The structure of gliovirin, a new antibiotic from Gliocladium virens.

In an earlier study, we reported the presence of the antibiotic, heptelidic acid, in the fungus, Gliocladium virens1). From this same organism we have isolated two additional compounds, one of which is selectively active against members of the Oomycetes2). We call this compound gliovirin (1). The second compound, L,L-phenylalanine anhydride (9), may be the biosynthetic precursor to gliovirin. Gliovirin had amp of 247-249°C. It gave a parent ion in the mass spectrum at 480 m/z (13%). The intensity of the P+1 (3.5%) peak and the P+2 (2.3%) peak and the fragment ions at m/z 448 (4%, P-32), and m/z 416 (17%, P-64) indicated the possibility of a disulfide group in the molecule. On silica gel plates, gliovirin gave a positive reaction when sprayed with AgNO3. Epipolythiodioxopiperazines give this reaction3). Disulfides, such as gliotoxin and related compounds, have been isolated from other Gliocladium species4,5). However, unlike gliotoxin which gives a base peak at P-646), gliovirin tends to lose both 64 and 65 amu to give peaks at m/z 416 (17 %) and m/z 415 (25 %), respectively. The intense peak at m/z 388 (79%) may arise by the loss of CO from the m/z 415 ion. This is a common fragmentation of diketopiperazines, but not of gliotoxin which contains an 2,5-epidithio-3,6-diketo group. A high resolution mass spectrum was not obtained because the sample rapidly decomposed at the temperature (360°C) required to volatilize it. However, an elemental analysis and the low resolution mass spectral data provided the formula C20H20N2O8S2, indicating 12 degrees of unsaturation. Table 1. 13C Chemical shift assignments for gliovirin in (CD3)2SO*.