| 摘要 |
A two step process for preparing a compound of formula I in salt or zwitterionic form, wherein R1 and R2 are each independently C3-C8-cycloalkyl or C6-C10-aryl; and R3 and R4 are each independently C1-C8-alkyl. The process minimizes variation in the relative proportions of diastereoisomers. |
