DeltaMass Asp transamidation with piperidine PSI-MOD D none none MOD:00983 From DeltaMass: Average Mass: 67 Average Mass Change:67 References:http://www.abrf.org/archives/hmail/0008/0007.html Notes:1.) Get rid of the DBU. It can cause piperidine amides at Asp residues. The tbu ester side chain comes off during synthesis and the residue is trans-amidated with piperidine (+67Da by MS). If you haven't yet seen this, you will. Even "normal" 20% pip/DMF (NMP) will cause this, but less frequently. Literature exists for this; I don't remember the exact reference. David H. Singleton Scientist Pfizer Central Research PO Box 8118-101 Eastern Point Road Groton, CT 06340 (860)441-4404. artifact modification from DeltaMass none