A process for the preparation of a compound of the formula I: ** Formula ** in a salt or zwitterionic form, wherein: R1 and R2 are each independently cycloalkyl of 3 to 8 carbon atoms, or aryl of 6 to 10 carbon atoms； and R3 and R4 are each independently alkyl of 1 to 8 carbon atoms； the process comprising the steps of: (a) reacting a compound of the formula II: ** Formula ** or a salt thereof, wherein R1 and R2 are each independently cycloalkyl of 3 to 8 carbon atoms, or aryl from 6 to 10 carbon atoms, with a compound of the formula III: ** Formula ** or with an ester-forming derivative thereof, wherein R 3 is alkyl of 1 to 8 carbon atoms, to form a compound of the formula IV: ** Formula ** wherein R1 and R2 are each independently cycloalkyl of 3 to 8 carbon atoms, or aryl of 6 to 10 carbon atoms, and R3 is alkyl of 1 to 8 carbon atoms； and wherein the reaction is carried out in the absence of sodium and sodium hydride； and (b) reacting a compound of the formula IV, wherein R1 and R2 are each independently cycloalkyl of 3 to 8 carbon atoms, or aryl of 6 to 10 carbon atoms, and R3 is alkyl of 1 to 8 atoms carbon, with a compound of the formula V: ** Formula ** wherein R4 is alkyl of 1 to 8 carbon atoms, and X is a leaving group, to form a compound of the formula I, in a salt form or zwitterionic, wherein: R1 and R2 are each independently cycloalkyl of 3 to 8 carbon atoms, or aryl of 6 to 10 carbon atoms； and R3 and R4 are each independently alkyl of 1 to 8 carbon atoms.Un proceso para la preparación de un compuesto de la fórmula I:**Fórmula** en una forma de sal o zwiteriónica, en donde: R1 y R2 son cada uno independientemente cicloalquilo de 3 a 8 átomos de carbono, o arilo de 6 a 10 átomos de carbono； y R3 y R4 son cada uno independientemente alquilo de 1 a 8 átomos de carbono； comprendiendo el proceso los pasos de: (a) hacer reaccionar un compuesto de la fórmula II:**Fórmula** o una sal del mismo, en donde R1 y R2 son cada uno independientemente cicloalquilo de 3
