Kutznerides 1−4, Depsipeptides from the Actinomycete Kutzneria sp. 744 Inhabiting Mycorrhizal Roots of Picea a bies Seedlings

Bioassay-guided fractionation of culture supernatants of the actinomycete Kutzneria sp. 744 resulted in the isolation of four new depsipeptides (1−4). Structure analysis revealed the general structure: cyclo[2-(1-methylcyclopropyl)-d-glycine-(2S,3aR,8aS)-6,7-dichloro-3a-hydroxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid-3-hydroxy-d-glutamic acid-O-methyl-l-serine-l-piperazic acid-(S)-2-hydroxy-3,3-dimethylbutanoic acid]. The 3-hydroxy-d-glutamic acid was present as its threo-isomer in 1 and 2 and as its erythro-isomer in 3 and 4. The piperazic acid was modified to its (R)-4-chloro analogue in 2 and to its C-5/N unsaturated analogue in 4. Compounds 1−4 displayed moderate spore germination inhibiting activity against several common root-rotting fungi.