How to quantify your first amino acid loading onto Wang resins

While many of the standard amino acids can be purchased pre-loaded onto Wang type resins, there are still cases where coupling the first amino acid onto Wang resin manually is necessary.  In my case, an unnatural amino acid was required on the C-terminus so there was not a commercially available source.

This coupling reaction comes with it’s own set of challenges, which is why many people perform a large scale batch preparation of the pre-loaded resin.  But that’s for a later discussion.  In today’s post I’ll address a different question. How do you quantify the amount of amino acid loaded onto the resin?

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2 thoughts on “How to quantify your first amino acid loading onto Wang resins”

  1. Hi Elizabeth,

    I have found that for most of my applications, doing the loading calculation by weight gives good enough results. Is there any major drawback to this approach? As with the spectrophotometric method, this one also relies on drying the resin well, but it is quite easy to do with a good vacuum source.

    1. Hi Federico,
      Thanks for your comment and for taking time to read the blog. I have never quantified resin loading by mass difference, and I’m sure it works fine for most applications. The one scenario that I can envision needing a more quantitative measure of loading is in the use of expensive reagents. These are often used with fewer equivalents to reduce reagent cost and in that case the stoichiometric ratio of amino acid to resin will need to be much more precise to ensure successful synthesis.

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