- 1H and13C nuclear magnetic resonance studies of the hindered phencyclone adducts of some smaller branched N-alkyl maleimides: Rigorous aryl proton assignments with high-resolution two-dimensional (COSY45) spectroscopy, and anisotropic shielding effects and ab initio geometry optimizations
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Phencyclone, 1, a potent Diels-Alder diene, reacts with a series of N-alkylmaleiniides, 2, to form hindered adducts, 3. The 300 MHz 1H and 75 MHz 13C NMR studies of these adducts at ambient temperatures have demonstrated slow rotations on the nuclear magnetic resonance (NMR) timescales for the unsubstituted bridgehead phenyl groups, and have revealed substantial magnetic anisotropic shielding effects in the 1H spectra of the N-alkyl groups of the adducts. The selected N-alkyl groups for the target compounds emphasized smaller branched alkyls, including C3 (isopropyl, a); C4 (isobutyl, b; and t-butyl, c); C5 (n-pentyl, d; isopentyl [isoamyl], e; 1-ethylpropyl, f; t-amyl, g;) and a related C8 isomer (1,1,3,3-tetramethylbutyl ["t-octyl"], h). The straight-chain n-pentyl analog was included as a reference. This present work on the branched N-al-kylmaleimide adducts appreciably extends our earlier compilation on the N-n-alkylmaleimide adducts. Key methods for proton assignments included "high-resolution" 1H-1H chemical shift correlation spectroscopy, COSY45. 13C NMR of the adducts, 3, verified the expected number of aryl carbons for slow exchange limit (SEL) spectra of the bridgehead phenyl groups. The synthetic routes involved reaction of the corresponding amines, 4, with maleic anhydride to give the N-alkylmaleamic acids, 5, which underwent cyclodehydration to form the maleimides, 2. Magnetic anisotropic shielding magnitudes for alkyl group protons in the adducts were calculated relative to corresponding proton chemical shifts in the maleimides. Geometry optimizations for the above adducts (and for the N-n-butylmaleimide adduct) were performed at the Hartree-Fock level with the 6-31G* basis set. The existence of different contributing conformers for the adducts is discussed with respect to their calculated energies and implications regarding experimentally observed anisotropic shielding magnitudes.
- Callahan, Ronald,Prip, Ron,Shariff, Navroz,Sklyut, Olga,Rothchild, Robert,Bynum, Kevin
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p. 354 - 365
(2007/10/03)
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- Synthesis and antimicrobial activities of N-substituted imides
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In the field of our research programs concerning novel antimicrobial agents, a series of N-substituted imides was synthesized. These compounds were obtained by cyclization of amido-acids in acetic anhydride/sodium acetate or hexamethyldisilazane/zinc bromide for the hydroxy-aromatic derivatives. The hydroxy-alkyl maleimides were directly prepared by condensation of the corresponding amino-alcohol with maleic anhydride in boiling toluene. Most of N-substituted maleimides showed an interesting antimicrobial activity towards bacteria from the ATCC collection (Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853) but the MIC values for P. aeruginosa were always high (128 μg/ml). The imides with alkyl substituents showed higher activities than aromatic analogues with MIC values in the range of 8-32 μg/ml. Comparatively, succinimides were practically inactive.
- Zentz, Frederic,Valla, Alain,Le Guillou, Regis,Labia, Roger,Mathot, Anne-Gabrielle,Sirot, Danielle
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p. 421 - 426
(2007/10/03)
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