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was different from that expected for a simple, fully
saturated 3′,3′-dimethylallyloxy side chain. The molec-
ular ion peak observed at m/z 366 (11.2%) in the EIMS
of the new metabolite, and the corresponding molecular
formula of C20H30O6, indicated the presence of both an
additional methylene group and unsaturation site in a
1a -related structure. That the difference of 16 mass
units between the new metabolite and 1a resided in the
side chain was clearly indicated by a strong fragment
ion peak at m/z 85 (84.7%) instead of the characteristic
one at m/z 69 for 1a . Finally, a one-proton multiplet at
Brian, P. W.; Elson, G. W.; Hemming, H. G.; Wright, J . M.
The phytotoxic properties of alternaric acid in relation to
the etiology of plant diseases caused by Alternaria solani
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1
4.05 ppm in the H NMR of the new metabolite allowed
for the correct positioning of the methyl doublet signal
at C-1′. In view of the data discussed we propose
structure 2a (Figure 1) for the new metabolite and the
name homozinniol for the parent metabolite 2 (Figure
1).
The phthalide 3 was first reported as one of the
isomeric products obtained upon chromic acid oxidation
of 1 (Starratt, 1968). It has also been reported as the
sodium borohydride reduction product of zinnolide, a
weak phytotoxin isolated from A. solani (Ichihara et al.,
1985), and as a natural product from A. porri, the causal
fungus of black spot disease in stone leek and onion
(Suemitsu et al., 1992b).
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CONCLUSIONS
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We have identified 1-3 as metabolites of A. solani.
Although 1 has already been reported as being produced
by a number of Alternaria species, including A. solani,
this is the first report of 3 as a metabolite of this
pathogen. Furthermore, and even though there is a
report of zinniol-related metabolites having a modified
3′,3′-dimethylallyloxy side chain (Stierle et al., 1993),
our identification of 2 constitutes the first report of a
zinniol-related phytotoxin having an additional carbon
atom in the side chain. Finally, it is interesting to point
out that our finding of 3 as a nontoxic metabolite from
A. solani coincides with the report of its lack of activity
when tested on lettuce and stone leek seedlings (Sue-
mitsu et al., 1992b). This, together with the reduced
phytotoxic activity observed in our assay for 1a and 2a
when compared to that of the parent compounds 1 and
2, is in agreement with the report that the hydroxy-
methyl groups are essential for the expression of phyto-
toxic activity (Barash et al., 1981).
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1114.
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1
ment of the H and 13C magnetic resonanace spectra by 2D
ACKNOWLEDGMENT
techniques. Can. J . Chem. 1984, 62, 549-553.
Strobel, G. A. Phytotoxins. Annu. Rev. Biochem. 1982, 51,
309-333.
Suemitsu, R.; Horiuchi, K.; Kubota, M.; Okamatsu, T. Produc-
tion of alterporriols, altersolanols and macrosporin by
Alternaria porii and A. solani. Phytochemistry 1990, 29,
1509-1511.
We thank Sinclair Mantell and Paulina Martinez,
Department of Horticulture, Wye College, Wye, Kent,
England, for providing the strain of A. solani used in
this investigation and for their many valuable com-
ments; Francisco Talamas, Syntex S.A., Cuernavaca,
1
Mexico, for 200 MHz H NMR and EIMS spectra; J ohn
Suemitsu, R.; Horiuchi, K.; Horiuchi, M.; Hanabata, M.
Detection of tentoxin by Alternaria solani, A. cucumerina,
A. bataticola and A. japonica. Biosci., Biotechnol., Biochem.
1992a , 56, 139.
A. Findlay, Department of Chemistry, University of
New Brunswick, Fredericton, New Brunswick, Canada,
for FTIR, EIMS, and 200 MHz 1H NMR spectra and for
supporting one of us (M.M.G-A.) to carry out a research
stay at the University of New Brunswick.
Suemitsu, R.; Ohnishi, K.; Horiuchi, M.; Morikawa, Y. Isolation
and identification of 6-(3′,3′-dimethylallyloxy)-4-methoxy-
5-methylphthalide from Alternaria porri. Biosci., Biotech-
nol., Biochem. 1992b, 56, 986.
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