Proc. Natl. Acad. Sci. USAVol. 74, No. 6, pp. 2189-2193, June 1977Chemistry

New methylcyclopentanoid terpenes from the larval defensivesecretion of a chrysomelid beetle (Plagiodera versicolora)*

(arthropods/iridoids/chrysomelidial/plagiolactone)

JERROLD MEINWALDt, TAPPEY H. JONESt, THOMAS EISNERf, AND KAREN HICKStt Department of Chemistry and * Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853

Contributed by Jerrold Meinwald and Thomas Eisner, April 11, 1977

ABSTRACT The defensive secretion of larvae of thechrysomelid beetle Plagiodera versicolora contains two un-stable, volatile methylcyclopentanoid terpenes: a dialdehyde(chrysomelidial) isomeric with dolichodial and anisomorphal,and a closely related enol lactone (plagiolactone). Chrysomel-idial and plagiolactone are shown to have structures III and IVon the basis of a detailed analysis of their spectra, coupled withchemical transformations to products of known structure.

CH3CHO

CHO

H3III

H3

0

H3IV

The structure of nepetalactone (I) was established over 20 yearsago (1, 2). At that time this compound, which had been isolatedfrom the essential oil of the mint Nepeta cataria (3), was re-garded chiefly as a chemical curiosity; it had gained somelow-keyed notoriety because of the bizarre behavioral responsesit was capable of eliciting in a variety of felids of both sexes (4).It subsequently developed, however, that nepetalactone wasthe first recognized representative of the methylcyclopentanoidterpenes, a large and diverse group of natural products basedon the 1,2-dimethyl-3-isopropylcyclopentane skeleton, whosechemistry was summarized in an extensive monograph pub-lished some 15 years later (5). These terpenoids are widelydistributed in nature, and members of the group have beenfound to serve many diverse functions, including insect repel-lent in plants (6), "anti-aphrodisiac" (ref. 5, p. 136) antibiotic(ref. 5, p. 136), and insect defense agent (ref. 5, pp. 203-238).The recognition of the central role played in the biosynthesisof many alkaloids by loganin (II), a methylcyclopentanoidterpene glycoside, has provided an important insight into themetabolic link between the alkaloids and the terpenes (5, 7, 8).We wish to report the isolation and characterization of two newmethylcyclopentanoid terpene derivatives, chrysomelidial (III)and plagiolactone (IV), from the defensive secretion of larvaeof a chrysomelid beetle, Plagiodera versicolora.

Plagiodera larvae occur commonly during the summermonths on leaves of willow trees (Salix spp.) in the environs ofIthaca, NY. The larvae have nine pairs of glands, arrangedsegmentally along the sides of the body. They discharge se-cretion readily in response to direct disturbance (Fig. 1). Related

CH3 o CH3 -Glucose

H

H3 CO2CH3I II

CH3 H3CHO / 0

CHO

-H3 H3la IV

species of Chrysomelidae have comparable discharge mecha-nisms, which have been described (9). Chemical work on thesecretion of some of these larvae has led to the isolation ofsalicylaldehyde from Phyllodecta vztellinae (10), Melasomapopuli (11), and Chrysomela scripta (12), and of fl-phenyl-ethyl isobutyrate and fl-phenylethyl 2-methybutyrate fromChrysomela interrupta (13). It was clear from the odor of thesecretion of Plagiodera that this animal produces a secretionof entirely different composition.

EXPERIMENTAL SECTIONGas chromatographic analyses were carried out using 2.5 m X2 mm columns packed with 5% OV-1 on Gas-Chrom Q (columnA), 3% OV-225 on Gas-Chrom Q (column B), or 5% FFAP onGas-Chrom Q (column C) (packing materials from AppliedSciences Laboratories, Inc). Mass spectra were obtained at 70eV using a Finnigan model 3300 gas chromatograph/mass

Abbreviations: GC, gas chromatography; MS, mass spectrometry; m/e,mass-to-charge ratio; IR, infrared; NMR, nuclear magnetic resonance;for NMR spectroscopy, s is a singlet peak, d is a doublet, t is a triplet,q is a quartet, m is a multiplet, and br is broad.* This is report no. 56 of the series "Defense Mechanisms of Arthro-pods." Report no. 55 is Brattsten, L. B., Wilkinson, C. F. & Eisner,T. (1977) Science, in press.

