False results of the Kaiser(ninhydrin)test after the Fmoc-deprotection of certain amino acids coupled to praline during SPPS

摘要

The Kaiser(ninhydrin)test,which detects primary amino groups,is one of the most popular qualitative tests used in Organic Chemistry.This test has been widely used in SPPS,especially for monitoring the presence of free primary amine after deprotection(dark blue colour)as well as for checking completeness of the successive coupling steps(yellow colour).Although the Kaiser test is generally reliable,it is known that in some cases it can lead to false results.More specifically,according to the literature,the test does not yield the typical dark blue colour with serine,asparagine,aspartic acid,or with arginine and cysteine when their lateral chains are deprotected.