Sjoerd：

Have you added any organic base like TEA or DiPEA(2-3 or more eq.) in the solution? Base is needed for dissolcing of glycine and reaction taking place for your case.

Thank you for answering my question. Would Piperidine also do the trick?

I think so!

You should avoid piperidine because this reagent is used to fmoc group deprotection in SPPS.

You could use a small quantity of DCM to dissolve de Fmoc-osu.

You also can consult this article ´´Formation of Fmoc-beta-alanine during Fmoc-protections with Fmoc-OSu´´.

I tried adding 2 grams of DIPEA to 50 ml of DMF whilst the 0.5 grams of Glycine was already in DMF also was the 2 grams of Fmoc-OSU, waited awhile and heated it up a bit. But no results. (In a previous experiment the Glycine turned into a very fine powder but it did not dissolve), I tried slowly adding water (20 ml in total). But weirdly no results it did turn a bit blurry. I still need help with my project. Do you guys have any other ideas. Or am I doing something wrong? I also read somewhere that water quench’s the reaction between fmoc-OSU and glycine. With that I mean the making of Fmoc-Glycine-OH won’t happen. Is that true? And how would I dissolve glycine then, if I can’t use water? And also I read somewhere that HCL and heated Acetone might work. But I have not tried!

And thank you all for your replies! It helps me a lot!

Yahson Varela

Guobing Xiang

Bases such as DIPEA, high concentration and a long time of reaction can deprotect some of the FMOC groups. So, you should use less amount of DIPEA just to take the proton from the amino group of Glycine in case it is protonated, and remember that Glycine, like other free amino acids, can interact with DMF (polar and aprotic solvent). Don't use water, You should use DCM (made before) only if it is necessary.

Thank you for your response. What wil DCM do?. And how should i do the experiment? Like do i add glycine to DCM? And than add DMF with Fmoc-osu?

DCM is a less polar solvent than DMF. So, it could dissolve Fmoc-Osu.

To glycine, you could try to dissolve in DMF.

Remember that the solubility depends on the quantity of solute and solvent.

Note:

-Consult in the bibliography the solubility of Glycine, Fmoc-OSU, and Fmoc-Gly-OH.

-Do not use water to form Fmoc-Gly-OH.

-Usually, Fmoc-amino acids are soluble in DMF, DMF/DCM, and DCM (in some cases).

-You could use ACN as a reaction solvent.

-Do not use water to form Fmoc-Gly-O-. Later you could use HCl/H2O to protonate Fmoc-Gly-O- to Fmoc-Gly-OH.

Follow the reaction by TLC of HPLC.