A nondestructive method using a combination of three 2D NMR techniques, DQF-COSY (double quantum filter correlation spectroscopy), HMQC (1H-detected multiple quantum coherence), and HMBC (heteronuclear multiple bond correlation), were developed for structural determination of microcystins, toxic heptapeptides produced by cyanobacteria. With this procedure we were able to assign all carbons and protons of microcystins LR (1) and RR (2), thus determining the constituent amino acid sequences. The procedure was also applied to the microcystin-associated nontoxic minor components, which have molecular weights and amino acid compositions similar to those of 1 and 2 and toxicities different from those of 1 and 2. From detailed analysis of these spectra we rapidly deduced that the minor components are geometrical isomers with respect to C-7 of the diene in Adda of the parent toxins. The structures were finally confirmed to be 3 and 4 by ROESY (rotating frame nuclear Overhauser and exchange spectroscopy) technique.
Novel tetraterpenes 1 and 3 have been isolated from an Okinawan soft coral Sarcophyton glaucum, and their structures have been deduced by means of spectroscopy and chemical transformation. Their carbon framework, presumably formed by Diels-Alder reaction of two cembranoids, has been found to be the same as that of methyl sartortuoate and methyl isosartortuoate.
The structure of tetrafibricin, a novel and potent fibrinogen receptor antagonist isolated from the culture broth of Streptomyces neyagawaensis NR0577,was determined. Tetrafibricin has a unique structure containing primary amine, conjugated tetraenoic acid, and polyhydroxy functionalities that is biosynthetically related to the polyene macrolide antibiotics.As described in the preceding paper, tetrafibricin was a new metabolite produced by Streptomyces neyagawaensis NR0577, which potently inhibited fibrinogen binding to its receptors. In this paper, we report on the structural elucidation of tetrafibricin.Results
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