[Ilaria]

Dear all,

I am going to perform a Cbz removal from an amino group by catalytic hydrogenation with ammonium formate and Pd-C 10%. The substrate is a dipeptide bound to a Wang resin. I have read in an article (Rapid microwave-assisted deprotection of N-Cbz and N-Bn derivatives, Tetrahedron Letters 42 (2001) 5191–5194) that this is possible, without cleavage from the support. However, I don't know how to separate the resin from the palladium catalyst afterwards. Anyone who tried this?

[rolnor]

Perhaps if you have a filterfunnel that is very coarse you can wash away he Pd/C wich is much more finely powder than the resin?

[TheUnassuming]

The paper used Pd/C with polymer bound substrate?

[Ilaria]

Perhaps if you have a filterfunnel that is very coarse you can wash away he Pd/C wich is much more finely powder than the resin?

The resin is 100-200 mesh (74-149 microns) whereas Pd/C 10% has a median diameter of 38 microns. I will try to find a coarse frit or filter paper with pore size around 50-60 microns, but maybe some of the catalyst will still remain with the resin.

The paper used Pd/C with polymer bound substrate?

They used Cbz-valine bound to Wang resin. They say microwave-assisted hydrogenation with ammonium formate and Pd/C is compatible with the resin and that the removal of Cbz happens selectively, without cleavage from the support. In fact, they write: "Finally, deprotection can be successfully carried out also on substrates supported on MeO-PEG (MW 5000) and even on a Wang-type resin. In this last case, after eight cycles we did not observe cleavage from the resin".

[Dan]

Do they say if/how they separated the Pd/C from the resin in the paper? Which paper is it (just post the citation and/or a link, don't upload the pdf here)?

[Ilaria]

Do they say if/how they separated the Pd/C from the resin in the paper? Which paper is it (just post the citation and/or a link, don't upload the pdf here)?

No, they don't say that. I wrote to the corresponding author five days ago and I hope he will reply. The paper is this one:

http://dx.doi.org/10.1016/S0040-4039(01)00969-8

Rapid microwave-assisted deprotection of N-Cbz and N-Bn derivatives, Tetrahedron Letters 42 (2001) 5191–5194

[kriggy]

What I think they did is that they did run the reaction and then cleaved the dipeptide and analyzed it by classical methods. Honestly, I dont find it realy useful for solid phase synthesis since you cant easily wash the Pd/C away. Maybe as last step when you then cleave it and filter the resin and Pd/C away from your product.

[Ilaria]

What I think they did is that they did run the reaction and then cleaved the dipeptide and analyzed it by classical methods. Honestly, I dont find it realy useful for solid phase synthesis since you cant easily wash the Pd/C away. Maybe as last step when you then cleave it and filter the resin and Pd/C away from your product.

Yes, I thought that as well. But then there's no point in claiming that they did not observe any cleavage from the resin. In fact, they write: "Finally, deprotection can be successfully carried out also ... on a Wang-type resin. In this last case, after eight cycles we did not observe cleavage from the resin". Who cares if you have to cleave it anyway?