.7M butyllithium 
in hexane (36 ml) from a syringe. The resulting bright red solution is 
cooled to 10.degree. C. and treated dropwise with ethyl 5-oxopentanoate 
[5.5 g, prepared as described in Example 2 (1B)] in dry ether (37.5 ml). 
After 10 minutes, the reaction mixture is worked up by the procedure 
described in Example 2(2) to give ethyl (Z)-dodec-5-enoate as a yellow oil 
(8.6 g). 
This oil is treated by the procedure described under Example 2(2) in order 
to effect hydrolysis and yield (Z)-dodec-5-enoic acid (3.5 g) as an oil 
(3.5 g). 
(2) dl-erythro-5,6-Dihydroxydodecanoic acid 
(Z)-Dodec-5-enoic acid (3 g) is treated with aqueous KOH/KMnO.sub.4 by the 
procedure described under Example 2(3) to yield 
dl-erythro-5,6-dihydroxydecanoic acid as a solid (0.2 g), m.p. 118.degree. 
C. 
(3) dl-erythro-6-Acetoxy-5-dodecanolide 
dl-erythro-5,6-Dihydroxydodecanoic acid (100 mg) is treated with acetyl 
chloride by the procedure described under Example 2(4b) to yield 
dl-erythro-6-acetoxy-5-dodecanolide as a colourless oil (78 mg), .sup.13 C 
n.m.r. (CDCl.sub.3 /TMS) -170.9 (&gt;C.dbd.O), -170.4 (&gt;C.dbd.O), -80.5 
(&gt;CH--O--), -74,3 (&gt;CH--O--) p.p.m. 
EXAMPLE 4 
Test of Oviposition Activity of dl-erythro-6-Acetoxy-5-hexadecanolide 
0.1 ml of a solution in hexane of synthetic 6-acetoxy-5-hexadecanolide (7.5 
.mu.g, 25 egg raft equivalents) prepared as described in Example 2 was 
pipetted onto a 12 mm.times.1 mm polystyrene disc. The disc was allowed to 
dry by evaporation of the solvent and was then floated on the surface of 
250 ml of tap water contained in a bowl of 13 cm diameter. 0.1 ml of 
hexane at the same temperature was pipetted similarly onto a control disc 
which was dried and then floated on the surface of 250 ml of tap water in 
a similar bowl. The two bowls were placed in a 30 cm.times.30 cm.times.30 
cm cage containing Culex pipiens fatigans mosquitoes, females of which had 
fed earlier on an anaesthetized guinea pig. A sugar pad was placed between 
the two bowls and equidistant from them. The number of egg rafts laid in 
both the test bowl and the control bowl was counted next day following a 
16 hour period of darkness. 
The activity of the synthetic compound was compared with that of the 
natural egg rafts by means of a similar experiment to that just described 
in which the two bowls instead contained, respectively, tap water and tap 
water on the surface of which floated from 7 to 25 Culex pipiens fatigans 
egg rafts. 
The results of seven replicate experiments with the synthetic compound and 
the natural egg rafts are given in the Table, the positions of the test 
and control bowls in the cage being alternated with each replicate. It 
will be seen that in both cases the number of egg rafts laid in the test 
bowl substantially exceeded the number laid in the control bowl. 
TABLE 1 
______________________________________ 
Number of egg rafts laid 
Synthetic Compound 
7-25 Egg rafts 
Test bowl 
Control bowl Test bowl Control bowl 
______________________________________ 
4 0 6 0 
11 0 11 1 
7 0 25 14 
6 0 9 2 
20 13 10 6 
15 3 21 13 
82 10 10 6 
Total 
145 26 92 42 
______________________________________ 
EXAMPLE 5 
Test of Oviposition Activity of dl-erythro-6-Acetoxy-5-hexadecanolide 
The same procedure as described in Example 4 was used to compare with a 
control the activity as observed for either 10 or 11 replicates of 
synthetic 6-acetoxy-5-hexadecanolide, prepared as described in Example 2, 
over a wide range of concentration from 0.01 .mu.g up to 7.5 .mu.g. The 
results obtained at each concentration, as a total for the 10 or 11 
replicates of the experiment and the same number of the control, are shown 
in Table 2 from which it will be seen that a statistically significant 
attractant effect was present over the range 0.02-7.5 .mu.g and that there 
was no evidence of a changeover to repellancy at the higher 
concentrations. 
In a second experiment a direct comparison was made between the attractancy 
at a concentration of 7.5 .mu.g of the synthetic and the natural 
6-acetoxy-5-hexadecanolide. This was done by using a pair of bowls in one 
of which the floating disc contained the synthetic compound prepared as 
described in Example 2 and the other of which contained the naturally 
occurring compound isolated as described in Example 1. Totalled for ten 
replicates, a similar level of attraction was observed (synthetic: 74 egg 
rafts; natural: 82 egg rafts; t=0.357, p&gt;0.7). 
TABLE 2 
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Attractant activity over range of concentration 
Number of egg 
rafts in test 
Number of egg 
Concentration 
bowl and (% of 
rafts in control 
Student t, 
.mu.g total number) 
bowl probability 
______________________________________ 
7.5 209(85) 37 t = 2.337 
p &lt; 0.05 
3.7 129(81) 31 t = 3.419 
p &lt; 0.01 
3.0 101(80) 25 t = 6.039 
p &lt; 0.001 
0.3 126(80) 31 t = 2.319 
p &lt; 0.05 
0.08 159(84) 31 t = 4.571 
p &lt; 0.01 
0.02 169(71) 70 t = 2.628 
p &lt; 0.05 
0.01 83(54) 70 t = 0.750 
p &gt; 0.4 
______________________________________