The toxin procl~~cccl by I-lelt~tintltospori?~i,t sativ~inz P.I<. and B.' has been isolated in crystalline form. It has tile formula CI~I-II.'BO? and has been shown to contain one satt~rated aldehyde function, olie o,p-unsaturated aldehyde, and two carbocyclic rings.The significance of toxins as agents in plant pathology is now generally recognized, and these substances may be of considerable economic significance. .EIelm.intkosporium satlvi~~tr' is a fungus which produces a seedling blight, foot and root rot, head blight, and leaf spot of cereals and grasses. The disease is widespread in North America and elsewhere and in particular affects wheat and barley crops. I t has been estimated that the loss of the wheat crops in Western Canada caused by the action of this fu~lgus has ranged from 3 to 13% during the past 25 years (2); an estiinated loss of the order of $50,000,000.00.Recently Ludwig (3) has demonstrated that the action of the fungus is dependent on the presence of a toxin produced by the fungus. >Ieans were found for the artificial growth of the fungus, and the cell-free culture filtrates were able to produce many of the general symptoms characteristic of seedling blight, the degree of dailzage being related directly to the dosage. However, the combined action of spore suspensions, themselves reported innocuous (3), and culture filtrate resulted in the plants becoming diseased and the plants generally died. Ludwig concluded that the nonspecific toxin predisposed the plants to invasion of the organism. For the preparation of the toxin 011 a large scale, the fungus was grown (see Experimental) in a 25-gal jacketed fermenter on sucrose-potato infusion. The culture filtrate was then stirred with charcoal upon which the active principle was absorbed. I t was eluted with chloroform, and after filtration through alumina it was then distilled a t low pressure. The distillate crystallized, and was purified by recrystallization.The substance so obtained, helminthosporal, showed characteristic absorptions in the ultraviolet (A, , , 266 111~) and infrared (v,,,, 1715 and 1685 cin-I). The original crude toxin concentrate before heat treatinent either did not show these bands or (in certain batches where perhaps inadvertent heating had occurred) they were present but very weal;, but, weight for weight, sho~ved essentially the same biological activity. I t rvould seem, therefore, that helminthosporal exists in the fungus as a precursor, froin which it is formed by the fungus. This change can also be effected by heat, acid or base.fIelmint1~osporal analyzed in accordance with the empirical formula C151-12202. I t is unstable to air, even a t low temperature, and a t room temperature takes up oxygeil in a quantity equivalent to half an atom in 5 days. The presence of two bands in the carbony1 region of the infrared a t 1715 and 1685 cm-' suggested that these accounted for both oxygen atoms. This was supported indirectly by the absence of any bands in the infrared attributable to hydroxyl or ether groupings. I t was d...

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i\n earlier investigation had shown that helminthosporal, the toxin isolated from gro\vths of Helnli?~tl~osporiunz sativun~, 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 a n aged fungus extract. The corresponding precursor of helminthosporol, also as the acetal (V), acconlpanied it. Iiydrolysis 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 diineric hemiacetals, which break down under very mild conditions. One of these has been obtained in moderately pure condition.Previous investigations fro111 these laboratories (1, 3) have established that helminthosporal, the toxin produced by Hel~minthosporiz~m sativz~m (4), has the structure and stereochemistry shown in (I). This structure has recently been coilfir~lled by a synthesis which has provided the absolute stereochemistry (5). This substance, \vhich along with the fungus is responsible for seedling blight, foot and root rot, and leaf spot of cereals, has growth-inhibiting activity possessed by the crude extract, but as has been pointed out (1) the unpurified toxin does not show the characteristic carbonyl absorption of the dialdehyde. These bands (at 1 715 and 1 685 cnl-l) only appear on heat treatment of the extract, as in distillation, or 011 treatment with acid or base. More recently we have delnonstrated, by thin-layer chromatography (t.l.c.), the total absence of l~elininthos~oral (I) of hellninthosporol (11) (2) from the extracts.I t was surmised t h a t the precursors present in the extract, in view of their ready conversion t o (I) and (11), were probably present as some form of hemiacetal.There was available t o us, froin an early isolation, a chloroforn~ extract of the active University Sub Post Ofice, London, Ontario.

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