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Biosynthesis of Iridodials in the Defense Glands of Beetle Larvae (Chrysomelinae).

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The positions of the H atoms of the anion were determined from difference
Fourier maps according to a high-angle refinement and refined as riding
on the relevant 0 and C atoms with a fixed U value. The powder diagrams
calculated from the single crystal data agree with those obtained from
experiment. Further details of the crystal structure investigations may be
obtained from the Fachinformationszentrum Karlsruhe. Gesellschaft fur
wissenschaftlich-technische Information mbH. D-W-7514 EggensteinLeopoldshafen 2 ( F R G ) on quoting the depository number CSD-56998.
the names of the authors, and the journal citation. From the difference
Fourier synthesis after a high-angle refinement. the following positions of
the hydrogen atoms were determined crystallographically for 3. 5. and 7:
for 3 those of all water molecules (water of crystallization and the guest
molecule): for 5 and 7 those of the anion, including the methyl protons of
7 (cf. Fig. 1-3). Through the determination of the bond valence sums
(I D. Brown in Strtrcrure und Bonding iii CrjsroL, Eii. 11 (Eds: M.
O'Keeffc. A. Navrotsky), Academic Press, New York, 1981. p 1) according
to the equation t i = exp[-(R-R,):B]
( r i is the bond calence, R = V - 0
distance in pm, R, = 179 pm, B = 31.9 pm), all protonated 0 atoms of the
anions of 1, 3. 4. and 6 were found by a characteristic lowering of the sum
of the bond valences. Thus one p,-O(H) bridge is found for 1. two for 3.
four for 4, and one for 6. which also has a ji2-O(H2)bridge (truns to
V=O,,,,) and two termiiial H,O ligands (/runs to p2-O(H)bridge). For the
anions of 2a and 2 b the protonations at the anion indicated by the equation followed from the charge balance. If not explicitly mentioned, the
protonations occur at bridging 0 atoms.
[4] Anions of organic acids. that is, those with a hydrophobic residue, can
function as terminal ligands to stabilize aggrezates of V + O , polyhedra
and screen these within the crystal lattice. (They adopt the function of the
O = V groups in the container compounds ) Small or highly charged ligands such as F - o r PO:- are not suitable. because they interact strongly
with the V centers.
[5] After the isolation of the first host-guest compound of the V - 0 system
with weak interaction and complementarity of the shell and the central
spherical unit, the synthesis of [H,V,,O,,(N,)]'and [HV,,O,,(CIO,)]b~
[6] were expected. However. an analysis of the cavities showed that. for
example. in the V,,O,, shell the incorporation of larger guests should also
he possible (instead of the N; ion. a NO.; ion, as in [H,V,,O,,(NO,)]"
;
unpublished results). This means that the space in this shell can also be
used thus. (A container or carcerand function 111, of course, does not
necessarily imply complementarity). A remarkable example of this is the
compound 2a. The size of the S C N - ion hinders the isomorphous substitution of the topologically analogous N.; ion in the shell of
[H,V,,0,,(N,)]5 - _Nevertheless control by the anionic template according to the argument in [6] is valid in all cases. because the size of the cluster
shells always correlates with the siLe of the template. In the above-mentioned context the following results are particularly impressive for the
control mechanism: 1. Shells of identical composition hut different structures occur as a direct result of the dependence o n the central anion (cf. O,,
arrangement as rhombicuboctahedron in the V,,O,, shell with central
XU, or as the 14th archimedean body with a spherical guest like a halide
ion: A. Miiller, M . Penk, R. Rohlfing, E. Krickemeyer, J. Doring, A r i g ~ i i
Clteni. 1990. 102, 927; Aiigeiv. C k m . h i . Ed. Engl. 1990. 29. 926, as well
which repreas [ 6 ] ) .2. The central cubelike {V,O,)O, unit in [V,,O,,]"'-,
sents a section (though strongly distorted) of a cubic solid-state defect
structure of the NaCl type, has almost a nucleation function for the genesis
of the cluster shell [13]. One can talk of an "initiation-causality". It is also
remarkable that all known cluster shells of type Lean formally he derived
from the V,O, lattice [12] (e.g.. the V,,O,, and V,,O,, shells (W. G. Klemperer, T. A. Marquart, 0 . M Yaghi. h i d . 1992. 104, 51 and 1992.31.49).
as well as the shell of[V,,0,,C1]6~ (A. Miiller, E. Krickemeyer. M. Penk.
