RE: synthesis with pyro-glu: +111 mass

Singleton, David H (david_h_singleton@groton.pfizer.com)
Fri, 28 May 1999 09:34:49 -0400

Is the by-product more or less polar? If less polar (longer retained on
C18), I'd bet on 2 t-butyl groups retained or migrated during cleavage.
(56Da x 2= 112Da, +- 1Da for elecrophilic substitution) Without knowing the
sequence, (Trp, Tyr, poly Ser?) this is just a guess.

Your hypothesis could be correct. One could imagine base ring opening the
pyroglu succinimide revealing free NH2 for coupling of an additional
pyro-glu. If this proves to be the case (MS/MS should nail which of these
happened), cut your excesses of activated amino acid and base to 1.1equiv.

David H. Singleton
Scientist
Pfizer Central Research
PO Box 8003
Eastern Point Road
Groton, CT 06340

-----Original Message-----
From: Michael Pereckas [mailto:msp@ace.biochem.mcw.edu]
Sent: Thursday, May 27, 1999 4:12 PM
To: Recipients of ABRF List
Subject: synthesis with pyro-glu: +111 mass

I synthesized a 10 amino acid peptide with pyroglutamic acid on the
N-terminus which I added as unprotected Pyr-OH in the synthesis,
which was done on a PerSeptive 9050 using HATU activation. RP-HPLC of
the product shows two peaks, the major peak with the expected
molecular mass and a not-so-minor peak (60% of the area of the major
peak) with a mass 111.1 mass units greater. This is the mass of a
pyro-glu. Has anyone seen multiple additions of pyro-glu during a
synthesis? 

-- 
Michael Pereckas  //  msp@mcw.edu  //  Michael.Pereckas@mixcom.com
Protein and Nucleic Acid Shared Facility, Medical College of Wisconsin
Research Technologist and sysadmin/webmaster of www.biochem.mcw.edu