0000000000681413
AUTHOR
Karel D. Klika
Hybrid compounds generated by the introduction of a nogalamycin-producing plasmid into Streptomyces argillaceus
The combination of genetic material from different antibiotic-producing organisms is a versatile and ever-expanding approach for the production of novel, hybrid compounds possessing bioactivity. The introduction of a plasmid (pSY21b) derived from Streptomyces nogalater and encoding PKS for nogalamycin production into the host strain S. argillaceus A43 led to the production of three new compounds in addition to the normally produced mithramycin. The new compounds are hybrids in the sense that they share features associated with the genes of both the host and the introduced plasmid. The structural elucidation of the novel compounds relied primarily on NMR spectroscopy, which revealed the thre…
Regioselective Synthesis of 2-Imino-1,3-thiazolidin-4-ones by Treatment ofN-(Anthracen-9-yl)-N′-ethylthiourea with Bromoacetic Acid Derivatives
The reaction between N-(anthracen-9-yl)-N′-ethylthiourea (1) and methyl bromoacetate yielded mainly 2-[(anthracen-9-yl)imino]-3-ethyl-1,3-thiazolidin-4-one (2), together with some of the regioisomeric 3-(anthracen-9-yl)-2-ethylimino-1,3-thiazolidin-4-one (3). The structures of the products were elucidated by NMR techniques and, for 3, X-ray crystallographic analysis. Treatment of 1 with bromoacetyl bromide again yielded 2 and 3, but with a reversed product distribution ratio, thus providing an interesting and unexpected regioselectivity, depending on the electrophile selected. The underlying cause of the observed regioselectivity is a result of different reaction pathways taken by the two e…
Frankiamide: A Structural Revision to Demethyl (C-11) Cezomycin.
A compound (née frankiamide) isolated from Frankia was initially structurally elucidated on the basis of NMR and MS. However, X-ray analysis provided a structure that is in discord with this structure and in light of this the structure has now been revised and the compound renamed as demethyl (C-11) cezomycin.
Synthesis and structural characterization of cis- and trans-fused 4a,5,6,7,8,8a-hexahydro-2H,4H-1,3-benzodithiines and their 2-methyl and 2,2-dimethyl derivatives.
Both cis- and trans-fused 4a,5,6,7,8,8a-hexahydro-2H,4H-1,3-benzodithiine together with their 2-methyl and 2,2-dimethyl derivatives were prepared as racemates from the appropriate dithiols obtained via multistep syntheses. The products were characterized by 1 H and 13 C NMR, mass spectrometry, and for two of the cis-fused compounds by X-ray diffraction. 1 H, 1 H vicinal coupling constants indicated that all compounds attain chair-chair conformations as their predominant conformations. All three trans-fused isomers exist in totally biased chair-chair conformations and are essentially conformationally locked, whereas the cis-fused compounds are conformationally mobile and can potentially atta…
Synthesis and NMR characterization of the cis and trans isomers of [Pt(II)(N9-adeH)2(pz)2] and X-ray crystallography of the trans isomer.
The reaction of tetrapyrazine Pt(II) with adenine under basic conditions yielded two products both disubstituted by adenine and bound in all cases to the N-9 nitrogen of adenine. Crystals amenable to X-crystallographic analysis were obtained for one product which was consequently identified as trans-[Pt(II)(N9-adeH)2(pz)2](NO3)(4).H2O. The other product, though, was identified as the cis isomer based on extensive and comparative NMR structural studies whereby the two compounds were examined as both neutral and tetraprotonated species in solution. The major product of the reaction was unexpectedly the cis isomer, thus obtained in contrast to the trans effect, and the reason for this result i…
Conformation of the galactose ring adopted in solution and in crystalline form as determined by experimental and DFT 1H NMR and single-crystal X-ray analysis.
The solution-state conformations of various galactose derivatives were determined by comparison of the experimental (1)H-(1)H vicinal coupling constants to those calculated using density functional theory (DFT) at the B3LYP/cc-pVTZ//B3LYP/6-31G(d,p) level of theory. The agreement between the experimental and calculated vicinal coupling constants for 1,2:3,4-di-O-isopropylidene-alpha-d-galactopyranose was good, thereby confirming an (O)S(2) skew conformation for it and its derivatives on the basis of their similar observed couplings. Single-crystal X-ray analysis of 1,2:3,4-di-O-isopropylidene-6-O-(3,4,6-tri-O-acetyl-2-deoxy-2-N-phthalimido-beta-d-glucopyranosyl)-alpha-d-galactopyranose and …