Kaiser test

After linker coupling, a positive Kaiser test is observed (note 8), which indicates a small amount of free NH2. The free NH2 can be capped with acetic anhydride. The above dried MicroTubes (1) were treated with a 100 mL solution of acetic anhydride (0.5 M) and DIEA (0.6 M) in DCM for 1-2 h. After the supernatant was removed by aspiration, the MicroTubes were washed three times with DMF, MeOH, and DCM and dried under vacuum for 3h after a final washing with ethyl ether. The Kaiser test was negative. 

A (SCA) HMPPA-PEG-PSty (TFA) c[-Tyr-D-Trp-Val- D-Trp-D-Trp-Arg- Asp-] PyAOP/ HOAt, PyBOP/ HOBt, HATU/HOAt, HBTU/HOBt Kaiser test and HPLC PyAOP/HOAt> then rest [367]... 

B pMeBHA (HF) dynorphin analogue HBTU, HATU, HAPyU, BOP, PyBOP, PyAOP Kaiser test phosphonium >>>uronium salts PyBOP>BOP [368]... 

B pMeBHA (HF) analogues of influenza virus hemagglutinin HATU/HOAt BOP/HOBt, DIC/HOBt Kaiser test BOP/HOBt (3 equiv) in DMF, DIPEA (7.5 equiv), 2 h [370]... 

A (SCA) 1. HMPPA-pMeBHA (TFA) 2. Nbz-pMeBHA (HF) somatostatin and gramicidin S analogues BOP/HOBt, PyAOP/HOAt Kaiser test yield and purity depends on anchoring Xaa and handle [374]... 

Generally, monitoring of the cyclization reaction on resin is recommended it is readily performed by the qualitative Kaiseb376 test and/or more correctly by HPLC/MS upon cleavage/deprotection of aliquots from the resin. In this context, attention must be paid to the false positive Kaiser test as resulting from the piperidyl amide formation.1366369375 ... 

Fmoc-Rink-Nle-pMeBHA-resin (1 g, 0.55 mmol g ) was swollen for 1.5 h in NMP in a reaction vessel equipped with a sintered glass bottom, and placed on a shaker. The Fmoc group was removed with 20% piperidine in NMP (8mL, 2 x 15 min) and after washing with NMP (8mL, 5 x 2 min), the Fmoc removal was monitored by the ninhydrin Kaiser test. Coupling of building blocks such as iV -Fmoc-/Va>-carb-oxyalkyl(OAl)Xaa-OH or /V -Fmoc-/V" -aminoalkyl(Aloc)Xaa-OH, or N -alkylated amino acids such as... 

A procedure for Boc-PNA manual synthesis is given below. If the coupling is incomplete (Kaiser test) double coupling is performed. The synthesis cycle is shown in Scheme 10 and the procedure is given in Table 1. 

Notes. The Kaiser test is generally reliable however, when used to test sterically hindered amines such as aminoisobutyric acid (Aib), results may be difficult to interpret. 

Notes. The presence of a secondary amine should be confirmed by a positive result obtained for the secondary test and a simultaneously obtained negative result for the primary test. Likewise the Kaiser test can be used in place of the primary amine version of the chloranil. 

The most popular test for the presence or absence of free amino groups is the Kaiser test.10 The test is simple and quick however it should be noted that some deprotected amino acids do not show the expected dark blue color typical of free primary amino groups (e.g., serine, asparagine, aspartic acid).11 Furthermore, for secondary amines such as proline, the resin will turn brown instead of blue. For secondary amines and aromatic amines, the chloranil test is recommended.12 In this volume, Albericio s research... 

The Kaiser test uses three solutions ninhydrin (5 g in 100 ml of ethanol), phenol (80 g crystalline phenol in 20 ml ethanol), and pyridine/KCN [dilute 2 ml of 0.001 mol/liter aqueous solution of KCN (potassium cyanide) with 98 ml of pyridine]. The test is performed by transferring a few resin beads to a 6 x 50-mm glass test tube. The beads are washed with ethanol and a drop of each of the three testing solutions is added. The tube is then heated to 100° for 5 min in a heating block. Blue (brown for proline)-colored beads and solution (positive test) indicate the presence of free amino groups on the resin. Colorless beads (negative test) indicate complete coupling. The quality of phenol is important. Impure phenol may result in a false-positive Kaiser test. 

In some cases double coupling needs to be carried out to ensure completion of the reaction. Monitoring the coupling efficiency with the Kaiser test may be misleading due to the relatively acidic sulfonamide NH. 

In the commonly used Kaiser test, a few milligrams of resin beads is withdrawn from the reaction, thoroughly washed with a range of solvents, and treated with stock ethanolic solutions of ninhydrin and phenol followed by a solution of KCN in pyridine at 100 °C for 10 min. If the beads turn deep blue in color, there are free primary amine... 

Kaiser test solutions (ninhydrin, pyridine, phenol) (see Note 1). 

Kaiser test. Solution A 5% Ninhydrin in ethanol (w/v). Solution B 80% phenol in ethanol (w/v). Solution C KCN in pyridine (2 mL 0.001 M KCN in 98 mL pyridine). After washings, sample a few resin heads in a small glass mbe and add 2 drops of each of the above solutions. Heat to 120°C for 4-6 min. Blue resin beads indicate the presence of resin-bound free amines. 

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