Hi Betul Bozdogan,

Please try the following three simple steps:

1. As suggested by Leonid Vladimivir, protect the amino group with an acid labile protecting group such as Boc (t-butoxycarbonyl) group. Isolate the pure product.

2. React the above obtained Boc-protected compound containing free carboxylic acid group (2 eqs.) with a diamino compound (1 eq.) such as 1,2-diaminoethane (i.e., H2NCH2CH2NH2) using a coupling agent such as DCC in a suitable solvent such as DCM or DMF. Isolate the pure product by using column chromatography.

3. Treat the above obtained Bis-(Boc-protected) dimer with an acid such as TFA (trifluoroacetic acid) (you can also use 1:1 TFA/DCM) to remove  the Boc group. After concentration of the mixture, add aqueous Sodium bicarbonate to the residue and extract the product (the required dimer containing terminal free amino groups) with an organic solvent such as DCM or ethyl acetate.

I wish you good luck.

AS

In order to accomplish your goal - at first you have to protect the amino-groups from condensation with COOH (from formation of Amide groups). For making a bridge between carbonyl groups - why not to use HO-R-OH - which after reaction with carboxyls will give you CO-R-CO bridge.

Leonid

I want to recommend a very good reference book for this type of crosslinking chemistry:"Bioconjugate Techniques" by Greg Hermanson. 

Hi Betul Bozdogan,

Please try the following three simple steps:

1. As suggested by Leonid Vladimivir, protect the amino group with an acid labile protecting group such as Boc (t-butoxycarbonyl) group. Isolate the pure product.

2. React the above obtained Boc-protected compound containing free carboxylic acid group (2 eqs.) with a diamino compound (1 eq.) such as 1,2-diaminoethane (i.e., H2NCH2CH2NH2) using a coupling agent such as DCC in a suitable solvent such as DCM or DMF. Isolate the pure product by using column chromatography.

3. Treat the above obtained Bis-(Boc-protected) dimer with an acid such as TFA (trifluoroacetic acid) (you can also use 1:1 TFA/DCM) to remove  the Boc group. After concentration of the mixture, add aqueous Sodium bicarbonate to the residue and extract the product (the required dimer containing terminal free amino groups) with an organic solvent such as DCM or ethyl acetate.

I wish you good luck.

AS

The suggestion by Apparao is good, protect one end, then couple to a diamine.  The only part I would add is to consider the use of phenylenediamine.  This comes in the 1,4-, 1,3- and 1,2- isomeric forms and will provide some rigidity and potentially some conformational control.  Of course the closer the amines in the aromatic ring the more problems will arise in the coupling.  That being said, the aromatic diamine should be better than normal anilines at coupling as it is electron rich.

Thank you so much for your answers. Especially Satyam's advice was a good guide for me.

I will try the procedure suggested by Apparao Satyam, because I have already Fmoc protected dipeptide, EDC/NHS, Ethylendiamine. Fmoc is base labile protecting group. Does this difference a problem?

Also could you please suggest me a method for Fmoc deprotection?

THX

Hi Betul,

Fmoc is frequently removed with excess of Piperidine in DMF, we use it for SPPS and for e.g. 4 mmol scale, about 50-55 mL of 20 vol-% Pip in DMF are applied twice after each other. Very important is that Pip is in excess, since the Fmoc leaving group can polymerize due to its double bond. Excess Pip is adding to this double bond and "disactivating" that thing completely.

Be aware: A collegue once tried a post-deprotection after cleavage of a peptide and he had a free cysteine and a StBu-protected one in his sequence. The result was an absolute mess: linear dimers, cyclic dimers, a peptide with two StBu groups... all but not the desired product! The reason is a reaction called disulfide exchange. It takes place under basic conditions.

Always start with a low scale and do proper analysis before upscaling! As long as you do not got to basic conditions during your reactions, Fmoc is really stable under acidic conditions (my collegue forgot the last deprotection that time and it got through the whole cleavage process with loads of TFA).