2189

FIG. 1. Larva of Plagiodera versicolora responding to pinchingofone of its legs with forceps by emitting secretion from its segmentaldefensive glands. (Reference bar = 1 mm.)

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spectrometer (GC/MS) coupled with a System Industries model150 computer. High resolution mass spectra were obtainedusing an AEI MS-902 instrument coupled with a VG DataSystem 2020 computer.Hydrogenation of Chrysomelid Secretion. The secretion

from 282 larvae was taken up in a few milliliters of ether. Thissolution was added to 1 ml of ether containing 25 mg of 10%Pd/C which had been saturated with hydrogen. The mixturewas stirred for 1 hr under a slight positive pressure of hydrogen.After filtration and concentration of the solution, GC/MSanalysis (column A) showed the presence of 7 to 10 peaks de-pending on theGC conditions. One of the minor components

(about 10%) had a mass spectrum identical to that reported for1-ethyl-3-methylcyclopentane (V) (14). The major component

of the mixture had MS, m/e peaks (relative intensities in pa-

rentheses) 140(1), 125(4), 111(11), 97(6), 95(3), 93(2), 91(2),83(27), 82(45), 81(21), 80(6), 79(7), 69(89), 67(38), 58(100),55(82), 43(16), 41(57). This mass spectrum corresponds wellwith that obtained for synthetic 2-(3-methylcyclopentanyl)-propionaldehyde (VI), prepared as described below.

2e(3-Methylcyclopentylidene)propionaldehyde. This al-dehyde was prepared in low yield using the general methoddescribed by Meyers et al. (15). A solution containing 5.0 g (32.2mmol) of 2-ethyl-4,4,6-trimethyldihydro-1,3-oxazine in 30 mlof tetrahydrofuran was cooled to -780 and treated with 17.5ml of 2 M 1-butyllithium. After stirring of the mixture for 1 hr,a solution containing 3.44 g (35.2 mmol) of 3-methyl-1-cyclo-pentanone in 10 ml of tetrahydrofuran was added dropwiseover 1k hr. The mixture was allowed to warm to room temper-ature over 1 hr, poured into ice, acidified with 10% HCI, andextracted with pentane. The aqueous layer was then made basicwith 10% NaOH and ice, and extracted with three 75 ml por-

tions of ether. The-ether extract was dried over anhydrousK2CO3 and concentrated under reduced pressure, and theresidue was taken up in a mixture of 30 ml of ethanol and 30ml of tetrahydofuran. The pH was adjusted to 7; the mixturewas cooled to-350, and treated with a solution containing 1.22g of NaBH4 in 5 ml of H20 containing 1 drop of 40% NaOH.During this addition, the pH was maintained at 6-8 by theaddition of dilute HCL. After stirring for 1 hr, 30 ml of H20 was

added and the mixture was extracted with ether (3 times at 75ml each). The ether was dried over K2CO3, and the solvent wasremoved under reduced pressure. After the addition of 50 mlof H20 containing 16.2 g of oxalic acid, the mixture was heatedto reflux for 2%, hr. Upon cooling, the mixture was extractedwith ether, the ether was dried over anhydrous MgSO4, and thesolvent was removed under reduced pressure. Kugelrohr dis-tillation gave 0.2 g of a colorless liquid (bp 120-130°/1.0 mmHg) which was >95% pure by GC (column A); infrared (IR)(neat) peaks at 2880, 2750, 1670, and 1640 cm-1; nuclearmagnetic resonance (NMR) shifts, 6, in ppm relative to tetra-

methylsilane 10.2 (1 proton, s, CHO), 3.0-2.0 (4, m), 1.73 (3,br s, CH3-C=C), 1.0-1.5 (3, m), 1.1 (3, d, J = 6 Hz, CH3-CH); MS, mle 138(10), 123(14), 109(12), 107(10), 105(13),95(41), 93(16), 91(26), 81(56), 80(38), 79(35), 77(31), 67(71),65(27), 57(16), 55(60), 53(53), 52(12), 51(31), 50(12), 43(74),41(100).

