Rapid Solid-Phase Synthesis of a Calmodulin-Binding Nonapeptide using Thermal and Controlled Microwave Irradiation

Introduction Recently, there are a growing number of publications that report the use of microwave heating for solid-phase organic synthesis, either by using a variety of polymeric supports or applying polymer-supported reagents and catalysts. Although solid phase synthesis was originally introduced for the preparation of oligopeptides in 1963 by R.B. Merrifield [1], surprisingly, there are only a few reports so far on the use of microwave irradiation for the preparation of peptides and related species [2,3]. In fact, it is widely accepted that microwave-assisted chemical reactions can be completed in minutes, providing less by-products and higher yields [4]. Moreover, due to the recent progress in microwave technology, a new generation of the microwave ovens reached the market. By using the latest developments in microwave technology, we developed various protocols for the synthesis test peptides under microwave irradiation. The syntheses were performed without temperature control or under temperature monitoring with a fiber optic sensor under pulsed microwave irradiation with intermittent cooling to room temperature or below. Thus, all synthetic steps were performed under very mild conditions, similar to that is used in traditional solid phase peptide synthesis. After the final cleavage step, the crude peptide products were subjected to HPLC-MS analysis. As it was expected, the reaction time of each step decreased to minutes (instead of hours), and the peptides were obtained in better yields and significantly higher purity by the MAPS strategy, as compared to peptides synthesized by classical SPPS protocols.