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Topic: solid phase synthesis coupling  (Read 6645 times)

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Offline aranel

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solid phase synthesis coupling
« on: August 10, 2009, 06:36:59 AM »
i am trying to couple my compound which has a carboxylic function to the resin which has an amine at the end. i tried PyBOP, HATU. both didnt work. i simply get no coupling product, but the phosphorylamide. any ideas?   ???

Offline sjb

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Re: solid phase synthesis coupling
« Reply #1 on: August 10, 2009, 01:00:16 PM »
Presumably you've eliminated conversion of the acid to the acid chloride or similarly highly activated equivalents? What happens when you treat your activated acid with, e.g. methanol or similar - do you get the carboxyl ester?

Offline aranel

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Re: solid phase synthesis coupling
« Reply #2 on: August 11, 2009, 06:13:06 AM »
i'm not sure if i get your question.. i simply want to couple the free amine of the resin with the free carboxylic acid of my protected amino acid and form the peptide bond, in the presence of a coupling reagent like PyBOP or HATU for activation. and a base.

it shouldnt be that complicated, but i always get the blue color from the kaiser test, and the ms shows the phosphorylamide peak. 

Offline kiwi

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Re: solid phase synthesis coupling
« Reply #3 on: August 11, 2009, 09:24:15 AM »
what are the two amino acids? not that I have a lot of peptide experience, but from memory couplings leading to certain sequences are relatively slow and require modified conditions

Offline aranel

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Re: solid phase synthesis coupling
« Reply #4 on: August 11, 2009, 11:38:52 AM »
on the resin there is a single Gly, and the carboxylic acid has an Ala. i expected it not to be a difficult coupling :-\

Offline kiwi

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Re: solid phase synthesis coupling
« Reply #5 on: August 14, 2009, 12:16:26 AM »
on the resin there is a single Gly, and the carboxylic acid has an Ala. i expected it not to be a difficult coupling :-\

Yeah can't say I'd expect that to be difficult either. What's your alanine NH2 protecting group? Are you getting some sort of competing diketopiperazine formation?

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