243-Methylcyclopentanyl)propionaldehyde (VI). A solutioncontaining 0.2 g (1.4 mmol) of 2-(3-methylcyclopentylidene)-propionaldehyde in 5 ml of ether was stirred with 30mg of 10%Pd/C under hydrogen at atmospheric pressure until the uptake

of hydrogen ceased. After filtration, GC analysis (column B)showed one major component (>90%). After removal of solventunder reduced pressure, 0.2 g of a colorless oil was obtainedwhich had IR (neat) 2870, 2705, 1728 cm-1; NMR 6 9.79 (1, d,

J = 2.5 Hz, CHCHO), 2.2-0.9(15 protons, complex multiplet);MS, mle 111(4),107(2),97(2),95(2),93(2),91(2),83(20),82(26),81(13), 80(5), 79(6), 69(87), 67(39), 58(100), 55(95), 43(20),41(65). Except for the parent peak and the peak for parent ionminus 15 mass units, which were not observed under the con-ditions used to obtain this mass spectrum, these data comparewell with the data obtained for the major hydrogenolysisproduct from the chrysomelid secretion.

Chrysomelidial and Plagiolactone. Gas chromatographicanalysis (column B) of fresh chrysomelid secretion showed twomajor components, the first, chrysomelidial, always more thantwice as abundant as the second, plagiolactone. Preparative GC(column B) of the concentrated ether washings of filter papersquares used to absorb the secretion of 2000 larvae gave ap-proximately 0.2 mg of chrysomelidial as a pale yellow liquid.IR (CC14) 1720, 1660, 1620 (shoulder) cm-1; NMR (100 MHz)a 10.19(1, s, C=C-CHO), 9.98, 9.85 (1, s, s, CH-CHO), 3.63[1, br m, C=C(CHO)-CHI, 3.08(1, m, CHCHO), 2.60(2, brt, CH2C=C), 2.18 (3, s, CH3-CC), 1.02 and 0.89 (3, pairof d, J = 7.2 Hz, CH3CHCHO); there was also an absorptionat a 1.3 due to water; MS (column C), m/e 166(4), 148(21),136(8), 134(8), 120(10), 109(52), 108(39), 107(32), 105(16),96(10), 95(20), 93(16), 91(19), 82(10), 81(100), 80(25), 79(71),78(15), 77(26), 67(20), 65(10), 55(22), 53(27), 51(10); calculatedmass for CloH1402 166.0994, found m/e 166.0997; calculatedmass for C7H9O 109.0655, found m/e 109.0632; calculatedmass for C7H80 108.0575, found m/e 108.0551.

Approximately 0.1 mg of plagiolactone was also isolated bypreparative GC of the same ether washings, as a waxy solidwhich melted as room temperature. This compound had thefollowing spectral data. UV XEt1' 244-252 nm, E _ 5,000 M-cm- 1; IR (CC14) 1764 cm-1; NMR (100 MHz) (assignable sig-nals) 66.53(1, br s, C-CH-0C=0), 5.73(1, br s, HCC),2.47 (1, d of q, J = 6.6 Hz and 14 Hz), 1.82 (3, br s, CH3-C=C), and 1.28 (3, d, J = 6.6 Hz, CH3-CH). Decoupling ofthe doublet at 51.29 collapsed the doublet of quartets at 52.47to a doublet, J = 14.0 Hz; MS, m/e 164(60), 136(21), 121(28),109(11), 108(48), 107(49), 106(15), 93(39), 91(45), -80(85),79(100), 78(16), 77(50), 65(16), 53(11), 51(18); calculated massfor CloH1202 164.0837, found m/e 164.0833; calculated massfor C9H12O 136.0888, found m/e 136.0895; optical rotatorydispersion at 18.8 ,g/ml, IbI 1275 rnm = -8000, 1l1 240 nm =24,000 degrees cm2 dmol-I (EtOH).

Nepetapyrone (Dehydronepetalactone) (XII). A mixtureof 31 mg of nepetalactone, 40 mg of N-bromosuccinimide, and1 ml of CC14 was heated to reflux for 15 min while under aGeneral Electric sunlamp. After cooling, the mixture was fil-tered, diluted with 3 ml of CC14, treated with 100 mg of 1,5-diazabicyclo[4.3.0lnon-5-ene, and heated to reflux for 30 min.The mixture was cooled, washed with 1 M H2SO4, and the or-ganic layer was dried over anhydrous MgSO4. Gas chromato-graphic analysis (column B) showed the product to be a 2:5mixture of nepetalactone and a material with a longer retentiontime. Preparative GC afforded XII as a pale yellow oil vhichhad IR (neat) 1715, 1690, 1555, 1115, and 940 cm-1; NMR (100MHz) 5 7.19 (1, s, -CH-OCO), 3.26 (1, br q, J = 7.1 Hz,CH3CH-C=C), 2.69 (2, m, CH2-C=C), 2.32 (2, m, CH.),1.93 (3, d, J = 1.2 Hz, CH3-CC), 1.27 (3, d, J = 7.1 Hz,CH3-CH); MS, m/e 164(37), 149(100), 136(26), 121(35),107(22), 93(35), 91(61), 79(24), 78(11), 77(56), 65(21), 53(14),51(17), 43(14), 41(16). This material decomposed on standingat -20° in 2 weeks.

