Cytochalasins Z4,Z5 and Z6, Three new 24-oxa[14]cytochalasans produced by Phoma exigua var. heteromorpha

Cytochalasins Z4, Z5 and Z6, three new cytochalasans, were isolated from the wheat culture of Phoma exigua var. heteromorpha together with the already known cytocalasin B, deoxaphomin, cytochalasins F, T, Z1 and Z2. The latter two, together with cytochalasin Z3, have been recently described as new 24-oxa[14]cytochalasans produced by Pyrenophora semeniperda, a fungus proposed for biological control of grass weeds. All the three new cytochalasins were characterised as 24-oxa[14]cytochalasans by the extensive use of NMR and MS techniques. Cytochalasins Z4 and Z5 proved to be structurally related to cytochalasin B, whereas cytochalasin Z6 was related to cytochalasin F. Assayed on tomato seedlings at 10-4 M, Z6 caused a very low inhibition of rootlet elongation (30%), whereas Z4 and Z5 were almost inactive. On brine shrimps, assayed at 10-4 M, only Z5 caused almost negligible effects, with 20% mortality, whereas the other two metabolites proved to be inactive.