Reverse-phase HPLC protected amino acids

Perhaps more troublesome than the moderate yields is the necessity for reversed-phase high-performance liquid chromatography (HPLC) to purify the Fmoc protected amino acid glycosides. It has been reported,23 that the carboxylic acid moiety of an amino acid can be protected as a phenacyl ester and after glycosylation be removed with HOAc/Zn° (Scheme 5.7). Thus, a thioglycosyl donor, having a nonparticipating functionality at C(2), was reacted with the Fmoc protected phenacyl ester... 

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. 

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