Iridopyrone (4,7-Dimethylcyclopental elpyran-3-one)(XIII). A solution of 20 g of cis and trans methyl pulegenates(16) in 50 ml of ether was reduced with 2.4 g of LiAIH4 in the

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usual way, yielding 16.2 g (96%) of 1-iso0propylii'y-droxymethyl-3-methylcyclopentane, bp 99-102°/12 mm Hg;IR 3360 cm-1 (OH); MS, m/e 154(12). To a well-stirred mixtureof 99 g of pyridine and 53.5 g of CrO3 in CH2Cl2 cooled to -5owas added-15 g of this alcohol. Work-up after % hr gave 9.0 g(68%) of 2-isopropylidene-5-methycyclopentane-carboxal-dehyde as a colorless liquid, bp 79-89°/12 mm Hg; IR 1715cm-1; MS, m/e 152(12). A solution of 8.1 g of this aldehyde wasrefluxed with 3.7 g of ethylene glycol and a crystal of p-tolu-enesulfonic acid in 90 ml of benzene in a Dean-Stark apparatusfor 14 hr to give 8.33 g (80%) of 1-isopropylidene-2-(1,3-diox-olan-2-yl)-3-methycyclopentane, bp 62-66°/0.6 mm Hg; MS,m/e 196(1). Ozonolysis of 1 g of this product in ether at -780gave 0.6 g (70%) of 2-(1,3-dioxolan-2-yl)-3-methylcyclopen-tanone, bp (Kugelrohr) 130-150°/14 mm Hg; IR 1740 cm-1;MS, m/e 170(1), 73(100).To a suspension of 300 mg of zinc dust in 40 ml of benzene

was added a mixture of 0.53 g of this ketone and 0.58 g ofmethyl 2-bromopropionate. After 1.5 hr of reflux, 0.2 g of zincand 0.2 g of bromo ester were added. The mixture was workedup in the usual way after 2.5 hr of additional refluxing. Gaschromatography (column A) allowed the collection of one peakwhose retention time corresponded to that of plagiolactone asa pale yellow, unstable liquid, IR 1720, 1645, 1575 cm-1; MS,m/e 164(43), 149(100), 136(23), 135(11), 121(23), 107(21),93(41), 91(68), 79(32), 78(13), 77(53), 65(23), 63(13), 55(15),53(22), 52(13), 51(28), 50(11), 43(22), 41(15).Hydrogenation of Plagiolactone. A solution containing

about 0.1 mg of plagiolactone in 1 ml of ether was hydrogenatedat atmospheric pressure in the presence of 2 mg of 10% Pd/C.Analysis by GC/MS using column B showed one major com-ponent with the following mass spectrum: m/e 168(6), 109(47),97(20), 96(30), 95(100), 94(30), 91(30), 82(53), 81(76), 79(35),78(29), 77(12), 76(30), 74(6), 73(24), 69(24), 68(53), 67(94),56(20), 55(30), 53(30), 51(30), 43(6), 42(6), 41(35). This is almostidentical to that reported for iridomyrmecin (14).

