Investigation of the regio- and stereo-selectivity of deoxyguanosine linkage to deuterated 2-hydroxyestradiol by using liquid chromatography/ESI-ion trap mass spectrometry.

From previous studies on the reactivity of estradiol 2,3-quinone towards deoxyribonucleosides, it was demonstrated that several isomeric adducts were formed. Although adduction on steroid ring A or B has been evidenced using sequential MS(n) experiments, in some cases attachment positions are difficult to identify unambiguously. In this work, 2-hydroxyestradiol labeled with deuterium at various positions [6beta (1); 6alpha-7alpha (2); 6alpha-6beta-7alpha (3)] have been used. Isomeric adduct differentiation could be achieved using LC-ESI-MS(n). The m/z shift of the quasi-molecular ions as well as the fragmentation pathways suggested that adduction could occur on both C6 and C9 sites of the steroid B ring: Nucleophilic attack of the base on the C6 position of the steroid led to major adducts and addition of the base on the activated C9 site gave minor adducts that were found to be unstable. LC-MS(n) experiments carried out under deuterated medium provided information about some fragmentation processes by studying the m/z shift of fragment ions: (1) the loss of deoxyribose from the quasi-molecular ions took place according to a process involving a deuterium transfer from the deoxyribose alcohol function; (2) the cleavage of the steroid-base linkage involved a deuterium transfer from the hydroxy group of the catechol and likely occurred via the formation of an ion-dipole complex. The model studies conducted in this work provide new information on the fragmentation mechanisms of covalent adducts formed from estrogen quinones and deoxyguanosine, the most reactive DNA base. Besides, the first unequivocal characterization of adducts involving the steroid C9 position is shown by using deuterium labeled estrogen quinones.

N-aryl 3-halogenated azetidin-2-ones and benzocarbacephems, inhibitors of beta-lactamases.

N-(3-Carboxy-6-methylphenyl)-3-fluoroazetidin-2-one and a series of related N-aryl-3-halo- and -3,3-dihaloazetidinones 3, in which the halo substituent is a fluorine or a bromine atom, were prepared by using the Wasserman procedure of cyclization of beta-bromopropionamides as a key step. Their affinities for the TEM-1 beta-lactamase were determined and compared with those of a series of tricyclic azetidinones, the benzocarbacephems 2, and known beta-lactamase inhibitors. The beta-lactams 2 and 3 behave as competitive inhibitors and not as substrates of the enzyme; neither halogen substitution (series 3) nor ring strain (series 2) induces enzymatic hydrolysis.