H.J. Walberg. H. Bogge, ihid. 1987,99.1060 and 1987,26.1045) and of 1).
(Some aspects of related host-guest chemistry are given in H. Reuter, ihid.
1992, f04, 1210 and 1992, 31. 1185. as well as in Nuiurii.is.c. Riinn'rcliuu
1992. 45, 368.)
[6] A. Miiller, E. Krickemeyer, M. Penk, R. Rohlfing, A. Armatage, H.
Bogge. Angrit. Cliern. 1991, 103, 1720; Ang13r. Chhrm. I n / . Ed. Engi. 1991.
30, 1674.
[7] However, a similar structure occurs in the [(iPrSn),,O,,(OH),I2+ ion: H.
Puff, H. Reuter, J. Orgonomet. Chem. 1989. 373. 173.
[XI H. T. Evans. Jr., J. S. White, Jr., Minerui. Rec. 1987, 18, 333; A. Miiller. J.
Doring, M. I. Khan, V. Wittiieben, Angeir. Client. 1991, 103. 203; Angm.
Cliem. Inr. Ed. Engl. 1991. 30, 210.
[9] I n the carcerands with a centered anion the repulsive ( 0 . . anion) and
attractive (V"'..-anion) forces are balanced (see also A. Muller, K.
Hovemeier, R. Rohlfing. Angew. Chern. 1992. 104, 1214; Anycn. Chmi.
I n r . Ed. Engl. 1992, 31. 1192). This is pIausibly demonstrated by the fact
that in the compounds (NEt,),[V,O,(NO,)(tca)~].H,O (D. D. Heinrich.
K . Folting, W. E. Streib, J. C Huffman, G. Christou. J. Chem. Sot.. Chern.
Coinmtin. 1989,141I ;tca = C,H,SCOO-) and [K ~V,O,(O,CCH,tBu),]][O,CCH,rBu]-2 rBuCH,CO,H (W. Priebsch. D . Rehder. M. von Oeynhausen. Chem. Ber. 1991. 124,761) the {V4OlbJunit can complex a cation
as well as an anion. Apparcntly more than four Lewis acidic V centers must
be present t o complex anions only.
[lo] The type of linkage of the O=V"+O, pyramids varies from weak, that is,
linkage only through [ii-O atoms according to the stoichiometry
{(O=V),O,), of the Keggin type. to maximal. that is. linkage only through
l 3 - Oatoms according to the stoichiometry ((O=V),O,), of the extended
V,,O,, Keggin shell (M T. Pope. A. Mullei-, A n p c Clwm. 1991, 103. 56:
A i i y i ~ i r .C/icm. Inr. Ed. Eng/. 1991, 30. 34). The molecular containers of
type I. but also V,O,. with both p2-0and p,-O functions have on thisscale
a n intermediate type of linkage, unpublished results.
[ l l ] Cf. also M. T. Pope. Nururc, 1992, 355, 27.
[12] R. Enjalbert, J Galy. A<./uCr~..rra/logr.
Secr. C 1986.42. 1467; A. F Wells.
Stnrcrurd Imrgunic Cliivti.rrrr. 5th ed.. Clarendon. Oxford. 1984, p. 568.
1131 A. Miiller. R. Rohlfing. J. Doring. M. Penk. Arigeu.. Clirm. 1991. 103. 575:
Angrii . C 7 i i w i . I r t l . Ed. Dig/. 1991, 30. 588.
[14] A. Miiller. M. Penk. E. Krickemeyer. H. Biigge. H.-J. Walberg. Angeir.
Chei??.1988. 100. 1787: Angrir. C/ieni. lnr. Ed. Engl. 1988, 27, 1719.
