The complete molecular structure of siccanin (I), a physiologically active compound isolated from the cultured broth of Helminthosporium siccans Drechsler, which is a parasitic organism of rye-grass, Lolium multifolium Lam. was established by three dimensional X-ray analysis. In order to seek the biogenetical intermediates or related compounds of siccanin, the screening of the prenylphenols by autoradiography and by color reaction with diazonium salt solution was attempted. Twelve prenylphenol derivatives have been isolated from the cultured broth and micellium of the fungi. The structure of siccanochromene-A (IV) was elucidated from the physiocochemical properties as well as by the chemical correlation through the compound V, which in turn was synthesized from dihydro-α-ionone. Siccanochromene-B, -C, -D, and -F were assigned structures (VII), (IX), (X), and (XII) respectively by the chemical reactions and by spectral properties. The acidic fraction was esterified with diazomethane and chromatographed. Three constituents were found to be present. These compounds are shown to possess structure XIII, XV, and XIX respectively. dl-siccanochromene-A was synthesized from compound XXIX, by five steps chemical reaction. Biosynthesis of siccanin and siccanochromenes are now under investigation.
