Dear David
I you put beta alanine on the N-terminus followed by the
PITC you can cleave the peptide normally and the PITC will be stable. If you
do not use the beta alanine then you will get Edman degradation of the peptide.
Regards
Denis Scanlon
>Hello
>
>I was recently asked a question concerning the chemistry involved in
>peptide synthesis and/or sequence analysis that I would like to pass on to
>the ABRF group.
>
>The question is how stable are thioureas, such as result from PITC
>addition to the amino end of a peptide, to acidic (or other) conditions.
>What I was hoping to do was attach something to the end of a peptide during
>solid-phase synthesis by treating the peptide on resin with an
>isothiocyanate, and then cleave the resulting PTC-peptide from the resin
>without losing the something I added during cleavage and purification. I
>think this would be equivalent to asking what it takes to get the thiourea
>PTC-peptide to cleave off with the last amino acid to give the thiazolinone
>in peptide sequencing. I know neat TFA at room temperature will do it, but
>I don't know how fast. I wonder if it might be possible to keep the
>thiourea linkage together (that is, preserve the PTC-peptide and avoid the
>rupture of the thiourea or peptide bonds) through resin cleavage conditions
>that are less rigorous than the usual 50% to 100% TFA. I could use a very
>acid sensitive resin that cleaves in 1% TFA in CHCl3, or a
>necleophile-labile resin that cleaves with saturated NH3 in MeOH. But
>there's no point in trying to pursue such lines unless I can cleave a
>PTC-peptide from a resin without losing the PTC.
>
>Thank you in advance for any thoughts.
>
>Sincerely,
>
>David Chiara
>
>
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