Summary. A group of highly toxic compounds was isolated from galled seedbeads of annual ryegrass (LoHiim rigidum Gaud.) containing Coryncbactcrium rathayi. Purified extracts were resolved by reverse-phase high-performance liquid chromatography into eight main fractions which have been parLially characterised and shown to be toxic to nursling rats. A mixture of Ihe toxins also produced clinical signs and brain lesions in Iambs consistent with annual ryegrass toxicity. The name 'corynetoxin' is tentatively proposed for the series, individual members being designated according to their order of elution from the high performance liquid chromalography column as corynetoxins 1 to 8. The two main fractions are corynetoxins 3 and 4 of which the former has been crystallised. They appear to be of glycolipid character, 3-hydroxyheptadecanoic acid and a C,i amino sugar being identified among the hydrolysis products of corynetoxin 3. and heptadec-2-enoic acid and a Cu amino sugar from corynetoxin 4.

The corynetoxins, toxic metabolities of Corynebacterium rathayi formed in galled seed-heads of infected annual ryegrass, Lolium rigidum, are shown to be new members of the tunicamycin group of antibiotics. They consist of N-acetylglucosaminyl-tunicaminyl-uracil in amide linkage with fatty acids which differ in certain respects from those present in the tunicamycins. The corynetoxin acids are of slightly longer chain length, C15-C19, occur in a β-hydroxy as well as saturated and α,β-un-saturated series, and have anteiso, iso and normal chain terminations. β-Hydroxy acids have not been observed previously in the tunicamycin group and anteiso chains were reported only recently in the streptovirudin subgroup. Stereochemical identity of the C11-aminosugar in the corynetoxins with the tunicamine part of the tunicamycins is demonstrated by formation of a common hydrolysis product, di(N-trifluoro- acetyl)glucosaminyl-tunicaminyl-uracil. Analysis of the carbon-13 and proton n.m.r. spectra of the main components, corynetoxins H17a and U17a, confirms the stereochemistry proposed for tunicamine except that the glycosidic linkages are changed to α-galactosamine, β-glucosamine.