(S)-2-Methyl-1-hexanol, characteristic mandibular gland substance of ants in the Cataglyphis bicolor group.

4 Pages·1992·0.12 MB·English

by  Agosti, D.

.
Chemoecology 7:57-60 (1996) 0937-7409/96/010057-04 $1.50+0.20
©
1996 Birkhauser Verlag, Basel
Short communication
(S)-2-Methyl-l-hexanol, characteristic mandibular gland substance of
ants of the Cataglyphis bicolor group
D. Agosti1 C. Austin2 O. A. Gokcen2 W. A. Konig3 E. D. Morgan2*, E. D. Scott2 and R. Wehner'
, , , , ,
'Zoologisches Institut der Universitat Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
2Department ofChemistry, Keele University, Staffordshire, ST5 5BG, United Kingdom
3Institut fur Organische Chemie, Universitat Hamburg, D-20146 Hamburg, Germany
Summary. In all the species of the Cataglyphis bicolor lol as the major mandibular gland substance, C. cursor
group examined yet, i.e. C. bicolor, C. diehli, C. isis, C. and C.frigidus ofthe cursor group contained citronellol
nodus, and C. viaticus, 2-methyl-l-hexanol is the char- and farnesene and C. ruber of the albicans group has
acteristic substance and almost the only substance the simple aldehydes nonanal and decanal, while the
found in the mandibular glands. Its chirality has been bicolor group species C. isis, C. niger, C. nodus and two
determined in C. bicolor and shown to be exclusively described there as C. bicolor-1 and C. bicolor-2 all
(S)-2-methyl-1-hexanol. contain a substance, new to pheromones, 2-methyl-l-
hexanol (Keegans et al. 1992).
Key words, mandibular glands - chemotaxonomy - We have now synthesized this compound in its
chirality - synthesis - 2-methyl-l-hexanol - Hy- optically active form and determined its chirality in the
menoptera - Formicidae - Formicinae - Cataglyphis Cataglyphis bicolor mandibular glands.
Experimental
Introduction
There are some 104 described species and others yet Ants of the Cataglyphis bicolor complex were collected
undescribed in the ant genus Cataglyphis, which are in Tunisia and Egypt and taken live to Zurich where
distributed in the Old World from Mauritania to the mandibular glands were dissected and sealed either
Gobi desert. Almost all species thrive in open habitats, singly or in pairs in small glass capillaries which were
either on Mediterranean evergreen vegetation or on taken to Keele for analysis by linked gas chromatogra-
deserts and dry salt plains. From an examination of phy-mass spectrometry, using the conditions described
existing museum collections and over 100 specimens by Keegans et al. (1992). Mandibular glands were
collected in North Africa and Asia Minor, Agosti introduced directly into the gas chromatograph, with-
c(1o9m9p0l)exhainsNroerctohgnAifzreidcaswehviercahlhaspveecibeeseninthethseubjbieccotloorf &outWiandtheravmenstio(n197o2f;sosleveenatl,sobyMtohregmaenth1o99d0)o.f SMaomrpglaens
intensive research for more than two decades, chiefly in were identified only by a code, and the species was only
neuroethology (Wehner 1994), and more recently in revealed after the work was completed.
taxonomy and biogeography (Agosti 1990; Wehner et For chiral chromatography, mandibular glands of
al. 1994), when it became apparent that "Cataglyphis C. bicolor were removed from their capillaries and
bicolor" included three species in the study area. Deter- crushed in hexane, and the hexane solution chro-
mination of species from morphological features alone matographed under the same conditions as racemic and
is difficult in some cases and so Wehner and co-workers (R)-2-methyl-1-hexanol
resorted to a combined analysis, using morphology, Enantmiomers were separated by gas chromatography
allozymes, DNA-sequences and chemical secretions of on a 25 fused silica capillary column coated with
exocrine glands to help in diagnosing species. octakis(6-O-methyl-2,3 -di -O-pentyl)-y-cyclodex-
In the chemical work we have found that mandibu- trin (Konig etal. 1990) at 75°C with hydrogen as carrier
lar gland secretion is variable with species groups in gas at 0.5 bar inletpressure and using a flame ionization
some representative Cataglyphis species (Keegans et al. detector.
1992). For example, two species from the altisquamis Racemic2-metThyMlE-lD-hAexanolwaspreparedfromallyl
