Qualitative colorimetric tests for solid phase synthesis

Results obtained in the application of these tests are summarized in Table II. We have encountered some variations in the reproducibility and accuracy of some tests. Due to the numerous factors that can influence colorimetric test results (e.g., test reagent stability, resin type, functional group interference, and lability of protecting group) we highly recommend performing a positive and a negative control for any test applied to a new synthesis. We also emphasize the importance of reagent solution purity on the outcome of test results, hence we strongly encourage the use of correctly prepared and carefully stored reactants. To minimize false results due to lability of the resin-product bond or the product itself (such as Fmoc-protected amino acids), colorimetric tests should be performed with the utmost immediacy in regards to completion of the step to be monitored. Hence the storage of resin over long periods of time (more than 24 h) before testing is not advisable. When the result of a colorimetric test is in doubt we advise repeating the test a few times until a reproducible result is obtained. The use of multiple tests for the same functional group may elucidate ambiguous or otherwise challenging cases.