From the Streptomyces spp. 815 and GW4184, four new 4-juglon-2-ylbutyric acid derivatives, the juglomycins G - J (3a, 4a, 4c, 5c), have been isolated and characterised. The structures were derived from the 1D and 2D NMR data and mass spectra and confirmed by comparison with structurally related compounds. The absolute configuration was deduced from the CD spectra. The new natural products exhibited weak antibacterial activity similar to juglomycin A (5a).
The hydrophilic extract of Microcystis sp. bloom material collected from Bror Hayil Reservoir in southern Israel afforded four new metabolites, (2 S,3 S)-3-hydeoxy-1,4-diphenylbutan-2-yl-acetate, aeruginosins BH604, BH462A and BH462B, and two known metabolites cyanopeptolins S and SS. The planar structure of 1–4 was established by analyses of their 1D and 2D NMR data and mass spectrometric data. The absolute configurations of the chiral centers of 1 were established by Mosher method and analysis of the coupling constants between H-2 and H-3, and those of 2–4 by Merfay's method and advanced Merfay's method and chiral HPLC. The compounds do not inhibit the serine proteases trypsin and thrombin.
This work shows how two expert systems, LSD and SISTEMAT, can be used together to solve structure elucidation problems that were selected from recent literature articles. The LSD system is a structure generator that mainly relies on homo- and heteronuclear 2D NMR data. It lacks the knowledge of chemical shift values and of natural product chemistry. Conversely, the SISTEMAT data base contains about 20000 natural compounds and refers to both their 13C NMR chemical shifts and their botanical origin. When exploited by dedicated computer programs it yields structural constraints such as skeletal types and ring systems. The botanical and spectroscopic data in SISTEMAT proved to be very complementary in the constraints extraction process. Several application examples of the proposed methodology are described in detail.
The red coloured ethyl acetate extract of the Streptomyces sp. isolate GW37/3236 delivered the two new antibiotics 13-O-acetyl-bisanhydro-13-dihydrodaunomycinone (3c) and 4,13-O-diacetylbisanhydro- 4-O-demethyl-13-dihydrodaunomycinone (3d) and additionally several known compounds. The quinones 3c and 3d are the first naturally occurring quinone acetates. Their structures were derived by comparison of the NMR data with those of bisanhydro-13-dihydrodaunomycinone (3b) and by interpretation of the 2D NMR data accompanied by the molecular weight and formula. 2-Acetamido-3-hydroxybenzamide (5) was also isolated from the extract and was identified by comparison of the NMR data with those of 2-acetamidobenzamide and by 2D NMR correlations. 6,9,11- Trihydroxy-4-methoxy-5,12-naphthacenedione (4) is isolated for the first time as a natural product.
Four steroids namely 3β-hydroxyergosta-5,24(28)-diene-7-one (1), dissesterol (2), 16α-hydroxysarcosterol (3), and sarcophytosterol (4) were isolated form the soft coral Sinularia nanolobata using various chromatographic methods. Their structures were elucidated by detailed analysis of the 1D and 2D NMR data and comparison with the reported values.
Isolation and Structure Elucidation of Secondary Metabolites from a Microcystis sp. Bloom Material Collected in Southern Israel