group, C. altisquamis and C. mauritanicus have citronel- alcohol (3.63 g) (0.58 g) and butyl lithium
(8.0 g) in hexane at 0°C by the method ofCrandall and
Rojas (1976) to give (+)-2-methyl-l-hexanol (bp.
* To whom correspondence should be addressed 156°C, IR, liquid film, 3350 cm (OH, broad), 1040 cm 1
58 D. Agosti et al. Chemoecology
Fig. 1 Gas chromatograms of 2-
methyl-1-hexanol from Cataglyphis
B bicolor mandibular glands (A),
racemic synthetic alcohol (B), 56%ee
(if)-alcohol (C), coinjection of ant
alcohol and racemic alcohol (D)
V
PL
min
2((dCH,-,OC)C,HH3N2)-,M0)1R.,3 (2(-mC3,C6U(H1,Ha,tCs2H,72O0)H,M)1H;.z6,(MmS<,,501.H9M,0 +C(tH,)(C,noH3t.34),s2e0e(.nd9)t2,, gteilnoaannnsd,tsioitwmeawrsas(cFhifgro.oumn1ad).totgoracopnhseidstuenxdcelursitvheelysoafmethecon(dSi)--
m/z98 (5%, M-H20), m/z 85 (10), 69 (23), 56 (38), 43 We are now seeking a route to prepared pure
(100), 41 (58), 31 (48). (>S)-2-methyl-l-hexanol to provide material to examine
(.R)-2-Mefhyl-l-hexanol was synthesized by the its behavioural effect on C. bicolor workers in the
method of Evans and Takacs (1980), from propionic laboratory. The function ofthe secretion is not known.
anhydride and the chiral auxiliary (S')-prolinol [(S)-2- Ants of the genus Cataglyphis do not forage by using
pyrrolidinyl-methanol, 2.5 g] to give as first product sand trails, nor do they recruit nest mates. Their navi-
N-propionyl-(5')-prolinol (2.8 g) as a viscous yellow oil, gation system is based exclusively on visual clues.
which was treated with lithium diisopropylamide (2
—
equivs) followed by bromobutane (2.5 ml) at 78°C to
give N-((2'5')-2'-methylhexanMoyl)-(S')-prolinol (3.16 g).
This was hydrolysed in 1 HC1 for 3 hrs to give
(7?)-2-methylhexanoic acid which was reduced to (R)-2-
methyl-1-hexanol with di-isobutyl aluminium hydride
and shown by enantioselective chromatography to be
56% enantiomeric excess (R)-isomer. The product had
IR, MS and NMR spectra as described above.
Results and discussion
The substance in the mandibular glands of Cataglyphis
bicolor group species was already identified as 2-methyl-
1-hexanol (Keegans et al. 1992) by comparison with
synthetic material prepared by Grignard reaction be-
tween 2-bromohexane and paraformaldehyde. The
racemic compound was prepared in much better yield
by the method ofCrandall & Rojas (1976), and shown
to be separable into its enantiomers by gas chromatog-
raphy using 6-methyl-2,-3-dipentyl-y-cyclodextrin phase
(Fig. 1). The chiral form of the alcohol was then
synthesized following the method of Evans & Takacs
(1980) for preparing {R)-2-methylhexanoic acid. Evans
& Takacs (1980) recorded 98% enantiomeric excess
(e.e.) for the acid using iodobutane and stated that the
reaction was very sensitive to the alkyl halide used,
among other things. Reduction ofthe acid with DIBAL C~) viaticus ^m bicolor ^p savignyi
give ()?)-2-methyl-l-hexanol in 56% e.e. (Fig. 1).
When the alcohol from the C. bicolor mandibular Fig. 2 Map ofTunisia showing sampling locations
Vol. 7, 1996 Mandibular secretion of Cataglyphis ants 59
Table 1 Mandibular gland contents ofCataglyphis samples from 25 locations. In every case where 2-methylhexanol was found it was the
major substance >90%)
(
Species and
60 D. Agosti el al. Chemoecology
Part VII: cyclodextrins with an inverse substitution pattern- compounds in small samples of biological materials. J Chro-
synthesisandenantioselectivity. J HighResChromatogr 13:702- matogr Sci 10:528-529
707 Wehner R (1994) The polarization-vision project: championing or-
Keegans SJ, Morgan ED, Agosti D, Wehner R (1992) What do ganismic biology. Pp 103-143 in Schildberger K, EisnerN (eds)
glands tell us about species? A chemical study of Cataglyphis Neural Basis of Behavioural Adaptions. Fortschr Zool 39:
ants. Biochem Syst Ecol 20:559-572 Wehner R, Wehner S, Agosti D (1994) Patterns of biogeographic
Morgan ED (1990) Preparation of small scale samples from insects distributionwithinthebicolorspeciesgroupoftheNorthAfrican
for chromatography. Anal Chim Acta 236:227-235 desert ant Cataglyphis Foerster 1850. Senckenbergiana biologica
Morgan ED, Wadhams LJ (1972) Gas chromatography of volatile 74:163-191