Biosynthesis of Iridodials in the Defense Glands
of Beetle Larvae (Chrysomelinae)""
By Micharf Loren=, Wil/2eh Bolund,* and Konrad Deftner
Cyclopentanoid natural products based on an iridoid
structure are widespread in plants and insects."] In plants
the iridoid glucosides, in particular, are of interest because
some of these compounds exhibit pharmacological activity,
while others are intermediates via secoiridoids in pathways
leading to many
Thus, the biosynthesis of these
compounds has been the subject of intensive investigation
over the last 30 years. The key steps in the biosynthesis are
the w-hydroxylation of geraniol to 8-hydroxygeraniol and its
further oxidation to 8-oxocitral. 8-oxocitral can be cyclized
directly or after further transformations to the iridoid
unit[2.31 (analogous to Scheme 1). Additional oxidation and
cyclization steps follow and lead to more than 1000 plant
iridoids known today.[',41 In insects some volatile iridoids
serve as pheromones,[5' while others such as 1-6 which are
produced in defense glands serve as glues, insecticides, fixatives, or fumigants in defense
,CHO
\
chrysomelidial
eptchrysomelidiai
piagiodial
anisomorphal
plagiolactone
actinidine
[*I Prof. Dr. W. Boland, Dr. M. Lorenz
Institut fur Organische Chemie der Universitat
Richard-WillstHtter-Allee 2, D-W-7500 Karlsruhe (FRG)
Telefax: Int. code + (721)698-305
Prof. Dr. K. Dettner
Tierokologie I1 der Universitat
Postfach 101252. D-W-8580 Bayreuth (FRG)
[**I This work was supported by the Deutschen Forschungsgemeinschaft
( D F G ) (SPP, Chemische Okologie) and the Fonds der Chemischen Industrie.
The larvae of the leaf beetles Phaedon cochleariae, Gastrophysa viridula, and Plagiodera versicolora have nine pairs of
glands which can be everted upon molestation. These are
located on the meso or metathorax as well as on the first
seven abdominal segments. A drop of a defense secretion
appears at the gland openings, and for P. cochleariae and G.
viridula this secretion consists mainly of chrysomelidial 1 and
epichrysomelidial 2 as low molecular weight component^^'^
(see Fig. 1 ) . In contrast, the glands of P. versicolora secrete
12
13
t [min]
-
14
15
experiments are based on the assumption that the synthetic
3-norprecursors are transformed in an analogous manner to
the naturally occurring substrates. The appropiate reference
substances, the l-n~r[~H,]chrysomelidials
such as ['HJlO,
can be obtained by biomimetic reactions from the acyclic
dialdehydes 9 by acid"'] or base'"] catalysis. Both variants
yield 1-n~r[~H,]chrysornelidial
10 without significant loss of
deuterium at the C4 position of the precursor[121(> 95 %
retention). This finding means that the mechanism of the
acid-catalyzed cyclization (50 Yo HCOOH)["] of 8-oxocitral
has to be partially modified. The base-induced cyclization of
9 (MeOH, 0.01 N NaOH, 10 min) is to be considered as a
tandem-Michael addition starting by addition of H,O or
MeOH followed by cyclization and elimination of the conjugate base. In incubation experiments 7 and 8 were quickly
converted by all three kinds of larvae into the corresponding
1-noriridodials, 10 and 11, respectively. In addition, for P.
versicolora and G. viridula the acyclic dialdehyde 9 was firmly
established as an intermediate in the biosynthesis of 1 and 3.
This means that the biosynthesis of chrysomelidial 1 and
plagiodial3 in larvae of the aforementioned insects proceeds
in an anologous manner to the biosynthetic sequence in
plants (similar to Scheme 1). It can therefore be expected
that both lifeforms possess similar enzymes.
Fig. 1. Part of the gas chromatographic profile of volatile compounds from the
defense secretion of P. cochleariae 24 h after the injection of ['HH,]-8into the
hemolymph. Elution conditions: RSL 300 (15 m x 0.32 mm) under programmed conditions (50 "C for 2 min, then at 10 "C min- ' to 200 "C); Finnigan
Ion Trap ITD 800 as detector (scan range 35 250 DasecC '). Identified compounds: 1 = chrysomelidial. 2 = epichrysomelidial, 3 = plagiolactone and epiplagiolactone. 6 = actinidme. 10 = l-nor[2H,]chrysomelidial, 12 = alkylindols.
