Hi all,
So I performed SPPS using Wang resin. After incorporation of the first amino acid (Ser), I did Fmoc quantification and the yield was around 30%. So I re-incorporated Serine once more into the same resin, but after the second Fmoc quantification, the absorbance value became really low (1/10 of the first one) and the yield has gone down to 2%. There is nothing wrong with the UV machine and I did the second incorporation and Fmoc quantification the same as the first one. So, I'm wondering what could possibly happened?
Hi Atika Nurani!
I think that a Fmoc-Ser-Wang cleavage during the recoupling is not an option, however, if you used DIC/DMAP as coupling partners and some water got into your reaction...then maybe, depending on your conditions, the NH-Fmoc got deprotected and thus your loading calculation gives you so low. You could get a small amount of your resin and couple either Fmoc-Cl or any Fmoc-aa and recalculate the loading.
Good luck!
This is quite low a coupling yield in the first place. The situations discussed by Leonardo may be there. However, the hindered moieties which are less in ratio 30% versus 2% upon reloading seem to be generating the second yields.
Thank you both Leonardo González Ceballos and Riaz A. Khan for the answers
I did use DIC/DMAP as coupling partner and I tried incorporating different aa into a new resin and tried to keep everything dry and I got better yield (~60%). So water might be the problem
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