Yoshiki Kono

Isolation of 5-(8′Z-heptadecenyl)-resorcinol from etiolated rice seedlings as an antifungal agent

Abstract A new antifungal substance against rice blast fungus ( Pyricularia oryzae ), 5-(8′Z-heptadecenyl)resorcinol, was isolated from etiolated rice seedlings together with a mixture of its homologues with C 13 , C 15 , and C 17 saturated alkyl chains. Its structure was determined by 1 NMR, 13 C-NMR, and MS spectra. Its ED 50 was ca 40μg/ml. These 5-alkylresorcinols were newly produced after germination and the concentration reached 50 μg g −1 fresh weight on day 6.

Novel Phytoalexins (Oryzalexins A, B and C) Isolated from Rice Blast Leaves Infected with Pyricularia oryzae.

Oryzalexins A, B and C were isolated as a group of novel phytoalexins from rice (Oryza sativa) blast leaves infected with Pyricularia oryzae. The basis of the structures of Oryzalexins A, B and C was laid by spectroscopic methods and their inhibitory activities against spore germination and germ tube growth of P. oryzae were assayed.Oryzalexins A, B and C, isolated from rice leaves infected with P. oryzae as a group of novel phytoalexins, were confirmed to be (+)-sandaracopimaradiene derivatives by chemical and spectroscopic studies, i.e. A: 3-oxy-7-oxo- (I); B: 3-oxo-7-oxy- (II) and C: 3,7-dioxo-(+)-sandaracopimaradiene (III).

Plant pathotoxins from Alternaria citri: The minor ACRL toxins☆

Abstract Five host-specific pathotoxins, ACRL toxins II, III, III′, IV and IV′, were isolated from the culture broth of Alternaria citri , the fungus causing brown spot disease of rough lemon. These toxins are related structurally to the major ACRL toxin, toxin I, and to its derivative compound A. Chemical and spectral studies indicated that the ACRL minor toxins were a group of analogous compounds of different chain lengths all of which have a α-pyrone group, in contrast to the dihydro-α-pyrone group in toxin I. Toxin II showed a very low biological activity ( ED 50 greater than 10 μg/ml) whereas the other minor toxins had slightly higher activities ranging from 1 to 10 μg/ml. The dihydropyrone group in ACRL toxin I was correlated with high biological activity ( ED 50 = 18–30 ng/ml).

Plant pathotoxins from Alternaria citri: Stereochemistry of the major and minor toxins

Abstract The absolute configuration of the previously characterized host-specific pathotoxins from Alternaria citri were elucidated by NMR, circular dichroism and X-ray crystallography. Each of the major tautomeric forms of the ACRL toxins are stereochemically analogous.

Identification of 5-n-(2′-oxo)alkylresorcinols from etiolated rice seedlings

Abstract Six 5- n -(2′-oxo)alkylresorcinols were isolated from etiolated rice seedlings. The identification of these compounds was achieved by spectroscopy. From a comparison of the double bond position between 5- n -alkyl- and 5- n -(2′-oxo)alkylresorcinols in rice seedlings, the predicted biosynthetic pathway of 5- n -alkylresorcinols was supported.

A potent antifungal benzoquinone in etiolated sorghum seedlings and its metabolites

Abstract A potent antifungal substance, 2-hydroxy-5-methoxy-3-(8′Z,11′Z,14′-pentadecatrien)yl-1,4-benzoquinone (Q-1), together with its metabolite Q-2, was isolated from etiolated sorghum seedlings and identified. [ED]50 of Q-1 was ca 6 μg m−1 against the rice blast fungus, Pyricularia oryzae. Exposure of the etiolated seedlings to light resulted in a rapid decrease in the Q-1 level, and an increase in the level of another metabolite, Q-3. Structures of the Q-2 and Q-3 metabolites, which were both derived as a result of oxidative cleavage of the quinone chromophore in Q-1, were determined from spectroscopic data.

Synthesis and biological activity of mimics of pm-toxins the host-specific cornpathotoxin produced by Phyllosticta maydis

Abstract To establish structure-activity relationships, 12 mimics of PM-toxin A, a component of the host-specific corn pathotoxin produced by Phyllosticta maydis , have been synthesized as stereoisomeric mixtures. All the mimics synthesized have four β-ketol groups spaced by varying lengths of methylene chains or by a 1,3-diene chain. Mimics with the shorter methylene side-spacers or with the diene side-spacers are 30- to 300-fold less toxic than the native toxin, but the remaining compounds are equally or more toxic than the native toxin. These results can be accounted for by postulating that intramolecular associations at the β-ketol groups may yield two types of cage structure with active and less active conformations.