-
the plagiodial 3 as well as the plagiolactone 5, named after
the insect itself.['] While the biosynthesis of plant iridoids has
been well-studied up to now there have been no detailed
investigations into the biosynthesis of iridodials in insects.
That the synthesis of iridodials in insects is part of terpene
metabolism was established by the incorporation of
[14C]mevalonotactoneinto the dialdehyde anisomorphal4 in
the stick insect Anisomorpha buprestoides.['] We report here
that the biosynthesis of the iridodials 1,2, and 3 in the larvae
of the aforementioned beetles is, in principle, similar to the
known plant metabolism but that the details reveal a surprising range of variations (see Scheme 1).
The experimental procedure was as follows: Aqueous solutions of deuterated precursors, (ca. l pL; 0.9% solut i ~ n ) ,were
~ ~ ] injected into the hemolymph of 10 to 14-dayold larvae. About 4-36 h after the injection of the
precursors, the animal is stimulated into secreting defense
secretion from the everted glands. The resulting secretion
was shown to contain [2H]iridodials by using mass spectrometry.
The first traces of deuterated metabolites are detected as
early as one hour after injection. Alternatively, the precursors can be fed to the larvae in the form of impregnated
leaves; however, with this technique it took three days before
significant incorporation could be detected. This experiment
reveals that the larvae of the leaf beetles are able to take up
plant precursors like geraniol or 8-hydroxygeraniol and to
use them for the biosynthesis of iridoids. In order to obtain
usable mass spectra from the minute quantities of ['HImetabolites present, 3-norprecursors of the types 7 and 8
were used; additional metabolic probes were labeled with
deuterium at positions C1, C2, or C8.[91The nor compounds
allow a complete gas chromatographic separation of the
metabolites and naturally occurring iridoids (Fig. 1). The
Angew. Chrm. Inl. Ed. Engl. 1993. 32, No. 6
GI VCH
D3C
9
1
....__ ......__ ........................................................................,...........
Scheme 1. The metabolism of deuterated 3-norgeraniols 7 and 3-nor-8-hydroxygeraniols8 in different leafbeetle larvae. A, B, and C refer to the synthetic
pathways of G . viriduia, P. versicoioru, and P. cochkxzriae, respectively.
However, the fate of the two deuterium atoms at position
C4 in the precursors 7 and 8 also reveals differences in the
biosynthetic pathways in the three leaf beetle larvae.
Analogous to the biomimetic cyclizations the larvae of G.
viridula convert 8, (via 9), into l-n~r[~H,]chrysomelidial10
(Scheme 1 , A) without loss of a deuterium atom from the C4
position of the precursor. The number of deuterium atoms at
Verlugsgesells~hr!/rm b H , W-6940 Wcinherm, 1993
0570-083319310n06-0913S 10.00+ 2 5 1 0
913
C5 can be reliably determined from the mass spectra of 10 by
using the base peak (m/z 69 corresponds to a fragment ion
with C5-'H2; m/z 67 corresponds to C5-'H,).1'2. 13] The
deuterium at C2 in 8 is lost as expected; the deuterium on the
aldehyde groups in 9 is not lost and thus rules out additional
redox reactions on the way to 10 or 11. The isomeric diol
(62)-8 is not metabolized.
When the larvae of P. versicolora are treated with the diol
8 and the resulting metabolites are subjected to analysis by
mass spectrometry, the results indicate that two separate
(Scheme 1, B) cyclases might be operating in the defense
glands of this larva. The resulting I-nor['H,]chrysomelidial
10 has two deuterium atoms attached to C5, whereas the
typical main product for this larva, I-nor['H,]plagiodial 1I ,
has lost one of the two hydrogen isotopes from the C4 atom
of the precursor 8. In addition, a 3-nor[2H,]plagiolactone
corresponding to 5 has also only one deuterium atom attached to C5, which shows that it is derived from I-norplagiodial 11. Whether the lack of the methyl group of the
nor precursor causes this kind of product distribution still
needs to be examined. The two deuterium atoms attached to
C5 of I-nor['H,]chrysomelidial 10 rule out the possibility
that l-nor[2H,]plagiodiaI 11 is first formed and that the thermodynamically more stable 10 is produced by isomerization
of 11.
