Conformational and Chiroptical Properties of N-Nitrosoazetidines
摘要:
Optically active N-nitrosoazetidines, containing the isolated nitrosoazetidine chromophore, i.e. (2R)-1-nitroso-2-methylazetidine (2) and (4S)-1-nitroso-2,2-dibutyl-4-methylazetidine (5), are synthesized, and their H-1 NMR, CD, and UV spectra are studied. A topomerization mechanism, structural features, and chiroptical properties of the individual isomers of the parent 1-nitrosoazetidine (1) and its (2R)-2-methyl, (4R)-2,2,4-trimethyl, and (4S)-2,2-diethyl-4-methyl derivatives 2-4 are studied theoretically by means of non-empirical quantum chemical calculations. It is shown that the CD spectra of N-nitrosoazetidines can be interpreted on the basis of the two-position Z,E-equilibrium, taking into account the nonplanarity of the nitrosoazetidine chromophore. The Cotton effect sign of the n-pi* transition at 380 nm is determined by the intrinsic chirality of the chromophore and obeys a spiral rule.
β-Lactams in synthesis: short syntheses of cobactin analogs
作者:Andrew J. Walz、Marvin J. Miller
DOI:10.1016/j.tetlet.2007.05.085
日期:2007.7
Mycobactins facilitate assimilation of iron by mycobacteria. Synthetic analogs with structural variation of the cobactin component have potent anti-TB activity. A new method for the synthesis of cobactin analogs is presented. The key process involves single-step coupling reactions between an amine of a cyclic (l)-lysine derived hydroxamic acid with cyanide activated β-lactams.