Química Orgánica 2 · Aminoácidos y conectividad de los péptidos
2-Aminopropanoate (alanine) from pyruvic acid by reductive amination
Condiciones: NH3, NaBH3CN
Dibuja este problema tú mismo
Arrastra desde los electrones que se mueven hasta donde van, o toca uno y luego el otro. Cada flecha se revisa; Pista te ayuda cuando te atascas. No necesitas cuenta.
El mecanismo, paso a paso
Siguiente reproduce las flechas curvas de cada paso y las explica. Los pasos escritos están abajo.
Leer los 9 pasos escritos
Ammonia neutralizes the acid
Ammonia is a base, so it first removes the carboxylic acid proton, giving pyruvate and ammonium. The ammonium ion is the mild acid that catalyses the later steps.
Las flechas curvas
- The ammonia lone pair takes the acidic carboxyl proton.
- The O–H pair stays on oxygen as carboxylate.
Ammonia adds to the ketone
A second ammonia adds its lone pair to the ketone carbon of pyruvate, giving a zwitterionic tetrahedral adduct.
Las flechas curvas
- The nitrogen lone pair attacks the ketone carbon.
- The C=O π pair moves onto oxygen.
Protonate the alkoxide
The ammonium ion, the strongest acid present, protonates the alkoxide and becomes ammonia.
Las flechas curvas
- An alkoxide lone pair takes a proton from ammonium.
- The N–H pair stays on nitrogen as ammonia.
Deprotonate the nitrogen
Ammonia removes the N–H proton of the adduct, giving the neutral carbinolamine and regenerating ammonium.
Las flechas curvas
- The ammonia lone pair takes the N–H proton.
- The N–H pair returns to nitrogen.
Protonate the hydroxyl
Ammonium protonates the carbinolamine OH so that it can leave as water.
Las flechas curvas
- An oxygen lone pair takes the ammonium proton.
- The N–H pair stays on nitrogen as ammonia.
Water leaves to give the iminium ion
The nitrogen lone pair forms the C=N π bond as water departs, giving the iminium ion that the hydride reagent targets.
Las flechas curvas
- The nitrogen lone pair forms the C=N π bond.
- The C–O pair leaves with oxygen as water.
Why cyanoborohydride
Reactivity matches the iminium ion.
Hydride reduces the iminium ion
A B–H hydride of cyanoborohydride is delivered to the iminium carbon and the C=N π pair moves onto nitrogen, giving the amine. Hydride can add to either face of the planar iminium ion, so the alanine is racemic.
Las flechas curvas
- The B–H pair carries the hydride to the iminium carbon.
- The C=N π pair moves onto nitrogen, neutralizing it.
2-Aminopropanoate
Alanine forms as its carboxylate (2-aminopropanoate) in the ammonia solution, with water and the cyanoborane. This is how transaminase enzymes and chemists alike turn an α-keto acid into an α-amino acid.
Qué vas a practicar
Draw iminium formation from pyruvate and ammonia and its reduction by cyanoborohydride to give alanine as its carboxylate.
Acabas de dibujar cada flecha de este problema.
Cada uno de los 5349 problemas de Orgánica 1 y 2 funciona así: comentarios en cada flecha, pistas cuando te atascas y un modo examen sin pistas. Gratis con una cuenta, sin tarjeta.
¿Atascado con tu propia tarea?
Tómale una foto: el primer escaneo es gratis, sin registrarte
¿Escaneas cada semana? Scan Standard: por unos problemas