( Overview Mass spe...)Direct Monitoring of Solid-Phase Peptide Synthesis by MALDI-TOF MS

Overview

Mass spectrometry has proven to be a valuable tool in verifying and improving peptide synthesis. Matrix Assisted Laser Desorption Ionization (MALDI) Time-of-Flight (TOF) MS is particularly useful in that it is rapid, easy to use and requires relatively little maintenance. This work shows the ability of MALDI-TOF MS to follow the progress of solid phase peptide synthesis. This work was first presented by A. Falick, G. Tarr and N. Sole at ABRF 96.

Key Features

Identification of peptide synthesis products

Ability to track reactions over time

Mass accuracy in DE linear mode

Method

PEPTIDE SYNTHESIS

Linear syntheses were carried out using Fmoc chemistry in the C to N direction on a PerSeptive Biosystems 9050 Plus continuous flow synthesizer. Coupling times were 1 hour, using 4 equivalents of amino acid/ activator and 8 of base. HATU, DIEA and DMF were used as solvents.

MASS SPECTROMETRY

Samples were analyzed on a Voyager-DE STR Workstation in linear mode. The laser was set at 337 nm and 50-100 laser shots were accumulated per spectrum.

Peptides were deprotected with 95% TFA at room temperature for the times noted. 1 mg of resin was treated with 20 μl of TFA, then a 1μl aliquot was removed and added to 50 μl of water. 1 μl aliquot of this diluted sample was mixed with 4 μl of a 10 mg/ml solution of alpha cyano 4-hydroxy cinnamic acid in 60% ethanol and 40% acetonitrile. A 0.5 μl droplet was placed on the MALDI target, air-dried and the target inserted into the instrument.

Results

Figure 1 shows the progress of the synthesis of the 21 mer peptide fragment from the targetting sequence of the precursor of mi
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