How to load the first amino acid onto Wang resin

While resins loaded with the natural 20 amino acids are commercially available these days, there may be times when loading the first amino acid onto the resin in house may be necessary.  And unlike loading the first amino acid onto amide-leaving resins, the first coupling reaction for C-terminal acids can be chemically more challenging.

There are several protocols published both in the literature as well as in technical notes from many peptide reagent and instrument suppliers, but they typically occur at room temperature over extended periods of time (3-24 hours and repeated).  In today’s post, I’ll evaluate several conditions suitable for efficiently loading the first amino acid onto Wang-type resin. Continue reading How to load the first amino acid onto Wang resin

Preventing aspartimide rearrangements during Fmoc-based solid phase peptide synthesis

Aspartimide rearrangements are a particularly nasty side reaction that can occur during fmoc-based solid phase peptide synthesis.  Not only is this a mass-neutral side reaction, chromatographically resolving the undesired, rearranged product can be particularly difficult.  To make matters worse, this side reaction can occur at any point during the synthesis after the Asp has been incorporated into the peptide.

In a prevous post, I described method that I have found useful for identifying whether or not an aspartimide rearrangment as occured during synthesis of a peptide that contains an aspartimide-susceptible sequence.  In today’s post, I’ll discuss some strategies that can be used to suppress, or even eliminate this side reaction. Continue reading Preventing aspartimide rearrangements during Fmoc-based solid phase peptide synthesis