New benzodioxepin type strobilurins from basidiomycetes. Structural revision and determination of the absolute configuration of strobilurin D and related beta-methoxyacrylate antibiotics

The new antifungal strobilurins I (1) and K (19) are 3,4-dihydra-2H-benzo[b ][1,4]dioxepin derivatives. Their structure and stereochemistry was determi ned by degradation to aldehyde 3. Both enantiomers of 3 were synthesised an d the absolute configurations assigned by the high-field H-1 NMR variant of Mosher's method. (S)3 is identical with the compound derived from the natu ral products. In the course of these investigations the epoxide structures 15, 16 and 17 previously assigned to strobilurin D, hydroxystrobilurin D an d 9-methoxystrobilurin K have to be changed in 18, 21 and 20, respectively. All these compounds possess the same benzodioxepin core structure and (S)- configuration as strobilurin I (1). (C) 1999 Elsevier Science Ltd. All righ ts reserved.