[aranel]

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?   

[sjb]

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?

[aranel]

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. 

[kiwi]

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

[aranel]

on the resin there is a single Gly, and the carboxylic acid has an Ala. i expected it not to be a difficult coupling

[kiwi]

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?