Investigation of solid-phase peptide synthesis by the near-infrared multispectral imaging technique: a detection method for combinatorial chemistry.

A near-infrared (NIR) multispectral imaging spectrometer was used to monitor solid-phase peptide synthesis. This imaging spectrometer has fast scanning ability and high sensitivity because it is based on an acousto-optic tunable filter and a NIR InGaAs focal plane array camera. This NIR imaging instrument possesses all the advantages of conventional NIR spectrometers; namely, it can be used for noninvasive monitoring of the reactions and identification of the products during the solid-phase peptide synthesis of glycine, alanine, and valine mediated by aminomethylstyrene resin beads. The reaction was determined by monitoring either the decrease of the band at 1529 nm, which is due to the amine group on the beads, or the increase of the amide band generated at 1483 nm. The amine band at 1529 nm was also used to determine the presence of the Fmoc protecting groups and the efficiency of its removal. More importantly, this NIR imaging spectrometer has additional features that conventional NIR spectrometers cannot offer; namely, its ability to measure spectra at different positions within a sample. This feature was utilized for the first demonstration in which reactions of three different solid-phase peptide syntheses (in a three-compartment cell) were simultaneously monitored. As expected, the kinetics obtained for three reactions are similar to those obtained when the each of the reactions was individually determined. In this study, data recorded by 16 x 16 pixels were used to calculate a spectrum for each sample. However, a relatively good spectrum can be obtained by using data recorded by a single pixel. Since the NIR camera used in this camera is equipped with 240 x 320 pixels, this NIR mutispectral imaging technique is not limited to the three-compartment cell used in this study but rather can be used as the detection method for the solid-phase peptide synthesis in combinatorial chemistry.