DISCUSSIONPlaglodera secretion was readily collected by wiping the flanksof stimulated larvae with small pieces of filter paper, fromwhich the organic components could be eluted with ether. Gaschromatographic examination of freshly prepared extractsshowed the presence of two principal volatile components, al-though changes in GC behavior with time made it clear thatthese components were unstable. (In fact, the instability of thesecompounds made their isolation and characterization unusuallydifficult.) Preparative GC allowed the isolation of only verysmall quantities of each component. Thus, from 2000 larvaewe were able to obtain ca 100 gg of plagiolactone and 200 ,gof chrysomelidial (molecular formulas CloH1202 andC10H1402, respectively, based on high-resolution mass spectra).An early clue to the carbon skeleton of these compounds wasobtained from a microhydrogenation experiment, carried outon the crude secretion obtained from 282 larvae. Analysis of theresultant complex mixture by GC/MS resulted in the identifi-cation of two significant products. One minor product (ca 10%)proved to be 1-ethyl-3-methylcyclopentane (V) (14). The majorcomponent had a mass spectrum suggestive of 2-(3-methylcy-clopentanyl)-propionaldehyde (VI), and an independentlyprepared sample of VI supported this identification (see Ex-perimental Section for details).The isolation of the C8 and C9 methylcyclopentane deriva-

tives, considered in the light of the known ability of aldehydesto decarbonylate in the presence of hydrogenation catalysts (17),strongly suggested that at least one of the chrysomelid com-

Proc. Natl. Acad. Sci. USA 74 (1977) 2191

VIV 1-

ponents is closely related to iridodial (VII), one of the bestknown methylcyclopentanoid terpenes of insect origin. In fact,the previously cited molecular formula (CioH1402), determinedfrom mass spectra, showed chrysomelidial to be isomeric withdolichodial and anisomorphal, stereoisomeric insect defensiveterpenes with structure VIII (18, 19). Analysis of the 100 MHz1H NMR spectrum of chrysomelidial strongly suggested itsstructure to be that given in formula III (as a mixture of onemajor and one minor stereoisomer). The observation of a pairof upfield methyl group doublets (6 0.89, J = 7.2 Hz in the majorisomer, 6 1.02, J = 7.2 Hz in the minor isomer) corresponds toexpectations for the methyl group on the secondary, saturatedcarbon atom. A downfield methyl group (6 2.18 closely spacedpair of unequal absorptions) is clearly on the ,B carbon of ana,,B-unsaturated aldehyde moiety, and cis to the aldehydegroup (20,21). Two highly deshielded protons (6 9.85 and 9.98;and 6 10.19, s) are easily identified as the saturated and conju-gated aldehydic protons of III, respectively. The absence of anyolefinic proton absorptions, along with the character of themethyl and aldehyde signals, serves to define structure III forchrysomelidial [as well as to rule out any significant equilibriumconcentration of the corresponding enol-hemiacetal structureIX, whose analogue seems to make an important contributionin the case of iridodial (22)].

H3 H3CHO CHO

CHO CHO

H3 CH2VlI Vill

H3 H

/0

H3Ix

The mass spectrum provides corroboration for this structure.Thus, aside from the parent ion at m/e 166 (CQoH1402), twoprominent fragments appear at m/e 109 (C7H90) and 108(C7H80). The first of these clearly corresponds to the loss of thepropionaldehyde side-chain from chrysomelidial, giving theallylic ion X, while the latter is the expected McLafferty re-arrangement product resulting from-cleavage of the sameside-chain along with a y-proton to give XI.

Plagiolactone, isolated (GC) as a waxy solid, melted at room

KH3 FH3 +

CHO <cH

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2192 Chemistry: Meinwald et al.

temperature. Its mass spectrum suggested a close relationshipto chrysomelidial, and in view of its C1oHI202 molecular for-mula, we were led at first to consider the two terpenoid a-pyrone structures XII and XIII before we had isolated quan-tities sufficient to obtain other spectral data. Samples of bothXII and XIII were obtained by synthesis as described below.The preparation of XII ("nepetapyrone") was accomplished

by a bromination-dehydrobromination sequence in whichnepetalactone (I) was treated first with N-bromosuccinimide,then with 1,5-diazabicyclo[4.3.0]non-5-ene (23). Because themass spectrum of XII did not agree with that of the naturalproduct, structure XIII ("iridopyrone"), with the alternativeorientation of the pyrone ring, became our next synthetic ob-jective. This synthesis required a longer route (summarizedbelow), and was equally disappointing. The mass spectrum ofXIII ws almost identical to that of XII and differed significantlyfrom that of plagiolactone. It was clear that further spectral datafor plagiolactone itself were required.

