Communications
DOI: 10.1002/anie.200702481
Chemical Defense
Chemical Defense of the Crust Fungus Aleurodiscus amorphus by a
Tailor-Made Cyanogenic Cyanohydrin Ether**
Bernhard L. J. Kindler and Peter Spiteller*
Aleurodiscus amorphus Rabenh. (German name: Orange-
farbene Mehlscheibe) is a crust fungus native to Europe, Asia,
and North America which occasionally can be found coating
the bark of dead or dying silver fir trees (Abies alba).[1] It is
worthy of note that its pinhead-sized brilliantly pink-orange
fruiting bodies are virtually never attacked by predators. Here
we report the detection of the tailor-made cyanohydrin
aleurodisconitrile (1) which, on injury of the fruiting bodies,
releases HCNby means of an oxidative mechanism so far
unknown in nature, thus deterring predators from feeding.
The characteristic odor of hydrocyanic acid is always
perceptible immediately after injury of the fruiting bodies.
This observation was confirmed by GC-MS after derivatiza-
tion of an aqueous crude extract with pentafluorobenzyl
bromide.[2] Moreover, the HPLC metabolic profiles of
methanolic extracts of intact and injured fruiting bodies
differed. Aleurodisconitrile (1) was the main component in
intact fruiting bodies, while aleurodiscoester (2) dominated in
injured ones. In contrast, neither 1 nor 2 were detectable in
mycelial cultures of A. amorphus.
In order to elucidate the structure of the two compounds,
737 mg of the relatively rare fruiting bodies were carefully
removed from the bark of the silver firs and immediately
extracted with methanol; the crude extract was separated by
preparative reverse-phase HPLC, resulting in the isolation of
2.9 mg of aleurodisconitrile and 1.2 mg of aleurodiscoester.
Absorption maxima in the UV spectrum of 1 at l = 212
and 246 nm indicate the presence of an aromatic moiety. This
is in agreement with the molecular formula C13H16N2O6
deduced by high-resolution atmospheric pressure chemical
ionization mass spectrometry (HR-APCIMS) and the
1H NMR spectrum, which contains signals of two CH protons
in the aromatic region at dH = 6.67 (H-6’’’) and 6.68 ppm (H-
2’’’) in addition to seven signals in the aliphatic region. The
aromatic protons are in a meta position to each other as shown
by a coupling constant of J = 1.8 Hz. The 13C NMR spectrum
consists of 13 signals; two of the seven signals in the aromatic
region can be attributed based on the HSQC spectrum to the
aromatic CH groups mentioned above, the remaining five
arise from quaternary carbons. The HMBC spectrum indi-
cates that the resonance at dC = 118.7 (C-1’’) does not
originate from the aromatic ring and that the CH group at
dH = 5.34 (H-1’) is adjacent to the quaternary carbon atom of
the aromatic ring at dC = 125.5 (C-1’’’), which is flanked by the
two aromatic CH groups at dC = 104.1 (C-6’’’) and 109.5 ppm
(C-2’’’). A nuclear Overhauser effect (NOE) between the
aromatic proton at dH = 6.67 (H-6’’’) and those at dH = 3.88
indicates that a methoxy group is located at C-5’’’, while the
remaining two downfield-shifted aromatic carbons, C-3’’’ and
C-4’’’, bear OH groups. The CH group at dH = 5.34 (H-1’) is in
addition linked—according to a 3JCH correlation in the HMBC
spectrum—to the OCH2 group at dC = 67.7 (C-4). The COSY,
HSQC, and HMBC spectra indicate that the signals of this
OCH2 group (dH = 3.74–3.78 and 3.85–3.89 ppm) represent a
part of a homoserine residue, to which the resonances of the
CH2 group at dH = 2.07–2.13 and 2.24–2.29 (H-3) and the CH
group at dH = 3.66 ppm (H-2) also belong. According to the
molecular formula and a 2JCH correlation of the proton at dH =
5.34 (H-1’) to the carbon at dC = 118.7 (C-1’’), the still
undefined substituent at the CH group at dH = 5.34 ppm (H-
1’) is a CNgroup. Hence, aleurodisconitrile corresponds to
the structure shown in Scheme 1. Comparison of the circular
[*] Dipl.-Chem. B. L. J. Kindler, Dr. P. Spiteller
Institut für Organische Chemie und Biochemie II
Technische Universität München
Lichtenbergstrasse 4, 85747 Garching bei München (Germany)
Fax: (+49)89-289-13210
E-mail: peter.spiteller@ch.tum.de
[**] We are grateful to Janina Erl for her support in the synthesis of
model compounds, to Prof. Dr. Michael Spiteller, Silke Richter, Dr.
Marc Lamshöft, and Dr. Sebastian Zülke (Institut für Umweltfor-
schung, Universität Dortmund), and Andreas Lagojda (Bayer AG,
Leverkusen) for LC-APCI-MS and HR-APCI-MS measurements, as
well as to Dr. Dieter Spiteller (Max-Planck-Institut für Chemische
Ökologie, Jena) for the measurement of optical rotations. In
addition, we thank the members of the Verein für Pilzkunde
München e.V., especially Dr. Christoph Hahn, for drawing our
attention to A. amorphus. We are obliged to Jakob Braun for showing
us several places of finding. Our work has been generously
supported by an Emmy Noether Fellowship for young investigators
of the Deutsche Forschungsgemeinschaft (SP 718/1-2).
Scheme 1. Aleurodisconitrile (1) with selected HMBC and ROESY
correlations.
dichroism (CD) spectrum of 1 with that of (R)-amygdaline
reveals the S configuration of the cyanohydrin carbon atom in
1. In contrast, the S configuration of the stereocenter of the
homoserine moiety was determined indirectly via the ester 2
(see below). The structure of 1 is in agreement with
considerations of its biosynthesis. In analogy to the biosyn-
thesis of cyanogenic glycosides,[3] the cyanohydrin could be
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Angew. Chem. Int. Ed. 2007, 46, 8076 –8078