H.W. Knoche

The structure of the toxin from helminthosporium carbonum

Using Fast Atom Bombardment Mass Spectrometry and Mass Spectrometry/Mass Spectrometry, the structure of HC-toxin a metabolite of Helminthosporium carbonum, is postulated to be structure 3.

Structure of the host-specific pathotoxins produced by Helminthosporium maydis, race T

Abstract Polyketo-polyalcohol structures of the host-specific pathotoxins (Band 1- and Band 2-toxins) from Helminthosporium maydis , race T were elucidated by NMR analysis and chemical degradations.

Analogs of host-specific phytotoxin produced by Helminthosporium maydis, race T: I. Synthesis

Abstract Fourteen analogs of the host-specific corn phytotoxin (T toxin) obtained from cultures of the fungal plant pathogen, Helminthosporium maydis, race T, were synthesized. Addition of difunctional Grignard reagents to aldehyde intermediates resulted in shorter versions (C15–C26) of native toxin (C35–C45), containing the β-polyketol functions which appear to account for the specificity and very high toxicity (10−8–10−9 M) of T toxin toward certain corn varieties.

Analogs of host-specific phytotoxin produced by Helminthosporium maydis, race T: II. Biological activities

Abstract Inhibition of dark CO2 fixation by susceptible corn leaves was used to compare the relative toxicity of synthetic analogs with that of the host-specific phytotoxin produced by the fungal corn pathogen, Helminthosporium maydis, race T. Analogs with C15, C25, or C26 chain lengths and 1,5-dioxo-3-hydroxy functions were only slightly less toxic (2–6 × 10−7 M) than native T toxin (C35–C45 chain lengths) or its individual components (3 × 10−8 M). Like native toxin, analogs were host-specific in that they did not inhibit dark CO2 fixation in leaf tissue of resistant corn at concentrations 102–103 times greater than those effective with susceptible corn. These findings support the structures previously proposed for native T toxin.

BIOLOGICAL ACTIVITIES AND STRUCTURES OF HOST-SELECTIVE PATHOTOXINS

Abstract Examples of host-specific or -selective toxins (HST) in plant diseases are now well-documented by an increasing number of reports. Knowledge of them is important in formulating theories of disease resistance and its genetics. This knowledge has potential importance to pesticide research because selective toxicity with minimal environmental impact is a major goal in the effective use of pesticide. A limiting factor in studies of HST has been lack of knowledge of their structure. In the last 6 years, elucidation of structures of several HST provides an oppotunity for determining mode of action and the basis of specificity.

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.