L N-BromosuccinimideI a2. Diazabicyclononene

3H02CH3

CH3

CH3

0

H3XIl

CH3

1.LiAJH4 CHO I. (HOCH2)2 H+2.CrO3/CH6N 2.I 03

CH3

1. H3OCHBrOO2CH3,Zn

2 fHCI

CH3

0

0CH3

XIIIThat plagiolactone is an enol lactone was suggested by its

characteristic infrared absorption at 1764 cm-'. Three suchstructures, all closely related to III, merit consideration: XIV,XV, and IV. Of these, XIV and XV can be eliminated on thebasis of the 100 MHz 1H NMR spectrum of plagiolactone,which shows two distinct olefinic proton absorptions rather thanthe one required for XIV or the three required for XV, atchemical shifts (6 6.53 and 5.73) appropriate for the olefinicprotons of IV. The two methyl absorptions (6 1.28, 3, J = 6.6 Hzand 6 1.82, 3, br s) correspond to expectations for IV, and areincompatible with the alternative formulas.

CH3 0

0 0

CH3

XlV

CH2

0

CH3XV

derivative (GC/MS), whose mass spectrum corresponds wellwith that reported for iridomyrmecin (XVI) (14), and whichdiffers significantly from that of the structurally isomericdihydronepetalactone (XVII) (14). The orientation of the lac-tone function in plagiolactone, therefore, as well as its overallcarbon skeleton is thereby confirmed. These data lead unam-biguously to IV as the correct expression for plagiolactone.

CH3

0

CH:XVI

CH-j 0

0

CH:XVII

Having established structures III and IV for these chryso-melid compounds, we would like to consider their stereo-chemistry briefly. Both of these compounds have a pair of ad-jacent asymmetric carbon atoms(*), corresponding to two pairsof enantiomers. Experimental difficulties of working with theseunstable compounds on such a small scale have prevented usfrom carrying out definitive configurational studies. However,chrysomelidial offers a clear indication (from its NMR spec-trum) of being a mixture of diastereomers, although it is cer-tainly possible that only one of these is present in the nativesecretion at the moment of discharge, and that the other arisesma a facile enolization of the nonconjugated aldehydicgroup.

CH;,CHO

**CHO1H1

III

H3

0

0

H3IV

In the case of plagiolactone, we can make at least a tentativeassignment of both its relative and absolute configuration.Spin-spin decoupling experiments suggest a trans relationshipbetween the hydrogen atoms on the two adjacent asymmetriccenters (Fig. 2). Thus, irradiation of the upfield methyl doublet(6 1.28) in IV results in the collapse of the doublet of quartets,corresponding to the enolizable proton a to the lactonic car-bonyl, to a doublet, J = 14 Hz. The large coupling constantimplies that this a proton and the one on the neighboringasymmetric center are trans, antiperiplanar to each other, and

/

.7~S

A..'

Chemical confirmation of the structure IV was obtained bya micro-hydrogenation experiment. Hydrogenation of pla-giolactone over 10% Pd/C in ether gave one major tetrahydro

FIG. 2. Dreiding molecular model of (S,S)plagiolactone, showingthe trans relationship between the hydrogen atoms on the chiralcenters (arrows).

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Proc. Natl. Acad. Sci. USA 74 (1977) 2193

that the methyl group occupies a pseude quat rmation. An assignment of the absolute configuration of IV canbe made on the basis of the negative Cotton effect shown byplagiolactone, since a correlation has been made between theabsolute configuration of transoid, nonplanar conjugated dienesand the sign of their optical rotatory dispersion curves (24). Fig.2 shows the probable (S,S)stereochemistry of IV based on theseconsiderations.The possibility that plagiolactone is produced biosynthetically

by oxidation of chrysomelidial is an obvious one. One can alsoimagine that when the tiny defensive droplets are exposed toair, autoxidation of the dialdehyde might give rise to the lac-tone. Since the unused secretion is taken back into the defensiveglands in Plagiodera, as it is in related larvae (9), it is possiblethat the composition of the secretion changes with storage. Thequestion of whether the potential for temporal variation hasbiological significance adds a new dimension to the study of thislarval defense mechanism.

Syntheses of chrysomelidial and plagiolactone that confirmthese structural assignments will be published elsewhere. Whenthis work was nearing completion, we learned that a CioH1402dialdehyde and CloH1202 lactone had been isolated andcharacterized independently from another chrysomelid species(Gastrophysa cyanea) by M. S. Blum, H. M. Fales, et al.Samples of both compounds were kindly provided by H. M.Fales. The two insect-derived aldehydes proved identical tosynthetic III. The G. cyanea lactone, however, is not identicalto plagiolactone. Compounds closely related to or identical toIII and IV have also been detected independently by J. E.Wheeler and G. W. K. Cavill in secretions from still other in-sects, but no direct comparisons have been carried out in thesecases.