Interestingly, the larvae of P. cochleariae have developed
precisely this pathway (Scheme I , C; see also Fig. 1). After
the injection of 8 exclusively 1-nor[2H,]chrysomelidial 10 is
found in their defense secretion. In 10, one of the two enantiotopic deuterium atoms attached to C4 in the precursor is
missing. The use of chiral (4R,5S)- o r (4S,5R)-3-nor[4,52H,]geraniol of the type 7 ( 297 % ee at C4) as precursor['l
leads to the enantiospecific removal of the C4-Hs hydrogen
atom. Since the loss of a hydrogen atom from the C5 atom
of the iridoid skeleton, regardless of the cyclization mechanism, determines the position of the ring double bond, for P.
cochleariae it must be assumed that plagiodial3 occurs as an
intermediate on the way to chrysomelidial 1. This finding is
in formal accordance with the current theory of an acid-catalyzed cyclization[lO1of 8-oxocitral to 1. It can be supposed
that the direct formation of 10 and 11 from a common intermediate of the cyclization occurs through the loss of a hydrogen atom from C2 and C5, respectively. Regardless of mechanistic aspects, it is, however, clear that in the course of
evolution, at least within the genus Phaedonini (subfamily
Chrysomelinae), two different pathways have been deveioped for synthesis of 1. Further biogenetic studies on iridoidproducing larvae of the Phaedonini should make it possible
to characterize members of this genus chemotaxonomically.
Received: December 17, 1992 [Z5755IE]
German version: Angeii. Chcm. 1993, 105, 904
[l] C. A. Boros, F. R. Stermitz, J Nut. Prod. 1990, 53, 1055.
[2] L.-F. Tietze, Angew. Chcm. 1983, 95. 840; Angew. Chem. h t . Ed. E q l .
1983, 22, 828.
[3] H. Inouye, S. Uesato, f r o g . Chem. Org. Nut. Prod. 1987, 50, 169.
[4] S. R. Jensen, 0. Kirk, B. J. Nielsen, fhytochemistry 1989, 26, 97.
[5] G. W. Dawson, D. C. Griftiths, N. F. Janes, A . Mudd, J. A. Picket. L. J.
Wadhams, C. M. Woodcock, Naiure. 1987, 325, 614.
[6] J. M. Pasteels, M. Rowell-Rahier, J.-C. Braekman, D. Daloze, Biochem.
Syst. Ecol. 1984,12,395; K. Dettner, R. Fettkother, 0.Ansteeg, R. Deml.
C . Liepert, B.Petersen, E. Haslinger. W. Francke, J. Appl. Entomol. 1992,
113, 128; A. Hutz, K. Dettner. J. Chem. Ecol. 1990, 16, 2691.
[7] J. M. Pasteels, J. C. Braekman, D. Daloze, R Ottinger, Tetrahedron, 1982,
38, 1891.
[S] J. Meinwald. G. M. Happ, J. Labows, T. Eisner. Science 1966, 1 5 / , 79
[9] M. Lorenz, W Boland, unpublished results.
[lo] S. Uesato, Y Ogawa, M. Doi, H. Inouye. J Chem. Soc. Chem. Commun.
1987. 1020.
914
Q VCH Verlugsgesellschali mbH, W-6940 Weinheim. 1993
[I 11 F. Bellesia, F. Ghelfi, U. M. Pagnoni, A. Pinetti, Tetrahedron Lett. 1986,
381.
