Cinchona 9-O-Carbamates as CSPs in HPLC

The conformational preferences of 9-O-carbamoyl cinchona free bases reflect in general those of the native cinchona alkaloids. 6 -Neopentoxy-9-0-tert-butylcarba-moylcinchonidine exists as a mixture of two major anti-closed and anti-open conformers in a 65 35 ratio, whereas upon protonation anti-open conformation has been observed exclusively [62]. 

From the practical point of view, 9-O-cinchona carbamates also offer additional benefits they are stable in a broad range of pH (3-10) and can be readily obtained in a one-step reaction of a cinchona alkaloid with an appropriate isocyanate. 

The major area of applications of cinchona 9-O-carbamate type CSPs embraces enantioseparation of diverse N-protected amino acids and peptides, carboxylic, phosphonic, and phosphoric acids as well as other acidic compounds. 

Successful enantioseparation of individual N -protected amino acids stimulated the development of a rapid method of their simultaneous enantioseparation and quantification in a mixture. A feasibility study on this topic has been recently published by Welsch et al. [69]. The two-dimensional HPLC method involves online coupling of a narrow-bore C18 reverse phase (RP) column in the first dimension (separation of racemic amino acids) to a short enantioselective column based on nonporous 1.5 pm particles modified with t-BuCQD in the second dimension (determination of enantiomer composition). Using narrow-bore column resulted in fast analysis time for example, the mixture of nine racemic N-DNB-protected amino acids was completely analyzed within 16 min. 

9-O-tert-Butylcarbamoylquinine (t-BuCQN) and 2,6-diisopropylphenylcarbamoyl-quinine (DIPPCQN) type CSPs have been evaluated for the enantiomer separation of a set of isoindolin-l-one fluorescent derivatives of a-amino adds obtained by their reaction with the ortho-phthalaldehydc, naphthalene-2,3-dicarboxaldehyde, or anthracene-2,3-dicarboxaldehyde. The latter reagent afforded the derivatives of the 

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