TERPENOIDS: VIII. THE IMMEDIATE PRECURSORS OF HELMINTHOSPORAL AND HELMINTHOSPOROL

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Abstract
An earlier investigation had shown that helminthosporal, the toxin isolated from growths of Helminthosporium sativum, does not exist as such in the culture, but is formed from a precursor on subsequent mild treatment with acid, base, or heat. What is believed to be the immediate precursor of helminthosporal has now been isolated, as the acetal (IV), from an aged fungus extract. The corresponding precursor of helminthosporal, also as the acetal (V), accompanied it. Hydrolysis of the latter gave prehelminthosporol (also isolated from fresh extracts), which was converted into helminthosporol. Hydrolysis of the acetal of prehelminthosporal gave helminthosporal directly.Although prehelminthosporol exists in the fresh extracts, it appears that more exists, together with prehelminthosporal, in the form of unstable complexes, possibly dimeric hemiacetals, which break down under very mild conditions. One of these has been obtained in moderately pure condition.

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