[12] A 1 : 1 mixture of I-norchrysomelidial and I-norepichrysomehdial [zHH,]-10
was obtained by boiling the dialdehyde ['H,]-9 (0.15g, 0.95 mmol) in 60%
HCOOH for 1 h [lo]. Chromatography on SiO, with hexdne/Et,O (3:7
vlv) yielded 63 mg (42%) ['HJlO. MS (Finnigan, Ion Trap ITD 800,
70eV): mi; 157 ( M ' . 1.4%), 139(6), 138(5). 129(14), 128(6), 114(4),
113(4), 112(8). 111(15), 110(11). 109(6), 100(18), 99(13). 98(12), 97(29).
96(35). 95(36), 94(17). 93(12), 92(6), 85(7). 84(9), 83(19). 82(18), 81(18),
80(18), 79(16), 78(1 I). 71(9), 70(29), 69(100). 68(75), 6?(43). 66(28). 65(1 I),
64(8), 59(12). 58111). 57(9), 56(11), SS(11). 54(11). 53(15), 52(14), 46(12).
High-resolution MS; calcd. for C,H,'HH,O,: 157.1151: found. 157.1182.
I131 According to high-resolution mass spectrometry (Finnigan MAT 90). the
base peak for ['HJ-lO (mi: 69) corresponds to a fragment ion of the
structural formula C,H,'H: and contains the C atoms of the ring; with
the exception of a deuterium atom from the aldehyde group (C?) (cf.
Scheme 1) n o deuterium from the side chain is transferred to the ring
during the fragmenation of 10. This was confirmed by using reference
substances of varying degrees and patterns of deuteration 191. A hypothetical fragmentation scheme for irtdodial is discussed in ref. [14].
1141 S. Uesato, Y Ogawa, H . Ihouye, K. Saiki, M. H. Zenk, Etruhid-on Lett.
1986, 27, 2893.
Cage Extension to Clusters with Co,/Co,MoAs,
Polyhedron Frameworks**
By Michaela Detzel, Karl Pfeiffer, Otto J. Scherer,* and
Gotthelf Wolmershauser
Dedicated to Professor Heinrich Noth
on the occasion of his 65th birthday
The synthesis of molecules exclusively constructed from
L,M and naked E, units (E = P, As, Sb, Bi) has developed
into an unusually manifold area of research, particularly in
recent tirnes."l Little is known, however, about the reactivity
of such complexes.[']
The desired extension of Co,/Co,As, cage frameworks to
nona- and decanuclear heteroatom clusters has now been
and 2['] (Cp* = $-C,Me,) to react
achieved by allowing lL2]
with [Mo(CO),(thf)]. The respective products, 3 (violet crystals) and 4 (black crystals), are stable in air for a short period
and dissolve scarcely in n-hexane, better in benzene and
toluene, and easily in dichloromethane. The complexes are
formed in satisfactory (3: 47%) and good (4: 74%) yields,
respectively.
The X-ray structure analysisC3'shows that for 3 the trapezoidal face of the As, ligand in 1 which is still free is capped
by the 12e- fragment [Mo(CO),], which, however, does not
change the total number of the skeletal electron pairs (SEP).
With 11 SEP, 1 belongs to the arachno type (n + 3) and 3 to
the nido type (n + 2) of structure. The framework of the
nonanuclear cluster 3 can be described as a stretched, triply
capped trigonal As,CoMo prism (Fig. l), in which the three
long edges are almost of the same length (As1 . . . As3 3.032,
As4...As6 3.023, Mo-Col 3.030 A; sum of the covalent
radii according to Pauling: As-As = 2.42, Mo-Co =
2.46 A). This leads to parallel triangular faces (dihedral angle 0.6 ") and to six As-As bond lengths, whose average value
is 2.47 A. The framework of the Co,MoAs, polyhedron of 3
[*] Prof. Dr. 0 . J. Scherer, Dipl.-Chem. M. Detzel, Dr. K. Pfeiffer,
['I
[**I
Dr. G. Wolmershiuser"'
Fachbereich Chemie der Universitit
Erwin-Schrodinger-Strasse,D-W-6750 Kaiserslautern (FRG)
Telefax: Int. code + (631)205-3200
X-ray structure analyses
This work was supported by the Fonds der Chemischen lndustrie.
0570-0833/93/0606-0914$ 10.00+.25jO
Angeu. Chem. h i . Ed, Engl. 1993, 32, No. 6
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