C-13-NMR SPECTRA AND STEREOCHEMISTRY OF ISOECHINULINS A, B AND C

13C-NMR spectra of isoechinulins A, B and C, metabolites from Aspergillus ruber, were fully assigned on the basis of chemical shifts and multiplicities and comparison with their analogues. Taking advantage of the symmetrical structure of the diketopiperazine ring, the stereochemistry of the trisubstituted carbon-carbon double bond in a dehydrotryptophyl moiety was determined as Z (cis) by measuring the coupling constants, 7hc=c-co, in the proton nondecoupled spectrum of isoechinulin B. © 1979 Taylor & Francis Group, LLC.