RESUMEN
Several possible reaction pathways are analyzed for the recently studied experimental reaction of diaminocarbenes with aroylimines, where the carbene acted as an oxygen-abstracting agent. A number of structures corresponding to local minima and transition states are located by geometry optimization. In contrast to the more recent interpretation of the mechanism of this process, the reaction does not proceed via the direct formation of the corresponding carbonyl ylide resulted from the electrophilic addition of diaminocarbene to the carbonyl oxygen atom. Two other, more favorable pathways were predicted instead: the nucleophilic attack of the carbene lone pair on the imino nitrogen (pathway "a") or on the carbon atom in the CâN moiety of aroylimine (pathway "b"), in agreement with predictions of the frontier molecular orbital (FMO) theory. Both intermediate adducts undergo a subsequent decomposition onto nitrile ylide and urea. Which of the two pathways becomes preferential depends on the nature of the substituents: pathway "a" is more favored for the experimentally studied species, whereas pathway "b" is thermodynamically preferable for the small-sized model structures.
RESUMEN
The synthesis of multifunctional magnetic nanoparticles (MF-MPs) is one of the most active research areas in advanced materials as their multifunctional surfaces allow conjugation of biological and chemical molecules, thus making it possible to achieve target-specific diagnostic in parallel to therapeutics. We report here a simple strategy to integrate in a one-step reaction several reactive sites onto the particles. The preparation of MF-MPs is based on their simultaneous modification with differently functionalized dopamine derivatives using simple solution chemistry. The formed MF-MPs show comparable magnetic properties to those of naked nanoparticles with almost unaltered particle size of around 25 nm. The different termini, amine, azide and maleimide functions, enable further functionalization of MF-MPs by the grafting-on approach. Michael addition, Cu(i) catalyzed « click ¼ chemistry and amidation reactions are performed on the MF-MPs integrating subsequently 6-(ferrocenyl)-hexanethiol, horseradish peroxidase (HRP) and mannose.
Asunto(s)
Dopamina/química , Compuestos Férricos/química , Nanopartículas de Magnetita/química , Alquinos/síntesis química , Alquinos/química , Alquinos/farmacología , Azidas/síntesis química , Azidas/química , Azidas/farmacología , Catálisis , Enlace de Hidrógeno , Magnetismo/instrumentación , Magnetismo/métodos , Maleimidas/química , Maleimidas/farmacología , Tamaño de la Partícula , Propiedades de SuperficieRESUMEN
Addition of anions derived from dialkyl methylphosphonates to (Ss)-N-tert-butanesulfinyl (3,3,3)-trifluoroacetaldimine afforded (Ss,R) addition adducts in moderate to good yield (53-75%) with excellent diastereoselectivity (94-95% de). After selective removal of the N-sulfinyl group, dipeptides containing enantiomerically pure diethyl 2-amino-3,3,3-trifluoropropylphosphonate were synthesized to investigate the influence of the trifluoromethyl substituent on N-terminal coupling.