Early contributions to this study were made by Dr. Arthur F. Kluge,and we are indebted to Marcia S. Cohen for valuable technical as-sistance. We thank Dr. Brian J. Willis for a generous gift of catnip oil,S. Daniels, M. Guzewich, T. Schmidt, and C. Smith for help in col-lecting Plagiodera, and Dr. Henry Dietrich for identifying the species.Partial support by the National Institutes of Health (Grants AI-12020and AI-02908 and Fellowship I-F32-CA05139 to T.H.J.) and the Na-tional Science Foundation (Grant BMS 75-15084) is gratefully ac-knowledged.The costs of publication of this article were defrayed in part by the

payment of page charges from funds made available to support theresearch which is the subject of the article. This article must therefore

b-eihereby marked "advertisement" in accordance with 18 U. S. C.§1734 solely to indicate this fact.

1. Meinwald, J. (1954) Chem. Ind. (London), 488.2. Meinwald, J. (1954) J. Am. Chem. Soc. 76,4571-4573.3. McElvain, S. M., Bright, R. D. & Johnson, P. R. (1941) J. Am.

Chem. Soc. 63, 1558-1563.4. McElvain, S. M., Walters, P. M. & Bright, R. D. (1942) J. Am.

Chem. Soc. 64, 1828-1831.5. Taylor, W. I. & Battersby, A. (1969) Cyclopentanoid Terpene

Derivatives (Marcel Dekker, New York).6. Eisner, T. (1964) Science 146, 1318-1320.7. Thomas, R. (1961) Tetrahedron Lett., 544-553.8. Wenkert, E. (1962) J. Am. Chem. Soc. 84,98-102.9. Garb, G. (1915) J. Entomol. Zool. 7,88-97.

10. Wain, R. L. (1943) Annu. Rep. Agric. Hortic. Res. Stn., LongAshton, Bristol, 108-110.

11. Pavan, M. (1953) Arch. Zool. Ital. 38, 157-184.12. Wallace, J. B. & Blum, M. S. (1969) Ann. Etomol. Soc. Am. 62,

503-506.13. Blum, M. S., Brand, J. M., Wallace, J. B. & Fales, H. M. (1972)

Life Sci. 11, 525-531.14. Stenhagen, E., Abrahamsson, S. & McLafferty, F. W. (1974)

Registry of Mass Spectral Data (John Wiley & Sons, NewYork).

15. Meyers, A. I., Nabeya, A., Adickes, H. W., Politzer, I. R., Malone,G. R., Kovelesky, A. C., Nolen, R. L. & Portnoy, R. C. (1973)J.Org. Chem. 38,36-56.

16. Wolinsky, J. & Chan, D. (1965) J. Org. Chem. 30,41-43.17. Hawthorne, J. O. & Wilt, M. H. (1960) J. Org. Chem. 25,

2215-2216.18. Cavill, G. W. K. & Hinterberger, H. (1961) Aust. J. Chem. 14,

143-149.19. Meinwald, J., Chadha, M. S., Hurst, J. J. & Eisner, T. (1962)

Tetrahedron Lett., 29-33.20. Sadtler Research Laboratories (1970) Sadtler Standard Spectra:

Nuclear Magnetic Resonance Spectra (Sadtler Research Labo-ratories, 3316 Spring Garden St., Philadelphia, Pa. 19104), No.9477.

21. Emsley, J. W., Feeney, J. & Sutcliffe, L. H. (1966) High Reso-lution Nuclear Magnetic Resonance Spectroscopy (PergamonPress, Oxford), Vol. 2, pp. 735-736.

22. Fish, L. J. & Pattenden, G. (1975) J. Insect Physiol. 21, 741-

23.

24.

744.Fieser, L. F. & Fieser, M. (1967) Reagents for Organic Synthesis(John Wiley and Sons, New York), pp. 189-190.Charney, E., Ziffer, H. & Weiss, U. (1965) Tetrahedron 21,3121-3126.

Chemistry: Meinwald et al.

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